CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
POPULATION ECOLOGY
I'
OF SOME BRAZILIAN RODENTS
.A thesis submitted in partial satisfaction of the
requirements for the degree of Master of Science in
Biology
by
Joseph Paul Abravaya
->
January, 1979
The 'l'hesis of Joseph Paul Abravaya is approved:
Date
Date
California State University, Northridge
ii
ACKNOWLEDGEMENTS
I extend thanks to Andrew Starrett for serving as my
thesis committee chairman, and to George Fisler and
Marvin Cantor for serving on my committee.
I am especially
grateful to Andrew Starrett and George Fisler for giving
their office a friendly and pleasant atmosphere in which
a great deal of conversation and idea exchange takes
place.
Their extraordinary patience and knowledge are
invaluable academic and personal resources to many students.
I thank Janet Hamilton for preparing the figures in
this thesis and for being more than a friend.
I am
grateful to Debra Koutnik, Donald Perry, and many other
students for their encouragement and friendship.
I thank
Jack Matson and Donald Christian for critically reviewing
this manuscript during its preparation.
Fieldwork was supported by the Institute Brasileiro
de Desenvolvimento Florestal.
The fieldwork was accomplished
\<7h.i1e I was a Peace Corps volunteer in Brazil.
I am especially indebted to Augusto Ruschi, Director
of the Museu de Biologia, "Prof. Mello
Leit~o"
for his
support of fieldwork and for his enthusiasm for conservation
and natural history.
iii
TABLE OF CONTENTS
Page
Acknowledgements
iii
Abstract
vii
Introduction
1
Materials and Methods.
3
Results.
10
Discussion
15
Conclusions.
24
Literature Cited
50
iv
TABLE OF TABLES
Page
Table 1.
Trapping schedule.
25
Table 2.
Number of individuals captured.
26
Table 3.
Number of individuals on grid in one
session, two sessions, etc.
27
Table 4.
Mean number of captures.
28
Table 5.
Predation evidence.
29
Table 6.
Average distance moved.
30
Table 7.
Home range.
31
Table 8.
Edge effect test.
32
Table 9.
Habitat preference test for the
dry season.
34
Table 10. Habitat preference test for the
wet season.
35
Table 11. Reproductive condition and age per
session.
36
Table 12. Morphological measurements and ratios.
38
v
TABLE OF FIGURES
Page
Figure 1.
Map of study grid.
39
Figure 2.
Monthly meal)S of rainfall at Santa
Teresa, Espirito Santo.
40
Figure 3.
Average distance moved.
41
Figure 4.
Numbers of individuals on grid.
47
vi
ABSTRACT
POPULATION ECOLOGY
OF SOME BRAZILIAN RODENTS
by
Joseph Paul Abravaya
Master of Science in Biology
A capture-mark-recapture grid was set up in southeastern Brazil to gather information on seasonal abundance,
reproduction, movements, habitat and interspecific relationships of the poorly known rodent fauna.
Two hundred
seventy one individuals of twelve rodent species were
captured 1293 times.
The rodents on the g-rid changed seasonally in density
and reproductive behavior.
Reproduction ~as correlated
with the rainy season when food resources were most
abundant.
Oryzomys moojeni was reproductively aseasonal,
although breeding activity was most intense during the
rainy season, whereas Thomasomys sublineatus and
Oxymicterus hispidus bred seasonally.
vii
These differences
may reflect different evolutionary histories or may be a
result of competitive interactions.
Declines in density
during the latter part of the wet season may be due to
the combined effects of flooding and reproductive stress.
Most species tended to avoid hill areas, and preferred
flat areas.
It appeared, however, that flooding affected
seasonal movements; 0. moojeni, T. sublineatus and
Thaptomys nigrita changed their habitat preference in
favor of hill areas during the wet season.
utilization was three dimensional:
there were fossorial,
aquatic, terrestrial, and arboreal species.
viii
Habitat
·INTRODUCTION
Most long term studies of small mammal populations
have been conducted in temperate areas in the northern
hemisphere, where severe seasonal climatic changes occur.
Few studies of more than a few months duration have been
conducted in the neotropics (Davis 1945; Enders 1935;
Fleming 1971, 1973) and in temperate South America
(Dalby 1975; Paulk 1975).
These studies have shown that
seasonal changes, which correlate with ecological necessities and phylogenetic patterns, occur in small mammal
populations.
In semi-arid Chile, where a Mediterranean
climate similar to that of coastal southern California
prevails, Faulk (1975)
found that rodents have adopted
seasonal reproductive strategies similar to those of their
ecological counterparts in California.
Fleming (1971)
reported that rodent species in tropical low-land
Panama employed reproductive strategies that fol.lor.-1
phylogenetic patterns:
the heteromyid, Liomys, with
temperate origins, showed marked seasonal fluctuations
in reproduction, while the tropical genera Oryzomys and
Proechimys were reproductively active all year.
In
temperate Argentina, Dalby (1975) found that Oryzomys
were seasonal in reproduction and densities.
1
2
These studies indicate that rodents tend to follow
phylogenetic patterns in reproductive seasonality but
environmental factors, such as food availability, climatic
conditions and species interactions may modify seasonal
behavior.
The present study was conducted in subtropical
Bra~il
to gather information on seasonal abundance,
reproduction, movements, habitat, and interspecific
relationships of the poorly known fauna of that area.
MATERIALS AND METHODS
Study Area
Des'2!"iptio!.!_
The study was conducted in the coastal mountains of
the state of Esplrito Santo, in the Forest Reserve Nova
Lombardia, Brazil.
The reserve is located nine kilometers
from the t.own of Santa Teresa and 48 kilometers in a
straight line from the ocean.
The terrain is.hilly;
small valleys with creeks are common.
A trapping grid .
was placed in one of these valleys such that a creek
flowed across i t from east to west.
During the dry
season the creek varied in width from about two to five
meters, and in depth from about one to one and a half
meters.
In the wet season the creek occasionally over-
flowed its banks and flooded some of the surrounding flat
area.
The elevation of the grid varied from 805 m at
creek level to 830 m on both north and south facihg slopes
(Figure 1) .
The forest reserve, an area of 4,350 ha, was established in 1941 and has remained virtually unchanged si~ce
then.
The vegetation is classified as Slilitropical Lower-
Montane-Moist forest by the Holdridge (1964) system, and
as "altimontana" forest by Ruschi (1950, 1969).
3
Emergent
4
trees rarely exceeded thirty meters in height; an upper
canopy occurred at about 20m.
Tree ferns.and palms were
common and trees were covered with lianas and epiphytes.
Climate
Ruschi (1950) gave climatic data for the forest
reserve.
The mean annual temperature was l7°C, the coldest
month was July with a l0°C mean and the warmest month
was February with a 22°C mean.
Freezing temperatures
were recorded in July and temperatures as high as 30°C
were recorded in February.
Although there is rainfall
every month, from April through September precipitation
is to a large degree in the form of fog or drizzle.
From
October through March rains are heavy and it is at these
times that flooding occurs.
Figure 2 (Ruschi 1950)
shows monthly means of rainfall in Santa Teresa 9 km
to the SW (see Jackson, 1978 for further discussion of
climatic conditions).
Trapping Procedure
The area selected for the live-trap grid was on
the eastern boundary in the southern extremity of the
Forest Reserve Nova Lombardia.
This area was selected
because of its relative freedom from human disturbance,·
its accessibility, and because it encompassed a riparian
situation typical of the area.
A 10 X 10 live-trap grid was established on the area,
5
wit.h 25 m spacing· between traps, forming a square grid
area 225 X 225 meters (5.06 ha.).
Trapping was conducted for 7 to 10 nights per month
over a twelve month period beginning (session one) in
May 19 73.
Nights with a bright moon v1ere avoided as
much as possible (see Table 1 for trapping schedule).
The 30 em X 15 em X 12 em hard wire traps, with
gravity fall doors, were manufactured in Brazil.
They
were baited with slices of casava and plantain banana;
slices of avocado and carrots were added occasionally.
At the onset of the wet season, traps were covered with
plastic bags to protect the animals from rain~
Trapped animals were marked by means of toe clipping
and reproductive condition was recorded.
For females,
.mammary activity (lactating or not), condition of vag·ina
(perforated or closed) , and presence or absence of palpable
embryos were noted.
Males were examined to determine
whether the testes were inguinal or scrotal.
Animals were
aged as juvenile, sub-adult, or adult on the basis of
pelage condition and relative body size.
The grid location
of each capture was noted.
Anirr0ls captured during session twelve were sacrificed
on the day of capture and were preserved as voucher
specimens.
They were deposited at the Museu Nacional,
Rio de Janeiro, and at the National History Museum of Los
Angeles County.
6
Twenty-two additional traps were set in trees during
session six in an attempt to capture arboreal species.
Twenty additional traps were added in line one during
session seven for three nights to determine if animals
with small home ranges might be missing the regular
traps.
These traps also served to check if animals were
being excluded from the re9ular traps because of trap
saturation.
Analysis
Moveme~~s
and Home Range
Average Distance Moved (Av-D) between captures was
calculated for wet and dry seasons for both males and
females.
Data from juveniles were excluded from the
compilations.
Recaptures at the same trap station were
used as indications of zero distance moved.
The means
and variances were calculated and comparison made
between sexes and between seasons.
Although Average Distance !,loved is a useful home
range index (Davis 1953), home range was also calculated
using the exclusive boundary strip method of Stickel
(1954).
This method uses data only from individuals
captured three or more times in a trapping session,
whereas the Av-D method includes data from non-resident
animals.
Because of small sample size, home range was
calculated for both sexes of Oryzomys moojeni and
Thom~~omys
sublineatus only.
Mean home range size and
7
variance were calculated between sexes and seasons.
Trap Response
Frequency of recapture, expressed as the average
number of recaptures per trapping session, was compared
between sexes and between wet and dry seasons.
Data from
session twelve were excluded from these compilations
since animals were removed from the grid the first time
captured.
Data from juvenile animals was also excluded
from the compilations.
Habitat Preference
The grid contained a riparian area, north- and southfacing slopes, and flat areas between the creek and the
slopes.
Although no objective analysis of edaphic or
floristic differences was conducted, it was assumed
that light penetration and ground moisture differed
among these areas.
Of the hundred grid traps, thirty-
two were on a hill, twenty-eight were within twenty-five
meters of the creek or in an especially moist area, and
the remaining forty were in flat areas.
Compilations of the total number of times each
individual was captured in traps in each of the three
areas was made for species and sexes for both the wet
and dry seasons.
These values were used to test the
null hypothesis of random distribution on the grid by
a chi-square analysis.
The possibility that animals
~esiding
near the edge
8
of the grid were attracted to traps inside the grid (edge
effect) was tested.
If edge effect were occurring it would
bias the habitat preference test since the majority of traps
on the perimeter of the grid were in hill areas.
For
this analysis, the grid was divided in·to three parts,
the outer perimeter of thirty-six traps, the next inner
row of twenty-eight traps, and the central thirty-six
traps.
Numbers of individuals in each area were tabulated
using the location of the first capture of that session
for each individual.
Compilations were made for each
session and the null hypothesis of no difference between
frequencies in the three areas was tested using a chisquare analysis.
Density
-~stimates
The direct enumeration method was used to determine
monthly population sizes.
After the first capture an
individual was included in population estimates during
sessions in which it was not captured if it was recaptured
in a subsequent session.
It was not determined, however,
if an individual was on or off the grid during sessions
in which it was not captured.
Reproduction
Since srunple sizes were small, a broad definition
of reproductive activity was used.
Lactation and the
presence of embryos were direct evidence of reproductive
activity.
Juveniles were
considere~
to be indicative of
9
the presence of sexually active females the previous
session.
Males were considered to be reproductively active
if testes were scrotal, and in a
non-reprodu~tive
state
if testes were inguinal.
Analytical Methods
Statistical tests conducted in this study were
from ·-sokal and Rohlf {1969).
Two sample analysis of
variance was used for comparisons of means, and chi-square
goodness-of-fit tests were used to test for randomness of
frequency distributions.
Results of analyses were
considered significant at the P<.OS level of significance.
Because of small sample size, compilations from each
session were frequently clumped into wet and dry seasons
for statistical analyses.
Data from sessions one through
four and eleven and twelve comprised the dry season, and
sessions five through ten provided the wet season data.
RESULTS
Trap Response
Captures
Two hundred seventy-one individuals of 12 rodent
species were captured 1293 times.
Six species, Oryzomys
moojeni, Thomasomys sublineatus, Thaptomys nigrita,
Nectomys squamiceps, Oxymicterus hispidus and Proechimys
iheringi were captured regularly through the study; six
others, Akodon arviculoides, Oryzomys ratticeps, Oryzomys
eliurius, Blarinomys breviceps, Rhipidomys sp. and Sciurus
ingrami were captured irregularly or only once.
Capture
frequencies are shown in Tables 2 and 3.
~ignificant
differences (P<.OS) in mean number of
recaptures were found between sexes of 0. moojeni, N.
squamiceps, and T. nigrita during the dry season, and
between seasons for female N. squamiceps, indicating
that differential trap response had occurred (see Table 4).
No new individuals were captured in the twenty
ancillary traps added to row one during session seven.
Animals known previously to be present were captured.
It was therefore assumed that trap competition was minimal
and that trap spacing was adequate to encompass home ranges
of animals on the grid.
No rodents were captured in the
22 tree traps, although arboreal species were known to
be present on the grid.
10
11
Predation
During sessions five through seven heavy predation
of trapped animals occurred.
Traps were found knocked
over and doors opened; and occasionally a trapped animal
was mutilated or pieces of fur were found in or near a
molested trap (see Table 3).
It was impossible to determine
how often trapped animals escaped the predator.
Unsuccessful efforts were made to -trap the predator
during session five.
Predation was again evident at the
beginning of session six.
Grid trapping was discontinued
for a few days during session six and again unsuccessful
efforts were made to capture the predator.
After session
six, a mantled (or white-necked) hawk, Leucopternis sp.
and a collared-forest falcon, Micrastur semitorquatus
were captured and removed from the area for the duration
of the study, no further significant predation of trapped
animals was observed after session seven.
Movements and Horne Range
Movements and Horne Range
Results of the two sample analysis of variance
used to compare Av-D values. are shown in Table 6.
Oryzomys rnoojeni females differed significantly from males
in the wet season.
No other species tested showed sig-
nificant differences, possibly due to small sample size.
Average distances moved are shown in Figure 3.
Although
means were not significantly different (P.>OS), both
12
0. moojeni and T. sublineatus males had larger home ranges
than did females during the dry season, as was the case
with 0. rnoojeni in the wet season (see Table 7).
Habitat Preference
Edge Effect
The only significant deviation from a random distribution between the three areas tested was shown by
2·
moojeni females in the wet season during session seven
(see Table 8).
Twelve females were captured; nine were
new individuals, of which five were juveniles.
Heavy
predation during session six and at the beginning of
session seven may have facilitated immigration by dispersing individuals onto the grid.
Habitat Preference
Only 0. moojeni, in the dry season only, showed
no preference (P<.OS) for any of the three designated
sub-habitats (Tables 9 and 10).
~ublineatus
0. moojeni, Thomasomys
(males) and Thaptomys nigrita_ (males and
fenales) changed their preferences significantly (P<.OS)
during the wet season in favor of hill areas. Oxymicterus
hispidus showed a significant (P<.05) aversion to hill
traps throughout the year.
N. squamiceps was almost
exclusively captured in riparian areas:
of a total of
93 captures only two were in traps located more than 50
meters from the creek.
13
Density Estimates
From May or June (session one) through September
(session five) population size was relatively constant
(Figure 4) .
These were the last four months of the dry
season when reproductive activity was minimal.
size decreased in 0. moojeni and
!·
Population
nigrita during October
(session six), shortly after the onset of the wet season.
Whether this decline was due to an adverse effect of rain,
or to hawk predation, was impossible to determine.
There
was a sharp increase in population size of 0. moojeni and
T. sublineatus during December, due to an abundance of
juveniles.
An unexpected decline then began during the
latter half of the wet season.
At the beginning of the
dry season in April, population levels began to increase
approaching those of the previous dry season, possibly
finishing a yearly cycle.
Reproduction
Reproductively active Oryzomys
moojen~
females were
trapped· in all sessions except sessions one, ten and eleven.
The presence of juveniles in sessions two, eleven and twelve
suggests that there were reproductively active females
present throughout the year.
During the wet season
(sessions five through ten) reproductive activity was
at a peak.
A female that was pregnant in session two
was again pregnant in session five.
were pregnant more than once.
No other females
Scrotal males were present
14
in every session but six and ten.
Table 11 summarizes
reproductive activity.
Reproductively act.i ve Thomasomys sublineatus were
present in sessions four through nine.
No juveniles
were captured in sessions one through four, but were
present in sessions eleven and twelve.
Scrotal males
were captured in sessions two through seven.
There
were indications that females have more than one litter
a season.
A female was pregnant during session four and
session six (but was not lactating during session five,
possibly indicating an abortion or post partum pregnancy?),
another gave birth in a trap during session four and was
trapped pregnant in session six, and a female lactating
in
sess~on
five was pregnant in session seven.
Reproductively active Oxymicterus hi.spidus females
were captured in sessions three, seven, eight, and nine.
The capture of a juvenile in session twelve suggests
reproductive activity during session eleven.
Scrotal
males were found in sessions three through eight and
eleven and twelve.
A lactating female in session three
was pregnant when captured in session eight.
Data were too sparse to indicate the seasonality
of reproduction in the other species.
DISCUSSION
Seasonal Variation
Movements and Home Range
Average Distance Moved calculations were not useful
for identifying seasonal differences because of the very
large variances in the calculated means.
Home range sizes of Oryzomys moojeni and
Thomasom~
sublineatus males were larger during the dry season.
This may have been due to increased sexual activity.
Female home range size did not change between seasons.
Habitat Preference
Three species, Oryzomys moojeni, Thomasomys sublineatus
and
Thapton~
nigrita changed their preference during the
rainy season in favor of hill areas.
This may have been
a seasonal response to flooding.
~ducti?_~
Oryzomys moojeni were reproductively active during the
entire year but the intensity of breeding activity was
greatest at the onset of the rainy season.
For
~homa~omys
sublineatus and Oxymicterus hispidus on the other hand
breeding began late in the dry season, continued through
the wet season, and ended early in the dry season.
15
These
16
reproductive patterns may be correlated with food availability.
During the early and mid rainy season fruit and
seed biomass was several times greater than during the
rest of the year (James F. Jackson, personal communication).
Population Size
A sharp decrease in abundance of Oryzornys moojeni
occurred during the early part of the rainy season.
This was followed by an increase during the middle part
of the rainy season, due to the presence of juveniles.
A decrease then occurred in both 0. moojeni and T.
sublineatus adults and juveniles in the latter half of
the wet season.
This pattern had a striking resemblance
to rodent demographic patterns in a study conducted in
nearby Teresopolis (Davis, 1945).
Teresopolis is a
montane area with seasonal climatic patterns similar to
those of the Forest Reserve Nova Lombardia.
It is likely,
therefore that environmental factors influence population
size in both areas in a similar manner.
Davis could not
explain the changes in abundance (see Davis, 1945, for
discussion) .
The rapid decrease in abundance is difficult to
understand since it occurred when fruit and seed biomass
was at a maximum.
However, ·the apparent increase in
productivity may not necessarily be so great in terms of
food available to the individual.
Fleming (1973) has
suggested that the poverty of rodent species in a Costa
17
Rican wet forest may be due to the production of secondary
tGxic compounds that protect fruits and seeds from herbivory
(Freeland and Janzen 1974).
Recently Glander (1975) in
a detailed study of howler monkey (Alouatta villosa)
feeding behavior found that the troops he studied actually
had very limited food resources because of plant defense
mechanisms.
His data dispelled the notion which has per-
sisted since Carpenter's (1934) study that howlers have
an unlimited food supply because they eat leaves.
Reichman
(1977) working with heteromyid rodents in southwestern
United S·tates found that those animals were very selective
in what they chose to eat even after they expended energy
to forage and bring food to their burrows.
These obser-
vations sug·gest that a large part of a species' behavioral
and physiological response to potential foods may be
directed at choosing not only what to eat but also what
not to eat.
Therefore, what appears to be an abundant
food supply may be limited because of factors that make
potential foods unpalatable.
The combined negative effect of the physiological
-
stress associated with increased activity of reproduction,
and environmental stress of flooding during the rainy
season, may be greater than the benefit of increased food
availability.
This would result in increased mortality
rates explaining the population decrease.
18
Habitat and Interspecific Relationships
E'_§!.tmal Composition
The small rodents on the grid were represented by
three families; Echimyidae, Cricetidae, and Sciuridae.
The echimyids included Proechimys iheringi and Echimys sp.
Although no Echimys were actually captured, a viper,
Bothrop~
jarraca, collected on the grid, contained an
Echimys carcass.
The cricetids included:
Oryzomys moojeni,
Oryzomys nigripes, Oryzomys ratticeps, Thomasomys
sub linea tus_, Nectomys squamiceps, Rhipidomys sp. ,
Oxymicterus hispidus, Akodon arviculoides, Thaptomys
nigrita, and Blarinomys breviceps.
The only sciurid seen
or captured on the grid was Sciurus ingrami.
Three other rodent species were known to occur on
the grid, making a total of 16 species.
~ca
grid.
The paca, Cuniculus.
and the agouti, Dasyprocta agouti were observed on the
The third species, Coendou prehensilis, was not
observed but is known to occur throughout the area of
the reserve (Ruschi, personal communication).
Sixteen
rodent species is not an unusually diverse fauna, and
compares favorably with other studies in neotropical and
North American temperate forests
(see discussion in Fleming
1970, 1973).
The most striking difference between the rodent fauna
studied by Fleming (1970, 1973) in Central America and
the rodent fauna of the present study is the absence of
19
akodont species in Central America and of heteromyids
in Brazil.
Of four akodonts occurring in the present
study, three were sub-terrestrial.
Results of the habitat preference tests, behavioral
observations and general morphological characteristics
of the rodent species help elucidate habitat utilization
and resource partitioning.
The species on the grid
included terrestrial, fossorial (including semi-fossorial),
semi-aquatic and arboreal forms.
Terrestrial Forms
Six species of the following genera were cursoriai:
Oryzomy~,
Thomasomys, Akodon and Proechimys.
The three
species of Oryzomys and Thomasomys have a similar habitus
in that they have typical "mouse-like" features and
proportions and a complex molar crown pattern typical of
seed eaters (Hershkovitz 1962).
Oryzomys moojeni and T. sublineatus are very close
in head and body and upper molar tooth row size.
Oryzomys
nigripes is smaller and 0. ratticeps larger than 0. moojeni
and T. sublineatus.
These size differences may act to
ecologically segregate these species and minimize competition (see Table 12).
Thomasomys sublineatus and
0. moojeni differ in the relative sizes of their tails
and feet.
Results of the habitat preference tests show
that 0. moojeni occupied the entire grid, showing little
preference for hill, riparian, or flat areas, whereas
20
T. sublineatus preferred flat and riparian areas.
These
differences may be indicative of differences in mobility
and foraging behavior of the two species.
In areas of
higher altitudes in Espirito Santo (900+ m) I have found
T. sublineatus to be the ecological dominant species
replacing Oryzomys.
It may be that T. sublineatus is
better adapted to high altitudes than 0. moojeni.
Davis
(1974), working in Teresopolis, reported that
Akodon arviculoides was the most common mammal in both
virgin and second-growth forests being more abundant in
the second-growth area.
Akodon arviculoides occurred in
the present study but was relatively rare, possibly
because the area was primary forest and at a lower
elevation than Davis' areas.
The echimyid, P. iheringi was the largest rodent
regularly trapped on the grid.
Fleming (1970) found
fruit and the fleshy coverings of palm nuts in stomachs
of P. semispinosus in Panama, but whether or not P. iheringi
has a preference for fruit is unknown.
Fossorial Forms
Bla.rinomys breviceps is an akodont that is the
extreme example of talpine form and habits among cricetines
(Hershkovitz, 1962).
Although only one individual was
captured, i t is possible that more may have escaped capture
because of the inappropriateness of the traps used.
The
bait was suspended on a hook inside the trap and B. breviceps
21
may not have been able to detect it, or it may have been
capable of escaping from the traps by separating the bars
with its powerful digging feet.
Abravaya and Matson
(1975) recorded an unusually high density of B. breviceps
in another locale of similar habitat, where all specimens
were captured in snap traps even though live traps
comprised twenty percent of the traps used.
Blarinomys is probably an active burrower whereas
Oxymicterus hispidus and Thaptomys nigrita utilizes the
spaces in the loose lattice of roots under the leaf layer.
Both 0. Hispidus and T. nigrita are semi-fossorial
akodonts but are dissimilar in features of their habits.
Thaptomys nigrita is diurnal and 0. hispidus is nocturnal.
~~aptomys
nigrita was noted by Davis (1947) to be diurnal
and fierce, which was confirmed by my observations.
During collecting forays I have found T. nigrita to be
uninterested in any bait except fruits found on the ground,
whereas Oxymicterus is specialized for insectivory and
probably uses its elongated snout to search for insects
in the leaf layer.
Oxymicterus hispidus showed a sig-
nificant avoidance of hill traps throughout the year.
'I'he
preference of flat areas may be a function of its
specialized foraging·behavior.
Although Oxymicterus
ruti~ans
was observed active
during the day by Dalby (1975), I did not observe diurnal
activity in 0. hispidus.
Barlow (1969) hypothesized that
the strong odor of 0. rutilans serves to discourage
.
...
_
22
potential predators.
Oxymicterus hispidus also has a
strong odor, but whether it functions to discourage predators or as a mechanism for intra-specific communication
is unknown.
Semi-Aquatic Form
Nectomys squamiceps is an oryzomine species that
is adapted for an aquatic habitat.
It swims by paddling
with its webbed hind feet and by lateral undulations of
its thick powerful tail.
When alarmed N. squamiceps
will jump in the water, dive and continue swimming submerged.
An individual, not on the grid, was seen to
forage in the late afternoon.
It would swim for several
meters then come to the bank to forage, return to the
water, continue swimming for a short distance and then
return to land to forage, repeating this pattern as it
made its way upstream.
It appeared that N. squamiceps
used the stream as a means to forage along the bank.
This species does not show the high degree of specialization
of rodents adapted to feed in water (see discussion in
Starrett and Fisler, 1970).
Davis (1964:323) stated
that "In mammals the major forces impinging on locomotion
are escape from enemies, pursuit of prey and wandering
in search of food or water."
The aquatic adaptations
of Nectomys may have evolved as a method of predator
escape, or as a method to exploit new food resources,
or both.
"''
- - - -
23
Arboreal Forms
Theie was little information gathered on the three
species of arboreal rodents.
Echimys and !,(hipidomys are
both nocturnal while Sciurus is diurnal, a difference that
may allow for partitioning of resources.
~chimys_
is
larger than Rhipidomys and may exploit different resources.
CONCLUSIONS
The rodents on the grid changed seasonally in
density and reproductive behavior.
Reproduction was
correlated with the rainy season when food resources
were most abundant.
Oryzomys moojeni was reproductively
aseasonal, although breeding activity was most intense
during the rainy season, whereas Thomasomys sublineatus
and Oxymicterus hispidus bred seasonally.
These dif-
ferences may reflect different evolutionary histories
or may be a result of competitive interactions.
Declines
in density in the latter part of the wet season may be
due to the combined effects of flooding and reproductive
stress.
Most species tended to avoid hill areas, and
preferred flat areas.
It appeared, however, that flooding
affected seasonal movements; 0. moojeni, T. sublineatus
and T. nigrita changed their habitat preference in favor
of hill areas during the wet season.
Habitat utilization was three dimensional:
there
were fossorial, aquatic, terrestrial, and arboreal species.
Size differences in species and differences in foraging
behavior probably serve to partition resources.
Rodent species diversity was not great relative to
other findings in neotropical and North Temperate forests
(see discussion in Fleming 1970 and. 1973).
24
25
TABLE 1.
Trapping Schedule, D.ry Season = sessions 1-4,
11, 12; Wet Season= sessions 5-10.
No. Trap Nights
Session
----
-
1.
24 May
2.
26 June
-
4 July
9
3.
21 July
-
28 July
8
4.
30 Aug
7 Sept
9
5.
29 Sept - 7 Oct
9
6.
30 Oct - 21 Nov
11
7.
15 Dec· - 29 Dec
10
8.
18 ,Jan - 25 Jan
8
9.
16 Feb - 23 Feb
8
10.
20 March - 26 March
7
11.
9 April - 19 April
8
12 •
2 .Hay - 12 May
-
1 June
9
11
Dry
Season
Wet
Season
Dry
Season
26
TABLE 2.
Numbers of individuals captured and total number
of captures for wet season (sessions 5-10) and
dry season (sessions 1-4, 11, 12).
No. individuals
Ca tured
Wet
Dry
Oryzomys moojeni
M
F
21
32
13
10
Delomys sublineatus
M
Proechimys_ iheringi
M
6
F
11
9
10
7
12
10
14
1
F
Thaptomys nigrita
M
""
F
Nectomys squamiceps
M
Oxy,micterus_ hisJ2idus
M
Akodon arvicu1oides
M
Oryzomys e1iurius
M
0
F
0
0
0
0
0
0
0
0
0
F
F
F
B1arimomys breviceJ2S
Oryzomys ra·tticeps
M
F
M
Rhipidomys sp.
M
Sciurus ingrami
M
F
F
F
·s
26
19
14
1.2
7
6
12
13
8
10
10
5
3
2
3
3
1
0
0
1
1
0
1
0
Total No.
Ca tures
Wet
Dr
163
114
48
35
13
29
34
27
71
48
19
25
7
32
0
0
0
0
0
0
0
0
0
0
173
95
58
33
33
13
28
32
22
43
43
18
15
4
8
6
1
0
0
1
1
0
1
0
TABLE 3.
Numbers of individuals on grid in one session, two sessions, etc.
Percentage of totals for each section is indicated in parentheses.
0. noojeni
M
1
2
3
4
5
6
7
31
(59.6)
10
(19.2)
4
( 7. 7)
2
( 3. 8)
4
( 7. 7)
1
(1.9)
-
9
-
10
-
8
F
17
(39)
10
( 2 3)
12
( 5)
4
( 9)
4 .
( 9)
2
(4.6)
4
( 9)
-
1
(2.3)
-
T. sublineatus
M .
12
(63.2)
3
( 15. 8)
1
:< 5. 3)
-
1
( 5. 3)
-
2
(10.5)
F
12
(57.1)
1
( 4. 8)
3
(14.2)
2
(9.5)
2
( 9. 5)
-
N. squarn.iceps
M
11
(57.9)
4
(21. 0)
1
( 5. 3)
2
(10. 5)
-
F
4
(33.3)
2
(16.7)
3
(25.0)
-
3
(25.0)
0. hispidus
M
9
(50.0)
6
(33.3)
2
(11.1)
l
(5.6)
-
F
7
(46.7)
2
(13.33)
1
(6.67)
l
(6.67)
-
1
(5.3)
-
-
1
(16.67)
-
·-
1
(6.67)
2
{13.33)
T. nigrita
M
5
(29.4)
5
(29.4)
2
(11.76)
l
( 5. 9)
3
(17.6)
1
( 5. 9)
F
6
(37.5)
5
(31.2)
4
(25.0)
1
( 6. 3)
1
( 4. 8)
-
-
-
-
-
-
-
t\J
-...J
28
TABLE 4.
t-1ean number of captures for individuals per session +1 S.E. Mean number of sessions in which
individuals were captured on the grid is underlined.
Significant differences (P<.OS} between
means of sexes and between means of seasons are
indicated by arrows.
Dry
Season
o.
moojeni
T. sublineatus
Wet
Season
M 2.5 ±.57
1.63
~
F 3.59± .56
2.43
3± .85
1.63
4.16± --:82
1.85
M 1.89± .66
1.7
F 2.53± .84
1.85
2.27± .96
1.25
2.88± .93
1.87
N.
~guamJ:..ceps
M 2.8 ±1. 07
1.5
~
F 4.86±1.58
2. 43<
3.3 ±1.69
1.5
2.0 ± . 72
>
1.63
o.
hispidus
M 1.31± . 38
1.36
F 1.27± ----:-44
1.7
1.89± .72
2.0
1.86± .55
2.3
~ 1.44± .39
1.65± .38
l. 54
l. 92± .84
1.16
T. nigrita
v
F
2.0
2.54± -:3"8
1.56
I;
1-
TABLE 5.
Predation Evidence. Number of traps knocked over (K.O.) and numbers of
animals known _to have been killed by predation.
DAY OF SESSION
SESSION
1
2
3
-
-
-
-
-
-
-
-
5
K.O.
Known
Killed
6
K.O.
Known
Killed
7
K.O.
Known
Killed
3
4
5
6
7
8
4
8
1
5
2
2
1
1
-
-
-
-
-
-
2
3
1
-
8
-
-
9
10
11
1
1
-
1
1
-
'~
('.)
~
30
TABLE 6.
Average distance moved (Av-D) for six species.
Means +1 S.E. Numbers of movements are in
parentheses. No significant differences (P<.OS)
between sexes and between seasons were found.
0. moojeni
T. sub1ineatus
N.
o.
squamic~
hispidus
T. nigrita
Dry Season
Wet Season
M
4 7. 03± 6.34
(59)
60.94± 7.86
( 4 7)
F
39.86± 3.28
(111)
41.51± 4.16
(102)
M
55.49±10.22
(15)
47.1 ±13.7
( 15)
F
50.57± 6.09
(26)
37.58± 5.71
{3 7)
M
27.67± 9.57
( 27)
51.62±10.66
( 28)
F
45.47± 6.9
(54)
45.0 3± 7.68
(9)
M
34.2 ±13.53
(4)
58.42±19.85
(8)
F
43.6 ± 9.48
( 3)
39.15±13.13
(19)
M
76.42±13.69
55.28±11.23
(11)
( 7)
65.23±11.26
( 20)
53.03±18~33
M
45.87±20.77
(9)
45.35±18.87
(4)
F
39.0 ±10.84
(4)
65.35± 7.00
( 18)
F
P. ;iherL1gi
( 12)
31
TABLE 7.
Home Range. Means in ha + 1 S.E., sample size
in parentheses. No significant differences were
found (P<.OS) between sexes or between seasons.
0. moojeni
M
,50±.105 (13)
F
.27±.039 (31)
M
.35±.105 (14)
F
.29±.02
Dry Season
Wet Season
( 28)
T. sublineatus
M
.55 ±.165 (4)
F
.30 ±.033 ( 7)
M
.33 ±.116 ( 4)
F
.036±.036 (8)
Dry Season
Wet Season
32
TABLE 8.
Edge Effect Test. Comparison of expected to
observed capture frequencies in outer perimeter,
next inner row, and center of trapping grid (see
text for explanation) . Significant chi square
values (P<.05) are underlined.
DRY SEASON
0. moojeni
Chi
Square
1.61
Exp.
Obs.
Exp.
Obs.
7.20
7.00
7.56
5.00
5.60
3.00
5.88
4.00
7.20
10.00
7.56
12.00
2.30
M Exp.
Obs.
F
Exp.
5.32
5.00
4.48
4.00
6.84
8.00
5.76
6.00
0.32
Obs.
6.84
6.00
5.76
6.00
Exp.
Obs.
Exp.
Obs.
7.20
4.00
5.04
3.00
5.60
5.00
3.92
6.00
7.20
11.00
5.04
5.00
3.49
Exp.
Obs.
Exp.
Obs.
Perimeter
12.24
18.00
16.20
28.00
Inner
Row
9.52
8.00
12.60
6.00
Middle
12.24
8.00
16.20
11.00
Exp.
Obs.
Exp.
Obs.
5.40
6.00
7.20
4.00
4.20
3.00
5.60
5.00
5.40
6.00
7.20
11.00
0.48
Exp.
Obs.
Exp.
Obs.
3.60
1.00
8.64
9.00
2.80
4.00
6.72
8.00
3.60
5.00
8.64
7.00
2.94
M
F
0. hispidus
Middle
19.44
16.00
17.64
14.00
Exp.
Obs.
Exp.
Obs.
M
F
T. sublineatus
Inner
Row
15.12
19.00
13.72
15.00
Perimeter
19.44
.19.00
17.64
20.00
F
1.19
4.07
.07
1. 93
·WET SEASON
o.
mooi~ni
M
F
T. sublineatus
M
F
0. hisEidus
M
F
Chi
Square
4.42
-13.72
--·
3.49
0.57
33
TABLE 8.
Edge Effect Test (Continued) •
·\.:
WET SEASON (Cont.)
T. nigrita
M
F
Exp.
Obs.
Exp.
Obs.
Perimeter
7.20
7.00
5.04
8.00
Inner
Row
5.60
8.00
3.92
3.00
Chi
Middle
7.20
7.00
5.04
3.00
Squar~
1.71
2.78
WET SEASON 0. i:noojeni FEJI.1ALES ONLY
----·-
Inner
Row
Exp.
Obs.
6
Exp.
Obs.
2.16
4.00
1.68
1.00
2.16
1.00
2.47
7
Exp.
Obs.
5.04
10.00
3.92
2.00
5.04
2.00
7.65
8
Exp.
Obs.
3.24
4.00
2.52
2.00
3.24
3.00
0.30
9
Exp.
Obs.
2.16
3.00
1. 68
1.00
2.16
2.00
0.614
10
Exp.
Obs.
1.00
0
0
Session
----s-
0
Middle
3"": 24
3.00
Chi
Sguare
4. 89
Perimeter
3.24
6.00
N.S.
34
TABLE 9.
Habitat preference test for the dry season.
Comparison of expected and observed capture
frequencies in riparian, hill and flat areas.
Significant chi square values (P<.05) are
underlined.
DRY SEASON
0. moojeni
T. sublineatus
o.
hispidus
T. nigrita
Chi
Square
M
Exp.
Obs.
Ri:e
31.92
34.00
Hill
36.48
40.00
Flat
45.60
40.00
F
Exp.
Obs.
45.64
51.00
52.16
39.00
65.20
73.00
4.88
M
Exp.
Obs.
9.80
8.00
11.20
4.00
·14.00
23.00
10.74
F
Exp.
Obs.
13.44
21.00
15.36
8.00
19.20
19.00
7.78
M
Exp.
Obs.
7.00
17.00
8.00
0.00
10.00
8.00
22.69
F
Exp.
Obs.
5.32
11.00
6.08
0.00
8.00
8.00
31.16
M
Exp.
Obs.
7.56
5.00
8.64
5.00
10.80
17.00
7.18
F
Exp.
Obs.
9.52
7.00
10.88
12.00
13.60
15.00
8.47
--r.-63
35
TABLE 10.
Habitat preference·test for the wet season.
Comparison of expected and observed capture
frequencies in riparian, hill and flat areas.
Significant chi square values (P<.05) are
underlined.
WET SEASON
o.
T~
o.
moojeni
sublineatus
hispidus
T. nigrita
Chi
Square
15.34
--
M
Exp.
Obs.
Rip
26.60
17.00
F
Exp.
Obs.
48.44
43.00
55.36
61.00
69.20
69.00
1.19
!~
Exp.
Obs.
9.24
10.00
10.56
10.00
13.20
13.00
0.095
F
Exp.
Obs.
16.24"
23.00
18.56
5.00
23.20
30.00
14.71
M
Exp.
Obs.
5.04
8.00
5.76
1.00
7.20
9.00
6.12
F
Exp.
Obs.
12.04
17.00
13.76
2.00
17.20
2.40
14.78
M
Exp.
Obs.
8.96
10.00
10.24
14.00
12.80
8.00
2.71
F
Exp.
Obs.
7.84
2.00
8.96
14.00
11.20
12.00
9.93
Hill
30.40
48.00
Flat
38.00
30.00
36
TABLE 11.
Oryzomys
moojeni
Thomasomys
sublineatus
Nectomys
squamice;es
Reproductive condition and age per session.
A=adult; S=subadult; J=juvenile; Emb=females
with embryos; Lact.=lactating females;
VP=vagina perforate; Scrot.=scrotal testes in
males.
Ses.
-12
3
4
5
6
7
8
9
10
11
12
1
2
3
4
5
6
7
8
9
10
11
12
1
2
3
4
5
6
7
8
9
10
11
12
A
11
18
15
15
15
5
7
7
6
2
5
9
3
9
5
8
10
6
4
3
s
6
3
2
1.
1
4
7
2
1
3
2
J
I
1
Lact.
1
1
1
1
2
1
2
2
4
1
1
3
1
1
5
1
1
1
1
1
2
1
5
1
2
1
Scrot.
5
5
8
6
8
2
2
2
3
1
4
2
1
6
1
3
2
3
1
2
1
2
3
1
1
3
3
1
2
4
3
3
5
2
1
1
2
1
1
2
2
3
1
1
3
5
4
4
2
2
VP
2
3
3
11
3
1
1
6
5
6
5
Emb
1
1
1
1
1
1
1
2
4
2
3
37
TABLE 11 (Continued) .
~roechimys
iheringi
Thaptomys
nigrita
Oxymicterus
hispidus
Ses.
--1
2
3
4
5
6
7
8
9
10
11
12
A
1
2
3
4
5
6
7
8
9
10
11
12
1
1
7
4
3
2
4
4
7
1
2
3
2
4
5
4
5
2
6
7
5
2
2
6
4
5
6
7
8
9
10
11
12
6
3
1
1
2
5
4
3
1
1
2
2
3
s
j
Emb
Lact.
VP
Scrot.
1
3
3
4
1
2
1
2
1
1
2
1
3
1
1
1
3
1
2
2
4
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
3
2
1
1
2
1
1
i
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
3
2
1
1
2
38
TABLE 12.
Morphological measurements and ratios. Means
are given in mm, size of sample is indicated
in parentheses, coefficients of variation are
underlined.
TL=total length; T=length of tail;
HF=length of hind foot; MT=length of maxillary
tooth row; T/TL=tail percent of total length;
FT/HB=hind foot percent of head and body.
TL
0. eliurius
0. ratticeps
0. hispidus
T/TL
FT/HB
50.64
24.79
--
5.11
(35)
4.21
--
208.33 111.83
(12)
(12)
5.81
7.35
23.85
(13)
7.03
53.68
24.72
--
3.33
(7)
3.76
---
302.00 135.00
(1)
(1)
47.00
(1)
6.10
(1)
44.70
28.14
138.67
(6)
6.68
40.00
( 6)
10.00
12.00
( 6)
5.27
28.84
12.16
--
3.60
(5)
4.39
--
265.00 112.76
( 17)
( 17)
7.13
6.36
33.18
( 17)
6.50
42.55
21.79
--
5.39
(16)
2.58
--
241. 96 '101.43 29.78
( 2 3)
(2 3)
( 2 3)
9.26
6.44
4.63
----
4.79
(14)
2.08
--
41.92
21.19
-
--
T. sublineatus
MT
288.33 146.00 35.28
(39)
(39)
(39)
6.38 8.47
5.96
--
-
T. nigrita
HF
T
--
-
-
39
J
H
G
F
E
D
c
B
A
2
3
1.5 C M:25M
4
5
6
7
8
9
N
~
FIGURE 1.
Map of study grid showing placement of traps
and topographical features.
10
40
400
360
320
280
240
mm:zoo
160
120
80
40 -
M
FIGURE 2.
J
J
A
s
0
N
D
J
F
M
Monthly means of rainfall at Santa Teresa
Espirito Santo from Ruschi (1950).
o =
• =
10 yr. ave. 1940 - 1949.
May 73 - May 74 (unpublished).
A
M
41
1
2
3
4
5
6
7
8
9
10
11
session
FIGURE 3.
Average distance moved in meters per trapping
session May 1973 - April 1974 for males (solid
circles) and females (open circles).
42
130
r
T. sublineatus
120
110
100
90
80
m
10
I
60
/
50
~
/
/
/
40
/
30
20
1
2
3
4
5
6
7
8
9
session
FIGURE 3 (Continued).
Average distance moved.
10
11
43
140
130
N. squamiceps
120
110
100
90
80
m
70
...
60
50
.,
''
40
'
'\
'\
' 'o
30
20
1
2
3
4
5
6
9
session·
FIGURE 3 (Continued).
Ave~age
distance moved.
10
11
44
1
2
3
4
5
6
7
8
9
session
FIGURE 3 (Continued) .
Average distance moved.
10
11
45
1
2
4
5
6
7
8
9
. session
FIGURE 3 (Continued).
Average distance moved.
10
11
46
120
~
P. iheringi
110 100
90
so
70
m
60
so
/
40
/
/
/
30
~'- ..., '-,
20
10
1
2
3
4
5
s
7
8
9
session
FIGURE 3 (Continued).
Average distance moved.
I
I
10
11
47
16
tt,
14
0. moojeni
I
I
I
12
10
n
I
,..... ...o----...'
I
. \ '''JI
8
6
4
2
1
2
3
4
5
6
7
8
9
J.O
12
11
session
8
T. suhlineatus
6
n
4
)'
~
\
2
\
\
..._.__ J..._
l
_..L,_.....J._
3
4
___Jii,...___l
5
6
I
7
8'
'It-- -r..,.
/
...
I
I
I
9
10
11
/
j_
12
session
FIGURE 4.
Numbers of individuals on grid per trapping
session, May 1973 - May 1974.
Males=solid line; females=broken line.
48
10
0. hispidus
8
6
n
.....
4
,..
......---·--...
'
/
............
'"f(
,.
/
/
/.
.
...\
\
\
\
\
/ /
... -
_..,,.,.
2
1
2
3
4
5
6
7
8
9
I
10
I
11
I
12
session
6
N. squamiceps
n
4
2
~L---~--~----L---~--~--~----~--~--~--~~--L__
1
2
3
4
5
6
7
8
9
10
11
12
session
FIGURE 4 (Continued) •
Numbers of individuals on grid.
49
8
T. n igrita
6
n
4
2
1
2
3
4
5
6
7
8
9
10
11
12
session
FIGURE 4 (Continued).
Numbers of individuals on grid.
50
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