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Leopold, Bruce David
ECOLOGY OF THE DESERT MULE DEER IN BIG BEND NATIONAL PARK,
TEXAS
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ECOLOGY OF THE DESERT MULE DEER IN
BIG BEND NATIONAL PARK, TEXAS
by
Bruce David Leopold
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF WILDLIFE, FISHERIES AND RECREATIONAL RESOURCES
In Partial Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
WITH A MAJOR IN WILDLIFE ECOLOGY
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 8 4
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Final Examination Committee, we certify that we have read
the dissertation prepared by ___B_r_u_c_e__D_a_v_i_d__
L_e_o~p_o_l_d__________________________
entitled
ECOLOGY OF THE DESERT MULE DEER IN BIG BEND NATIONAL
PARK, TEXAS
and recommend that it be accepted as fulfilling the dissertation requirement
for the Degree of
Doctor of Philosophy
Date
/q~ ~y
Date
If'JA-V~
Date
Final approval and acceptance of this dissertation is contingent upon the
candidate's submission of the final copy of the dissertation to the Graduate
College.
I hereby certify that I have read this dissertation prepared under my
direction and recommend that it be accepted as fulfilling the dissertation
requirement.
Dissertation Director
STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of
requirements for an advanced degree at the University of Arizona and is
deposited in the University of Arizona Library to be made available to
borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without
special permission, provided that accurate acknowledgement of source
is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by
the head of the major department or the Dean of the Graduate College
when in his judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission
must be obtained from the author.
SIGNED
P
:- - : g=,f. . : ;.=t. . ;:.~=:;I-"'_ _.........
<.oj) _L=~c!P,~~""'.
--'----,/
,T--
ACKNOWLEDGEMENTS
I would like to extend gratitude to the Rob and Bessie Welder
Wildlife Foundation for financial assistance throughout this study.
I
would also like to thank The Graduate Student Program Development Fund
and the Big Bend Natural History Association for additional funding.
Special thanks is extended to Paul R. Krausman for his friendship, guidance, and encouragement throughout all phases of this study.
Drs. Norman S. Smith, R. William Mannan, William J. Matter, and
William L. Shaw served as committee members and their comments and
reviews of the dissertation are greatly appreciated.
Gratitude is extended to the many people of Big Bend National
Park, Texas for their friendship and encouragement during the two
years of data collection.
They include John and Tina Pearson, Kathi
Hambly, George and Helen (Mama) West, Dan and Lynda Cockrum, Vidal
Davila, Felix and Stella Hernandez, Jim Li:es, Judge Charlie Shannon,
Jim Chambers, Frank and Gloria Deckert, Robert DeVine, Vee McElligott,
Marshall Smith, Bob and Judy Huggins, H. Gilbert Lusk, Russel and
Jeannie Berry, C. Michael Fleming, Bi+l Grether, Jim Milburn and
personnel of National Park Concessions, Billy Lum and personnel of the
United States Customs Patrol, and Rick LoBello.
All of these people
made me feel welcome in this "remote" region and many directly assisted in data collection.
To all of them, a special thanks.
iii
To Dr. Philip Spencer and Charlette Spencer, I give my sincere
thanks.
Their friendship and encouragement throughout this study is
deeply appreciated.
To many of my colleagues at the University of Arizona including
·John Hervert, Mark Wallace, and Brian Mauer, gratitude is extended for
their discussions and ideas during the interpretive stages of the
study.
I would like to thank Janet Wallace who accepted the arduous
task of typing this manuscript.
Finally, I would like to thank my parents W·illiam and Jane
Leopold, .and my sister, Sandra.
Their great interest in my studies,
and their encouragement and faith in my abilities aided me in completing this study.
It is to these three people to whom I dedicate
this work.
iv
PREFACE
This dissertation was prepared in the form of four manuscripts
written in a format which would facilitate immediate submission to
scientific journals for publication.
The first three manuscripts were
written according to the format specifications of THE JOURNAL OF WILDLIFE MANAGEMENT.
The final manuscript, entitled "Plant Associations
of the Lower Desert Shrubland in Big Bend National Park, Texas"
follows the format of THE JOURNAL OF MAMMOLOGY.
Approval for presenting the dissertation in this format was
based upon (1) approval by the Graduate College, and (2) my graduate
committee's agreement.
v
TABLE OF CONTENTS
Page
LIST OF TABLES • • • • •
vii
LIST OF ILLUSTRATIONS
ix
ABSTRACT
x
INTRODUCTION
1
STUDY AREA •
3
MATERIALS AND METHODS
4
Vegetational Analysis
Climatic Factors • • • .
Deer Observations
Deer Density Estimation • • . . •
Deer Density-Habitat Relationships
Productivity Assessment • • • .
Deer Condition • • . • . . • . .
Diurnal Activity Patterns • . • • •
RESULTS AND DISCUSSION •
4
4
5
5
6
6
6
6
7
Habitat Analysis and Plant Species Abundance
Temperature and Precipitation Patterns • . • •
Herd Composition of Desert Mule Deer in BBNP . • . • • •
Habitat-Deer Relationships • • • . . •
Productivity and Fawn Survival • . . .
Seasonal and Diurnal Activity Patterns
Temperature Relationships
Diurnal Activity Patterns
7
7
8
9
12
13
13
14
SUMMARY AND CONCLUSIONS
17
LITERATURE CITED . . . .
20
APPENDIX I
APPENDIX II
DIETS OF TWO DESERT MULE DEER HERDS
IN BIG BEND NATIONAL PARK, TEXAS . •
39
CHANGES IN PREY UTILIZATION BY PREDATORS
IN BIG BEND NATIONAL PARK, TEXAS . . . .
72
vi
vii
TABLE OF CONTENTS--Continued
Page
APPENDIX III -
APPENDIX IV -
INFLUENCE OF SPRING RAINFALL ON ANTLER
DEVELOPMENT OF DESERT MULE DEER IN BIG
BEND NATIONAL PARK, TEXAS • • . • • • • •
DIETS OF THE PAINT GAP AND PANTHER
JUNCTION DESERT MULE DEER HERDS IN BIG
BEND NATIONAL PARK, TEXAS FOR 1980 1981-
APPENDIX V
APPENDIX VI
. . . • . . • . . • . . . . . . .
SCAT ANALYSIS FOR MOUNTAIN LION (FELIS
CONCOLOR), BOBCAT (LYNX RUFUS), AND
COYOTE (CANIS LATRAN-sr-IN BIG BEND
NATIONAL PARK, TEXAS •• • . . • •
-
103
108
110
PLANT ASSOCIATIONS OF THE LOWER DESERT
SHRUB LAND IN BIG BEND NATIONAL PARK,
TEXA.S . . • • • • • • • . • • • . • . .
115
LIST OF' TABLES
Table
1
Page
Delineation of desert mule deer habitat and
pellet-group transects within desert regions in
Big Bend National Park, Texas
....
2
.....
2
Absolute density (stems/m ) of plants found
within desert mule deer habitats in Big Bend
National Park, Texas from September 9, 1980 to
~eptember 19, 1981
27
Herd composition data for desert mule deer in
Big Bend National Park, Texas during the period
of 1979 to 1981 • • • • • • • • • . • • • • • •
29
Herd composition data from studies of mule deer
in western United States • • • . . • • . .
30
Availability of bedsites and forage species
abundance in wash systems within desert mule
deer habitats in Big Bend National Park, Texas
during 13 September, 1981 to 9 October, 1981
31
..............
3
4
5
26
viii
LIST OF ILLUSTRATIONS
Figure
Page
1
Big Bend National Park, Texas • • • • • •
32
2
Total monthly precipitation recorded at Panther
Junction, Texas for 1980 and 1981 . • • •
33
3
4
5
6
7
Relationships between (A) total desirable
forage, (B) total plant density and (C) lechuguilla with deer abundance (pellet-groups/
transect) in Big Bend National Park, Texas.
All models were significant at the 0.05 significance level . . . . . . . . . . . . . . . . . . . . .
34
Percentage of fawns of total number of deer
observed between January 16, 1980 and December
9, 1981 in Big Bend National Park, Texas
35
Relationship between observed fawns and spring
rainfall (em) in Big Bend National Park, Texas
36
Seasonal relationships between deer activity
and temperature (oC) in Big Bend National Park,
Texas during 1980 and 1981 . . . • •
Seasonal relationships of desert mule deer
activity and time of day in Big Bend National
Park, Texas between 1980 and 1981 • • . • • .
ix
.....
37
......
38
ABSTRACT
Desert mule deer (Odocoileus hemionus crooki) abundance and
distribution, deer activity and diet, fawn survival, and predation
were studied in Big Bend National Park, Texas from 15 January 1980 to
9 December 1981.
Deer abundance was correlated with total plant,
forage, and succulent densities but was also related to perennial
water abundance and bed site availability.
vival were related to spring rainfall.
Fawn production and sur-
Diurnal and annual deer activ-
ity were influenced by temperature where spring and winter had longer
daily activity compared to summer.
during the morning and evening.
Daily activity by deer was highest
Forage use varied seasonally with
browse use decreasing from spring to winter with a corresponding increase in use of forbs.
Diets of two deer herds were compared and
during drought periods forb use decreased until summer rains occurred.
Prior to the rains, deer relied on evergreen browse species.
Addi-
tionally, deer within mesic areas had a higher use of forb species
contrasted with deer within xeric areas.
Predator diet significantly
changed with a decline in the deer population determined from pelletgroup transects.
Mountain lions (Felis concolor) used smaller prey
including javelina and lagomorphs.
Coyotes (Canis latrans) fed oppor-
tunistically by increasing use of insects, birds, reptiles, and lagomorphs.
Bobcats (Lynx rufus) increased use of lagomorpha with little
change in other prey species.
Given alternate prey species, predator
populations remained relatively constant given the deer decline.
x
INTRODUCTION
Nutrition and climate are two related factors that influence
deer (Odocoi1eus spp.) productivity and survival.
The nutritional plane
of does is affected by range and food quality (Cheatum and Severinghaus
1950, Robinette and Crane 1955, Ju1ander et a1. 1961, Desai 1962,
Pederson and Harper 1978) which in turn influences fawn survival
(Urness et a1. 1971, Baker et a1. 1979).
Temperature and amount of
rainfall usually affect range quality (Dasmann and Dasmann 1963,
Margurger and Thomas 1965).
Mule deer
(Q. hemionus) productivity is
generally low when pregnant does winter on poor range (Tolman 1950) and
fawn mortality is high in habitats of poor forage quality and during
periods of hot summers and severe winters (Taber 1953).
Adequate food
production resulting from seasonal rainfall is a major factor influencing fawn survival in Arizona (Hanson and McCulloch 1955, Jantzen
1964, Hungerford 1970).
of desert mule deer
(Q.
Drought also influenced the diet and numbers
~.
crooki) in Arizona (Anthony 1976).
Climatic
factors influence fawn production (Picton 1979, Smith and LeCount
1979), although predation by coyotes (Canis 1atrans) is a major mortality factor for fawns (Cook et a1. 1971, Logan 1972, Trainer 1975,
Garner et a1. 1976, Carroll and Brown 1977, Dickinson et a1. 1980,
Steigers and Flinders 1980).
The majority of studies of deer population regulation have been
on hunted populations.
Few ecological studies have been conducted on
naturally occurring ungulate populations.
1
Peek (1980) discussed the
2
importance of such studies.
Information on basic habitat and climatic
influences on naturally occurring deer populations is warranted.
Regulatory mechanisms including predation, starvation, and changes in
productivity are assessed with minimal bias when mans' influence on
habitat and animal density is absent.
The opportunity to study undisturbed desert mule deer populations is rare because areas supporting deer populations are generally
hunted.
Big Bend National Park (BBNP) is an area containing a
naturally occurring desert mule deer population which has not been
actively exploited since establishment of the park in 1945.
I studied
desert mule deer in BBNP between 15 January 1980 and 9 December 1981.
Data on mule deer collected by Krausman (1974) between 5 June 1972
and 16 April 1974 also are used in several of my analyses.
The
purposes of the study were to determine deer abundance and distrtbution relative to plant associations, and to assess the influence of
rainfall on fawn production and survival.
I also analyzed diurnal and
annual activity relative to temperature patterns.
STUDY AREA
Big Bend National Park (BBNP) in Brewster Co., Texas is
located 112.7 km from Marathon, Texas (Figure 1).
The Big Bend region
is included in the Chisos biotic district (Dice 1943, Blair 1947) and
2
occupies over 2866 km •
Elevations extend from 573 m along the Rio
Grande to 2384 m at Mt. Emory in the Chisos Mountains.
The park is characterized by hot summers, mild'winters, and
low rainfall.
Temperatures may exceed 28
0
e
in the desert regions
during the summer and are rarely freezing during the winter.
Precip-
itation occurs primarily from May through October ranging from
~
28
cm in the desert and the surrounding foothills to 41 cm in the
mountainous regions.
Plant associations and soils are discussed by
Leopold (1984).
3
MATERIALS AND METHODS
Vegetational Analysis
Classification schemes of major plant associations were
modified after Denyes (1956) and Wauer (1971).
Species abundance was
evaluated using the point-centered quarter method (Dix 1961).
A
minimum of 48 plots were sampled per transect except in areas of low
plant species diversity where 24 plots were sampled.
The initial plot
was determined randomly and subsequent plots were 10 m apart.
The method discussed by Dix (1961) was modified to adequately
sample all plant types.
Four categories of plants were sampled in-
cluding woody (perennial shrubs), grass, forb (annual herbaceous
plants), and succulent (Cactaceae and Agave spp.).
At each plot,
distance to the nearest plant within each category was obtained resulting in equal sampling intensity of each type.
All common and
scientific names are based on Correll and Johnston (1970).
Transects also were run in washes within each habitat.
The
initial plot was randomly established and all plants on either side
of plot center, perpendicular to the direction of the wash, were
tallied.
Subsequent plots were 10 m apart.
Plants were classified
for potential bed sites and forage.
Climatic Factors
Maximum and minimum temperatures and daily precipitation data
were obtained at Panther Junction (1140 m) which is located within
habitats representative of the areas frequently inhabited by deer.
4
5
Deer Observations
Most observations of deer were obtained by hiking throughout
the study area.
Kucera's (1978) observations were used in addition to
my data to determine fawn production.
Information from Krausman (1972-
1974) and Kucera (1978) was based on 2 herds.
the same 2 areas plus 2 additional groups.
I studied animals in
Independent observations
are observations of deer whose actions are not influenced by another
observation.
Information collected for each observation included air
temperature 2.13 m above the ground, time, habitat deer were initially
observed in, weather conditions, principle activity when initially
observed, age (adult, yearling, fawn), sex, and total number of deer.
Deer Density Estimation
. Pellet-plot
tra~sects
(Bennett et al. 1940) were established
in 10 of 12 habitats (Table 1).
I did not sample 2 habitats, the
river floodplain and brushy wash due to periodic flooding and extensive visitor use of the river for rafting and other recreational
activity.
Deer density was indexed by average number of pellet-groups/
transect and is referred to as deer abundance in the succeeding
sections of this paper.
Each transect contains 20 paired, 0.004 ha, circular plots.
Fifteen transects were sampled in spring (February-April), summer
(May-July), late summer (August-October), and winter (NovemberJanuary) to estimate deer abundance.
6
When the plant transects were sampled, I ran them within 3.1 m
of their corresponding pellet-group transects.
Deer Density-Habitat Relationships
Simple linear regression analysis was used to relate densities
of important forage plants (plants frequently observed eaten by deer)
with deer abundance.
Goodness of fit tests were made to determine the
distribution and the appropriate transformation required to normalize
the pellet-group data (Bartlett 1947, Anscombe 1948).
Productivity Assessment
Productivity was estimated by fawn counts throughout the study
period.
Fawns of the previous year were classified as yearlings on
August 1 to provide a standard for analysis.
Deer Condition
The condition of 15 car-killed deer was determined by examining
amount of fat surrounding the intestinal mesentary, heart, and kidneys
(Riney 1955, Anderson et al. 1972).
Diurnal Activity Patterns
Frequency histograms for the number of deer observed within
temperature and time of day categories were grouped seasonally.
Time
is expressed as the number of hours after sunrise as recorded for
Panther Junction (National Almanac Office, U.S. Naval Observatory 1980).
RESULTS AND DISCUSSION
Habitat Analysis and Plant Species Abundance
Variation in vegetation existed within habitats (Table 2).
For
example, the Creosotebush-tarbush association on the lowlands of Paint
Gap Hills had a density of New Mexico da1ea (Da1ea neomexicana) that
was 5 times higher than that in the same habitat located at Ash Creek.
For this reason, regression analyses of deer abundance and plant density were performed by location instead of combining transects of each
habitat.
The habitats were differentiated into three categories based
on dominant plant cover (Table 2).
They included creosotebush (Larrea
tridentata), non-creosotebush, and habitats with no dominant shrub
cover.
The soto1 (Dasy1irion 1eiophy11um) - 1echugui11a(Agave 1eche-
gui11a) - grass (Boute1oua spp.) habitat is found on elevations exceeding 967 m and the 1echugui11a-grass habitat, with no dominant shrub
species, is common on gently rolling hills.
The drier habitats con-
taining creosotebush including creosotebush-1echugui11a, creosotebush1echugui11a-prick1y pear (Opuntia rufida), creosotebush flats, and
creosotebush-1echugui11a-cande1i11a (Euphorbia antisyphi11atica) are
2
typically low in plant density (less than 1 stem/m ), plant diversity,
and perennial water sources.
Temperature and Precipitation Patterns
Monthly maximum and minimum temperatures at Panther Junction
o
0
0
during the study periods ranged from 13.9 C to 37 C, and 2.8 C to
7
8
o
23.3 C, respectively.
The average maximum temperature for June and
o
July was 37.2 C for 1980 and 33.6 o C for the same period in 1981 (Figure
2).
The average maximum temperature for June and July during 1960 to
0
1979 was 33.9 C thus 1980 had above average temperatures during the
period of highest, maximum temperatures.
Monthly rainfall averaged 3.13 cm.
The difference in total
rainfall for January through May in 1980 (2.64 cm) and for the same
period in 1981 (13.28; Figure 2) had a major effect upon the plant arld
deer populations.
The average rainfall for January to May between
1960 and 1979 was 7.81 cm therefore the spring of 1980 had below
average and 1981 had above average rainfall.
Herd Composition of Desert Mule Deer in BBNP
Herd composition statistics are based on 750 independent observations
of 2002 deer (Table 3).
Yearlings were classified as
adults to eliminate bias resulting from the possible misclassification
of large yearlings as adults and small adults as yearlings.
The sex ratios observed in 1980-1981 are comparable with those
of other studies within desert environments (Table 4).
Fawn produc-
tion, as shown by the fawn/doe ratio, is higher for non-arid environments.
The lower fawn/doe ratios observed by Anthony and Smith (1977)
may be a result of a drought which reduced the survival of young
(Anthony 1976).
Higher proportions of bucks are observed for unhunted
populations and may reflect the selective nature of hunting for adult
males.
9
Habitat-Deer Relationships
The goodness of fit tests made to determine the frequency
distribution of the pellet-group data for each habitat indicated that
the Poisson distribution was appropriate (p < 0.05) and the square root
transformation (Bartlett 1947) was applied.
Simple linear regression
was performed with deer abundance as the dependent variable, and total
desirable forage (Figure 3A), total plant density (Figure 3B), and
lechuguilla (Figure 3C) as independent variables.
The sotol-yucca (Yucca carnerosana) habitat was deleted from
the regression analysis.
This habitat is found within a valley
(Dagger Flat) surrounded by the Deadhorse Mountains in the northern
region of the park.
The deer abundance was estimated as 0.98 pellet-
groups/transect; however, the plant densities were high (4.34 stems/
2
m ) compared to other areas (x
=
2
2.3 stems/m ) but Dagger Flat does
not have the highest deer abundance
for all habitats).
(x =
1.11 pellet-groups/transect
Dagger Flat is within a large valley and receives
considerable rainfall (> 15 cm) which supports lush vegetation.
During the winter of 1981 after a snowfall the mountains and flats
surrounding Dagger Flat had less than 4 cm of snow whereas the valley
floor had snow drifts as high as 2 m.
There are virtually no peren-
nial springs in the surrounding Deadhorse Mountains and deer abundance
is low even though forage within Dagger Flat is abundant.
I selected lechuguilla as an independent variable because it
is the most common succulent species within the park and is an integral
vegetative component of those habitats with moderate rainfall.
10
Additionally, observations of feeding deer indicated that lechuguilla
was an important food.
Krausman (1978) found that lechuguilla consti-
tuted 23.8% of 29 desert mule deer rumens collected in BBNP during
1973 and 1974.
Lechuguilla abundance in rumens ranged from 3.3% for
the summer to as high as 40% in the spring.
Anderson (1949) reported
that desert mule deer spent 9.5% of total feeding minutes consuming
lechuguilla.
Therefore, it was not surprising that lechuguilla was
an important variable in predicting deer abundance.
Lechuguilla is a
dominant plant throughout the study area and being succulent may
provide water in an environment where springs are scarce and periodically dry up.
The strong relationship between deer abundance and plant density suggests that the plant
~ommunity
abundance of a large herbivore.
influences the distribution and
Habitats low in total plant density
lacked desirable forage species as suggested by the relation between
forage and deer abundance (r
= 0.796)
(Figure 3A).
Additionally, the
low plant densities associated with habitats such as the Creosotebush
Flats are also low in available bed sites which afford shade during
the afternoon.
Unshaded soil temperature at Paint Gap Hills dominated
o
by the sotol-lechuguilla-grass habitat was 52.2 C on 14 July 1980 at
1700 and was as high as 57.S o C on Tornillo Flats dominated by the
Creosotebush Flats habitat at 1700 on the same date (SCS records,
1980).
tion.
These measures indicate the need for shade produced by vegetaHowever, deer are present in all habitats identified and may
11
rely upon the diversity of forage
pl~nts
and bed sites within the
nearby wash systems (Table 5).
The plant-deer relationships (Figures 3A, B, C) may additionally reflect water abundance.
Areas with low deer abundance (i.e.,
Creosotebush Flats), have fewer perennial springs and less rainfall.
The creosotebush-lechuguilla-candelilla habitat occurs along the
slopes of the Deadhorse Mountains, an area devo.id of springs.
The
transect is located 5.6 km from the Boquillas weather station which
reported an average annual rainfall between 1960 and 1981 of 24.3 cm
contrasted with 35.2 cm for Panther Junction.
Average maximum tempero
ature for summer (May-September) for Boquillas was 37.6 C compared to
o
Panther Junction's 32.4 C.
Thus, the relationships reflect a complex
interaction of the deer population and environmental factors including
plant abundance, rainfall, and temperature.
The concept of permanent water abundance in influencing deer
distribution and abundance is additionally supported by the Dagger Flat
transect.
Although removed from the plant density-deer abundance
regressions, Dagger Flat represents the need to consider several factors including water abundance when assessing deer habitat use.
High
forage abundance may not always indicate high deer use when other
factors are lacking.
Studies of deer-habitat relations note similar differential
habitat use by deer as found in this study (White 1960, Julander 1966,
Miller 1968).
Additional studies in desert environments also found
similar differential habitat use (Clark 1953, Anthony and Smith 1977,
Dickinson 1978).
Food availability and quality have been cited as
12
important factors (Taber 1956) in influencing deer distribution.
The
nonrandom spatial distribution of mule deer observed by Loveless
(1964) was attributed to forage abundance and microclimatic factors
influencing tempe!ature and humidity.
Productivity and Fawn Survival
Climatic factors, particularly temperature and rainfall, influence fawn survival in deserts (Hanson and McCulloch 1955, Anthony
1976, Smith and LeCount 1979).
Rainfall during the growing season of
forage plants influences the nutritional quality of the forage (Payton
and Garner 1980) which also varies seasonally (Gastler et al .• 1951,
Hagen 1953, Swank 1956, Boeker et al. 1972).
Reduced forage quality
results in a reduction of the nutritional plane of does influencing
pre- and postnatal fawn mortality (Cheatum and Severinghaus 1950, Kitts
et al. 1956, Jones et al. 1956, Desai 1962, Pederson and Harper 1978).
Late winter and spring rainfall during this study was different (2.64 cm for 1980 and 13.28 cm for 1981).
The number of fawns
observed (Figure 4) was related to rainfall patterns.
Averaging the
monthly percentages for each year (1973-1974, 1980-1981) and combining
the results with those of Kucera (1978) yields very suggestive results
(Figure 5).
The Arcsin square root transformation was used on the
percentage data to comply with regression assumptions (Zar 1974,
p. 220).
Even though the regression is based on 4 degrees of freedom,
2
the high R value (0.922) indicates a strong influence of rainfall on
fawn survival.
Smith and LeCount (1979) also found a significant re-
lationship between precipitation and fawns/100 does (R
Arizona.
2
=
0.41) in
13
Necropsies of car-killed deer indicated that the general condition of the deer in 1980 was poorer than in 1981 where 1 out of 7
deer had high kidney fat ratings in 1980 compared to 5 out of 8 deer in
1981.
However, younger animals consistently had lower condition
ratings than did older adults even in 1981 when adults had medium'to
high ratings of fat.
This may reflect the greater nutritional re-
quirements of younger age classes.
The relationship between rainfall,
temperature, and deer health and nutrition has been studied previously
(Dasmann 1956, Leach and Hickle 1957, Anderson et al. 1972) and my
results concur with their conclusions.
Seasonal and Diurnal Activity Patterns
Temperature Relationships
The summer and late summer seasons have a period of peak deer
activity each day which occurs whem temperatures are below 30°C in the
summer and below 25°C in the late summer (Figure 6).
0
Diurnal tempera-
0
tures generally reached 33 C in summer and 31 C in late summer within
5 to 7 hours after sunrise.
Thus, deer activity decreases when maxi-
mum diurnal temperatures are attained.
Studies have found similar
activity changes by deer regarding diurnal and annual temperature
patterns (Clark 1953, Dasmann and Taber 1956b, Miller 1970).
Spring and winter activity did not show any discernible peak
within a given temperature range apparently because the colder temperatures during these seasons permitted deer to be more active.
In
winter, white-tailed deer in southern Texas were active 82% of the time
compared to a summer percentage of 45 (Michael 1970).
During the
14
winter in Arizona, 60% of the day was spent feeding by desert mule
deer (Clark 1953).
Different herds of deer were observed during
diurnal hours on 17 different occasions during my study.
For adult
does, there was a seasonal increase from spring to winter in the percentage of the day spent feeding.
Does were active 18% of the day in
spring (n=7 days of observation) increasing to 19.7% (n=5 days) and
22.7% (n=2 days) during the summer and late summer respectively.
highest percentage of the day spent feeding
n=3 days).
o~curred
The
in winter (35.5%,
Thus, does were more active throughout the day in winter
than in any other season, causing no discernible peak to appear.
This increase may be a result of the breeding season when bucks are
actively pursuing does.
Twenty-five percent of the movements during
the winter in the Tucson Mountains were a result of the rut (Clark
1953).
The lack of a spring peak is more difficult to explain.
The
spring is the season of lawest rainfall, possibly resulting in deer
requiring more forage to meet energy requirements.
Also, group size
was largest in the spring (3.22) compared to other seasons (summer 2.44, late summer - 2.12, winter - 2.95).
similar results.
Michael (1970) found
Dickinson (1978) stated that the only period of
significant inactivity during the spring was between 5 and 8 hours
after sunrise.
Diurnal Activity Patterns
All seasons had two diurnal peaks of activity that occurred in
early morning and early evening (Figure 7) substantiating the crepuscular activity classification of most deer species.
Patterns for
15
white-tailed deer in Texas are similar (Michael 1970).
The time of
the early morning period does not differ seasonally with activity
which decreases 2 hours after sunrise.
Dasmann and Taber (1965a)
found that early morning feeding decreased in the summer by 1 to 2
. hours after sunrise.
The time of peak evening activity and length of the daytime
bedding period differ seasonally.
In the spring, evening activity
begins 9 to 10 hours after sunrise following a 7-hour bedding period.
As the year progresses, the period shifts, thus in the summer, activity is initiated 11 to 12 hours after sunrise following an inactive
period of 9 hours.
The major factor is temperature which remains high
later into the afternoon.
By late summer, daily maximum temperatures
decrease allowing activity to resume in the evening 9 to 10 hours
after sunrise with an afternoon bedding period of 7 hours.
By winter,
feeding initiates as early as 8 to 9 hours after sunrise with the
shortest bedding period of 5 hours.
The morning feeding period in
winter extends to 2 to 3 hours compared to the 1 to 2-hour period in
the other seasons.
The lack of a winter peak in diurnal deer activity (see the
previous section) is a result of the shorter bedding period and an
earlier initiation of the evening feeding period.
The lack of a peak
in daily activity in the spring may be due to the relatively equal
distribution of activity within the temperature classes due to the
short period of activity (4 hour) during the warm evenings and a
shorter bedding period.
16
The bulk of afternoon activity by deer was of short duration
and was associated with deer relocating to better bed sites.
In
nearly 80% of the 136 times deer became active in the afternoon during
the 17 days when deer herds were observed, the duration of this
activity was less than 30 minutes in length.
vations involving activity exceeded 1 hour.
Only 7% of the obserIn practically all cases,
the deer moved and subsequently bedded beside taller or more dense
vegetation.
During
~he
summer, the relocation sites afforded more
shade and during the winter and spring months, greater protection from
the winds.
Feeding was observed during the move to new bed sites but
feeding was not the primary cause of afternoon activity.
SUMMARY AND CONCLUSIONS
Deer were abundant in regions where forage species density was
high, cover from afternoon sun was available, perennial springs were
present, and daytime temperatures were not severe.
The occurrence of
one of these factors does not guarantee deer presence.
For example,
areas with abundant forage but lacking year-round water did not support
high deer densities.
Therefore, my results indicate that several
factors mutually act in maintaining deer densities with "suitable
limits" although hunting is not present.
The fact that the study population is unhunted provides evidence that in naturally occurring deer populations in arid environments, deer distribution and density are maintained at levels not
indicative of irruptions.
Much literature exists which states that
all North American deer species under limited mortality irrupt
(Leopold et al. 1947).
However, within desert environments, the
severity of the climate and habitat act as regulatory pressures maintaining deer populations below irruptive levels.
Additionally, the
existence of healthy predator populations in the study area undoubtedly aids in herd size stability.
Additional information concerning "natural" regulation is
based on my results of fawn survival and spring rainfall.
My results
with those of Kucera (1978) suggest that spring rainfall influences
fawn mortality.
Delayed forage production due to periods of low
rainfall adversely affects the pregnant or lactating doe.
17
The effect
1S
of rainfall on fawn survival in desert environments has also been
found in the unhunted deer population of the Three-Bar Wildlife area
in Arizona (Smith and LeCount 1979).
Water abundance and distribution are important within the
desert environment.
Management intended to increase deer herd size in
arid areas for sport hunting usually begins with considerations regarding artificial water source development.
Wood et al. (1970)
found higher deer densities in areas where earthen tanks were established.
Pre-park records indicate higher deer populations than occur
today.
Matthews (1937) stated that several earthen tanks were estab-
lished for livestock and maintained by ranchers.
"at all times".
Most held water
Ten tanks were monitored during this study at differ-
ent times of the year and rarely did tanks hold appreciable amounts of
water for more than 3 weeks after a thundershower.
Thus, the lower
herd size as observed today may be a result of a gradual decline in
water-holding capacity of the unmaintained tanks.
My results support
management obj ectives concerning installation of artificial ,..rater
sources to increase deer densities.
However, as stated earlier,
other factors also must be considered including abundance of forage
and cover.
Desert mule deer activity patterns relative to diurnal temperature varies seasonally.
As one proceeds from winter to late
summer, the afternoon bedding period lengthens as a result of high
daily temperatures which exceed 3SoC during mid-summer.
During the
winter and in part, the spring, daytime high temperatures do not
19
exert any appreciable thermoregulatory stress upon the deer and
activity may be observed throughout the day.
My results indicate that under natural conditions (lacking
hunting), desert mule deer populations may be limited by densitY7
independent factors.
These factors include climate (primarily temper-
ature and precipitation), density of plant cover, and abundance of
perennial water sources.
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21
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------::-
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22
Desai, J.H. 1962. A study of the reporductive patterns in the desert
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Dickinson, T.G. 1978. Seasonal movements, home range, and home range
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the Sierra Nevada. Calif. Fish Game. 39:163-175.
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20:568-588.
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Interstate Deer Herd Committee. 1951.
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The Devil's Garden deer herd.
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23
Jones, D.A., W.L. Robinette, and O. Julander. 1956. Influences of
summer range condition on mule deer reproductivity in Utah.
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Julander, O. 1966. How mule deer use mountain rangeland in Utah.
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and D.A. Jones. 1961. Relation of summer
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25:54-60.
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the Big Bend National Park, Texas. J. Wildl. Manage. 42:
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24
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Big Bend Proposed National
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25
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Prentice-Hall Inc.
New
TABLE 1.
Delineation of desert mule deer habitat and pellet-group transects
within desert regions in Big Bend National Park, Texas.
Habitat (Vegetative Association)
Creosotebush-Iechuguilla-grass
pear
Creosotebush-tarbush (Flourencia cernua)
Creosotebush-Iechuguilla
Creosotebush-Iechuguilla-candelilla
Creosotebush Flats
Sotol-Iechuguilla-grass
Viguieria-Iechuguilla-grass
Sotol-Giant Dagger
Lechuguilla-grass
Badlands
Creek-Bed
River Floodplain
Creosotebush-L~chuguilla-prickly
Totals
Acreage
(Hectares) *
% of
Park
Number of
Transects
20,099
7,309
13,313
4,698
63,690
82,484
12,790
11,746
15,662
38,632
3,132
2,088
5,220
7.01
2.55
4.64
1.64
22.22
28.78
4.46
4.10
5.46
13.48
1.09
0.73
1.82
2
1
2
1
1
1
2
2_
1
2
0
0
0
280,863
97.98
15
*Acreage determined following Marcum and Loftsgaarden (1980).
N
(J\
TABLE 2.
2
Absolute density (stems/m ) of plants found within desert mule deer habitats in Big Bend
National Park, Texas from SeEtember 9, 1980 to SeEtember 19, 1981.
2
Absolute Plant Densit; (stems/m )
Habitat
I.
II.
Creosotebush
1. Creosotebush-tarbush
1. Creosotebush-tarbush
2. Creosotebushlechuguilla-grass
2. Creosotebushlechuguilla-grass
3. Creosotebush-Iechuguilla-prickly pear
4. Creosotebush-Iechuguilla-candelilla
5. Creosotebushlechuguilla
6. Creosotebush Flats
Non-Creosotebush
1. Viguierialechuguilla-grass
1. Viguierialechuguilla-grass
2. Sotol-Iechuguillagrass
2. Sotol-Iechuguillagrass
3. Sotol-yucca
Forage
Density
Lechuguilla
Density
Location
Elev Woody
Forb
Grass
Succul
Total
Density
Paint Gap
Ash Creek
Nugent Mtn
1051
1067
1067
0.59
0.86
0.67
0.58
0.85
0.75
0.58
0.84
0.76
0.59
0.83
0.75
2.31
3.38
3.01
1.15
1.69
1.17
0.49
0.80
0.67
DOW Lacol.
945
0.59
0.58
0.58
0.58
2.34
1.16
0.57
6.8 kmE DOW 762
1.16
0.17
0.16
0.16
0.65
0.23
0.14
Lower Old
640
Ore Road
Dagger Flat 914
Road
Tornillo Crk 841
0.19
0.19
0.18
0.19
0.74
0.29
0.14
0.06
0.06
0.06
0.06
0.24
0.10
0.06
0.16
0.16
0.16
0.16
0.64
0.02
0.00
Government
Spring
S K-Bar
Road
Juniper
Canyon
Horse Mesa
1097
0.61
0.62
0.62
0.62
2.46
0.98
0.51
1097
0.53
0.54
0.53
0.54
2.14
0.83
0.39
1310
0.82
0.82
0.80
0.81
3.24
0.73
0.73
1158
1.05
0.98
1.01
1.01
4.05
1.51
1.00
Dagger Flat 1049
1.07
1.08
1.09
1.09
4.34
2.20
1.00
'"
-...,J
2
TABLE 2 CONTINUED. Absolute density (stems/m ) of plants found within desert mule deer habitats in
Big Bend National Park, Texas from September 9, 1~8~_to September 19, 1981.
2
Absolute Plant Density (stems/m )
Habitat
Location
Elev Woody
III. Non-Shrub
1. Lechuguilla-grass
1. Lechuguilla-grass
Hannold Draw 960
DOW Hills
975
0.43
0.26
Forb
Grass
Succul
0.43
0.26
0.43
0.43
0.26
0.26
Total
Density
Forage
Density
Lechuguilla
Density
1.72
1.04
0.74
0.41
0.45
0.25
I'.)
00
29
TABLE 3.
Herd composition data for desert mule deer in Big Bend
National Park, Texas during the period of 1979 to 1981.
Herd Statistic
1979
1980
1981
Com)2osite
100 F:Male:Fn
100:28:43
100:17:13
100:29:43
100: 22: 26
Group Size
3.11
2.28
1.65
2.44
"Male/Group
0.51
0.30
0.28
0.37
II F/Group
1.82
1. 75
0.96
1.64
II Fn/Group
0.78
0.22
0.41
0.43
TABLE 4.
Source
Herd composition data from studies of mule deer in western United States.
Species
Clark (1953)
D.h. crooki
Krausman (1974)
D.h. crooki
Kucera (1978)
D.h. crooki
Hanson and
D.h.
McCulloch
Anthony and
D.h. crooki
Smith (1977)
Schnee gas and
D.h.
Franklin (1972)
californicus
Cronemiller and
D.h.
Bart (1950)
californicus
Interstate dr
D.h.h.
herd Com (1954)
Chattin (1948)
D.h.h.
Dasmann and
D.h.h.
Blaisdell (1954)
Interstate dr
D.h.h.
herd Com (1951)
Cowan (1950)
D.h.h.
Richens (1967)
D.h.
This study
D.h. crooki
Habitat
Hunted
Location
Doe:Buck:Fawn
Ratio
Group
-Size
-4.5
5.2
desert
desert
desert
desert
yes
no
no
yes
Tucson Mts, AZ
BBNP, Texas
BBNP, Texas
3 Bar Mgmt Area, AZ
100:30:51.2
100:24:24.2
100:63:28.8
100:57.3:94.3
desert
yes
chaparral
yes
San Cayetano Mts, AZ
Dos Cabezas Mts, AZ
Tulare Co, CA
100:--:27.0
100:--:30.4
100:1.2.0:47.0
chaparral
yes
Southern California
100:56.0:57.4
chaparral
yes
Modoc Co, CA
100:14.0:67.1
chaparral
chaparral
yes
Modoc Co, CA
Lassen & Washoe Co, CA
100:17.5:145.8
100:14.0:60.0
Modoc Natl For, CA &
Fremont N.F., DR
Alberta & B.C., Canada
Daggett Co, Utah
BBNP, Texas
100:16.5:77.1
?
woodland
chaparral
desert
?
yes
no
yes
no
100:53.0:---100:34.8:82.8
100:40.2:27.2
3.8
4.8
2.7
w
o
31
TABLE 5.
Availability of bedsites and forage species abundance in wash
systems within desert mule deer habitats in Big Bend National
Park, Texas during 13 September, 1981 to 9 October, 1981.
Percent of
Total Providing
Shade
Habitat
Creosotebush-lechuguilla-grass
Sotol-lechuguilla-grass
Skeletonleaf-lechuguilla-grass
Creosotebush Flats*
Lechuguilla-grass
Creosotebush-tarbush
Creosotebush-lechuguilla-Opuntia*
Creosotebush-lechuguilla-candelilla*
Yucca-Sotol
Creosotebush-lechuguilla*
30.5
21.4
21.7
40.0
28.7
29.3
27.0
36.7
25.0
14.9
Percent of
Total Providing
Forage
18.0
33.0
27.2
16.0
27.7
18.8
15.6
20.7
11.9
27.6
*Sites typically drY with low plant densities and rainfall.
32
t
N
oI
10
t
20
I
Miles
FIGURE 1. Big Bend National Park, Texas (1. Dagger Mtn., 2. Dagger
Flat, 3. Upper Tornillo Flats, 4. McKinney Hills,S. Lower Tornillo
Flats, 6. Onion Spring, 7. Hannold Draw, 8. Croton Spring, 9. Government Spring, 10. Green Gulch, 11. Panther Junction, 12. Pine Canyon,
13. Juniper Canyon, 14. Boquillas, 15. Sotol Vista, 16. Kit Mountain).
33
"-
E15.0
9
C
010.0
-.....
...,«J
-a 5.0
--o
d:
1.0
L,:::;::~~~--.--.-,......,......-.--.-~-r-r-~
Ja Ap Jul Oc Ja Ap Jul Oc De
1980
1981
Month
FIGURE 2. Total monthly precipitation recorded at Panther Junction,
Texas for 1980 and 1981.
34
A.
it :
I,
Y. 0.689+0A29X
~ 0.633
8,
.. I
c!
!
n·1A
02~__~~__~__~____
02
0.8
1A
2.0
Total Dealrable Forage
Denalty (stem..,...2)
B.
Y = 0.630 +0.206X
HZ-0.730
n -14
1.0
2.0 3D 4.0
5D
Total Plant Denalty (atemllm 2 )
c.
Y·0.677+0.83X
~0.742
n .14
0.2
0.1
o.s
1.0
Lechuguilia cstemlllm2)
FIGURE 3. Relationships between (A) Total Desirable Forage, (B) Total
Plant Density, and (C) lechuguilla with deer abundance (pellet-groups/
transect) in Big Bend National Park, Texas. All models were significant at the 0.05 significance level.
35
0.45 1979
7em
1980
3em
1981
13 em-
0.30
Ja Ap Jut Oc Ja Ap Jul Oc
1980
1981
Month
FIGURE 4. Percentage of fawns of total number of deer observed between
January 16, 1980 and December 9, 1981 in Big Bend National Park, Texas.
36
-eCD
.c
c
.- 40.0
....c
..
...
v = 14.902 +1.677X
CD
u
R2-0a922
CD
a.
n =6
c
~
<C
1
5
10
15
Rainfall tem)
FIGURE 5. Relationship between observed fawns and spring rainfall (em)
in Big Bend National Park, Texas.
"tJ
G)
>
'-
G)
(/)
.Q
o
c
:E
c
Sp
S
LS
W
Composite
Temperature (OC) Classes
FIGURE 6. Seasonal relationships between deer activity and temperature "(oC) in ~ig
Bend National Park, Texas during 1980 and 1981. (DMD = Desert Mule Deer, Sp = Spring,
S = Summer, LS = Late Summer, W = Winter)
w
"
-..
II
=I:
""
.... 11
0-
o~
z
~
:!!
'0· -- rl'"'· .... .,~o. . -"".:.· ·0'- ·$:!-".-..,.·.,-oo·..........
t
• • • • • • • • ~";"'"":"
•
-:-7":"";", ~ ':'"
-O-"~.~G~.~O_"~.~G~
.
winter - - - - - - - -
....
II
=I:
""
'OS!
zo ~
O_"" .. .,Oh.~=~~~~!~~
I
•
I
•••
I
"
'"
I
•
I
•••
~~O-""""o""·2=~~!~!~
~O-"ft • .,~ ..... ~e=~~s=!~~
I'I"
• • • • • • • • • 0' • • • • • • • • • •
0 _ fie
11ft G" • ~·o - .... ,., _ 11ft 00 ....
('lit -
"
--------
summer
spring
No. of hrs. after sunrise
Figure 7. Seasonal relationships of desert mule deer activity and time
of day in Big Bend National Park, Texas between 1980 and 1981.
w
co
APPENDIX I
Diets of two desert mule deer herds in Big Bend National Park, Texas.
39
TABLE OF CONTENTS
Page
LIST OF TABLES
41
LIST OF ILLUSTRATIONS
42
ABSTRACT
43
INTRODUCTION
44
MATERIALS AND METHODS
46
46
47
Study Area
Deer Diet Analysis
RESULTS
49
Cornposited Deer Diets
Annual and Topographic Differences in Deer Diets
."
DISCUSSION
Cornposited Deer Diets
Annual and Topographic Differences
49
49
52
52
53
SUMMARY
58
LITERATURE CITED
60
40
LIST OF TABLES
Table
1
2
3
Page
Composite summary of desert mule deer diet in
Big Bend National Park, Texas, 1980-1981
64
Coefficients of overlap for plant species
composition of the diets of two desert mule deer
herds in Big Bend National Park, Texas
65
Habitat distribution within panther Junction and
Paint Gap Hills in Big Bend National Park, Texas
66
41
LIST OF ILLUSTRATIONS
Figure
Page
1
Big Bend National Park, Texas . • • • •
67
2
Total monthly precipitation recorded at Panther
Junction, Texas for 1980. and 1981 . • •
68
Seasonal and annual forb utilization by the
Panther Junction and Paint Gap Hills desert mule
deer herds in Big Bend National Park, Texas
69
Seasonal and annual woody browse utilization by
the Panther Junction and Paint Gap Hills desert
mule deer in Big Bend National Park, Texas • • • • • • •
70
Seasonal and annual succulent utilization by
the Panther Junction and Paint Gap desert mule
deer herds in Big Bend National Park, Texas • • .
71
3
4
5
42
ABSTRACT
Two desert mule deer herds (Odocoileus hemionus crooki) in Big
Bend National Park, Texas were studied in 1980-1981 to compare diets
and test the hypothesis that topographic and climatic differences
(degree of aridity) result in different forage use.
Seasonal patterns of forage use were similar between the two
herds.
Generally, browse use decreased from spring to winter with a
corresponding increase in forb use.
Utilization of succulents was
greatest during the dry seasons (spring and winter).
The herds differed in the use of available plant species.
Deer in the more xeric region consumed evergreen browse species during
periods of low rainfall and relied less upon forbs.
Deer in the
mountain foothills also showed decreased forb use during drought
periods; however, the more mesic character of the washes extending
from the hillsides provided more herbaceous forage.
Once summer rains
occurred, differences in browse and forb use by the two herds became
less pronounced.
43
INTRODUCTION
Mule deer (Odocoi1eus hemionus) are browsers and woody species
compose over 50% of their diet (DeNio 1938, Ferra1 and Leach 1950,
Richens 1967, Constan 1972, McCulloch and Urness 1973, Tue11er 1979)
but forbs (Lovaas 1958, Deschamp et a1. 1979) or grass (Hill 1956,
Morris and Schwartz 1957) may compose a large percentage of the diet
during certain periods of the year.
Although the diet of mule deer
has been documented, studies determining foods of desert mule deer are
limited (Anderson 1949, McCulloch 1972, Keller 1975, Anthony 1976,
Short 1977, Krausman 1978, Krys1 and Simpson 1980).
Most of these
studies concern general diet and rarely assessed food preferences
and environmental and topographic influences on individual deer
herds in relation to plant species availability.
Understanding deer
food preferences and changes resulting from biotic influences are
important in interpreting basic deer biology.
Anthony (1976) found
that desert mule deer foods in Arizona changed during a drought.
Nellis and Ross (1969) determined that changes in Rocky Mountain mule
deer
(Q.
~.
hemionus) herd size resulted in a corresponding change in
utilization of browse species.
Leach (1956) found different browse
use between distinct mule deer herds in California.
Data are limited concerning forage preferences and factors
which affect utilization particularly within desert environments where
seasonal forage abundance is significantly affected by environmental
factors including temperature and rainfall.
44
I initiated a study in
45
Big Bend National Park (BBNP), Texas in 1980 and 1981 to determine if
differences in forage use by two deer herds existed.
MATERIALS AND METHODS
Study Area
Big Bend National Park (BBNP), Brewster Co., Texas is located
2
113 mk south of Marathon, Texas (Figure 1) and occupies over 2866 km
Elevations range from 573 m along the Rio Grande to 2384 m at Mt.
Emory in the Chisos Mountains.
The park is characterized by hot summers, mild winters, and
low rainfall.
Temperatures often exceed 38°C in the desert regions
during the summer and rarely are freezing during the winter.
The
majority of the precipitation occurs· from June through October ranging
from < 28 cm in the desert and the surrounding foothills to 41 cm in
the mountains.
The 2 herds studied were located at Paint Gap Hills (PG:
desert lowlands) and at Panther Junction (PJ:desert mountain foothills).
The Paint Gap Hills are an igneous intrusion located approxi-
mat ely 9.25 km from Park headquarters at Panther Junction.
Elevations
.
range from 1067 m on the flats surrounding the hills to 1299 m on the
top of the intrusion.
The PJ herd is on the flats surrounding the
foothills of the southeastern portion of the Chisos Mountains and is
9.25 km northwest of Paint Gap.
The vegetation on the 2 areas is variable with a dispersion
of 6 plant associations including viguieria (Viguieria stenoloba) lechuguilla (Agave lecheguilla) - grass, creosotebush (Larrea
tridentata) - tarbush (Flourencia cernua), creosotebush-lechuguilla46
47
grass, sotol (Dasylirion leiophyllum) - lechuguilla-grass, lechuguillagrass, and creosotebush flats.
A more thorough description of these
plant associations is found in Leopold (1984).
Water is available
for both herds throughout the year.
Deer Diet Analysis
Diets were determined from fecal pellets collected in the
middle of each season (Spring: February-April, Summer: May-July, Late
Summer: August-October, Winter: November-January).
Five fresh fecal
groups were collected for each season and herd during the two years of
the study.
The pellet-groups were stored in 70% alcohol until labora-
tory analysis was performed at the University of Arizona following
procedures outlined by Sparks and Malechek (1968).
One slide per fecal group was analyzed and 20 randomly selected
microscopic fields per slide were sampled.
Holechek and Vavra (1981)
found that major forage species can be accurately determined using
one slide per animal.
Plant species were identified using epidermal
or cuticular characteristics and frequencies for each forage species
were compubed.
Frequencies were then converted to particle density
(Fracker and Brisckle 1944) (Equation 1).
Relative density is ob-
tained by equation (2) based upon the discussion of Sparks and
Malechek (1968).
Frequency = 100 x (1 - e -density)
Density of particles of species A x 100
Relative density
Total density of particles of all species
(1)
(2)
48
Plant species were delineated as woody (perennial shrubs), grass,
forb (annual, herbaceous plants), or succulent (Agave spp. and Cactaceae) to facilitate comparisons with previous studies.
Scientific
and common names are based on Correl and Johnson (1970).
Fecal analysis studies assessed dietary differences with an
index of overlap or similarity or used nonparametric rank-correlation
coefficients (Hansen and Reid 1975, Hubbard and Hansen 1976, Reynolds
et al. 1978, Squires 1982).
I made my comparisons using the coeffi·,·
cient of overlap (C) proposed by Marista (1959) and used by Alcoze and
Zimmerman (1973) and Krausman (1978).
Additionally, I compared pooled
percentages of the 4 forage classes to assess basic patterns in diet
'between and within the two herds studied.
Recently authors have
questioned usage-availability analysis (Johnson 1980, Nudds 1980).
Since the plant associations within Paint Gap and Panther Junction are
very diverse, any attempt to correlate food species abundance with
utilization by deer considering the mobility of deer while feeding,
would be extremely difficult.
By selecting two herds which inhabit
different habitats, desert lowlands and mountain foothills, I can
test the hypothesis that plant composition of the diet of deer will be
influenced by the habitat.
RESULTS
Composited Deer Diets
Diets were composited for both herds and years and compared
seasonally (Table 1).
Woody forage use decreased from spring to winter
with a corresponding increase in forb use.
Thus, as the summer rainy
season initiated (July-October), herbaceous annual and perennial plant
species resumed growth and deer began to feed on these more succulent
forage species.
Use of succulents was high during the spring which is
the driest period of the year (Figure 2).
Low succulent usage occurred
during the late summer when rainfall and growing forage are greatest.
Grass use was consistantly below 1% of the deer's diet.
Annual and Topographic Differences in Deer Diets
A drought in the winter and early spring (November-May) of
1979-1980 followed by a very wet period during 1980-1981 (Figure 2),
created two contrasting periods.
During the late winter and spring of
1979-1980, 3.35 cm of precipitation was recorded at Panther Junction
(1140 m) compared with 16.9 cm during the same period in 1980-1981.
Therefore, the diets of the two herds were compared by year (1980 vs
1981) to determine whether similar forage use resulted from the spring
drought.
Both herds consistently decreased woody browse use with a
corresponding increase of forb usage from spring to winter (Figures 3,
4).
However, comparing each year by season, forb utilization was
generally greater for 1981 than 1980 (Figure 3).
For example, the
Panther Junction herd had forb percentages for 1980 (spring to winter)
49
50
of 12.5, 25.2, 57.5, and 32.9 compared to those for 1981 of 23.8,
61.0, 43.4, and 58.3.
Derivation of the coefficients of overlap (C)
(Table 2a) yielded C values below 0.6, the limit suggested by Marista
(1959) to indicate significant overlap.
The lower percentage for late
summer (as well as the highest C value) during 1981 was a result of
heavy use of mariola (Parthenium incanum) by both herds which exhibited
tremendous growth and flowering following the drought when summer rains
in-itiated in 1980 and continued through the winter of 1980-81.
The
Paint Gap herd had a similar pattern in forb use but differences
existed in the amount of seasonal increase in forb utilization between
the two years.
For instance, in 1980, the percentage for forb from
spring to winter was 4.2, 3.0, 56.5, and 47.9 contrasted with 1981
with 36.3, 53.8, 61.8, and 82.9.
The C values of forbs for the four
seasons also indicated significant differences in species composition
by the PG herd between 1980-81 (Table 2b).
As with the PJ herd, the
largest value was observed in late summer.
This is after the rainy
season had initiated and annual forb production is high from increased
precipitation.
Both herds preferred forbs throughout the year except
during the drought period when woody browse was the principle forage
component.
However, the PG herd in most seasons had considerably
greater forb use than the PJ herd during 1981.
An explanation may
rest upon differential availability once the rainy season started.
Use of woody browse including ceniza (Leucophyllum spp.),
range ratany, polygala (Polygala macradentia), and all evergreen
species by both herds decreased once the summer rain period began
51
(Figure 4).
Use of deciduous woody species increased with a corre-
sponding increase in annual forbs.
Reviewing the C values for browse, several patterns are found.
Both herds exhibited similar composition of browse species between
1980 and 1981 during the spring (Table 2a, b).
Spring is usually a
dry season and deer may rely on woody species since forbs are not
common until the summer rains occur.
The PJ herd had similar diet
patterns for browse during the summers of 1981 and 1980 whereas late
summer and winter the C values were exceedingly lower (Table 2a).
However, the PG herd had very low C values for summer through winter
(Table 2b) never exceeding 0.30.
Comparing herds for a given year
(Table "2c, d), generally indicates similar woody browse species in the
diet.
Succulent utilization during 1980 was greater for both herds
than during corresponding seasons in 1981 (Figure 5), particularly
during spring and summer.
Additionally, although only two species were
used to determine the overlap values, both herds exhibited differences
in succulent composition in the diet when comparing years (Table 2a,
b) with C values rarely exceeding 0.6.
DISCUSSION
Composited Deer Diets'
My results were similar to those of Carpenter et al. (1979)
concerning forb and woody use during the winter for Rocky Mountain mule
deer.
Utilization of forbs and grasses was high during the beginning
of their 60-day trial, however, as the forb and grass species became
dormant, the deer began to use woody browse more extensively.
Similar
results have been found in other studies (Smith 1952, Smith 1953,
Crouch 1966).
Payton and Garner (1980) found that moisture, crude fat,
and to a lesser extent crude protein levels increased for forb species
preferred by desert mule deer once the summer rains began.
The in-
crease in the percentage of woody species was not as significant as
that of the forbs.
Also, the higher palatability and nutrient content
of preferred forage species has been demonstrated (Nichol 1938, Hagen
1953, Swank 1956, McCulloch and Urness 1973, Radwan and Crouch 1974).
Thus, by selecting the most abundant and succulent forage species
during the spring and summer as observed in my study, deer may also be
acquiring the most nutritious forage.
This is important because
females are carrying and subsequently nursing fawns and males are
recovering from the rigors of the breeding season which extends from
December to February in BBNP (Kucera 1978).
The results of my study are comparable with those of other
deer food habit studies where deer utilize a relatively high amount of
browse (Boeker et al. 1972, Tueller 1979, Krysl and Simpson 1980).
52
53
The spring and summer periods, however, show signs of an increase in
forb and grass consumption.
Grass utilization of deer inhabiting
desert regions is low (less than 0.5 percent) (McCulloch and Keller
1975, Krausman 1978, Krysl and Simpson 1980).
Krausman (1978) found succulent use to be very large throughout the year whereas in this study, usage of succulent species was
low.
This may be a result of the technique used to assess deer diet.
Krausman (1978) based his findings on examination of rumen contents.
Anthony and Smith (1974) stated that differential digestion of plant
species may result in biasing plant species frequency determination.
Succulents, particularly lechuguilla, compose a large portion of
desert mule deer diet in Texas.
Anderson (1949) studying desert mule
deer in Texas found that deer spent 9.5 percent of total feeding
minutes consuming lechuguilla.
Extensive field observations of feeding
deer during this study also indicated that desert mule deer relied
heavily upon lechuguilla and to a lesser extent on prickly pear.
Deer
would feed upon the lower portion of the leaf, thoroughly masticating
it without ingesting appreciable amounts of plant material.
There-
fore, deer were apparently utilizing the more succulent portions of
the lechuguilla and this material may have been thoroughly digested by
rumen microfauna precluding detection via fecal analysis.
Annual and Topographic Differences
The low use of forbs for the PG herd during the spring and
early summer in 1980 compared to PJ reflects in part the more xeric
condition farther from the Chisos Mountains.
Deer at PJ may have
54
utilized forb species found within riparian areas in the foothills
during the drought period.
The PG herd inhabits the more arid desert
lowlands and may have to rely upon evergreen browse species during
prolonged dry periods because forb response is delayed due to higher
temperatures and irregular
rainfall~
Observations made after a snow-
storm which occurred in April, 1980 exemplify the more mesic conditions
for the Chisos Mountains and the surrounding foothills.
Snow remained
in selected areas along the slopes and washes of the higher elevations
for as long as 6 days.
within 24 hours.
However, at Paint Gap Hills, snow melted
The more gradual melting of snow over a prolonged
period may have prompted forb growth earlier at PJ than at PG.
It
was not until the summer rains occurred that forb growth was significant enough for deer at PG to begin using them as a principle food.
The effect of the drought during this study was similar for
both herds, where evergreen browse composed a substantial proportion of
the diet.
This is evidenced by the high overlap values for browse
(Table 2C, D).
Anthony (1976) also reported that a late winter-spring
drought during his study in Arizona resulted in desert mule deer
utilizing the more drought resistant and evergreen browse species.
Similarly, McCulloch and Urness (1973) found that mule deer diet during
the fall season following dry and wet summers respectively were different with a reduction in woody browse utilization following the wet
summer (89% versus 77%).
Consumption of browse decreased with a cor-
responding increase in forb use by deer in the Guadalupe Mountains
during a period of above average rainfall (Anderson et al. 1965).
55
The shift in forage use from evergreen browse to the more
succulent growth of annual and perennial forbs may be a reflection of
increased forage quality.
Dry matter digestibility of immature
grasses was 94% compared to 20% for mature grass stems (Short et al.
1974, Short et al. 1975).
Similarly, immature forbs had a digesti-
bility of 69% contrasted with 27% for mature plants.
Woody browse
digestibility was 75% for immature twigs versus 40% for mature stems.
The extremely low C values for succulents when comparing 1980
with 1981 for both herds may indicate a reliance upon the water contained within these plants during the drought period.
The lower
usage of lechuguilla and prickly pear during the late summer possibly
.
indicates an increased use of the abundant
. pools of water resulting
from summer thundershowers.
Krausman (1974) found that succulent use
decreased during the rainy season by white-tailed deer
(Q.
virgin-
ianus carminus) in BBNP where they used water available from summer
showers.
The results from this study support his conclusions.
Short
(1977) studying desert mule deer diet in Arizona reported that consumption of cacti during the dry periods of the year increased,
apparently to obtain the water found within these succulent plant's
tissues.
I expected the Paint Gap herd to utilize more succulents than
the Panther Junction herd due to the more arid nature of the desert
lowlands.
Krausman (1978) found that succulent usage by desert mule
deer on the more xeric lowlands was greater than the use by whitetailed deer and mule deer inhabiting the mesic habitats of the foothills of the Chisos Mountains.
However, succulent use by the Paint
56
Gap herd was comparable to that of Panther Junction during 1980 as
evidenced by the C values (Table 2C) and even more so for 1981 (Table
2D).
A possible reason concerns the perennial nature of the spring
system at Paint Gap Hills, and. possibly the use of browse and forb
species to obtain additional water.
The spring system is composed of
3 principle sources of water north of Paint Gap Hills.
During the
23 months of the study, water was found in at least one of the three
locations. collectively called Onion Spring.
Therefore, the Paint Gap
herd may not have needed to depend upon the succulent component of
the plant community for water.
The low dependence of desert mule deer on standing water and
the subsequent dependence upon plant material for water has been discussed by several authors (Mearns 1907, Anderson 1949).
FelV- deer
observations were made at perennial springs throughout the park.
Deer were more commonly observed far from springs.
However tracks of
mountain lion, bobcat, and coyote were commonly seen in washes leading
to and from flowing springs and these predators may have caused deer to
more heavily use plant material as a primary water source.
Addition-
ally, of 749 observations of deer groups during the study, only 16
observations were of deer drinking water.
The differences observed between the two herds may also be a
function of the distribution and percent occurrence of the habitats
found within the areas.
Although both regions contain similar
habitats, their relative abundance significantly differ (p < 0.001,
df = 5; Table 3).
The occurrence of creosotebush flats at PG indi-
cates the tendency for habitats associated with more xeric conditions
57
to occur (See Leopold 1984).
Thus, the food habits may be a reflec-
tion of the aridity of the areas inhabited by the herds which influences the distribution of habitats within their range.
SUMMARY
Diets of 2 desert mule deer herds inhabiting desert lowlands
and mountain foothills respectively within BBNP, Texas were studied
using fecal analysis.
Diet was analyzed in two stages.
The first
stage was an analysis of a composited sample comparing utilization of
four plant classes (woody, forb, grass, succulent) on a seasonal
basis.
Stage two assessed differences in forage utilization of two
herds relative to season, plant class, and drought effects.
Use of woody browse
seasons.
wa~
high during the spring and summer
Forbs became dominant forage once summer rains began in late
June and early July.
Unlike deer inhabiting more mesic environments,
desert mule deer use of grass species was low for both herds throughout the year.
This result was supported by other studies of mule deer
in desert habitats (McCulloch and Keller 1975, Krysl and Simpson 1980).
Succulent use was relatively low throughout the year and increased use
was observed during the drier periods.
Results of Krausman (1978)
indicated a significantly greater use of succulents compared to my
results.
However, he used rumen content to determine diet whereas I
used fecal analysis.
Differential digestion of the more fleshy succu-
lent plant species may be a partial explanation concerning the low
occurrence within my samples.
The drought which occurred between November 1979 and May 1980
resulted in a decrease in the available herbaceous forb species and
caused deer to rely on evergreen browse species.
58
Once summer rains
59
started, both herds increased forb consumption.
The principle dif-
ference observed between the herds was in forb and subsequently woody
use.
The deer inhabiting the more xeric site relied upon woody browse
during the drought whereas the animals inhabiting the foothills of
the Chisos Mountains were able to find sufficient quantities of forbs
in riparian areas.
Diet of desert deer are obviously affected by several factors
including annual and seasonal rainfall patterns which influence plant
abundance and distribution and secondly, topographic location of
individual herds.
ta~n
Those animals inhabiting desert foothills of moun-
ranges experience more mesic conditions than those found on lower
elevations.
This results in each herd relying upon different vegeta-
tive components of the habitat and requires an extreme generalist
feeding pattern regarding the deer population as a whole.
LITERATURE CITED
Alcoze, T.M. and E.G. Zimmerman. 1973. Food habits and dietary overlap of two herero myid rodents from the mesquite plains of
Texas .. J. Mamm. 54:900-908.
Anderson, A.E., W.A. Snyder, and ·G.W. Brown. 1965. Stomach content
analysis related to condition in mule deer, Guadulupe Mountains, New Mexico. J. Wildl. Manage. 29:352-364.
Anderson, A.W. 1949. Early summer foods and movement of mule deer
(Odocoileus hemionus) in the Sierra Vieja Range of southwestern Texas. Texas J. Sci. 1:45-50.
Anthony, R.G. 1976.
desert deer.
Influence of drought on diets and numbers of
J. Wildl. Manage. 40:140-144.
, and N.S. Smith.
---------analysis to describe
1974. Comparison of rumen and fecal
deer diets. J. Wildl. Manage. 38:535-
540.
Boeker, E.L., V.E. Scott, H.G. Reynolds, and B.A. Donaldson. 1972.
Seasonal food habits of mule deer in southwestern New Mexico.
J. Wildl. Manage. 36:56-63.
Carpenter, L.H., O.C. Wallmo, and R.B. Gill. 1979. Forage diversity
and dietary selection by wintering mule deer. J. Range.
Manage. 32:226-229.
Constan, K.J. 1972. Winter foods and range use of three species of
ungulates. J. Wildl. Manage. 36:1068-1076.
Correll, D.S. and M.C. Johnston. 1970. Manual of the vascular plants
of Texas. Texas Res. Found. Renner, Texas. 1881 pp.
Crouch, G.L. 1966. Preferences of black-tailed deer for native forage
and Douglas fir seedlings. J. Wildl. Manage. 30:471-475.
DeNio, R.M. 1938. Elk and deer foods and feeding habits.
Amer. Wildl. Confer. 3:421-427.
Trans. N.
Deschamp, J.A., P.J. Urness, and D.D. Austin. 1979. Summer diets of
mule deer from lodgepole pine habitats. J. Wildl. Manage.
43:154-161.
Ferrel, C.M. and H.R. Leach. 1950. Food habits of a California deer
herd. Calif. Fish Game. 36:235-240.
60
61
Fracker, S.B. and J.A. Briskle.
bution of Ribes. Ecol.
1944. Measuring the local distri25:283-303.
Hagen, H.L. 1953. Nutritive value for deer of some forage plants in
the Sierra Nevada, California. Calif. Fish Game. 39:163-175.
Hansen, R.M. and L.D. Reid. 1975. Diet overlap of Deer, Elk, and
Cattle in Southern Colorado. J. Range Manage. 28:43-4?
Hill, R.R. 1956. Forage, food habits, and range management of the
mule deer. pp. 393-414. In: Taylor, W.P. 1956. The deer of
North America; the white-tailed, ule, and black-tailed deer,
genus Odocoileus, and their history and management. Stackpole
Co., Harrisburg, PA. and the Wildl. Manage. Insti. Wash. D.C.
668 pp.
Hubbard, R.E. and R.M. Hansen. 1976. Diets of wild horses, cattle,
and mule deer in the Piceance Basin, Colorado. J. Range Manage.
29:389-392.
Johnson, D.H. 1980. The comparison of usage and availability measurements for evaluating resource preference. Ecol. 61:65-71.
Keller, G. 1975. Seasonal food habits of desert mule deer (Odocoileus
hemionus crooki) on a specific mule deer-cattle range in Pecos
County, Texas. M.S. Thesis. SuI Ross State University 80 pp.
Krausman, P.R. 1978. Forage relationships between two deer species in
Big Bend National Park, Texas. J. Wildl. Manage. 42:101-107.
Krysl, L.J. and C.D. Simpson. 1980. Food habits of mule deer and elk
and their impact on vegetation in Guadalupe Mountains National
Park, Texas. Texas Tech. Univ. ColI. Agric. Proj. No. TTA9-78. Final Rep. 119 pp.
Kucera, T.E. 1978. Social behavior and breeding system of the desert
mule deer. J. Mamm. 59:483-476.
Leach, H.R. 1956. Food habits of the Great Basin deer herd of
California. Calif. Fish Game. 42:243-308.
, and J.L. Hiehle. 1957. Food habits of the Tehoma deer
herd. Calif. Fish Game. 43:161-178.
--------~
Leopold, B.D. 1984. Ecology of the desert mule deer in Big Bend
National Park, Texas. Diss. University of Arizona
Lovaas, A.L. 1958. Mule deer food habits and range use, Little Belt
Mountains, Montana. J. Wildl. Manage. 22:275-283.
62
Marista, M. 1959. Measuring of interspecific association and similarity between communities. Mem. Fac. Sci. Kyushu Univ.,
Ser. E. Biol. 3:65-80.
McCulloch, C.Y. 1972. Deer foods and brush control in southern
Arizona. J. Ariz. Acad. Sci. 7:113-119.
__________ , and P.J. Urness. 1973. Deer nutrition in Arizona chaparral and desert habitats. Ariz. Game Fish Dept. Spec. Rep.
No. 3 VI. 68 pp.
Mearns, E.A. 1907. Mammals of the Mexican boundary on the United
States. Bull. U. W. Nat. Mus. 56:1-530 •
. Morris, M.S. and J.E. Schwartz. 1957. Mule deer and elk food habits
on the National Bison Range. J. Wildl. Manage. 21:189-193.
Nellis, C.H. and R.L. Ross. 1969. Changes in mule deer food habits
associated with herd reduction. J. Wildl. Manage. 33:191195.
Nichol, A.A. 1938. Experimental feed~ng of deer. Ariz. Agric.
Exper. Sta. Tucson, Ariz. Tech. Bull. No. 75. 39 pp.
Nudds, T.O. 1980. Forage "preference": Theoretical considerations
of diet selection by deer. J. Wildl. Manage. 44:735-740.
Payton, T.W. and G.W. Garner. 1980. Nutritional values for selected
forages of desert mule deer in southwest Texas. Proc. Ann.
Confer. West. Assoc. Fish Wildl. Agencies. 60:601-619.
Radwan, M.A. and G.L. Crouch. 1974. Plant characteristics related
to feeding preferences by black-tailed deer. J. Wildl. Manage.
38:32-41.
Reynolds, H.W., R.M. Hansen, and D.G. Peden. 1978. Diets of the
Slave River Lowland bison herd, N. W. Territories, Canada.
J. Wildl. Manage. 42:581-590.
Richens, V.B. 1967. Characteristics of mule deer herds and their
range in northeastern Utah. J. Wildl. Manage. 31:651-666.
Short, H.L. 1977. Food habits of mule deer in a semidesert grassshrub habitat. J. Range Manage. 30:206-209.
__________ ' R.M. Blair, and E.A. Epps Jr. 1975. Composition and
digestibility of deer browse in southern forests. USDA For.
Ser. Res. Pap. SO-Ill. 10 pp.
63
_________ , R.M. Blair, and C.A. Segelquist. 1974. Fiber composition
and forage digestibility by small ruminants. J. Wildl. Manage.
38:197-209.
Smith, A.D. 1953. Consumption of native forage species by captive
mule deer during summer. J. Range Manage. 6:30-37.
Smith, J.G. 1952. Food habits of mule deer in Utah.
16:148-155.
J. Wildl. Manage.
Spark, D.R. and J.C. Malachek. 1968. Estimating percentage dry weight
in diets using a microscope technique. J. Range Manage. 21:
264-265.
Squires, U.R. 1982. Dietary overlap between sheep, cattle, and goats
when grazing in common. J. Range Manage. 35:116-119.
Swank, W.G. 1956. Protein and phosphorous content of browse plants
as an influence on southwestern deer herd levels. Trans. N.
Amer. Wildl. Conf. 21:141-158.
Tueller, P.T. 1979. Food habits and nutrition of mule deer on Nevada
Ranges. Final Rep. F.A. Wildl. Res. Proj. W-48-5, Study 1,
Job 2. 104 pp.
64
TABLE 1.
Composite summary of desert mule deer diets in Big Bend
National Park, Texas 1980-1981.
Season
Species
Spring
Sunnner
Leucophyllum spp.
Krameria glandulosa
Poly gala macradentia
Parthenium inc anum
Janusia gracilis
Gaura spp.
Salaz aria mexicana
Diospyrus texana
Other Woody
57.0
3.7
1.1
3.7
0.1
0.2
19.5
25.8
3.2
3.1
Woody Total
Life Form:
Late
Sunnner
Winter
Combined
Woody
T
1.5
6.3
6.7
17.6
10.0
15.0
5.9
3.5
8.3
1.1
1.1
2.5
0.0
37.3
23.3
10.4
3.6
8.2
2.9
1.3
1.3
2.8
3.3
0.0
0.0
1.1
0.0
70.0
56.6
43.1
38.4
52.0
Dalea neomexicana
Euphorbia spp.
Lesquerella spp.
Nerisyrenia campo rum
Psilotrophe spp.
Sphaeralcea spp.
Erodium spp.
Melampodium leucanthum
Abutilon spp.
Tidestromia lanuginosa
Connnelinia spp.
Other Forb
10.3
2.9
1.0
2.3
16.1
16.3
17.0
16.9
15.9
12.3
4.9
T
1.6
14.9
11.9
4.5
2.3
1.0
1.0
T
T
Forb Total
Life Form:
T
T
T
T
T
T
1.4
Forb
U.8
4.1
T
T
1.0
0.3
0.4
2.0
2.9
1.3
1.3
T
T
T
T
T
2.1
T
1.9
1.4
3.4
0.0
0.0
1.5
2.3
9.5
0.0
1.7
2.3
20.0
38.3
54.9
56.4
42.4
Agave lecheguilla
Opuntia spp.
4.1
5.6
1.0
4.0
1.2
4.1
1.0
2.4
2.9
Succulent Total
9.6
5.0
1.6
5.0
5.3
Life Form:
T
0.7
1.2
T
T
T
T
T
T
1.7
Succulent
T
*Trace item, percent occurrence less than 1.0%.
65
TABLE 2.
Coefficients of overlap for plant species composition of the
diets of two desert mule deer herds in Big Bend National
Park, Texas. (Panther Junction, PJ; Paint Gap, PG)
Coefficients of Overlap
Season
a.
Grass
All Classes
0.98(15)
0.84(12)
0.56(5)
0.10(11)
0.44(9)
0.12(15)
0.09(13)
0.58(2)
0.31(2)
0.28(2)
0.05(2)
0.47(1)
0.00(1)
0.00(0)
0.00(2)
0.95(27)
0.54(30)
0.56(21)
0.24(28)
0.14(16)
0.13(9)
0.52(13)
0.44(11)
0.27(2)
0.07(2)
0.73(2)
0.77 (2)
0.00(1)
0.00(1)
0.00(3)
0.00(1)
0.92(36)
0.16(22)
0.43(28)
0.36(25)
0.13(11)
0.04(11)
0.64(12)
0.79(10)
0.93(2)
0.97(2)
0.92(2)
0.38(2)
0.00 (1)
0.00(1)
0.00(2)
1. 00 (1)
0.90(30)
0.44(24)
0.60(24)
0.84(25)
0.87 (13)
0.88(1l)
0.34(12)
0.55(1l)
0.87(2)
0.37(2)
0.83(2)
0.10(2)
0.80(1)
0.00(1)
0.00(1)
0.00(1)
0.96(29)
0.88(26)
0.58(23)
0.51(24)
0.56(14)
0.96(17)
0.19(10)
0.24(10)
0.09(11)
PJ 1980 vs PG 1980:
Spring
Summer
Late Summer
Winter
d.
Succulent
PG 1980 vs PG 1981:
Spring
Summer
Late Summer
Winter
c.
Forb
PJ 1980 vs PJ 1981:
Spring
Summer
Late Summer
Winter
b.
Browse
0.91(16)
0.44(10)
0.51(8)
0.91(12)
PJ 1981 vs PG 1981:
Spring
Summer
Late Summer
Winter
0.97(13)
0.89(12)
0.89(8)
0.31(10)
*Numbers in parentheses represent number of species found
within the diet and compared for degree of overlap.
66
TABLE 3.
Habitat distribution within Panther Junction and Paint Gap
Hills in Big Bend National Park, Texas.
Habitat
(Vegetative Association)
Panther Junction
Acreage (ha) Percent
Paint GaE Hills
Acreage(ha) Percent
65
2.6
0
0.0
Sotol-lechuguilla-grass
288
11.5
694
10.2
Lechuguilla-grass
257
10.3
354
5.2
1049
41.8
4814
70.9
850
33.9
411
6.1
0
0.0
521
7.7
Creosotebush-lechuguillagrass
Creosotebush-tarbush
Viguieria-lechuguillagrass
Creosotebush Flats
67
oI
10
20
t
I
Miles
ega de
~~nquila
\..
• Canyon
...
-tll)t~~.~~
Flag
...
I;/en'a ' ':\,
anyon
"
C
.
A
VT/.
. '\:0
~
'- Q
\~~Qe
"',
,,~
'-' ...
.,
", ... "'
FIGURE 1. Big Bend National Park, Texas (1. Dagger Mountain, 2. Dagger
Flat, 3. Upper Tornillo Flats, 4. McKinney Hills,S. Lower Tornillo
Flats, 6. Onion Spring, 7. Hannold Draw, 8. Croton Spring, 9. Government
Spring, 10. Green Gulch, 11. Panther Junction, 12. Pine Canyon,
13. Juniper Canyon, 14. Boquillas, 15. Sotol Vista, 16. Kit Mountain)
68
"E15.0
9
C
010.0
-...., .
CU
....,
-s.. 5.0
-o
J: 1.0 ~~~....--r-r-'-'-~~r-r-"9"-r-r-~
Oc
Ja Ap Jul
1980
Ja Ap Jul Oc De
1981
Month
FIGURE 2. Total monthly precipitation recorded at Panther Junction,
Texas for 1980 and 1981.
COO]
j
/
/
/
/
/
,,/
60.0
+'
:J
CD
g» 40.0
+'
..
C
8
-Panther
Junction
,
- --Paint Gap Hills
~
Sp
S
LS
1980
w
Sp
S
LS
1981
w
FIGURE 3. Seasonal and annual forb utilization by the Panther Junction and Paint Gap Hills
desert "mule deer herds in Big Bend National Park, Texas. (Sp = Spring, S = Summer, LS =
Late Summer, W = Winter)
0'1
1.0
8 80.0
,--
......
«J
N
::60.0
.....
::l
CD
g»40.0
........
.....c:
' .....
CD
(,)
G; 20.0
a.
Panther .JunctionPaint Gap Hills---Sp
S
LS
1980
,,
,,
"
w
Sp
S
LS
1981
w
FIGURE 4. Seasonal and annual woody browse utilization by the Panther Junction and the
Paint Gap Hills desert mule deer herds in Big Bend. National Park, Texas. (Sp = Spring,
S = Summer, LS = Late Summer, W = Winter)
-...J
o
c
0
.-
...,
CO
-Panther Junction
---Paint Gap
N
.....,-
-
:J
30.0
8,
co
C
...~
~
10.0
~--Sp
S
LS
1980
w
Sp
S
--LS'
w
1981
FIGURE 5. Seasonal and annual succulent utilization by the Panther Junction and the Paint
Gap desert mule deer herds in Big Bend National Park, Texas. (Sp = Spring, S = Summer,
LS = Late Summer, W = Winter)
""-oJ
.....
APPENDIX II
Changes in prey utilization by predators in Big Bend National Park,
Texas.
72
TABLE OF CONTENTS
Page
LIST OF TABLES
74
LIST OF ILLUSTRATIONS
75
ABSTRACT
76
INTRODUCTION
77
STUDY AREA
79
MATERIALS AND METHODS
80
Deer density assessment
Predator diet determination
RESULTS AND DISCUSSION
80
81
82
Trends in deer density
Predator diet and changes in prey density
Mountain lion
Coyote
Bobcat
Lagomorph population levels
82
84
84
85
87
88
SUMMARY AND CONCLUSIONS
90
LITERATURE CITED
92
73
LIST OF TABLES
Table
1
3
Page
2
Desert mule deer density (deer/km ) for areas in
Big Bend National Park, Texas for 1972-1974 and
1980-1981 • • • • • • • • • • • • • • • • • • •
98
Comparison of group size distribution of desert
mule deer in Big Bend National Park, Texas for
1972-1974 and 1980-1981 • • • • • . • • • • • •
99
Comparative analysis of mountain lion, coyote,
and bobcat s.cats collected in Big Bend National
Park, Texas between 1972-1974 and 1980-1981 • •
100
74
LIST OF ILLUSTRATIONS
Page
Figure
1
Big Bend National Park, Texas • . • • . • • • • • • • • •
75
101
ABSTRACT
Mountain lion (Felis concolor), bobcat (Lynx rufus), and
coyote (Canis latrans) scats were collected during 1972-1974 and 19801981, in Big Bend National Park (BBNP), Texas.
Deer declined signifi-
cantly during this period as evidenced by pellet-group transects.
Associated with the decline in deer density was a change in the diet
of predators.
Mountain lions utilized smaller prey items including
javelina and lagomorphs while the lion population remained relatively
constant.
Coyote fed opportunistically by increasing use of insects,
birds, reptiles, and lagomorphs while percent deer in the diet declined.
Bobcats were more selective in their feeding response with
a greater utilization of lagomorphs while other prey utilization remained the same.
Given the presence of alternate prey species,
predator population levels remained relatively constant.
76
INTRODUCTION
Diet studies of mountain lion, bobcat, and coyote primarily
determine diets over a short period of time.
Although valuable, these
studies do not provide information on the impact of long-term changes
in prey abundance on predator diets.
Early studies on predation
(Utida 1957, Huffaker 1958) provided data supporting hypotheses on
predator-prey relationships (Lotka 1925, Volterra 1926).
However,
these studies involved invertebrates in laboratory conditions.
Studies concerning vertebrate predators and invertebrate prey (Holling
1959, Buckner and Turnock 1965) report changes in prey utilization
relative to prey abundance but provide little information on the use
of. other prey
interactions.
speci~s.
Most studies concern simple predator-prey
Mountain lion predation on white-tailed deer (Odo-
coileus virginianus) and elk (Cervus elaphus) in Idaho did not
control density of these two ungulate species (Hornocker 1970).
The
classic lynx-hare cycle (MacLulich 1937) probably involves additional
parameters beside the simple lynx-hare interaction including factors
associated with the plant community (Keith 1973).
Thus, the question
arises concerning the effect of changes in prey abundance on predator
food habits within populations where several mechanisms are acting
to maintain suitable predator and prey densities.
Studies indicating terrestrial predator diet changes corresponding with changes in primary prey species abundance are limited.
77
78
Beasom and Moore (1977) found bobcat utilization of cottonrat
(Sigmodon spp.) proportional to its abundance in Texas.
Similar
conclusions were made by Brand and Keith (1979) concerning lynx (Lynx
~)
and snowshoe hare (Lepus americana) in Alberta.
tion of jackrabbits
(1.
Coyote utiliza-
californicus) was related to jackrabbit density
(Clark 1972, Wagner and Stodart 1972).
Additional studies concerning
coyote diets and prey density changes found similar relationships
(Fitch 1955, Korschgen 1957).
No previous studies concerned mountain
lion diet and changes in prey abundance over time.
However, Shaw
(1980) reported that differences observed in percentages of prey
species in scats from two locations in Arizona may have been related
to different prey population densities.
I examined diets of mountain lions, bobcats, and coyotes in
Big Bend National Park (BBNP), Texas in 1972-1974 and in 1980-1981 to
examine the general diets as well as the impact of changes in prey
abundance on the diet of these predators.
I test the hypothesis that
the diets of mountain lion, bobcats, and coyotes change as the available prey base changes.
STUDY AREA
Big Bend National Park in Brewster Co., Texas is located 113
km from Marathon, Texas (Figure 1).
The Big Bend Region is included in
the Chisos Biotic district (Dice 1943, Blair 1947) and occupies over
2
2866 km.
Elevations extend from 573 m along the Rio Grande to 2384 m
at Mt. Emory in the Chisos Mountains.
The park is diverse in plant
communities including Pinyon-Oak-Juniper woodlands within the higher
elevations of the Chisos Mountains, creosotebush (Larrea tridentata)
associations on the flats surrounding the Chisos, and extensive
riparian areas along the Rio Grande (Leopold and Krausman, in press).
The park is characterized by hot summers, mild winters, and
low rainfall.
0
Temperatures often exceed 38 C in the desert regions
during the summer and are rarely freezing during the winter.
Precip-
itation occurs primarily from May through October, ranging from
~
28 cm
in the desert and the surrounding foothills to 41 cm in the mountains.
79
MATERIALS AND METHODS
Deer Density Assessment
Twenty-five pellet-group transects (Bennett et al. 1940) were
established and sampled by the National Park Service (NPS) from 1968
to 1972.
Nine of these transects were in desert mule deer habitat
and 4 (3 in Green Gulch and 1 in Pine Canyon) were sampled by Krausman
(1974) in 1972.
Additionally, Krausman (1974) sampled a transect in
Juniper Canyon.
In 1980 and 1981, 4 of the 5 transects were resampled
for comparative purposes (2 in Green Gulch and 1 in Pine and Juniper
Canyons respectively).
Each transect comprised two parallel lines
21.9 m apart with 20 paired, 0.004-ha circular plots.
paired plots was at 88.1 m intervals.
Each of the
The transects were sampled
quarterly in August, November, February, and June.
Before initial
sampling, all plots were.cleared of previously deposited fecal groups
as well as after each sampling.
A pellet-group was considered within
the sampling area if 50% of the pellet-group was within the plot.
Changes in deer abundance were assumed to be directly proportional to
changes in pellet-group abundance between 1972-1974 and 1980-1981.
Group size of deer has been related to density in red deer
(Cervus elaphus) (Clutton-Brock et al. 1982).
I therefore additionally
compared frequency distributions of deer group sizes obtained from
independent observations of desert mule deer from 1972-1974 and 19801981 as a second index to assess population change.
80
Independent
81
observations were observations of deer whose actions were not influenced by another observation.
The frequency distributions were
compared using Chi-square analysis.
I assumed that if the deer popu-
lation changed significantly between the 2 time periods, group sizes
would significantly differ.
Predator Diet Determination
Diets of the mountain lions, bobcats, and coyotes were estimated from scat analysis.
The usefulness of this technique was demon-
strated by Scott (1941) and Murie (1946).
Scats were collected
throughout the study area during field excursions.
could be readily identified were collected.
Only scats that
Scat identification was
based on size and shape (Murie 1975).
Scats were broken apart by hand and separated according to
prey species.
Micro and macroscopic hair characteristics in conjunc-
tion with miscellaneous bone material were used to identify prey items.
Museum specimens maintained at park headquarters and keys of hair
characteristics (Hausman 1920, Mayer 1952, Stains 1958, Moore et al.
1974) were used to identify individual prey items.
Estimates of
frequency of occurrence were determined for each prey species and
proportions were compared on an individual species basis.
This was
necessary because an individual scat often contained more than one
prey item.
RESULTS AND DISCUSSION
Trends in Deer Density
Pellet-group data for Lower Juniper Canyon, Lower Green Gulch,
and Lower Pine Canyon indicated that the desert mule deer population in
BBNP declined between 1974 and 1980 (Table 1).
The reason for the decline is unclear.
fall for the 2 periods were similar (1972-1974:
x = 37.6
Average annual rain-
x = 37.5
vs 1980-1981:
em) and no drying trends occurred between the 2 periods.
Examination of NPS Annual Wildlife Reports for BBNP between 1944 to
1973 indicates that the deer population fluctuated.
deer population was estimated at 1000 animals.
In 1952-1953 the
However, following
this period, the population gradually declined and by 1957 the deer
population was estimated to be between 300 and 400 animals.
By 1963,
the deer population had increased to approximately 3000 deer.
The
cause of the decline in the mid-1950's was attributed to drought and
mountain lion predation (NPS Wildl. Reps., BBNP, Texas).
The influ-
ence of spring droughts on fawn survival and production has been discussed previously (Leopold 1984) as an important factor in deer herd
regulation in BBNP.
During 1975 and 1977, total annual rainfall was
24.2 cm and 17.4 cm respectively compared to an overall average of 34.3
cm for 1960 to 1979.
The spring seasons of 1975 and 1977 had 3.43 and
3.96 cm respectively contrasted with the 1960-1979 average of 7.67 cm.
Therefore, these 2 spring droughts occurring only 1 year apart
combined with a spring drought in 1980 with only 2.64 cm of spring
82
83
rainfall, may have contributed to the significantly reduced mule deer
population.
Chi-square analysis of group sized (Table 2) support the
pellet-group results when testing the null hypothesis that frequencies
of group size classes are similar for 1972-1974 and 1980-1981.
The
probability of observing groups of 9 or more deer during 1972-1974 was
greater than during 1980-1981 (Table 2).
Predator Diet and Changes in Prey Utilization
Mountain Lion
Diets of the mountain lion on the study area as well as for
the bobcat and coyote for 1972-1974 have previously been reported
(Krausman and Ables 1981).
The scat analyses for mountain lions during
1980-1981 (Table 3; For more detailed analysis, see Leopold 1984,
Appendix V) are comparable to other studies where large ungulate
species are the principle prey item (Dixon 1925, Hibben 1939, Connolly
1949, Robinette et al. 1959, Hornocker 1970, Spalding and Lesowski
1971, Nero and Wigley 1977, Shaw 1980).
Comparative analysis of the results for 1972-1974 with 1980-
1981 indicate significant changes in prey use (Table 3).
Percentage
of scats with deer, porcupine (Erethizon dorsatum), and skunks
(Mephitis spp.) decreased whereas percent occurrence of javelina
(Dicoty1es tajacu), Lagomorpha, and ringtai1 (Bassariscus astutus)
increased.
I suspect that the decrease in the desert mule deer
population resulted in mountain lions shifting their food habits to
smaller prey.
84
Porcupines, which were abundant during 1972-1974, were very
rare during 1980-1981.
along the Rio Grande.
During 1980-1981 only one animal was reported
The importance of porcupines in the diet of
mountain lions was reported by Hibben (1937), Robinette et al. (1959),
and Spalding and Lesowski (1971).
Javelina populations were large during the 1980-1981 period
with herd sizes ranging from 10 to 15 animals.
McKinney Hills totaled 45 animals.
One herd within the
Bissonette (1976) observed the
average group size of javelina herds during 1973-1974 to be 14.2 from
November to February and 9.3 and 9.8 from March to June and July to
October respectively.
These data indicate that the javelina population
in BBNP remained at similar levels between the two periods.
This is
not surprising since javelina may breed during any time of the year
(Sowls 1966).
However, there was limited breeding during summer in
BBNP (Bissonette 1976).
Most studies of simple predator-prey relationships indicate
the classic predator-prey oscillations where productivity of the
predator decreases with the decline of the prey (MacLulich 1937, Mech
1966, pp. 167-168).
However, our evidence does not indicate that the
mountain lion population in BBNP declined during the decline in the
deer population.
Sightings of mountain lions reported by park
visitors between 1967 and 1980 show no discernible change, even though
visitation within the park has gradually decreased over the past 5
years.
Additionally, I estimated that 14 to 16 resident lions and
approximately 6 to 8 cubs were present in the study area during 1980-
85
1981.
This estimate is based on my observations of scats, lion kills,
tracks, scrapes, as well as visual sightings and reports by park
visitors.
I wish to emphasize that this estimate is presented as a
minimum and corresponds with figures estimated by local authorities
(R. McBride, pers. comm).
Krausman and Ables (1981) estimated 6 to
12 lions (for the period of 1972-1974) inhabited the park and was
based on conversations with McBride.
Therefore, it is reasonable to
assume that the mountain lion population within the park boundaries
remained relatively constant.
The results indicate that when the deer population declined,
mountain lions may have shifted to javelina and lagomorphs as alternate
food sources.
This is contrary to simple predator-prey
~odels
which
predict that the lion population should have declined with the deer
population.
My results indicate that the mountain lion is able to
change its diet if alternate prey items are available.
The basic
premise that mountain lions depend upon deer as a source of food may
not be as valid as believed and may be a function of the locations
of previous studies where alternate prey was limited.
Coyote
A comparison of prey found in 410 scats collected during 19801981 (Table 3; For more complete analysis, see Leopold 1984, Appendix
V) with other coyote diet studies indicate that coyote food prefer,!Ilee
appears to be quite diverse and somewhat dependent on geographical
location.
In general, however, lagomorphs and rodents were primary
prey items (Sperry 1941, Crater 1943, Fitch 1948, Tiemeier 1955,
Ellis 1959, Mathwig 1973, Michaelson 1975) with deer and other large
86
ungulates being important secondary food items in many locations (Bond
1939, Ferrel et al. 195'3, Knowlton 1964, Ozoga and Harger 1966, Ogle
1971, Hawthorne 1972, Gipson 1974, Richens and Hugie 1974, Holle 1978,
Litvaites and Shaw 1980).
Comparison of the 1972-1974 scat collectior.s with the 19801981 collections indicate similar diet changes as found with the mountain lion (Table 3).
Percentage of scats containing deer and javelina
decreased with a corresponding increase in the percentage of lagomorphs, birds, insects, and reptiles (Table 3).
rat (Neotoma albigula) and
cottonrat~
Frequencies of wood-
remained unchanged.
Utilization
of seeds and fruit decreased indicating that coyotes relied on another
food source instead of utilizing this sedentary food item.
However,-
vegetation is subject to extreme variation resulting from yearly
climatic conditions.
Positive correlations have been found between coyote prey use
and prey abundance (Fitch 1955, Tiemeier 1955, Korschgen 1957, Ellis
1959, Clark 1972).
Rodents and lagomorphs were the most important food
items in these diet studies.
However, the importance of coyote preda-
tion on deer in Texas has been demonstrated by several authors
(Knowlton 1964, Cook et al. 1971, Garner et al. 1976, Carroll and
Brown 1977, Dickinson et al. 1980).
On the study area, a reduction in
lion predation on deer during the two periods probably would result
in a decrease in abundance of carrion for coyotes.
I expected javelina occurrence in coyote scats to increase as
it had in the diet of lion.
However. utilization of javelina was
greater for 1972-1974 than in 1980-1981.
An adult javelina weighs
87
13.6 to 27.2 kg (Schmidt and Gilbert 1978) which is considerably
smaller than the average weight of an adult desert mule deer (68.6 kg,
Krausman and Leopold, unpubl. data).
Approximately 3.3 javelina must
be killed to equal the meat obtaj.ned from one adult deer.
Thus an
adult mountain lion consuming a javelina would leave less carrion
compared to a lion consuming an adult deer.
Two fresh lion-killed
javelina were encountered and visited on successive days.
On both
occasions, the carcass was completely consumed within 2 days whereas
lions may feed upon a deer for 3 to 4 days.
Observations of car-killed
deer carcasses showed that vultures found carcasses within 2 to 3
hours whereas coyotes did not appear until 24 to 48 hours after the
kill
Bobcat
Analysis of bobcat scats (Table 3; For a more complete
analysis, see Leopold 1984, Appensix V) indicated that rodents and
lagomorphs are principle food items.
Studies indicating the dominance
of lagomorphs include Davis (1955), Progulske (1955), and Fritts and
Sealander (1978).
Cottonrat was the principle prey item in Georgia
(Knight 1960) whereas woodrat and lagomorphs were important components of the diet of bobcats in Arizona (Jones and Smith 1979).
Deer
were found to compose significant percentage of the diet of bobcats
in a variety of habitats (Hamilton and Hunter 1939, Rollings 1945,
Pollack 1951, Westfall 1956, Gashwiler et al. 1960, McCord 1974).
However, heavy predation of deer by bobcats occurs more commonly in
the northern portions of the bobcats' range.
The ability of bobcats
88
to kill deer has been documented (Marston 1942, Smith 1945, Matson
1948, Petraberg and Gunvalson 1962).
The results of 1972-1974 scat analyses indicate that rodents
are imp'ortant to the bobcat as a food source.
Additionally, 25% of
the scats contained deer hair and/or remains, but percentage of deer
in scats significantly decreased from 25.0 to 2.8 percent between
1972-1974 and 1980-1981 (Table 3).
Percent occurrence of lagomorphs
increased, indicating a shift in prey utilization to the relatively
more abundant lagomorphs.
Other prey items, including birds, woodrat,
cottonrat and javelina remained unchanged.
(Spermophilus spp.) decreased however.
The occurrence of squirrel
Additionally, changes 'of prey
abundance in Texas resulted in changes in bobcat diets (Beasom and
Moore 1977).
Jones and Smith (1979) found that bobcat prey utilization in
Arizona did not shift with changes in the principle prey species.
'They concluded that bobcats are not opportunistic predators.
results of my study differ with their findings.
The
Bobcats reacted to
the decrease in the deer population, a secondary food source, by
maintaining lagomorphs as their principle food.
This is supported by
the fact that percentages of the scats containing other prey items
remained the same, whereas percentage of lagomorphs increased.
Lagomorph Population Levels
One assumption underlying the above discussions of all three
predators is that the lagomorph population remained relatively constant
between 1972-1974 and 1980-1981.
The prolific reproductive character
89
of the lagomorpha needs little discussion and several authors have
stated that natural predators have not been a major force in controlling rabbit populations (Garlough et al. 1942, Johnson 1964, French
et ale 1965, Evans et ale 1970).
Productivity of the desert cotton-
tail (Sylvilagus auduboni) in Arizona was not correlated with
climatic factors such as rainfall (Sowls 1957) however, Sadlier (1969,
pp. 132-136) found that rainfall directly and positively affected
lagomorph reproduction.
Spring droughts would have a greater impact
on the lactating doe who fawns once per year compared to lagomorphs
who have up to an 8 month breeding season (Sowls 1957).
Summer
showers even after a spring drought would result in summer plant
regrowth and increased productivity by rabbits (Sadlier 1969, pp. 132136).
Given a spring drought (January-June) however, rainfall during
the summer would not reverse the pre-natal fawn mortality from poor
doe nutrition during the spring period.
Additionally, French et ale (1965) found that delayed
breeding by jackrabbits resulted in a "compensation" by the population
by increasing production of young in later months.
Vorhies and Taylor
(1933) found that jackrabbits in southern Arizona displayed a 10month breeding season extending from December to September, further
substantiating my claim that a spring drought would not drastically
reduct rabbit densities compared to mule deer density.
SUMMARY AND CONCLUSIONS
Diets of mountain lions, bobcats, and coyotes in BBNP, Texas
for the distinct periods of 1972-1974 and 1980-1981 were compared.
General patterns of prey utilization changed significantly (p < 0.005)
for each predator species and the shifts were associated with a major
decline in deer density.
Proportions of javelina and smaller mammals including lagomorphs and ringtails in mountain lion scats increased, possibly a
result of the decreased abundance of deer.
The javelina population
did not suffer the severity of population decline seen for deer
between the two periods as indicated by large herd sizes and frequent
observations of javelina during field excursions.
The results show
that a large predator such as the mountain lion is able to change prey
species given that an alternate food source is available.
Coyote utilization of deer decreased from 21% to less than
5%.
Increased occurrence of lagomorphs, ringtail, birds, insects,
and reptiles were observed within scats indicating the opportunistic
nature of the coyote.
The lower utilization of deer by coyote was
partially attributed to fewer deer carcasses from lion kills and cardeer collisions.
Lagomorph percentages in bobcat scats increased in association
with the lower deer abundance.
Percent occurrence of deer in scats
decreased from 25% to less than 3%.
90
Utilization of other mammalian
91
prey beside the lagomorphs remained unchanged possibly indicating
that bobcats are opportunistic concerning prey utilization.
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98
TABLE 1.
2
Desert mule deer density (deer/km ) for areas in Big Bend
National Park, Texas for 1972-1974 and 1980-1981.
2
Deer Density (deer/km )
Location
Lower Pine Canyon
Lower Juniper Canyon
Lower Green Gulch
1972-1974
1980-1981
11 (1. 7, 8)*
0.8 (0.8, 3)
8 (1.0, 8)
1.0 (0.6, 7)
19 (2.2, 24)
0.4 (0.2, 6)
*Numbers within parentheses are the standard error of the mean
and the number of times the transect was sampled.
99
TABLE 2.
Comparison of group size distribution of desert mule deer in
Big Bend National Park, Texas for 1972-1974 and 1980-1981.
Group Size Frequencies
Gro·up Size Class
1972-1974
1980-1981
1-2
135
446
3-4
68
190
5-6
38
65
7-8
23
32
9-10
15
8
36
7
>10
TABLE 3.
Comparative analysis of mountain lion, coyote, and bobcat scats collected in Big Bend
National Park, Texas between 1972-1974 and 1980-1981.
Relative
Mountain Lion
1972-74 1980-81 P-Val.*
Freguenc~
of Occurrence and P-Values
Co~ote
1972-74
1980-81
P-Val.
1972-74
Bobcat
1980-81
P-Val.
Odocoileus spp.
0.76
0.38
<.001
0.21
0.05
<.001
0.25
0.03
<.001
Dicotyles tajacu
0.16
0.38
<.001
0.10
0.03
<.001
0.06
0.01
0.02
Lagomorpha
0.03
0.15
<.001
0.39
0.57
<.001
0.50
0.78
<.001
Erithizon dorsatum
0.06
0.01
<.001
Bassariscus astutus
0.00
0.03
0.02
0.00
0.02
0.01
0.00
0.01
0.21
Mephistus spp.
0.04
0.01
0.01
0.02
0.01
0.14
0.02
0.01
0.07
Neotoma albigula
0.00
0.01
0.14
0.13
0.17
0.08
0.14
0.18
0.17
Spermophilus spp.
0.02
0.02
0.42
0.04
0.02
0.05
0.11
0.02
<.001
Canis
- latrans
0.00
0.02
0.03
0.00
0.01
0.06
0.00
0.01
0.21
Urocyron cinereo.
0.00
0.02
0.06
0.00
0.01
0.09
Avian
0.00
0.01
0.14
0.00
0.04
0.00
0.08
0.10
0.23
Arthropoda
0.00
0.02
0.04
0.00
0.12
<.001
0.00
0.02
0.01
0.00
0.01
0.14
0.48
0.39
0.01
0.00
0.00
0.24
0.02
0.01
0.27
Reptilian
Seed and Fruit
Sigmodon spp.
0.06
0.04
0.11
-----**
* P-Value calculated from testing the hypothesis PI = P2' where PI = 1972-1974; P2
percentages
** not occurring in scats collected
1980-1981
.....
0
0
101
t
N
o,
10
!
20
,
Miles
FIGURE 1. Big Bend National Park, Texas (1. Dagger Mountain, 2. Dagger
Flat, 3. Upper Tornillo Flats, 4. McKinney Hills,S. Lower Tornillo
Flats, 6. Onion Spring, 7. Hannold Draw, 8. Croton Spring, 9. Government
Spring, 10. Green Gulch, 11. Panther Junction, 12. Pine Canyon,
13. Juniper Canyon, 14. Boquillas, 15. Sotol Vista, 16. Kit Mountain).
APPENDIX III
Influence of spring rainfall patterns on antler development of desert
mule deer in Big Bend National Park, Texas.
102
103
The dates when hard antlers (velvet loss) were first observed
were recorded for 1973-74 and 1980-81 (Figure 1).
The effect of very low spring rainfall (January 1 - May 31)
occurring in 1980 of 2.64 cm resulted in delaying velvet loss until
October 31 compared to velvet loss for 1981 occurring on October 1
when spring rainfall totaled 13.28 cm.
Low rainfall reduces the
nutritional quality of forage thus affecting the nutritional plane of
deer as it did for fawn survival (see Appendix I).
Winter'dietary
deficiencies in protein and minerals are reflected in antler development (Taber 1958).
Leach (1956) stated that rainfall affected the
food habits of California Great Basin deer through reducing plant
growth and availability.
Payton and Garner (1980) in analyzing 37
forage plants of desert mule deer found that nutrient quality varied
depending on plant maturation.
Given the low rainfall observed in
1980, plant growth was significantly delayed causing vegetative sampling to be delayed until late 1980 and 1981.
McEwen et al. (1957)
reported differences in antler development based on nutrient intake.
Body growth took precedence over antler growth when diet was restricted.
Long et al. (1959) found that restricting food intake over a 5 to 10
week period delayed antler development, changed pelage characteristics,
and increased length of time for velvet loss.
However, Anderson and
Medin (1969) reported that environmental factors were not strongly
correlated with antler development.
My data suggests that antler
development is influenced by rainfall patterns.
High rainfall prior to
104
the period of antler development resulted in earlier plant greenup and
a higher nutritional plane in bucks with earlier velvet loss indicating
more rapid antler growth (Figure 1).
LITERATURE CITED
Anderson, A.E. and D.E. Medin. 1969. Antler morphometry in a Colorado
mule deer population, J. Wildl. Manage. 33:520-533.
Leach, H.R. 1956. Food habits of the Great Basin deer herds of
California. Calif. Fish Game. 42:243-308.
Long, T.A., R.L. Cowan, C.W. Wolfe, T. Rader, and R.W. Swift. 1959.
Effect of seasonal food restrictions on antler development of
w'hite-tailed deer. Penna. State Univ. Agric. Exp. Stn. Prog.
Rep. 209. 11pp.
McEwen, L.C., C.E. French, N.D. Magruder, R.W. Swift, and R.H. Ingram.
1957. Nutrient requirements of the white-tailed deer. Proc.
N. Amer. Wildl. Confer. 22:119-132.
Payton, T.W. and G.W. Garner. 1980. Nutritional values for selected
forages of desert mule deer in southwest Texas. Proc. Confer.
West. Assoc. Fish Wildl. Agencies 60:601-619.
Taber, R.D. 1958. Development of the Cervid antler as an index of
late winter physical condition. Proc. Montana Acad. Sci.
18:27-28.
105
"........,
514.0
I
.......,..
-~.... 10.0
-co
a:: 6.0
m
c::
•
l
•
•
•
-~ 2.0
en
,
30
Sep
I
05
10
15
20
25
31
Day in Oct
FIGURE 1. Date when hard antler (velvet loss) initially observed and rainfall (em) for data
obtained in 1972-1974 and 1980-1981 in Big Bend National 'Park, Texas.
.....
o
0\
APPENDIX IV
Diets of the Paint Gap and Panther Junction desert mule deer herds in
Big Bend National Park, Texas for 1980-1981.
107
108
TABLE 1.
Summary of diets of the Paint Gap (PG) and Panther Junction
(PJ) mule deer herds in Big Bend National Park, Texas, 19801981.
Season
S:eecies
S:ering
PJ
PG
Life Form:
Sununer
PJ
PG
Late
Sununer
PJ
PG
Winter
PJ
PG
Wood~
Leuco:eh~llum spp.
Krameria glandulosa
Polygala macradentia
Parthenium incanum
Janusia gracilis
Gaura spp.
Salazaria mexicana
Dios:e~rus texana
Other Woody
49.5
6.0
1.6
7.3
0.0
T
T
2.6
2.4
64.5
1.3
T*
T
T
T
0.0
0.0
3.2
4.8
30.4
5.8
3.1
1.0
1.5
0.0
0.0
1.4
35.7
20.8
T
3.0
T
5.2
0.0
0.0
1.0
0.0
5.8
6.4
19.3
17.0
0.0
0.0
0.0
T
2.9
6.7
7.0
16.0
3.5
1.0
T
0.0
T
16.7
6.0
6.1
14.3
1.7
T
T
0.0
1.2
13.3
5.8
T
1.9
Woody Total
69.6
70.3
47.9
66.1
48.7
37.9
47.1
29.2
9.9
4.4
1.4
2.4
0.0
0.0
T
0.0
T
0.0
0.0
T
10.6
1.4
T
2.1
T
T
1.0
2.4
0.0
0.0
0.0
2.4
15.5
14.6
7.7
T
1.0
T
T
T
3.4
T
T
4.2
16.8
8.3
T
0.0
T
T
T
0.0
T
0.0
0.0
T
4.0
24.6
T
T
2.1
1.0
T
T
13.0
0.0
2.0
1.5
27.6
10.1
T
3.7
3.6
1.6
1.8
0.0
6.2
0.0
1.4
3.0
6.9
20.7
14.0
T
T
1.3
T
0.0
T
1.6
T
T
27.5
10.9
10.5
9.9
T
1.8
T
T
3.7
1.1
0.0
1.0
19.2
20.8
47.6
28.0
49.7
59.8
46.3
67.0
5.5
5.2
2.6
6.0
T
3.9
1.6
4.0
T
1.3
T
1.0
5.1
1.2
3.1
T
10.7
8.6
4.3
5.6
1.5
1.7
6.3
3.6
Life Form:
Forb
Dalea neomexicana
Eu:ehorbia spp.
Lesquerella spp.
Nerisyrenia cam:eorum
PSilotro:ehe spp.
SEhaeralcea spp.
Erodium spp.
Melampodium lellcanthum
Abutilon spp.
Tidestromia lanuginosa
Conunelinia spp.
Other Forb
Forb Total
Life Form:
Agave lecheguilla
Opuntia spp.
Succulent Total
l'
1.9
4.3
0.0
1.0
Succulent
*Trace item, percent occurrence less than 1.0%.
APPENDIX V
Scat analysis for mountain lion (Felis concolor), bobcat (Lynx rufus),
and coyote (Canis latrans) in Big Bend National Park, Texas for 19801981.
109
110
APPENDIX V-A. Analysis of 272 mountain lion scats collected in Big
Bend National Park, Texas during 1980 and 1981.
Species
Frequency of
Occurrence
Volumetric
Percentage
38.6
38w2
14.7
2.6
2.2
1.1
1.5
Mammalian
Odocoileus spp.
Dicotles tajacu
Lagomorpha
Bassiariscus astutus
Spermophilus spp.
Mephitis spp.
Urocyron cinereoargenteus
Cratogeomys castano~
Canis latrans
Felis concolor
Neotoma albigula
Erethizon dorsatum
Unidentified rodent
T
96.0
95.3
85.6
93.9
68.3
84.3
97.0
49.0
89.8
71.7
21.5
T
100.0
1.5
18.9
T
2.2
1.1
. Arthropoda
Coleoptera
Lepidoptera
Unidentified insect
1.1
T*
T
T
T
26.8
9.9
1.5
T
T
1.5
T
T
T
T
T
1.1
T
T
20.6
1.5
T
3.7
15.1
3.8
T
T
T
T
5.3
T
T
T
T
T
T
1.2
T
T
33.1
1.6
T
Plant Material
Grass
Diospyrus texana (leaves)
Juniperus spp. (leaves)
Quercus spp. (leaves)
Agave lecheguilla (spine)
Forestieria angustifolia (leaves)
Porlieria angustifolia (leaves)
Yucca spp. (seed)
Pinus cembroides (leaves)
Berberis trifoliata (leaves)
Jatropa dioica (leaves)
Prosopsis glandulosa (seed)
Salix spp. (leaves)
Opuntia spp. (seed)
Unidentified vegetation
Unidentified seed
Spine
Other
Rock
*Trace items constitute less than 1% of the scats
111
APPENDIX V-B. Analysis of 410 coyote scats collected in Big Bend
National Park, Texas during 1980 and 1981.
Frequency of
Occurrence
Volumetric
Percentage
56.8
4.9
82.9
69.0
9.0
18.5
68.4
85.0
7.0
7.0
47.6
61.5
48.7
63.0
86.7
100.0
61.4
Avian
3.9
14.7
Reptilian
2.2
22.9
Species
Mammalian
Lagomorpha
Neotoma albigula
Dipodomys spp.
Canis latrans
Bassariscus astutus
Sigmodon spp.
Peromyscus spp.
perognathus spp.
Dicotles taj acu
Odocoileus spp.
Spermophilus spp.
Urocyron cinereoargenteus
Mephitis spp.
Thomomys spp.
Unidentified rodent
17.1
T*
1.0
2.2
T
T
T
2.7
4.9
2.2
T
T
T
Arthropoda
Unidentified insect
Coleoptera
Diploda
Hymenoptera
Hemiptera
Diptera
Lepidoptera
Dermacenter spp.
Orthoptera
~cTrace
2.2
7.1
5.9
1.5
T
T
T
T
T
4.2
6.4
25.9
2.4
T
T
40.0
T
32.6
items constitute less than 1% of the scats
112
APPENDIX V-B CONTINUED. Analysis of 410 coyote scats collected in Big
Bend National. Park, Texas during 1980 and 1981.
Species
Frequency of
Occurrence
Volumetric
Percentage
13.2
4.1
1.5
67.7
3.0
5.0
Plant Material
Grass
Diospyrus texana (leaves)
Diospyrus texana (seed)
Dasylirion leiophyllum
Juniperous spp. (leaves)
Jatropa dioicus (leaves)
Prosopsis glandulosus (seed)
Forestieria angustifolia (leaves)
Opuntia spp. (seed)
Yucca spp. (seed)
Quercus spp. (leaves)
Spine
Unidentified seed
Unidentified vegetation
4.2
32.9
T*
T
5.6
3.7
T
28.7
T
T
2.4
3.3
5.1
7.4
T
T
T
T
2.0
19.8
4;6
2.5
38.5
T
T
T
T
1.5
T
T
T
3.0
Other
Rock
Foil
String
Deer pellets
Bone Fragment
*Trace items constitute less than 1% of the scats
113
APPENDIX V-C. Analysis of 216 bobcat scats,collected in Big Bend
National Park, Texas during 1980 and 1981.
Species
Frequency of
Occurrence
Volumetric
Percentage
78.2
19.0
4.2
T*
1.4
1.4
T
1.0
2.8
2.3
T
T
T
91.9
j7 .4
35.3
99.0
45.0
93.3
100.0
42.5
71.4
82.8
97.0
100.0
50.0
10.2
12.9'
1.0
54.5
4.2
1.0
T
T
1.9
3.3
6.5
T
T
3.3
14.4
T
3.6
1.0
29.6
1.4
T
5.1
1.4
13.7
T
2.5
Mammalian
Lagomorpha
Neotoma albigula
Unidentified rodent
Taxidea taxus
Dicotles taj acu
Sigmodon spp.
Canis latrans
Perognathus spp.
Odocoileus spp.
Spermatophilus spp.
Cratogeomys castanops
Bassiariscus astutus
Mephitus spp.
Avian
ReEtilian
ArthroEoda
Coleoptera
Orthoptera
Dermacenter spp.
Diplipoda
Unidentified insect
Vegetation
Grass
Other
Other
Rock
Tin foil
Paper
Deer pellet
*Trace items constitute less than 1% of the scats
APPENDIX VI
Plant associations of the lower desert shrub land in Big Bend National
Park, Texas.
114
TABLE OF CONTENTS
Page
LIST OF TABLES
116
LIST OF ILLUSTRATIONS
118
ABSTRACT
120
INTRODUCTION
121
MATERIALS AND METHODS
122
122
122
Study Area
Vegetational Analysis •
125
RESULTS AND DISCUSSION
General Presentation of Plant Associations . • . .
Analysis of Plant Associations
• • • •
Creosotebush-tarbush
Viguieria-Iechuguilla-grass . .
Sotol-Iechuguilla-grass . . .
Lechuguilla-grass and Hechtia-grass
Sotol-Giant Dagger . • . • • • • • •
Creosotebush-Iechuguilla-grass
Creosotebush-Iechuguilla-prickly pear •
Creosotebush-Iechuguilla-candelilla
Creosotebush-Iechuguilla
Creosotebush Flats
125
127
127
128
129
131
132
132
135
136
137
l38
SUMMARY ••
140
LITERATURE CITED
141
115
LIST OF TABLES
Table
1
2
3
4
5
6
7
8
9
10
11
Page
Classification systems for plant communities
in Big Bend National Park, Texas
• • • •
142
2
Absolute density (stems/m ) of plants found
within plant associations in Big Bend National
Park, Texas • • • • . • • • • • •
143
Delineation of plant associations within the
lower desert shrub land of Big Bend National
Park, Texas • • • • • • .
144
Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush-tarbush association in
Big Bend National Park, Texas • • • • • • • • . .
145
Relative frequencies (RF) and absolute densities
(AD) for the Viguieria-Iechuguilla-grass association in Big Bend National Park, Texas • . . . .
147
Relative frequencies (RF) and absolute densities
(AD) for the Sotol-Iechuguilla-grass association
in Big Bend National Park, Texas . • • • • . . •
150
Relative frequencies (RF) and absolute densities
(AD) for the Lechuguilla-grass plant association
in Big Bend National Park, Texas • • • . • . . .
153
Relative frequencies (RF) and absolute densities
(AD) for the Sotol-Giant Dagger association in
Dagger Flat, Big Bend National Park, Texas
155
Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush-Iechuguilla-grass
association in Big Bend National Park, Texas
157
Relative frequencies (RF) and absolute densities
for the Creosotebush-Iechuguilla and the Creosotebush-Iechuguilla-prickly pear associations in Big
Bend National Park, Texas
...•.•..•..
159
Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush-Iechuguilla-candelilla
association in Big Bend National Park, Texas
161
116
117
LIST OF TABLES--Continued
Table
12
13
14
15
Page
Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush Flats association in
Big Bend National ~ark, Texas • • • • • , • • •
163
Relative frequencies of plant species occurring
in washes within plant 'associations found in Big
Bend National Park, Texas , • • • • •
164
Comparison of important plant species found
within Dagger Flat, Big Bend National Park,
Texas and other common plant associations •
167
Summary of characteristics of plant associations
found within Big Bend National Park, Texas
168
LIST OF ILLUSTRATIONS
Figure
Page
.,
1
Big Bend Na,tional Park, TeJ:Cas
2
Density relationships between ass.ociations found
within the lower des.e·rt shrubland qf Big Bend
National Park, Texas· • • • • • • • • • • • • •• , , ,
3
4
5
6
7
8
9
10
11
t
17Q
.
171
. ..
172
The Creosotebush-tarbush plant association at
Paint Gap Hills, Big Bend National Park, Texas
., ..,
173
The Viguieria-lechuguilla-grass plant association south of Oak Spring, Big Bend National
Park, Texas (Note the absence of creosotebush)
.....
173
'!
•••
"",
••
Diversity relationships between plant associations.
found within the lower desert shrubland.of Big
Bend National Park, Texas • • • • • • • • • • • • •
!
The Sotol-Iechuguilla-grass plant association
at Burro Mesa, Big Bend National Park, Texas
174
The Lechuguilla-grass plant association on the
slopes north-west of Dugout Wells, Big Bend
National Park, Texas (Note the lack of any
dominant shrub species, grass is chino grarna)
174
The slopes north-west of Dugout Wells demonstrating the hillsides dominated by lechuguilla
and chino grama and the level ridgetops composing
less than 10 percent of the land surface
(Vegetation in foreground indicative of plant
species found in the washes) • . • . • • • • • . • . . •
175
The Sotol-Giant Dagger plant association found
in Dagger Flat, Big Bend National Park, Texas.
175
The Creosotebush-Iechuguilla-grass plant association north of Nugent Mountains, Big Bend
National Park, Texas . . • • . . . . . . . • • .
176
The Cresostebush-Iechuguilla-grass plant association east of Kit Mountain, Big Bend National
Park, Texas (Note the lower plant density as
compared to Figure 10)
. . . . . . . . . . . . . .
176
118
119
LIST OF ILLUSTRATIONS--Continued
Figure
12
13
14
15
Page
The Creosotebush-lechuguilla-prickly pear plant
association 6.4 kilometers east of Dugout Wells,
Big Bend National Park, Texas • . • • • • • •
177
The Creosotebush-lechuguilla-candelilla plant
association along the southern portion of the
Old Ore Road, Big Bend National Park; Texas •
177
The Creosotebush-lechuguilla plant association
south of Dagger Flat Road, Big Bend National
Park, Texas • • • • • • •
178
The Creosotebush Flats at the Fossil Bone Exhibit,
Big Bend National Park, Texas
178
ABSTRACT
A plant association classification system was developed for
Big Bend National Park, Texas using three categories based on
dominant shrub cover:
creosotebush dominated, non-creosotebush
dominated, and non-shrub dominated associations.
Excluding the river floodplain, ten plant associations were
identified:
Creosotebush-tarbush, Creosotebush-Iechuguilla-grass,
Creosotebush-Iechuguilla-prickly pear, Creosotebush-Iechuguillacandelilla, Creosotebush-Iechuguilla, Creosotebush Flats, Viguierialechuguilla-grass, Sotol-Iechuguilla-grass, Lechuguilla-grass, and
Sotol-Giant Dagger.
Plant transects were sampled with the point-centered quarter
method (Dix 1961) to determine plant species density and frequency
of occurrence.
Differences and similarities between plant associ-
ations are discussed.
120
INTRODUCTION
The Big Bend Region of Texas is included in the Chihuahuan
biotic province (Dice 1943, Blair 1949) which is divided into the
Davis Mountains biotic district and the Chisos biotic district.
Big
Bend National Park (BBNP) is located in the latter.
The diverse and complex nature of the plant communities found
within the Chihuahuan Desert has resulted in several classification
systems for plant communities in the Chisos biotic district (Table 1).
I found that none of these systems provided enough detail for analysis
of relationships between habitat and desert mule deer (Odocoileus
hemionus crooki) in the desert shrubland formation.
For this reason,
I expanded on the existing systems (Table 1) and produced a more
detailed classification scheme for 5hrublands in BBNP, Texas.
The
riparian and woodland conmunities of the Rio Grande and Chisos Mountains respectively are not discussed in this paper because mule deer
abundance was low in these associations.
121
MATERIALS AND METHODS
Study Area
BBNP, Brewster Co., Texas is located 113 km south of Marathon,
Texas (Figure 1).
2
2
The park occupies over 2,666 km of which 57 km
are composed of the Chisos Mountains.
Elevations range from 573 m
along the Rio Grande to 2,384 m at Mt. Emory in the Chisos Mountains.
The soils of the Chisos Biotic district include the Gila,
Reagan, Rio Grande, Reeves, Ector, and Brewster series (Denyes 1956).
The Gila and Rio Grande series are found within the floodplain of the
Rio Grande.
The Reagan series is most connnon on the basal areas of
the Chisos Mountains.
Its soil is gravelly loam supporting plant
associations consisting of various desert shrubs.
The calcareous
mountain and hill soils are of the Ector series.· The Brewster series
supports the forest communities of the higher elevations and the
desert grassland and shrub connnunities of the lower elevations.
The park is characterized by hot sunnners, mild winters, and
low rainfall.
0
Temperatures often exceed 38 C in the desert regions
during the sunnner and are rarely freezing during the winter.
The
majority of the precipitation occurs from May through October ranging
from less than 28 cm in the desert and the surrounding foothills to
as much as 41 em in the mountainous regions.
Vegetational Analysis
Plant associations were classified by 3 criteria.
Dominant
shrub cover was the primary basis for identification followed by the
122
123
dominant succulent species.
Plant(s) which were distinctive to a
plant association made up the third criteria for classification.
For
example, the slopes of the Deadhorse Mountains support a plant association dominated by creo$otebush (Larrea tridentata).
The dominant
succulent· is lechuguilla (Agave lecheguilla) and in some areas, a
forb, candelilla (Euphorbia antisyphilitica) is widespread.
Thus,
areas containing creosotebush, associated with lechuguilla and
candelilla were classified as the Creosotebush-lechuguilla-candelilla
formation.
Plant species abundance was evaluated using the point-centered
quarter method (Dix 1961).
A minimum of 48 plots were sampled per
transect except in areas of low plant species diversity where 24 plots
were sampled.
Two transects were sampled in the more diverse commu-
nities and one in the less diverse areas (Table 2).
Less than 50
plots were necessary per transect to detect principle plant species as
indicated by species-area curves.
The initial plot was determined
randomly and subsequent plots were established at intervals of 10 m.
The method discussed by Dix was modified (1961) to adequately sample
all plant types.
Four categories of plants were sampled including
woody plants (perennial shrubs), grasses, forbs, (herbaceous, annual
plants), and succulents (Cactaceae and Agave spp.).
At each plot,
point-to-plant distances were obtained for plants from each category.
All common and scientific names are based on Correll and Johnston
(1970).
124
Transects were also run within washes in each plant association
identified.
A plot was randomly established and all plants on either
side of plot center, perpendicular to the direction of the wash, were
tallied.
RESULTS AND DISCUSSION
General Presentation of Plant Associations
Ten plant associations were identified within the lower elevations of the desert region within BBNP.
The classification system for
the desert shrubland formation was divided into 3 categories,
those dominated by creosotebush, those dominated by a shrub other than
creosotebush, and associations with no dominant shrub species (Table
2).
The sotol-lechuguilla-grass (S-L-G) association is found on the
foothills of the Chisos Mountains above elevations of 975 m (Wauer
1971).
However, a shrub common with sotol is resin-bush (Viguieria
stenoloba) which dominates the Viguieria-lechuguilla-grass (V-L-G)
association found on the more level areas adjacent to the Chisos
Mountains.
The sotol-giant dagger (Yucca incarnerosana) (So-Yuc)
association is found primarily in the basins between Dagger Mountain
and the western slopes of the Deadhorse Mountains.
Ignoring the
presence of the giant dagger, the So-Yuc association resembles a mixture of the S-L-G and the V-L-G associations.
The lechuguilla-grass (Le-Gr) association is similar to the
hechtia-grass association differing primarily in location.
The hech-
tia (Hectia scariosa)-grass association is common on the slopes of the
Deadhorse Mountains and in some locations where hechtia is absent, the
association closely resembles the lechuguilla-grass association.
125
126
The associations
wher~
creosotebush is dominant differ pri-
marily due to differences associated with plant density, diversity,
and rainfall (Figures 2, 3).
Proceeding east from Panther Junction
(1140 m) to Boquillas (573 m), .the differences of 4 of the 5
creosotebush associations resulting from elevational changes can be
observed.
Extensive areas of the creosotebush-Iechuguilla-grass
(C-L-G) association occur on the flats north of Nugent Mountain and
extend 6.4 km east of Dugout Wells.
Beyond this distance, precipita-
tion is less resulting in the appearance of the more barren creosotebush-Iechuguilla-prickly pear (C-L-P) association.
This occurs at an
elevation of 701 m with chino grama (Bouteloua brevisata) abundance
diminishing resulting from lower rainfall (Cockran, SCS, per. comm.).
The creosotebush-Iechuguilla-candelilla (C-L-C) association appears
once the calcareous influence of the Deadhorse Mountains occurs near
the southern entrance to the Old Ore Road.
The creosotebush-
lechuguilla-candelilla association finally yields to the Creosotebush
Flats (Cr-Ft) adjacent to the Rio Grande.
These flats extend from
Gravel Pit on the River Road to the mouth of Santa Elena Canyon.
The creosotebush-tarbush (Flourencia cernua) (Cr-Tr) association is unique in that it resembles no other plant association found
within the park.
It is the most locally distributed association
along with the So-Yuc association of Dagger Flat.
Using a grid system (Marcum and Loftsgaarden 1980), acreage
and percentage occurrence of the shrub land associations were determined (Table 3).
The V-L-G association as well as the Le-Gr
127
association includes areas in the Sierra Quemadas which are considered
part of the Chis os Mountains complex.
Analysis of Plant Associations
Vegetational analysis of the plant associations (transect
data) are summarized in Tables 4-12.
Results of the wash transects
are found in Table 13 and total plant densities are summarized in
Table 2.
Creosotebush-tarbush (Cr-Tr)
This plant association resembles no other plant association in
the park (Figure 4, Denyes 1956, Warnock and Kittams 1970).
Compared
with other areas, the soils found within the Cr-Tr association are
more clayey and lack the extremely gravelly surface common to the
other associations (Denyes 1956).
The distribution of this association
is very limited and is found west of Lone Mountain and continues to
Todd Hill.
Additionally, it is found on the more level areas north-
west of Pullium Ridge.
The plant that is distinctive to this association is tarbush
which only occurs elsewhere within the creosotebush-Iechuguilla (CrLe) association.
This is due to the abundance of non-gravelly, clayey
depressions common the that area (south of Dagger Flat Road) which
hold water for extended periods of time.
The Cr-Tr association is very common on the overgrazed areas
on the communal ranches within Mexico.
In fact, tarbush is the
dominant shrub cover with creosotebush being rare.
Muller (1940)
128
stated that the Larrea-Flourencia association has the ability of
forming a stable climax within the Chihuahuan Desert ecosystem.
The washes of this association are not densely vegetated and
are characterized by plants which are less than 1.5 m in height (Table
13).
These plants include Snakeweed (Xanthocephalum spp.) (24.9%),
and Guayacan (Porlieria angustifolia) (7.1%).
Tarbush occurs with a
frequency of 18.0% with creosotebush being low at 4.4%.
Viguieria-lechuguilla-grass (V-L-G)
This association, identified by Warnock (1970) is very common
in the park and is found ou the flats adjacent to the Chisos Mountains
as well as the small hills found along the Rio Grande.
The plant
community of the Sierra Quemadas resemble the V-L-G association but
the mountainous terrain and close proximity to the Chisos Mountains
result in the presence of plants not common the the V-L-G community on
the desert flats such as Gregg ash (Fraxinus Greggi).
The association is iderLtified by the abundance of resin-bush
with little or no creosotebush (Figure 5).
is black grama
(!.
The primary grass species
eriopoda) with frequencies of occurrence not
exceeding any other plant association (Table 5).
The total plant
density of this formation is within the range of densities (Table 2)
for plants found within the moderate density category (Figure 2).'
The wash systems of the V-L-G association are generally narrow
(4-6 m) and sparsely vegetated.
The principle shrub species include
resin-bush (16.5%), catclaw (Acacia Greggi), snakeweed, feather plume
(Dalea formosa), and a high abundance of lechuguilla (12.8%).
The
129
only other wash system containing such a large amount of 1echuguil1a
are those within the Le-Gr association (11.0%) (Table 13).
In both
associations, 1echugui11a occurs in large colonies under shrub
species on areas where soil has collected.
Other associations have
1echugui11a but it occurs as individual plants randomly scattered
throughout the wash bed.
Feather-duster (Ca11iandra humilus), more common to the S-L-G
association, appeared on transects sampled within the washes of the
V-L-G association.
Additionally, Damianita (Chrysactinia mexicana)
another plant more common on the more mesic S-L-G association, was
found within washes of the V-L-G association further indicating the
similarity of these two plant associations.
Soto1-1echugui11a-grass (S-L-G)
The S-L-G association is found on the foothills of the Chisos
Mountains above elevations of 975 m.
It is most conspicuous on the
slopes extending west of Ward Mountain, an area called Sotol Vista
(Figure 6).
Denyes (1956) identified three foothill plant associations,
two included the sotol-lechuguilla and the sotol-sacahuiste (Nolina
erumpens).
I found that these two communities were difficult to
objectively separate.
Therefore, the two associations were combined,
similar to the classifications of Wauer (1971) and Warnock and
Kittams (1970).
Plants unique or more common within the S-L-G association
compared to other associations include Tanglehead (Heteropogon
130
contortus), sotol, sacahuiste, and feather duster (Table 6).
The
similarity between the S-L-G and the V-L-G associations is seen by
comparing the frequency of occurrence of resin-bush for the V-L-G
(24.5 and 30.2) and S-L-G (15.7 and 17.1) associations.
In Juniper
Canyon, resin-bush is the most abundant shrub closely followed by
mescat acacia (A. constricta) whereas on Horse Mesa, resin-bush is the
third most abundant shrub exceeded only by feather duster and sotol.
The S-L-G association receives more rainfall than the plant
associations common on the lower desert flats.
The greater precipi-
tation results in a greater density of plants (e.g. 4.05 and 3.24
2
stems/m) on Horse Mesa and Juniper Canyon respectively (Table 2).
The S-L-G association is also found on the southeastern half
of the Mesa de Anguilla (Figure 1) which occurs within the western
border of the park.
The northwestern section is primarily C-L-C and
once elevations exceed 945 m, southeast of Canyon Flag, the sotol
becomes the dominant shrub species.
The washes of this association are very diverse in plant
species (Table 13).
Two species which are of particular interest
include the single-seeded juniper (Juniperus monosperma) and Gregg ash.
Single-seeded juniper is unique to the S-L-G association and reflects
the greater rainfall associated with the Chisos Mountains.
Gregg ash
also occurs in the So-Yuc association and further illustrates the
similarity of these two associations.
Additionally, Acacia Roemeriana
appears within the S-L-G as well as the So-Yuc wash systems.
131
Lechuguilla-grass and Hechtia-grass (Le-Gr)
These associations are typical of the vegetation found on the
sloping terrain bordering large washes where no dominant shrub species
can .be identified (Figure 7).
It should not be inferred that no shrub
species are found within these associations, only that the woody life
form is not the dominant cover type.
The Le-Gr association is the most widespread plant community in
BBNP.
Wherev~r
flat terrain slopes downward to the bed of a large
wash, the shrub cover diminishes and dense stands of lechuguilla and
chino grama dominate.
Therefore, even though a vegetative map such as
the one produced by Warnock and Kittams (1970) depict large expanses of
a particular plant association, it is interspersed with the Le-Gr
association wherever a wash is present.
A more realistic map would be
a mosaic of the flats dominated by a shrub species, (i.e. creosotebush
or resin-bush with Le-Gr on the slopes of igneous-based soils or
hechtia-grass on limestone-based soils) and the wash community bordering the wash bed.
The diversity of shrub species within the Le-Gr association is
high but few species exceed a frequency of 10% (Table 7).
On the
Dugout Wells (DOW) Hills, leather stem (Jatropha diocia var. graminea)
occurs with a frequency of 19.8%.
However, letherstem is a low
growing plant whose single stems form colonies with heights rarely
exceeding 45 cm.
This low growth form makes leatherstem an incon-
spicuous component of the community.
Additionally, the abundance of
sotol on Hannold Draw is high with a frequency of 11.1%.
In some
areas within Hannold Draw, the plant association resembles the S-L-G
132
association with sotol being locally abundant.
Both associations are
common on sloping terrain, S-L-G on the slopes of the Chisos Mountains
and Le-Gr on the slopes of large washes within the desert flats.
The analysis of the wash system within the Le-Gr association
is based on two areas where the slopes were extensive and the ridgetops were small.
Since the Le-Gr association may be found with any
other association where the terrain changes to a slope, vegetation
within the wash bed would typically resemble the plant association of
the level areas.
Hannold Draw and DOW Hills were sampled because the
level ridgetops occupy less than 10% of the land surface (Figure 8).
Therefore, the vegetation found within the washes between the series
of slopes characteristic of these two areas would not be significantly
affected by the vegetation on the level ride1ines.
The vegetation
found within the washes was not different from washes found within
other plant association.
Of particular interest is the occurrence
of resin-bush (9.1%) which had the highest frequency next to that of
1echuguil1a (11.0%).
The vegetation of the ridgetops was generally
C-L-G and/or S-L-G.
Sotol-Giant Dagger (So-Yuc)
The giant dagger only occurs naturally within the United
States in BBNP.
In Mexico, extensive stands of giant daggers are
common on the lower desert slopes of the Fronteriza Mountain range.
In BBNP, the giant dagger occurs in the northern region of
the park in Dagger Flat and along the slopes of Deadhorse Mountains.
The two large basins between Dagger Mountain and the Deadhorse
133
Mountains support a very dense and diverse plant community
sup~orted
by the runoff from the western slopes of the Deadhorse (Figure 9).
The plant density of Dagger Flat was found to be the highest with 4.3
2
stems/m •
The diversity of the plant association within Dagger Flat
represents a mixture of several associations found throughout the
park.
The occurrence of sotol as an integral component of the So-Yuc
association results in many regions of Dagger Flat resembling the
S-L-G association.
Additionally, the frequency of occurrence of
resin-bush of 6.2% further supports this conclusion.
Several plant
species found in other plant associations in moderate densities are
also found within Dagger Flat.
In areas where the giant dagger is
sparse or absent, classification is difficult.
species which
oc~ur
Table 14 lists plant
in Dagger Flat in moderate abundance but also are
important plants in other associations.
Obviously, the uniqueness of
the So-Yuc association is not only due to the presence of the giant
dagger, but also due to its great plant species diversity.
The
influence of the limestone slopes of the adjacent Deadhorse Mountains
is seen by the occurrence of candelilla as an important forb species
(Table 8).
The washes in this association are dominated by several plant
species including Poreleaf (Porophyllum spp., 19.1%), resin-bush
(15.0%), Texas persimon (Diospyrus texana) (9.3%), catclaw (7.7%),
sotol (6.7%), and giant dagger (6.2%).
It was previously stated that
the S-L-G and the So-Yuc associations were the only associations to
134
have Gregg ash.
study period
a~d
Additionally, several washes were hiked during the
in many instances, small stands of single-seeded
juniper were encountered indicating that these two associations are
very similar.
Creosotebush-Iechuguilla-grass (C-L-G)
This plant association is the most variable and difficult to
identify in the field because it intergrades with the other two
associations found on the flats, the Cr-Tr and the V-L-G associations.
Creosotebush is the most abundant shrub with frequencies of 39.2 and
44.2% for Nugent Mountain and DOW anticline respectively.
Lechuguilla
is the most dominant succulent particularly on the DOW anticline transect with a frequency of occurrence of 94%.
The Nugent Mountain
transect had a lower lechuguilla abundance at 76.2% with prickly pear
(Opuntia spp.) being the other major succulent species with a frequency
exceeding 11.0% (Table 9).
The dominant grass is chino grama.
How-
ever, the smaller grass species, fluffgrass (Erioneuron pulchellum)
occurs with a frequency of 52.3% on the Nugent Mountain transect with
chino grama occurring 32.0% of the time.
The opposite occurs on the
DOW anticline with chino grama having a frequency of over 52.0%
compared to that of fluffgrass, 22.1%.
Thus, it can be seen that the
exact delineation of the C-L-G association may be difficult when too
few plant species are used to identify it.
The association occurs primarily on level areas throughout the
park.
It may be densely vegetated as observed north of Nugent Moun-
tain (Figure 10) or sparse as seen east of Kit Mountain (Figure 11).
135
The identifying characteristics of this association is the abundance of
creosotebush with other shrub species, specifically tarbush and resinbush absent.
Denyes (1956) identified two creosotebush dominated
associations and stated that they were relatively barren plant communities.
The time that his study was performed (1947 to 1948) was when
livestock grazing was extensive and may have resulted in a barren,
"early developmental stage" of the more diverse C-L-G association found
in the park today.
Warnock (1970) identified the Larrea-mesquite
(Prosopsis glandulosa) association which he found surrounding the
Chisos Mountains.
The C-L-G association identified in this study is
part of Warnock's more general association.
The washes found within this association are not unique in
plant species abundance.
The principle plants include mario1a
(Parthenium incanum) (10.2%), resin-bush (14.6%), creosotebush
(14.4%), catc1aw (7.8%), and Pore1eaf (9.5%).
Creosotebush-1echugui11a-prick1y pear (C-L-P)
This association is readily identified by the occurrence of
blind prickly pear
(Q. rufida) (Figure 12, Table 10). Additionally,
the principle grass species is f1uffgrass (82.8%).
This association
grades into the C-L-C association, however, the soils are not limestone based and therefore, cande1i11a was not found on the transects.
The association is most conspicuous at approximately 6.4 km
east of Dugout Wells proceeding toward Boqui11as.
The absence of
chino grama is not a result in a change in the soil type but a
136
reduction in precipitation (Cockran, SCS, per. comm.).
This occurs
at approximately 700 m elevation.
The wash systems are dominated by four shrub species including
poreleaf, resin-bush, creosotebush, and catclaw (Table 13).
The
washes are generally broad (9 m or greater) and the vegetation forms
a dense thicket along the wash borders.
Creosotebush-lechuguilla-candelilla (C-L-C)
The limestone soils of the Deadhorse Mountains and the areas
on the Mesa de Anguilla support this plant association.
It resembles
the C-L-G association except for the lower plant density (Table 2) and
the presence of candelilla (Figure 13).
Similarity to the C-L-G
association results from the occurrence of creosotebush, lechuguilla,
and unlike the C-L-P association, the presence of chino grama with a
frequency of 15.8% on the Old Ore Road and 50.8% along the McKinney
Hills (Table 11).
The higher plant density common on the flats north
2
of McKinney Hills (2.1 stems/m ) results from the higher elevation
(914 m) and its more northerly location (Figure 1).
Both transects
are along the foothills of the Deadhorse Mountains, the Old Ore Road
transect is on the southern portion of the range whereas the McKinney
Hills transect is along the northern boundary of the C-L-C association
where rainfall is greater.
The washes found within the C-L-C association resemble those
found in the C-L-G association (Table 13).
The major shrub species
include mariola (23.0%), resin-bush (20.9%), creosotebush (16.3%),
Torrey yucca (Yucca Torreyi) (6.6%), and desert olive (Forestieria
137
angustifolia) (6.1%).
Candelilla is distinctive to these washes
except within the So-Yuc association which has a frequency 2.5 times
greater than the washes in the C-L-C association.
This reflects the
limestone influence of the Deadhorse Mountains surrounding Dagger Flat.
Creosotebush-lechuguilla (Cr-Le)
This is a relatively barren plant community with a total plant
2
density of 0.24 stems/m (Figure 14).
Although lechuguilla is found
within the Cr-Le association it is very sparse with a density of 0.06
2
stems/m.
The plant diversity is also low with only 4 forb, 8 woody,
6 grass, and 4 succulent plant species (Table 10).
This association is associated with the Cr-Ft association and
is a transition community between the more diverse creosotebush associations and the Cr-Ft association.
It typically does not occupy large
expanses of land and usually occurs as a band between two associations.
One area containing a large expanse of the Cr-Le association is found
south of Dagger Flat Road and west of the Old Ore Road.
The dominant plants within the woody category include creo(47.6~),
sotebush
mariola (16.7%), and heliotrope (Heliotropium
confertifolium) (16.7%).
The major grass species is fluffgrass with
a frequency of 77.4% although isolated patches of chino grama may be
found.
The dominant succulent is lechuguilla (70.6%) followed by
tasajillo
(Q. leptocaulis) (17.6%).
The washes are similarly low in diversity with only three
shrub species exceeding 10% frequency.
weed, and tarbush.
These include mariola, snake-
However, since this association is a transition
138
zone between the more diverse creosotebush associations and Cr-FT,
the washes within these zones often contain plants common to other
associations bordering them.
Creosotebush Flats (Cr-Ft)
This association is the most barren plant community (Figure
15).
The Cr-Ft found on Tornillo Flats is less barren than the flats
found closer to the Rio Grande at lower elevations (Lower Tornillo
Creek transect) which has the lowest stem density of any association
2
(0.17 stems/m ).
Creosotebush (81.2% and mesquite (18.2%) are the only shrubs
common on the Upper Tornillo Flats.
Near Lower Tornillo Creek
(near the Rio Grande), three shrubs are found, creosotebush, leatherstem, and heliotrope (7.1%, Table 12).
Forb abundance is variable
depending upon precipitation patterns because most are annuals with a
growing period of less than three weeks.
No forbs were found on the
Lower Tornillo Creek transect whereas seven species were found on
Upper Tornillo Creek.
Two forb species found on Upper Tornillo Creek
occur' in no other association.
These unique species include rushpea
(Hoffmanseggia spp.) and rain-lily (Zephranthes longifolia).
are uncommon and the annual, red grama
(~.
frequent on Upper Tornillo Flats (85.7%).
Grasses
trifida) was the most
A similar dichotomy exists
with the succulent species where tasajillo dominates the Tornillo
Flats area and dog cactus (Q. Schottii) dominates the succulent
category on the Cr-Ft association bordering the Rio Grande.
139
The washes, however, were very similar in shrub species
abundance for both transect locations.
The dominant shrubs include
creosotebush (24.8%), catclaw (12.0%), guayacan (8.9%), and a plant
only found within the Cr-Ft association on Upper Tornillo Creek, saltbush (Atriplex obovata) (8.7%).
The surprizing point concerning
washes within the Cr-Ft association is the density of plants compared
to
th~
surrounding terrain which is very sparsely vegetated.
This is
most dramatically seen along the River Road where areas virtually
devoid of any vegetation has a wash flowing through it populated by
plants including Texas persimon, desert hackberry (Celtis pallida),
desert willow (Chilopsis linearis), and mesquite.
The increase in
water availability makes a considerable difference in the plant
population.
SUMMARY
Previous plant classification systems for Big Bend National
Park, Texas were found to be too general for an analysis of the relationships between mule deer and plant communities, therefore, a more
detailed classification system for the shrubland region of the park
was developed.
Ten plant associations were delineated.
The plant associations
were divided into three categories, those dominated by creosotebush,
those dominated by shrub(s) other than creosotebush, and those with
no dominant shrub species.
Plant transects
we~e
sampled within
th~
plant associations to determine frequency of occurrence and absolute
density of individual plant species.
Additionally, wash systems within
a plant association were indicative of the association they were in,
therefore, a sampling procedure was developed to determine frequency
of occurrence of common shrubs found within the wash.
Each plant association was discussed relative to plant species
abundance, elevational and climatic differences.
A summary of identi-
fying characteristics for each association is found in Table 15.
The
creosotebush associations primarily differ in elevation relative to
rainfall patterns.
The other shrub dominated associations differed in
dominate plant species, geographical location, soil type, and/or
topographic position.
Similarities between plant associations are
discussed and are primarily based on plant species common only to
those specific plant communities.
140
LITERATURE CITED
Blair, W.F. 1949.
93-117.
The biotic provinces of Texas.
Texas J. Sci.
2:
Correll, D.S. and M.C. Jonston. 1970. Manual of the vascular plants
of Texas. Tex. Res. Found. Renner, Texas. 1881 pp •
. Denyes, H.A. 1956. Natural terrestial communities of Brewster County,
Texas with special reference to the distribution of the mammals. Amer. Mild. Nat. 55:289-320.
Dice, L.R. 1943. The biotic provinces of North America.
Press. Ann Arbor, Mich 78 pp.
Univ. Mich.
Dix, R.L. 1961. An application of the point-center quarter method to
the sampling of grassland vegetation. J. Range Manage. 14:
63-69.
Johnston, M.C. 1974. Brief resume of botanical, including vegetational, features of the Chihuahuan Desert region with special
emphasis on their uniqueness. In: Trans. Sympos. BioI. Res.
Chihuahuan Desert. Alpine, Texas. 658 pp.
Muller, C.H. 1940. Plant succession in the Larrea-Flourencia climax.
Ecol. 21:206-212.
Warnock, B.H. 1970. Wildflowers of the Big Bend country, Texas.
Ross State Univ. Alpine, Texas. 157 pp.
SuI
Warnock, B.H. and W.H. Kittams. 1970. Vegetation Map: Plant communities of Big Bend National Park. SuI Ross State Univ. and
Nat. Park Servo 1 pp.
Wauer, R.H. 1971. Ecological distribution of birds in the Chisos
Mountains, Texas. Southwest. Nat. 16:1-29.
141
142
TABLE 1.
Den~es
Classification systems for plant communities in Big Bend
National Park, Texas.
(1956)
Wauer (1971)
A. Chisos Biotic District
1. Desert Plains Life Belt
a.
b.
c.
d.
Riverbank Association
Baccharis Association
Mesquite Association
Creosote-Tarbush
Association
e. Creosote-OcotilloMesquite Association
f. Creosote-Tasajillo
Association
2. Foothills Life Belt
a. Sotol-Lechuguilla
b. Creosote-Lechuguilla
c. Sotol-Sacahuiste
3. Encinal Life Belt
a. Oak Chapparal
b. Pinyon-Oak-Juniper
c. Yellow-pine-Fire
d. Grama-Bluestem
e. Feathertop-Grama
A. Chisos Biotic District
1. River Flodplain-Arroyo
Formation
a. Arroyo-Mesquite-Acacia
Association
2. Shrub Desert Formation
a. Lechuguilla-CreosotebushCactus Association
3.
Sotol~Grassland Formation
a. Sotol-Grass Association
4. Woodland Formation
a. Deciduous Woodland
Association
b. Pinyon-juniper-Oak Woodland
Association
5. Moist Chisos Woodland
Formation
a. Cypress-Pine-Oak
Association
Warnock and Kittams (1970)
A. Chisos Biotic District
1. Desert Shrub Formation
a. Mesquite-Giantreed
b. Creosotebush
c. Creosotebush-Tarbush
2. Grassland Formation
a. Chino Grama-Lechuguilla
b. Chino Grama-Black Grama-SkeletonleafGoldeneye
c. Chino Grama-Candelilla
d. Hechtia-Chino Grama-Sotol
e. Grama-Sotol
f. Giant Dagger-Sotol
3. Woodland Formation
a. Mexican Pinyon-Oak-Juniper
b. Ponderosa pine-Douglas fir
TABLE 2.
2
Absolute density (stems/m ) of plants found within plant associations in Big Bend National
Park, Texas
Absolute Plant Density
2
(stems/m )
I.
Lechuguilla
Densit;y
Creosotebush-tarbush
Creosotebush-tarbush
Creosotebush-Iechuguilla-grass
Creosotebush-Iechuguilla-grass
Creosotebush-Iechuguilla-Opuntia
Creosotebush-Iechuguilla-candelilla
Creosotebush-lechuguilla-candelilla
Creosotebush-Iechuguilla
Creosotebush-Flats
Creosotebush-Flats
Paint Gap
Ash Creek
Nugent Mtn.
DOW Lacol.
4.2 mi E. DOW
Lower Old Ore Road
McKinney Hills
Dagger Flat Road
Upper Tornillo
Lower Tornillo
1052
1067
1067
945
762
640
914
914
841
628
2.30
3.38
3.01
2.34
0.65
0.74
2.05
0.24
0.64
0.04
0.49
0.80
0.67
0.57
0.14
0.14
0.47
0.06
0.00
0.17
Government Springs
K-Bar Road
Juniper Canyon
Horse Mesa
Dagger Flat
1097
1097
1310
1158
1049
2.46
2.14
3.24
4.05
4.34
0.51
0.39
0.73
0.99
1.00
960
975
1.72
1.04
0.41
0.25
Non-Creosotebush
1.
1.
2.
2.
3.
II I.
Total
Densit;y
Creosotebush
1.
1.
2.
2.
3.
4.
4.
5.
6.
6.
II.
Elevation
Location
Habitat
Viguieria-Iechuguilla-grass
Viguieria-Iechuguilla-grass
Sotol-lechuguilla-grass
Sotol- h~chuguilla-grass
Sotol-Giant Dagger
Non-Shrub
1. Lechuguilla-grass
1. Lechuguilla-grass
Hannold Draw
DOW Hills
.......
-i:'W
144
TABLE 3.
Delineation of plant associations within the lower desert
shrubland of Big Bend National Park, Texas.
Acreage
(Hectares) *
% of Park
20,099
7.01
7,309
2.55
13,313
4.64
4,698
1.64
Creosotebush-Iechuguilla-candelilla
63,690
22.22
Creosotebush Flats
82,484
28.78
Sotol-Iechuguilla-grass
12,790
4.46
Viguieria-Iechuguilla-grass**
11,746
4.10
Sotol-Giant Dagger
15,662
5.46
Lechuguilla-grass**
38,632
13.48
Badlands
3,132
1.09
Creek Bed
2,088
0.73
River Floodplain
5,220
1.82
280,863
97.98
Habitat (Vegetative Association)
Creosotebush-Iechuguilla-grass
Creosotebush-Iechuguilla-prickly pear
Creosotebush-tarbush
Creosotebush-Iechuguilla
Totals
*Acreage determined following Marcum and Loftgaarden (1980).
**Includes the Sierra Quemadas which are inhabited primarily
by white-tailed deer: excluding them yields lechuguilla-grass
(24,853 ha, 8.67%), viguieria-Iechuguilla-grass (10,177 ha, 3.55%).
145
TABLE 4.
Relative frequencies (RF) and absolute densities (AD) for the
Creosotebush-tarbush association in Big Bend National Park,
Texas.
Plant Species
Location
Paint GaE
RF
AD
-
Ash Creek
RF
AD
25.4
1.0
4.5
0.28
T
0.03
14.5
10.0
3.6
1.8
0.15
0.06
0.02
0.02
6.4
3.6
0.9
0.9
0.04
0.04
11.8
0.08
4.5
1.8
6.4
0.9
0.9
0.9
0.03
0.02
0.06
T
0.01
T
49.4
0.48
21.0
2.5
0.20
0.02
6.2
0.04
1.2
1.2
1.2
1.2
2.5
2.5
7.4
T
T
T
0.01
0.01
0.04
Woody:
Larrea tridentata
Dyssodia acerosa
Krameria glandulos~
Acacia constricta .
Flourensia cernua
Mendora spp.
Viguieria stenoloba
Parthenium incanum
Acacia Greggii
Dalea formosa
Prosopsis glandulosa
Xanthocephalum spp.
Forestieria angustifolia
Ephedra aspera
Zexmania brevifolfa
Mimosa biuncifera
Coldenia canescens
Dasylirion leiophyllum
Leucophyllum frutescens
Porophyllum spp.
Lycium spp.
Condalia spathulata
17.9
12.8
0.9
2.6
23.9
2.6
2.6
12.0
3.4
1.7
4.3
11.1
2.6
0.9
0.12
0.07
T*
0.16
0.01
0.01
0.06
0.01
0.01
0.02
0.02
0.07
0.01
0.01
1.7
0.02
T
T
Forbs:
Euphorbia spp.
Pilptrophe spp.
Dalea neomexicana
Nerisyrenia campo rum
Coldenia canescens
Pectis angustifolia
Gutierrezia spp.
Verbena neomexicana
Melampodium leucanthum
Croton spp.
Hibiscus denudatus
Allionia incarnata
Kallstroemia hirsutissima
Bahia absinrhifolia
D~ssodia Eentachaeta
Unknown
54.8
4.3
16.1
3.2
1.1
7.5
5.4
1.1
1.1
5.4
0.35
0.01
0.10
0.01
T
0.04
0.02
T
0.01
0.02
T
146
TABLE 4 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush-tarbush association in Big Bend National
Park, Texas.
Plant Species
Location
Paint Gap
RF
AD
14.1
15.5
39.4
4.2
9.9
7.0
1.4
1.4
2.8
1.4
2.8
0.07
0.08
0.28
0.02
0.04
0.05
Ash Creek
RF
AD
7.4
35.3
13.2
1.5
1.5
1.5
2.9
0.05
0.35
0.07
0.02
1.5
1.5
2.9
25.0
1.5
4.4
0.02
0.03
0.23
0.01
0.03
85.1
4.3
0.80
0.01
Grasses:
Tridens muticus
Aris tida spp.
Erioneuron pulchellum
Bouteloua trifida
Aristida divaricata
Bouteloua curtipendula
Trichachne californica
Muhlenbergia Porteri
Bouteloua eripoda
Sporobolus cryptandrus
Bothriochloa saccaroides
Bouteloua aristoides
Aristida adscensionis
Cathestecum erectum'
Bouteloua brevisata
Setaria spp.
Hilaria mutica
T
T
T
0.01
0.02
0.02
0.01
0.02
T
Succulents:
Agave lecheguilla
Echinocereus enneacanthus
Neolloydia spp.
Echinocactus horizonthalonius
Opuntia Schottii
O. violacea
Coryphantha spp.
Echinocereus chloranthus
Opuntia Kleinae
O. leptocaulis
O. phaeacantha
*Trace.
64.0
5.3
2.7
1.3
5.3
6.7
2.7
1.3
2.7
1.3
6.7
0.49
0.01
0.01
T
0.02
0.02
0.01
T
2.1
2.1
T
T
4.3
0.01
2.1
T
0.01
T
0.02
2
Absolute density less than .01 stems/m .
147
TABLE 5.
Relative frequencies (RF) and absolute densities (AD) for the
Viguieria-lechuguilla-grass association in Big Bend National
Park, Texas.
Plant Species
Location
Government SEring
RF
AD
3.8
15.1
8.5
2.8
0.02
0.10
0.06
0.02
24.5
8.5
3.8
5.7
0.19
0.04
0.02
0.03
1.9
0.01
2.8
9.0
3.8
1.9
0.9
0.9
1.9
0.01
0.06
0.03
0.01
T
T
0.01
K-Bar Road.
RF
AD
2.1
30.2:
19.0
1.0
3.1
10.4
10.4
3.1
0.01
0.22
0.10
0.01
0.01
0.04
0.05
0.01
3.1
1.0
0.02
T*
3.1
2.1
1.0
3.1
3.1
2.1
2.1
0.01
0.01
0.01
0.01
0.02
0.01
0.01
20.0
1.0
2.0
2.0
4.0
0.14
T
0.01
0.01
0.02
5.0
0.04
Woody:
Larrea tridentata
Krameria glandulosa
Acacia constricta
Flourencia cernua
Menodora spp.
Viguieria stenoloba
Parthenium incanum
Acacia Greggii
Dalea formosa
Prosopsis glandulosa
XanthoceEhalum spp.
Forestieria angustifolia
Ephedra aSEera
Zexmania brevifolia
Calliandra conferta
Bernardia obovata
Yucca Torreyi
Mimosa bimlcifera
Coldenia canescens
Leucophyllum frutescens
Porlieria angustifolia
Porophyllum spp.
Poly gala macrodentia
Carlowrightia linearfolia
Scaefferia cunefolia
A1o~sia Wrightii
Unknown
2.8
0.01
38.8
4.3
1.7
0.9
0.26
0.02
0.01
T
0.9
1.7
9.5
T
0.01
0.06
Forbs:
Euphorbia spp.
Psilotrophe spp.
Dalea neomexicana
Pectis angustifolia
Melampodium leucanthum
Cassia bauhinioides
Erigonum lachnogynum
Croton spp.
148
TABLE 5 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Viguieria-lechuguilla-grass association in Big Bend
National Park, Texas.
Plant Species
Location
Government Sl2rinB
Hibiscus denudatus
Boerhaavia spp.
Ayenia l2ilosa
Pec tis £iIi l2es
Allionia incarnata
Sida spp.
Dalea Wrightii
Baileya multiradiata
Acleisanthes lonBifolia
Janusia gracilis
Tidestromia languinosa
Macrosil2honia macrosil2hon
Kallstroemia hirsutissima
Bahia absinthifolia
Ditaxis neomexicana
Dyssodia l2entachaeta
Euphorbia extipulata
Dalea aurea
Pectis paPl20sa
Talinum aurantiacum
Unknown
K-Bar Road
RF
AD
RF
AD
1.7
11.2
0.9
4.3
0.9
4.3
0.9
2.6
0.9
1.7
0.01
0.08
T
0.04
T
0.03
T
0.02
T
0.01
1.0
14.0
T
0.11
5.0
0.02
3.0
0.01
5.0
2.0
8.0
3.0
2.0
2.0
7.0
1.0
2.0
2.0
6.0
0.04
0.01
0.05
0.01
0.01
0.11
0.03
T
0.01
0.01
0.03
7.0
7.0
14.1
1.4
2.8
8.5
26.8
0.03
0.03
0.06
0.01
0.02
0.04
0.19
1.4
0.01
1.4
19.7
1.4
8.5
0.01
0.11
0.01
0.02
1.7
0.02
11.2
0.06
4.2
4.2
8.5
8.5
4.2
0.01
Q.02
0.05
0.03
0.02
1.4
53.5
2.8
2.8
1.4
1.4
1.4
5.6
T
0.41
0.01
0.02
0.01
T
T
0.03
Grasses:
Tridens muticus
Aristida spp.
Erioneuron pulchellum
Bouteloua trifida
Aristida divaricata
B. Curtipendula
Trichachne californica
B. eriol2oda
B. aristidoides
Heterol2ogon contortus
Panicum bulbosum
A. adscensionis
Leptoloma cognatum
Cathestecum erectum
B. brevisata
Setaria spp.
Unknown
149
TABLE 5 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Viguieria-lechuguilla-grass association in Big Bend
National Park, Texas.
Plant Species
Location
Government Spring
K-Bar Road
RF
AD
RF
AD
67.1
0.51
4.3
2.9
2.9
0.01
0.01
0.01
55.3
1.3
11.8
14.5
2.6
0.39
T
0.04
0.05
0.01
Succulents:
Agave lechuguilla
Echinocactus horizonthalonius
Opuntia violacea
Q. phaeacantha
Mammillaria spp.
*Trace.
2
Absolute density less than 0.01 stems/m .
150
TABLE 6.
Relative frequen~ies (RF) and absolute densities (AD) for the
sotol-lechuguilla-grass association in Big Bend National
Park, Texas.
Plant Species
Location
Juniper Canyon
RF
AD
11.8
0.12
14.7
2.9
15.7
9.8
2.9
2.0
1.0
5.9
3.9
12.8
3.9
5.9
2.9
1.0
1.0
1.0
0.15
0.02
0.11
0.07
0.02
0.02
0.01
0.04
0.03
0.12
0.02
0.05
0.01
Horse Mesa
RF
AD
0.1
0.07
4.2
17.0
1.1
0.03
0.21
0.01
18.2
3.4
5.7
39.8
0.18
0.03
0.03
0.45
1.1
1.1
6.4
0.01
0.01
0.03
19.8
0.8
0.22
0.01
9.5
8.7
0.09
0.10
14.3
0.14
3.2
0.03
0.8
0.02
7.9
0.09
Woody:
Dyssodia acerosa
Krameria glandulosa
Acacia constricta
Mendora spp.
Viguieria stenoloba
Parthenium incanum
Dalea formosa
Forestieria angustifolia
Epedra aspera
Calliandra conferta
Dasylirion leiophyllum
Jatropha dioica
Leucophyllum frutescens
Calliandra humilus
Rhus microphylla
Lantana microphylla
Porlieria angustifolia
Tecoma stans
Polygala macrodentia
Coldenia mexicana
Gaura spp.
Unknown
T*
0.01
0.02
1.0
0.01
14.4
1.7
5.9
0.09
0.02
0.03
24.6
1.7
0.9
2.5
3.4
20.3
0.9
3.4
1.7
0.9
0.23
0.03
0.01
0.01
0.02
0.16
Forbs:
Euphorbia spp.
Dalea neomexicana
Verbena neomexicana
Melampodium leucanthum
Croton spp.
Hibiscus denudatus
Boerhaavia spp.
Ayenia pilosa
A1lionia incarnata
Sida spp.
Acleisanthes longiflora
Astragulus spp.
Tidestromia langinosa
Macrosiphonia macrosipho
T
0.03
0.03
T
151
TABLE 6 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the sotol-lechuguilla-grass association in Big Bend National
Park, Texas.
Plant Species
Location
Juniper Canyon
RF
Kallstroemia hirsutissima
Gnaphalium spp.
Bahai absinthifolia
Ditaxis neomexicana
Evolulus alsinoides
Euphorbia extipulata
Phyllanthus polygonoides
Ruellia P arryi
Erigeron modestus
Hymenoxys scaposa
Perezia runcinata
Cynanchum barbigerum
Eupatorium Wrightii
Evolvulus Nuttallianus
Hibiscus Coulteri
Impomea costellata
Unknown
5.1
1.7
4.2
3.4
0.9
AD
0.05
0.01
0.04
0.03
0.01
Horse Mesa
RF
AD
3.2
1.6
0.02
0.01
0.8
7.1
2.4
0.8
1.6
0.8
0.8
1.6
1.6
1.6
1.6
0.01
0.03
0.08
0.02
0.01
0.01
0.01
0.01
0.02
0.02
0.04
0.01
13.0
0.91
33.3
0.37
2.9
4.4
31.9
0.04
0.05
0.37
14.5
0.10
6.4
2.5
0.02
3.1
9.2
15.4
3.1
7.7
0.01
0.08
0.12
0.02
0.04
13.9
3.1
41.5
3.1
0.08
0.01
0.43
0.01
Grasses:
Aristida spp.
Erioneuron pulchellum
Aristida divaricata
Bouteloua curtipendula
Trichachne californica
Bouteloua eriopoda
Bothriochloa saccharoides
Heteropogon contortus
Panicum bulbosum
Bouteloua brevisata
Panicum arizonicus
Bouteloua hirsuta
152
TABLE 6 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the sotol-lechuguilla-grass association in Big Bend National
Park, Texas.
Plant Species
Location
Juniper Canyon
Horse Mesa
RF
AD
RF
AD
82.1
0.73
92.3
3.9
1.9
0.99
0.01
0.01
17.9
0.10
1.9
0.01
Succulents:
Agave lecheguilla
Opuntia violacea
Echinocereus chloranthus
Q. phaeacantha
Mammillaria spp.
*Trace.
2
Absolute density less than 0.01 stems/m •
153
TABLE 7.
Relative frequencies (RF) and absolute densities (AD) for the
Lechuguilla-grass association in Big Bend National Park,
Texas.
Plant Species
Location
Hannold Draw
RF
AD
1.5
11.1
1.5
0.01
0.05
0.01
0.03
0.03
0.01
Dugout Wells
Hills
RF
AD
8.1
3.6
0.9
0.02
0.01
Woody:
Larrea tridentata
Krameria glandulosa
Menodora spp.
Viguieria stenoloba
Acacia Greggi
Dalea formosa
Prosopsis glandulosa
Xanthocephalum spp.
Forestieria angustifol.i.a
Epedra aspera
Calliandra conferta
Mimosa biuncifera
Coldenia canescens
Dasylirion leiophyllum
Jatropha dioica
Leucophyllum frutescens
Porlieria angustifolia
Porophyllum spp.
Polygala macrodentia
Schaefferia cunei folia
Coldenia mexicana
Leucophyllum violaceum
Croton neomexicana
~UCO:Phyllum minus
Gaura spp.
Koeberlinia spinosa
Condalia ericoides
Unknown
7.4
5.9
3.7
0.7
1.5
3.7
5.9
4.4
3.7
11.1
T*
0.9
1.8
7.2
0.01
0.02
1.8
0.9
1.8
T
T
T
T
T
0.01
0.32
0.03
0.02
0.01
0.05
2.2
1.5
0.7
9.6
0.02
0.01
0.01
0.03
7.4
2.2
11.1
1.5
0.03
0.01
0.05
0.01
0.7
0.8
0.01
0.9
19.8
0.9
22.5
T
0.05
T
0.06
0.9
12.6
0.04
12.6
0.04
0.9
0.9
0.9
T
T
T
T
T
Forbs:
Euphorbia spp.
Psilotrophe spp.
Dalea neomexicana
Pectis angustifolia
Melampodium leucanthum
Croton spp.
Kallstroemia hirsutissima
36.0
0.17
8.0
0.02
3.0
5.0
2.0
0.01
0.02
0.01
28.0
1.9
10.3
0.9
2.8
1.9
13.1
0.08
T
0.03
T
T
T
0.03
154
TABLE 7 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Lechuguilla-grass association in Big Bend National Park,
Texas.
Plant Species
Location
Hannold Draw
RF
Bahia absinthifolia
Ditaxis neomexicana
Phyllanthus polygonoides
Hibiscus Coulteri
Lupinus Havardii
Kallstroemia grandiflora
Dalea Greggi
Cevalia sinuata
Tetraclea Coulteri
Unknown
3.0
1.0
1.0
32.0
1.0
1.0
Dugout Wells
Hills
AD
RF
AD
0.01
6.5
4.7
0.01
0.01
2.8
16.8
0.01
0.04
T
0.01
0.16
0.01
T
1.0
0.03
6.7
10.0
1.7
5.0
1.7
75.0
0.02
0.02
0.01
0.02
2.8
0.9
1.9
2.8
T
T
0.01
0.01
Grasses:
Aristida spp.
Erioneuron pulchellum
Bouteloua trifida
Aristida divaricata
Bouteloua curtipendula
Bouteloua brevisata
3.8
1.9
T
0.37
60.0
0.16
90.4
1.9
0.41
0.01
88.7
3.8
1.9
0.25
1.9
5.8
0.01
0.01
1.9
1.9
1.9
0.01
T
T
Succulents:
Agave lecheguilla
Echinocereus enneacanthum
Neolloydia spp.
Echinocactus horizonthalonius
Opuntia violacea
Coryphanta. spp.
Echinocereus pectinatus
*Trace.
2
Absolute density less than 0.01 stems/m •
T
T
T
0.01
155
TABLE 8.
Relative frequencies (RF) and absolute densities (AD) 'for the
Sotol-Yucca association in Dagger Flat, Big Bend National
Park, Texas.
Plant Species
Location
Dagger Flat
RF
AD
2.7
9.7
9.7
6.2
1.8
7.1
16.8
0.9
2.7
0.9
10.6
1.8
3.5
1.8
1.8
5.3
10.6
1.8
1.8
1.8
0.9
0.03
0.15
0.09
0.07
0.01
0.10
0.16
0.01
0.02
0.01
0.09
0.02
0.03
0.02
0.02
0.06
0.14
0.01
0.01
0.02
0.01
15.2
8.4
9.8
12.5
4.5
3.4
6.3
0.9
1.8
4.5
2.7
7.1
8.9
9.4
2.7
3.6
0.21
0.09
0.10
0.11
0.04
0.02
0.05
0.01
0.01
0.03
0.02
0.22
0.11
0.03
0.02
0.02
Woody:
Larrea tridentata
Dyssodia acerosa
Menodora spp.
Viguieria stenoloba
Acacia Greggii
Dalea formosa
Xanthocephalum spp.
Forestieria angustifolia
Epedra aspera
Mimosa biuncifera
Dasylirion leiophyllum
Heliotropium confertifolium
Mimosa borealis
Yucca carnerosana
Polygala macrodentia
Coldenia mexicana
Leucophyllum violaceum
Croton neomexicana
Coldenia Greggii
Acacia Roemeriana
Yucca elata
Forbs:
Euphorbia spp.
Psilotrophe spp.
Nerisyrenia camporum
Melampodium leucanthum
Bahia absinthifolia
Dyssodia pentacaeta
Ruellia Parryi
Dalea Greggii
Hedoema Drummondii
Hedyotis spp.
Polygala alba
Euphorbia antisyphilitica
Chamaesarcha Coronopus
Talinum angustifolia
Caesalpinia Jamesii
Unknown
156
TABLE 8 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Sotol-Yucca association in Dagger Flat, Big Bend National
Park, Texas.
Plant Species
Location
Dagger Flat
RF
AD
14.3
1.6
3.2
3.2
1.6
73.0
3.2
0.11
0.02
0.01
0.01
0.01
0.91
0.02
80.0
3.3
1.7
3.3
5.0
1.7
5.0
1.7
1.00
0.01
0.01
0.01
0.02
0.01
0.04
0.01
Grasses:
Aristida spp.
Erioneuron pulchellum
Bouteloua curtipendula
Trichachne californica
Aristida adscensionis
Bouteloua brevisata
Unknown
Succulents:
Agave lecheguilla
Echinocactus horizonthalonius
Echinocereus chloranthus
Opuntia Kleiniae
O. leptocaulis
Q. phaecantha
O. Lindheimeri
Ariocarpus fissuratus
157
TABLE 9.
Relative frequencies (RF) and absolute densities (AD) for the
Creosotebush-lechuguilla-grass association in Big Bend
National Park, Texas.
Plant Species
Location
Nugent
Mountain
Dugout Wells
Anticline
RF
AD
RF
AD
39.2
2.0
0.36
0.01
44.2
2.9
13.7
1.0
2.0
1.0
0.01
0.10
0.02
4.2
0.35
0.02
0.07
T*
0.02
T
T
2.1
3.2
1.1
0.01
0.01
1.0
0.01
4.2
14.7
2.0
0.11
0.01
0.01
'0.07
0.01
Woody:
Larrea tridentata
Krameria glandulosa
Acacia constricta
Menodqra spp.
Viguieria stenoloba
Parthenium incanum
Acacia Greggi
Dalea formosa
Prosopsis glandulosa
Epedria aspera
Calliandra conferta
Dasylirion leiophyllum
Jatropha dioica
Leucophyllum frutescens
Lycium spp.
Condalia spathulata
Polygala macrodentia
Coldenia mexicana
Leucophyllum violaceum
Colden.ia Greggii
Fouquieria splendens
Condalia ericoides
1.0
5.3
12.6
1.1
12.6
2.1
1.1
T
T
1.1
4.9
3.9
9.8
1.0
T
0.02
0.02
0.08
0.01
T
3.2
0.01
2.1
0.01
60.7
1.1
25.8
1.1
0.39
3.4
0.01
Forbs:
Euphorbia spp.
Psilotrophe spp.
Dalea neomexicana
Nerisyrenia camp 0 rum
Pectis angustifolia
Croton spp.
Boerhaavia spp.
Pectis filipes
Allionia incarnata
Sida spp.
Tidesstroemia languinos.a
Kallstroemia hirsutissima
Bahia absinthifolia
28.6
3.1
5.1
3.1
7.1
7.1
2.0
2.0
1.0
4.1
18.4
0.30
0.02
0.05
0.02
0.06
0.05
0.01
0.01
T
0.15
T
T
0.03
0.12
158
TABLE 9 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Creosotebusb~lechuguilla-grass association in Big Bend
National Park, Texas.
Plant Species
Location
Nugent
Mountain
RF
Ditaxis neomexicana
Dyssodia pentacaeta
Hibiscus Coulteri
Sarcostemma cynanchoides
Unknown
6.1
1.0
Dugout Wells
Anticline
RF
AD
0.03
AD
2.3
0.01
0.01
0.01
0.01
T
10.2
0.05
1.1
1.1
2.3
0.44
0.01
0.02
0.26
7.4
22.1
14.7
2.9.
52.9
0.03
52.3
3.1
6.2
32.3
76.2
6.4
0.67
0.02
0.57
0.01
4.8
0.02
94.1
3.9
2.0
2.0
Grasses:
Aristida spp.
Erioneuron pulchellum
Bouteloua trifida
Trichachne californica
Bouteloua brevisata
0.11
0.04
0.02
0.39
Succulents:
Agave lecheguilla
Echinocereus enneacanthus
Neolloydia spp.
Opuntia phaeacantha
*Trace.
2
Absolute density less than 0.01 stems/m •
T
T
159
TABLE 10.
Relative frequencies (RF) and absolute densities (AD) for
the Creosoteoush-Iechuguilla and the Creosoteoush-Iechuguilla-prickly pear associations in Big Bend National Park,
Texas.
Plant Species
Vegetative Association
and (Location)
C-L
(Dagger Flat Road)
C-L-P
(East Dugout)
RF
AD
RF
AD
47.6
0.04
T*
70.2
0.14
Woody:
Larrea tridentata
Dyssodia acerosa
Flourensia cernua
Viguieria stenoloba
Parthenium incanum
Prosopsis glandulosa
Xanthocephalum spp.
Jatropha dioica
Heliotropium confertifolium
Polygala macrodentia
'Carlowrightia linearifolia
Coldenia mexicana
C. Greggii
4.8
4.8
T·
16.7
2.4
2.4
0.01
16.7
0.01
4.8
1.5
1.5
T
19.4
0.02
1.5
4.5
T
T
1.5
T
4.4
1.8
20.4
26.6
0.9
0.9
22.1
20.4
0.01
T
T
T
T
Forbs:
Euphorbia spp.
Dalea neomexicana
Nerisyrenia campo rum
Cassia bauhinioides
Allionia incarnata
Bahia absinthifolia
Ditaxis neomexicana
Euphorbia exstipulata
Dyssodia aurea
Hibiscus Coulteri
Thamnosma texana
Machaeranthera pinnatifida
Unknown
41.2
0.02
2.0
T
17.7
T
T
0.03
T
0.01
0.9
0.9
37.3
2.0
T
0.04
0.04
T
0.01
0.03
T
0.5
T
5.2
82.8
T
Grasses:
Aristida spp.
Erioneuron pulchellum
Aristida divaricata
Trichachne californica
6.5
77 .4
3.2
3.2
0.05
0.01
0.15
T
T
3.5
T
160
TABLE 10 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush~lechuguilla and the Creosotebush-lechuguillaprickly pear associations in Big Bend National Park, Texas.
Plant Species
Vegetative Association
and (Location)
C-L
(Dagger Flat Road)
Aristida adscensionis
Bouteloua brevisata
Unknown
C-L-P
(East Dugout)
RF
AD
RF
AD
3.2
6.5
T
T
5.2
T
3.5
T
Succulents:
Agave lecheguilla
Echinocereus enneacanthus
E. chloranthus
Opuntia Kleiniae
Q. phaeacantha
o. rufida
*Trace.
70.6
0.06
5.9
T
5.9
T
2
Absolute density less than 0.01 stems/m •
75.0
6.3
1.6
3.1
0.14
T
T
T
161
TABLE 11.
Relative frequencies (RF) an4 absolute densities.(AD) for
the Creosotebush-Iechuguilla-candelilla association in Big
Bend National Park, Texas.
Plant Species
Location
McKinney
Hills
Old Ore Road
RF
AD
RF
AD
49.4
0.01
3.5
0.01
25.6
2.6
1.7
9.4
0.15
0.01'
0.01
0.04
2.3
T*
0.9
25.6
1.7
T
0.15
0.01
9.4
.0.9
0.9
0.9
2.7
12.8
0.04
0.01
T
T
0.02
0.06
2.6
1.7
0.01
0.01
4.8
14.3
0.02
0.07
1.9
1.0
18.1
0.01
20.0
0.10
31.4
3.8
2.9
0.21
0.01
0.01
Woody:
Larrea tridentata
Dyssodia acerosa
Krameria glandulosa
Menodora spp.
Viguieria stenoloba
Epedra aspera
Coldenia canescens
Dasylirion leiophyllum
Jatropha dioica
Heliotropium confertifolium
Tidestromia suffuticosa
Rhus microphylla
~orlieria angustifolia
Polygala macrodentia
Coldenia mexicana
Leucophyllum violaceum
L. minus
Coldenia Greggii
Yucca elata
5.8
18.4
2.3
0.01
0.03
T
5.8
10.3
0.01
0.02
1.2
1.2
T
T
28.7
3.2
2.1
6.4
0.06
T
T
0.01
11. 7
2.1
4.3
10.6
1.1
2.1
20.2
0.02
T
0.01
0.03
T
T
0.05
7.5
0.01
Forbs:
Psilotrophe spp.
Nerisyrenia ~mporum
Cassia bauhinioides
Croton spp.
Allionia incarnata
Astragulus spp.
Bahia absinthifolia
Ditaxis neomexicana
Dyssodia pentachaeta
D. aurea
Hibiscus Coulteri
Cevallia sinuata
Euphorbia antisyphilitica
Caesalpinia Jamesii
Linum rigidum
Unknown
T
0.08
162
TABLE 11 CONTINUED. Relative frequencies (RF) and absolute densities
(AD) for the Creosotebush-Iechuguilla-candelilla association in Big
Bend National Park, Texas.
Plant Species
Location
McKinney
Hills
Old Ore Road
RF
AD
RF
AD
1.5
47.8
0.25
50.8
0.27
77.4
0.47
8.1
0.01
4.8
9.7
0.01
0.02
Grasses:
Aristida spp.
Erioneuron pulchellum
Bouteloua trifida
Aristida adscensionis
Bouteloua brevisata
Hilaria mutica
Unknown
1.8
68.4
3.5
5.3
15.8
3.5
1.8
T
0.14
0.01
0.01
0.03
T
T
T
Succulents:
Agave lecheguilla
Neolloydia spp.
Echinocactus horizonthalonis
Opuntia Schottii
Echinocereus choloranthus
Opuntia Kleiniae
O. leptocaulis
o. Lindheimeri
Ariocarpus fissuratus
Hechtia scariosa
Unknown
*Trace.
53.6
6.0
3.6
6.0
3.6
2.4
6.0
14.3
0.14
0.01
2.4
2.4
T
T
0.01
0.01
T
0.01
0.01
T
2
Absolute density less than 0.01 stems/m •
163
TABLE 12.
Relative frequencies (RF) and absolute densities (AD) for
the Creosote Flats association in Big Bend National Park,
Texas.
Location
Plant Species
Upper Tornillo
Flats
Lower Tornillo
Flats
RF
AD
RF
AD
81.8
18.2
0.15
0.01
85.7
0.04
7.1
7.1
T
14.3
85.7
0.04
7.7
92.3
0.04
Woody:
Larrea tridentata
Prosop·sis glandulosa
Jatropha dioica
Heliotropium conferifolium
T*
Forbs:
Nerisyrenia camporllm
Xanthocephalum spp.
Allionia incarnata
Bahia absinthifolia
Dyssodia aurea
Hoffmanseggia spp.
Zephryanthes longifolia
3.3
10.0
3.3
16.7
10.0
36.7
20.0
0.01
0.01
T
0.02
0.01
0.09
0.03
Grasses:
Aristida spp.
Erioneuron pulchellum
Bouteloua trifida
Unknown
84.2
15.8
T
0.15
0.01
Succulents:
Echinocereus enneacanthus
Echinocactus horizonthalonius
Opuntia Schottii
o. leptocaulis
*Trace.
9.5
T
4.8
85.7
T
0.15
2
Absolute density less than 0.01 stems/m •
T
TABLE l3.
Relative frequencies of plant species occurring in washes within plant associations found
in Big Bend National Park, Texas.
Plant Association
Plant SEecies
C-L-G
S-L-C
Cel tis pallida
POEophyllum spp.
Menodora spp.
Parthenium incanum
Viguieria stenoloba
Acacia Greggii
Aloysia gratissima
Chilopsis linearis
Jatropha dioica
Larrea tridentata
Artemisia ludoviciana
Xanthocephalon spp.
AtriElex canescens
Epedra aSEera
Machaeranthera pinnatifida
Aloysia Wrightii
Porlieria angustifolia
Yucca torreyii
Brickellia lacinata
Condalia spathulata
Lantana macropoda
Gutierrezia spp.
Opuntia leEtocaulis
Dalea formosa
-Gaura spp.
Carlowrightia linearifolia
Trixus californica
Schaefferia cunei folia
0.7
9.5
0.3
10.2
14.6
7.8
3.2
2.0
5.6
14.4
0.3
2.9
0.3
1.0
0.7
0.3
4.4
0.5
0.3
0.3
0.5
0.7
0.2
1.0
0.3
0.5
1.7
0.5
0.2
0.7
4.0
1702
7.2
1.4
4.1
3.1
0.5
2.4
4.1
0.2
6.7
0.7
1.7
1.0
0.7
1.0
1.2
1.7
V-L-G
0.0
16.5
6.1
1.0
Cr-Ft
Le-Gr
Cr-Tr
0.2
6.5
0.3
1.2
2.7
12.0
1.8'
4.6
9.1
7.1
1.0
5.4
2.2
2.7
0.5
0.5
0.2
24.8
8.5
0.8
9.7
9.2
0.8
1.2
0.2
3.5
2.8
7.2
4.7
0.3
8.9
0.7
0.8
5.7
4.4
0.5
7.1
3.5
0.7
0.8
3.4
5.1
0.5
1.8
1.0
7.4
17.7
1.5
0.3
0.5
3.2
1.2
0.7
2.2
9.1
4.4
C-L-P
C-L-C
0.2
0.2
'0.3
2.5
0.5
Cr-Le
2.6
14.0
1.0
0.5
12.2
6.6
0.5
1.0
4.1
10.7
23.0
21.0
1.5
0.5
19.1
1.6
7.2
15.0
7.7
0.5
1.0
16.3
50.4
5.3
0.5
5.2
0.5
4.1
2.1
0.4
3.1
0.5
1.8
0.9
3.6
6.6
2.1
2.1
0.4
0.4
1.0
5.6
0.5
0.5
0.7
0.5
So-Dg
0.5
0.5
3.1
0.5
10.5
0.5
0.5
I-'
0'\
~
TABLE 13 CONTINUED. Relative frequencies of plant species occurring in washes within plant associations found in Big Bend National Park, Texas.
Plant Association
Plant Species
Pol~gala macradentia
Agave lecheguilla
Diospyrus texana
Fouquieria splendens
Krameria glandulosa
Leucophyllum frutescens
Muhlenbergia Porteri
Zexmania brevi folia
Dasylirion leiophyllum
Opuntia violaceum
Prosopsis glandulosa
Rhus microphylla
Koeberlinia spinosa
Hoffmanseggia spp.
Lycium spp.
Condalia ericoides
Dyssodia acerosa
Opuntia phaecantha
Fraxinus Greggii
Juniperous monosperma
Tecoma stans
-Acacia Roemeriana
Acacia constricta
Janusia gracilus
Forestieria angustifolia
Perezia runcinata
Mimosa biuncifera
Calliandra humilus
CQEYsactinia mexicana
Mimosa borealis
C-L-G S-L-C
--
0.3
0.5
1.7
0.3
0.7
4.4
0.3
3.4
1.0
1.2
0.3
V-L-G
Cr-Ft
Le-Gr
Cr-Tr
C-L-P
2.9
8.1
12.8
5.6
0.5
11.0
0.5
1.5
4.1
1.0
0.7
1.2
1.0
1.0
4.1
0.5
5.0
0.2
0.5
0.2
0.2
0.5
0.2
1.0
0.7
1.4
0.2
0.7
0.5
01. 7
0.2
0.2
5.4
0.7
3.3
0.5
0.7
2.4
0.2
1.2
0.7
0.2
0.2
0.2
0.5
So-Dg
Cr-Le
1.0
9.3
1.8
2.6
1.0
1.4
0.2
5.0
6.7
3.1
4.8
0.8
0.8
1.0
6.4
2.7
0.7
1-0
0.5
6.7
0.5
1.5
0.3
0.5
C-L-C
2.0
0.5
1.8
0.5
0.2
0.3
0.5
0.5
0.5
1.9
0.2
1.2
1.5
6.6
5.3
2.2
2.6
0.5
0.3
1.5
0.5
0.5
6.1
1.6
.....
'"
IJ1
TABLE 13 CONTINUED. Relative frequencies of plant species occurring in washes within plant associations found in Big Bend National Park, Texas.
Plant Association
Plant Species
Berberis trifoliolata
Bernardia obovata
Flourensia cernua
Ceanothus Greggii
Clematis Drummondii
Dicraurus leEtocladus
Nolina erumpens
Yucca elata
Atriplex obovata
Opuntia Lindheirmeri
Sarcostemma spp.
Dalea frutescens
Acacia Berlandieri
Echinocereus enneacanthus
LeucoEh~llum minus
Croton neomexicana
Acacia Schottii
Erigeron spp.
Hymenoclea spp.
LeucoEhyllum violaceum
Euphorbia antisyphilitica
Yucca carnerosana
Fallugia paradoxa
Soil
Unknown
C-L-G
S-L-C
V-L-G
Cr-Ft
0.3
1.2
0.3
0.2
0.2
0.7
1.7
Le-Gr
Cr-Tr
C-L-P
C-L-C
1.0
8.7
0.2
0.2
Cr-Le
2.6
0.8
0.3
SO-Dg
18.0
9.7
0.3
0.5
0.8
0.8
0.3
0.3
0.3
0.3
0.5
0.7
1.5
3.1
1.0
1.0
0.3
1.2
3.1
0.5
0.5
2.6
9. 2
3.6
0.8
1.0
0.5
2.6
6.2
0.5
16.7
I-'
0\
0\
TABLE 14.
Comparison of important plant species found within Dagger Flat, Big Bend National Park,
Texas and other cornmon plant associations.
Dagger Flat
Plant Species
Frequency of
Occurrence
Euphorbia spp.
15.2
"
tr
"
"
"
"
Helampodium leucanthum
Xanthocephalon spp.
Menodora spp.
"
"
Dyssodia acerosa
Dasylirion leiophyllum
Leucophyllum violaceum
Euph~rbia antisyghilitica
..
"
"
"
"
12.5
16.8
9.7
"
9.7
10.6
10.6
7.1
"
Location where plant occurs in moderate occurrence
Frequency of
Location
Plant Association
Occurrence
Paint Gap
Government Springs
Hannold Draw
Nugent Mountain
Horse Mesa
K-Bar Road
Hannold Draw
Ash Creek
Paint Gap·
Horse Mesa
Old Ore Road
"
"
"
McKinney Hills
Creo-tar
Vig-Iech-grass
Lech-grass
Creo-Iech-grass
Sotol-Iech-grass
Vig-Iech-grass
Lech-grass
Creo-tar
Creo-tar
Sotol-Iech-grass
Creo-Iech-can
"
"
"
"
"
"
54.8
38.8
36.0
28.6
9.5
6.3
11.1
10.0
12.8
18.2
10.3
20.2
31.4
I-'
0\
'-J
TABLE 15.
Summary of characteristics of plant associations found within Big Bend National Park,
Texas.
Characteristic
Eleva- TopoTotal
Plant Species
Plant Association
Plant
tion
Rainfall
graphic
Position
Densit~
Creosotebush dominated
I.
II.
1. Creosotebush-tarbush
a. Flourencia cernua
b. Larrea tridentata
2.1-3.4
Moderate
10001100
Flats
2. Creosotebushlechuguilla-grass
a. Larrea tridentata
b. Bouteloua brevisata
2.3-31.
Moderate
9001100
Flats
3. Creosotebushlechuguilla-prickly
pear
a. Larrea tridentata
b. Erineuron pulchellum
c. Opuntia rufida
0.55-0.70
Low-Moderate
620770
Flats
4. Creosotebushlechuguillacandelilla
a.
b.
c.
d.
0.70-2.1
Low-Moderate
600920
Flats
5. Creosotebushlechuguilla
a. Larrea tridentata
b. Agave lecheguilla
0.06-0.07
Low-Moderate
800900
Flats
6. Creosotebush Flats
a. Larrea tridentata
b. Q£untia leptocaulis
0.15-0.70
Low
600850
Flats
Larrea tridentata
Bouteloua brevisata
Euphorbia antisyphilitica
Opuntia Lindheimeri
Non-creosotebush dominated
1. Viguierialechuguilla-grass
a. Viguieria stenoloba
b. Bouteloua eriopoda
2.0-2.5
Moderate
10501200
Flats
2. Sotol-lechuguillagrass
a.
b.
c.
d.
3.1-4.4
Moderate-High
11001400
Slopes
Dasylirion leiophyllum
Calliandra humilus
Herteropogon contortus
Viguieria stenoloba
.....
0\
(Xl
TABLE 15 CONTINUED.
Park, Texas.
Summary of characteristics of plant associations found within Big Bend National
Plant Association
Characteristic
Plant Species
Total
Plant
Rainfall
Eleva- Topotion
graphic
Position
Moderate-High
1000-
Densit~
3. Sotol-giant dagger
a. Yucca carnerosana
b. Dasylirion leiophyllum
4.0-4.5
a. Agave lecheguilla
b. Bouteloua brevisata
0.25-0.45
llOO
FlatsSlopes
III. No shrub dominant
1. Lechuguilla-grass
Low-High
9001000
Slopes
I-'
0\
\0
170
t
N
oI
Miles
Figure 1. Big Bend National Park, Texas (1. Dagger Mountain, 2. Dagger
Flat, 3. Pullium Ridge, 4. Ward Mountain,S. Panther Junction,
6. Boquillas, 7. Dugout Wells, 8. Nugent Mountain, 9. Gravel Pit,
10. K-Bar, 11. Government Spring, 12. Lone Mountain, 13. Todd Hill,
14. Sotol Vista, 15. Horse Mesa, 16. Juniper Canyon, 17. Hannold Draw,
18. Dugout Wells Anticline, 19. Kit Mountain, 20. McKinney Hills,
21. Upper Tornillo Flats, 22. Lower Tornillo Flats).
171
Density Relationships
stemSJ!D2
4.5
High
Sotol-Yucca
•
.,
4.0
as
Sotol-Iech guilla-grass
creosote~sh-tarbuSh
, l
3.0
Creosotebush-Iechugui lIa-grass
2.5
ViqUieria-JJhUgUilla-graSs
2.0
1.5
1.0
•
•
•
•
Creosotebush-Iech uilla-candel i II a
Lechuguilla-grass
,
1
Creosotebush-Iechuguilla -pl'ickly pear
0.5
•
•
J
Creosot~bush
•
•
•
Low
Flats
CreosotebusH-lechugu ilia
0,0
Figure 2. Density relationships between plant associations found
within the lower desert shrubland of Big Bend National Park, Texas.
172
Diversity Relationships
High
Viquieria -leCrugUi lIa - grass
Sotol -Yucca
Sotol-Iechu~uilla- grass
~eosotebu'h-tarbush
LeChugUilta -grass
•
•
•
creosotebuSh-leChU~uilla -cande I i II a
•
Creosotebush - fechuguilla-grass
•
•
creosot8busl.8chU9uilla
Creosotebush-Iechuglli lIa - prickly pear
•
•
•
•
•
Creosotebush Flats
Low
Figure 3. Diversity relationships between plant associations found
within the lower desert shrubland of Big Bend National Park, Texas.
173
Figure 4. The Creosotebush-tarbush plant association at
Paint Gap Hills, Big Bend National Park, Texas.
~>
•
. ··,"-.·.i··.'·..
"~:'/~
,
.,: 'I.:'~I ",' •
..~:,,\,,"!.
,~ ... ~;li:,:'::,S~;~;',/i:t~·
,.
I'
.
Figure 5. The Viguieria-lechuguilla-grass plant association
south of Oak Spring, Big Bend National Park, Texas (Note the
absence of Creosotebush).
174
Figure 6. The Sotol-lechuguilla-grass plant association at
Burro Mesa, Big Bend National Park, Texas.
Figure 7. The Lechuguilla-grass plant association on the
slopes northwest of Dugout lvells, Big Bend National Park,
Texas (Note the lack of any dominant shrub species, grass
is Chino grama).
175
Figure 8. The slopes north-west of Dugout Hells demonstrating the hillsides dominated by lechuguilla and chino
grama and the level ridgetops composing less than 10
percent of the land surface (Vegetation in foreground indicative of plant species found in the washes.
Figure 9. The Sotol-Giant Dagger plant association found
in Dagger Flat, Big Bend National Park, Texas.
176
Figure 10. The Creosotebush-lechuguilla-grass plant
association north of Nugent }wuntains, Big Bend National
Park, Texas.
Figure 11. The Creosotebush-lechuguilla-grass plant
association east of Kit ~1ountain, Big Bend National Park,
Texas (Note the lower density of plants as compared to
Figure 10).
177
Figure 12. The Creosotebush-Iechuguilla-prickly pear plant
association 6.4 kilometers east of Dugout Hells, Big Bend
National Park, Texas.
Figure 13. The Creosotebush-Iechuguilla-candelillia plant
association along the southern portion of the Old Ore Road,
Big Bend National Park, Texas.
178
Figure 14. The Creosotebush-lechuguilla plant association
south of Dagger Flat Road, Big Bend National Park, Texas.
Figure 15. The Creosotebush Flats at the Fossil Bone
Exhibit, Big Bend National Park, Texas.