INTERSPECIFIC COMPETITION BETWEEN MULE DEER, OTHER GAME ANIMALS AND
LIVESTOCK
Richard J. Mackie
Department of Biology
Montana S t a t e U n i v e r s i t y
Bozeman, Montana
59715
Abstract
Comparisons of a v a i l a b l e d a t a on d i s t r i b u t i o n s , range use
and food h a b i t s , and behavior i n d i c a t e t h a t mule d e e r may i n t e r a c t i n a competitive r e l a t i o n s h i p w i t h each of t h e o t h e r s p e c i e s
of wild and domestic ungulate w i t h which they a s s o c i a t e on weste r n rangelands. E x i s t i n g s t u d i e s , however, have not produced
s u b s t a n t i v e evidence f o r t h e e x i s t e n c e of competition g e n e r a l l y
nor more than very g e n e r a l conclusions about i t s e x a c t n a t u r e
and importance; and most c u r r e n t t h i n k i n g remains rooted i n inf e r e n c e and s p e c u l a t i o n and i s c o n t r o v e r s i a l a t b e s t . This
e s s e n t i a l l y precludes any f i r m conclusions a s t o t h e p o s s i b l e
s i g n i f i c a n c e of i n t e r s p e c i e s r e l a t i o n s and competition i n c u r r e n t
t r e n d s of mule d e e r p o p u l a t i o n s i n western North America.
Mule deer (OdocoiZeus hemionus) r a r e l y , i f e v e r ,
e x i s t i n s p e c i e s populations completely i s o l a t e d from
c o n t a c t w i t h o t h e r wild and domestic ungulates.
Throughout t h e i r d i s t r i b u t i o n , they c o h a b i t rangel a n d s a t l e a s t s e a s o n a l l y w i t h one o r more of t h e
o t h e r wild ungulates n a t i v e t o western North America.
Most o f t h e s e rangelands a r e a l s o grazed by domestic
l i v e s t o c k , i n c l u d i n g c a t t l e , sheep, h o r s e s , and,
o c c a s i o n a l l y , mules, b u r r o s , g o a t s , and hogs. Locall y , f e r a l o r "wild" p o p u l a t i o n s of domestic animals
a s w e l l a s introduced wild ungulates a l s o occur.
Because of t h i s , t h e p o s s i b i l i t y of competitive i n t e r a c t i o n s has occupied t h e minds of w i l d l i f e , range,
and l i v e s t o c k managers and s c i e n t i s t s f o r many y e a r s ;
and i t i s not s u r p r i s i n g t h a t i n t e r s p e c i e s r e l a t i o n s h i p s of mule d e e r now loom a s a p o s s i b l y s i g n i f i c a n t
f a c t o r contributing t o recent declines i n populations
of t h i s s p e c i e s over much of t h e western United S t a t e s
and Canada. What i s s u r p r i s i n g , i n view of t h e widespread a t t e n t i o n given g e n e r a l l y t o i n t e r s p e c i f i c
r e l a t i o n s h i p s of l a r g e h e r b i v o r e s and s p e c i f i c a l l y
t o mule d e e r during t h e p a s t half-century o r more,
is t h a t remarkably few f i r m conclusions of g e n e r a l
a p p l i c a t i o n have emerged. Much of our c u r r e n t thinki n g remains rooted i n i n f e r e n c e and s p e c u l a t i o n and
i s c o n t r o v e r s i a l a t b e s t . This a p p a r e n t l y a p p l i e s
a l s o t o almost a l l of our conclusions about t h e
importance of competition i n n a t u r a l ecosystems
g e n e r a l l y ( M i l l e r 1967).
INTERSPECIES RELATIONS AND COMPETITION
I n t e r s p e c i f i c r e l a t i o n s h i p s of l i v i n g organisms
have been viewed i n many ways. Odum (1959) l i s t e d
e i g h t important i n t e r a c t i o n s which may occur between
(1) n e u t r a l i s m , i n
two o r more s p e c i e s populations:
which n e i t h e r p o p u l a t i o n is a f f e c t e d by a s s o c i a t i o n
w i t h t h e o t h e r ; (2) competition, i n which each popul a t i o n a f f e c t s t h e o t h e r ; (3) mutualism, i n which
i n t e r a c t i o n is o b l i g a t o r y f o r t h e growth and s u r v i v a l
of both populations; ( 4 ) protocooperation, i n which
both p o p u l a t i o n s b e n e f i t from a non-obligatory asso-
c i a t i o n ; (5) commensalism, i n which one population
i s b e n e f i t e d but t h e o t h e r u n a f f e c t e d ; (6) amens a l i s m , i n which one population i s i n h i b i t e d and t h e
o t h e r u n a f f e c t e d ; (7) p a r a s i t i s m and (8) p r e d a t i o n ,
wherein one population i s dependent upon and adversel y a f f e c t s t h e o t h e r by d i r e c t a t t a c k .
I n t h e above c o n t e x t , competition i s l i m i t e d t o
t h o s e i n t e r a c t i o n s which a d v e r s e l y a f f e c t growth
and s u r v i v a l of both s p e c i e s p o p u l a t i o n s involved
and u l t i m a t e l y r e s u l t i n t h e e l i m i n a t i o n of one a s
defined by t h e competitive exclusion p r i n c i p l e
(Hardin 1960). Others have defined i t a s a c t i v e
demand by two o r more i n d i v i d u a l s of t h e same s p e c i e s
p o p u l a t i o n ( i n t r a s p e c i e s competition) o r members of
two o r more s p e c i e s a t t h e same t r o p h i c l e v e l
( i n t e r s p e c i e s competition) f o r a comon r e s o u r c e o r
requirement t h a t is a c t u a l l y o r p o t e n t i a l l y l i m i t i n g
( M i l l e r 1967). I n p r a c t i c a l usage, "competition"
u s u a l l y has been a p p l i e d r a t h e r l o o s e l y t o i n c l u d e
almost any i n t e r a c t i o n w i t h a n assumed o r r e a l ,
n e g a t i v e outcome, i n c l u d i n g t h o s e i n which t h e welf a r e of only one s p e c i e s may be adversely a f f e c t e d
(amensalism of Odum 1959).
Competition may involve elements of " i n t e r f e r ence" a s w e l l a s "exploitation" ( M i l l e r , 1967).
I n t e r f e r e n c e r e f e r s t o any a c t i v i t y which d i r e c t l y
o r i n d i r e c t l y l i m i t s a competitors a c c e s s t o a
necessary r e s o u r c e , u s u a l l y i n a s p a t i a l c o n t e x t .
E x p l o i t a t i o n r e f e r s t o u t i l i z a t i o n of a r e s o u r c e
once a c c e s s has been achieved, u s u a l l y i n t h e sense
t h a t two i n d i v i d u a l s o r s p e c i e s w i t h unlimited a c c e s s
t o a common source of food o r n u t r i e n t s w i l l have
d i f f e r e n t a b i l i t i e s o r opportunity t o exploit the
a v a i l a b l e supply.
The r o l e of i n t e r f e r e n c e i n competition among
l a r g e herbivores i s l a r g e l y unknown. I n t e r s p e c i e s
a g g r e s s i o n approaching t e r r i t o r i a l i t y , a s r e q u i r e d
by M i l l e r ' s (1967) d e f i n i t i o n of i n t e r f e r e n c e , i s
not known among u n g u l a t e s , a t l e a s t i n western North
However, a n element of i n t e r f e r e n c e i s
America.
i m p l i c i t i n Denniston's (1956) concept of " d i s t u r b ance" competition between moose (Alccs a l c e s ) and
c a t t l e . Disturbance r e f e r s t o t h e movement of one
animal from, and/or avoidance o f , a r e a s used by
another, a t l e a s t t o the extent t h a t a l t e r n a t e areas
o r h a b i t a t s a r e a v a i l a b l e (Schladweiler 1974). Other
wild ungulates, e s p e c i a l l y e l k (Cervus canadensis),
may r e a c t s i m i l a r l y t o t h e presence of domestic l i v e s t o c k ( J e f f e r y 1963, Dzlke e t a l . 1965, Skovlin e t a l .
1968, Knowles 1975, Lonner 1975, Komberec 1976).
Knowles (1975) i n d i c a t e d t h a t radio-marked mule deer
j n r e s t - r o t a t i o n a l l y grazed p a s t u r e s e i t h e r moved from
t h e a r e a o r moved f u r t h e r and used a l l p a r t s of t h e i r
home range more f r e q u e n t l y a f t e r c a t t l e were turned
i n t o t h e p a s t u r e s i n which they occurred. Between wild
u n g u l a t e s , bighorn sheep (Ovis canadensis) may avoid
e l k (Mair 1952) but dominate mule deer (Hunter and
Kinghorn 1949), and mule d e e r may dominate over whitet a i l e d deer (Oducoileus v i r g i n i a n u s ) (Anthony 1972,
Kramer 1973). Although t h e e f f e c t of d i s t u r b a n c e on
t h e biology of wild ungulates has received l i t t l e
study t o d a t e , G e i s t (1970) i n d i c a t e d t h a t repeated
d i s t u r b a n c e could r e s u l t i n voluntary withdrawal from
a v a i l a b l e h a b i t a t and confinement of t h e population
t o a s m a l l e r and l e s s f a v o r a b l e a r e a .
Evaluations of i n t e r s p e c i e s r e l a t i o n s and compet i t i o n among l a r g e r h e r b i v o r e s , i n c l u d i n g mule d e e r ,
have l a r g e l y involved t h e e x p l o i t a t i o n a l a s p e c t .
Thus, t h e e x t e n t t o which two s p e c i e s graze t h e same
a r e a and p r e f e r t h e same f o r a g e is g e n e r a l l y recognized a s t h e main f a c t o r i n i n t e r s p e c i f i c competition
on western rangelands (Julander 1958). I t might a l s o
be important t h a t f o r a g e p l a n t s used i n common be an
important source of food f o r e i t h e r o r both animals,
i n l i m i t e d supply, and o v e r - u t i l i z e d o r d e t e r i o r a t i n g
a s a r e s u l t of t h e combined use (Cole 1958).
Smith and J u l a n d e r d i f f e r e n t i a t e d two kinds o r
l e v e l s of competition among l a r g e h e r b i v o r e s :
"forage" competition and "land use" competition.
Though both i n v o l v e t h e element of e x p l o i t a t i o n , t h e
former r e f e r s t o common usage of p r e f e r r e d f o r a g e
p l a n t s a t l e v e l s above those considered proper f o r
s u s t a i n e d p r o d u c t i v i t y and y i e l d , while t h e l a t t e r i s
a s s o c i a t e d with comon use of a f o r a g e supply which
i s adequate t o meet requirements of both animals but
where removal of one would permit i n c r e a s e d numbers
of t h e o t h e r . I n e i t h e r c a s e , i t i s n o t necessary
t h a t competitors use t h e same a r e a o r f o r a g e p l a n t s
a t t h e same time (Cole 1958). Use of a food by one
animal during one season may preclude subsequent
usage of t h a t a r e a o r food by another. Also, i n t e n s i v e usage of an a r e a o r f o r a g e source by one animal
over a period of y e a r s may d i r e c t l y o r i n d i r e c t l y
reduce f o r a g e y i e l d s o r a l t e r p l a n t s p e c i e s composit i o n t o t h e e v e n t u a l detriment of another animal.
INTERSPECIFIC RELATIONS OF MULE DEER AND OTHER
UNGULATES
Mule Deer I n t e r a c t i o n s With Other Wild Ungulates
White-tailed Deer.--The range of w h i t e - t a i l e d deer
o v e r l a p s t h a t of mule d e e r g e n e r a l l y a c r o s s t h e northe r n United S t a t e s from t h e western Dakotas t o e a s t e r n
Washington, from western Manitoba westward t o A l b e r t a
and s o u t h e a s t e r n B r i t i s h Columbia i n Canada, i n northe a s t e r n Wyoming, t h e western p o r t i o n s of Nebraska,
Kansas, Oklahoma, and Texas, and p a r t s of Colorado,
New Mexico, and Arizona.
I n t e r s p e c i f i c Competition
Kramer (1972) r e c e n t l y evaluated e c o l o g i c a l
r e l a t i o n s h i p s of t h e s e two s p e c i e s i n d e t a i l . Within
t h e i r zone of o v e r l a p , h a b i t a t p r e f e r e n c e s and some
a s p e c t s of behavior were d i s t i n c t l y d i f f e r e n t , while
food h a b i t s were f a i r l y s i m i l a r . The l a t t e r , p l u s
some o v e r l a p i n h a b i t a t usage where t h e two s p e c i e s
occupied t h e same a r e a suggested t h e p o s s i b i l i t y of
competition i n l o c a l a r e a s ; however, competition did
not appear t o be an important f a c t o r e i t h e r g e n e r a l l y
o r i n r e c e n t e x t e n s i o n s of t h e range of w h i t e - t a i l e d
deer i n n o r t h e r n a r e a s where mule deer p o p u l a t i o n s
were d e c l i n i n g .
EZk.--Elk occur g e n e r a l l y a c r o s s much of t h e range
of mule deer. Wherever s t u d i e s have been conducted,
p a t t e r n s of h a b i t a t usage of e l k appear q u i t e s i m i l a r
t o t h o s e of mule d e e r ; though e l k appear t o be l e s s
d i s c r i m i n a t i n g i n t h e i r s e l e c t i o n of h a b i t a t t y p e s
and move more widely. Foods u t i l i z e d by e l k f r e q u e n t l y o v e r l a p p r e f e r e n c e s of mule d e e r ; but both
vary considerably by season and l o c a t i o n and food
h a b i t s of e l k g e n e r a l l y appear t o be broader and
more f l e x i b l e than t h o s e of d e e r . On p r a i r i e montane f o r e s t mountain ranges, both animals consume
s i m i l a r g r a s s e s and f o r b s during s p r i n g and appear
t o p r e f e r s i m i l a r f o r b s during summer. Both may
a l s o browse on t h e same s p e c i e s during summer;
though, i f f o r b s a r e not a v a i l a b l e , e l k o f t e n switch
t o g r a s s e s while mule deer browse more i n t e n s i v e l y .
I n f a l l and w i n t e r , where a v a i l a b l e , e l k t r e n d t o
g r a s s e s , b u t u t i l i z e some f o r b s and may browse
i n t e n s i v e l y during p e r i o d s of snow cover o r when
c r u s t i n g l i m i t s a c c e s s t o g r a s s . Though mule deer
tend t o browse most e x t e n s i v e l y during w i n t e r i n
most a r e a s , they may depend h e a v i l y on f o r b s and/or
g r a s s e s i n some a r e a s where a v a i l a b l e and shrubs
a r e l i m i t e d . On h e a v i l y f o r e s t e d ranges of western
Montana and n o r t h e r n Idaho, both mule d e e r and e l k
may browse e x t e n s i v e l y throughout t h e year and
p r e f e r s i m i l a r species.
I n g e n e r a l , a v a i l a b l e d a t a suggest c o n s i d e r a b l e
o p p o r t u n i t y f o r i n t e r s p e c i f i c competition between
mule deer and e l k where s p e c i e s populations occupy
t h e same range. Because e l k appear t o be more
adaptable and flexib1.e i n t h e i r choice of h a b i t a t s
and f o r a g e p r e f e r e n c e s , most a u t h o r i t i e s have concluded t h a t , i n t h e event of i n t e r a c t i o n , e l k would
be t h e more e f f i c i e n t competitor and s u r v i v e a t t h e
expense of mule deer. However, t h e r e i s a s y e t
l i t t l e q u a n t i t a t i v e support of competition between
t h e two s p e c i e s being an important f a c t o r i n t h e
population ecology of e i t h e r one. Among t h e few
accounts of elk-mule deer i n t e r a c t i o n s i n t h e l i t e r a t u r e , C l i f f (1939) a s c r i b e d heavy d e e r m o r t a l i t y
i n Idaho during t h e s e v e r e w i n t e r of 1931 t o heavy
u t i l i z a t i o n of important mule d e e r f o r a g e p l a n t s by
elk.
Bighorn Sheep.--Although t h e d i s t r i b u t i o n of mule
deer almost completely o v e r l a p s t h a t of bighorn
sheep throughout t h e western United S t a t e s and
Canada, bighorn ranges comprise only a very small
p r o p o r t i o n of t h e t o t a l d i s t r i b u t i o n a l range of mule
deer. S t u d i e s of l o c a l s p e c i e s populations i n d i c a t e
t h a t i n many a r e a s a t l e a s t they may u t i l i z e s i m i l a r
h a b i t a t s and p r e f e r much t h e same f o r a g e ; while i n
o t h e r s , h a b i t s diverged. I n g e n e r a l bighorns appear
t o u t i l i z e g r a s s e s t o a much g r e a t e r e x t e n t and
browse t o a l e s s e r e x t e n t than deer i n most a r e a s of
comparative study, but s u f f i c i e n t o v e r l a p i n p l a n t
species utilized occurred to suggest competition at
least locally.
Moose.--Moose occur within the range of mule deer in
Canada from Saskatchewan west to British Columbia,
in Montana, Idaho, and Wyoming, northeastern Utah.
and possibly very locally in a few other areas,
Prescott (1974) recently reviewed interrelationships
with mule deer. Some similarities in habitat and
forage selection were evident in most areas. In
Montana, as elsewhere, they may share both summer and
winter ranges and eat many of the same plants; and
these overlaps probably result in competition in some
areas. Overall, competition probably would affect
mule deer more drastically than moose (Schladweiler
1974).
Pronghorn Antelope.--Pronghorn antelope (AntiZocapra
americanal occur in association with mule deer on
prairie and mountain valley or basin grass and shrublands in many areas of western North America.
Although they may utilize much the same habitats and
prefer many of the same forage plants throughout the
year comparative studies are lacking. Opportunities
for competition probably exist in many areas, especially where higher mule deer densities occur on
extremely open prairie lands.
Mountain Goats.--Mountain goats ( O r e m s americana)
occur locally within the range of mule deer in many
areas of the northern Rocky Mountains. Distributions
may overlap in these areas during summer and/or
winter, with some similarities in habitat usage and
forage selection. Although competition could occur,
few comparative studies have been conducted and
interrelationships are generally obscure.
Other WiZd Ungu2ates.--Locally, Bison (Bison bison)
may occur in association with mule deer as in the
case of the National Bison Range. In the southwest,
collared peccary (Pecari tajacu), barbary sheep
(Ananotragus leruia), and locally perhaps some additional exotic ungulates may occur on mule deer
ranges. Knipe (1957) suggested the possibility of
competition between pecarry and deer during some years
or in some areas where the availability of forage was
low. Ogren (1962) indicated that barbary sheep eat
some of the same foods taken by deer, but that field
observations indicated that the apparent competition
may not be real because of differences in use of
local habitats.
Mule Deer Interactions With Domestic Ungulates
Domestic livestock grazing has been a dominant
use of western rangelands since the late 1800's; and
the vast majority of mule deer range has been or is
grazed at least seasonally. Viewed either on the
basis of its historical and long-term impacts on the
kinds and amounts of vegetation on these ranges or
in terms of annual forage removal and associated
short-term grazing affects, this usage has to rate as
one of, if not the single most important land use or
environmental factor affecting mule deer habitat
values.
Cattle.--Findings of intensive competition studies
as well as general comparisons of range use and food
habits of mule deer and cattle have indicated that
some competition may occur wherever the two species
occur together. Most comparative studies have
indicated broad differences in use of local habitat
types and physiographic sites as well as in forage
preferences of mule deer as compared with cattle
such that competition is likely to be minimal in
most cases where ranges are properly stocked and
in good to excellent condition. However, cattle
often make sufficient use of important deer forage
plants and feeding areas to compete seriously where
stocking rates are high, when plant growth is
reduced by drought or prior heavy usage, or when
grazing begins too early, extends too long, or
occurs on critical winter or other seasonal range
areas. Because of this, both the actual occurrence
and the intensity of conflict probably vary widely
in time and space.
That cattle may "interfere" with deer usage of
all available habitats and exclude deer use in
some areas has been suggested by McMahan (1966),
Firebaugh (1969), Dusek (1971), and Knowles (1975).
However, direct evidences of exclusion and quantification of the effects of competition by cattle on
mule deer populations is generally lacking. McMahan
and Ramsey (1965) reported a low carrying capacity
for white-tailed deer in all pastures continuously
grazed by a mixture of livestock including cattle,
as compared with deer-only managed areas. Reproduction and survival of fawns in these pastures
varied in relation to stocking rates with no fawns
ever surviving to yearling age on heavily stocked
pastures.
Sheep.--Range usage and food habits of domestic sheep
may overlap those of mule deer even more closely
than in the case of cattle. Cumulative data on
interactions do little to alter the basic conclusion
of Smith and Julander (1953) that "the similarity
of sheep and mule deer diets is sure to cause conflict wherever the supply of preferred (forage)
species is inadequate to satisfy the requirements
of both animals...even though an adequate forage
supply obviates any actual conflict, there is competition in the sense that if part of the deer
population was removed, sheep numbers could be
increased and vice versa." Evidences of "interference" or local exclusion of mule deer from areas
grazed by sheep have not been recorded quantitatively in the literature.
Other Livestock and Feral Ungukxtes.--Both domestic
and "wild" horses and burros may be associated with
mule deer, grazing similar local areas and habitat
types. While "wild" populations have increased due
to protection in recent years, concern for possible
competition has also increased; but as yet few
quantitative data have appeared. Available information suggests considerable differences in forage
preferences, but use of herbage as well as winter
browse species of mule deer may constitute serious
competition affecting mule deer adversely.
Multi-species Relationships
Frequently, mule deer occur in species populations associated with more than one other ungulate.
For example, both elk and cattle occur broadly
across the range of mule deer. Where they occur
together, interactions may be intensified and/or
vary from those of observed when only one is present.
Interspecific Competition
Numerous s t u d i e s have shown a h i g h d e g r e e of s i m i l a r t y i n r a n g e u s a g e and y e a r l o n g f o r a g e p r e f e r e n c e s of
e l k and c a t t l e . I n most r e s p e c t s t h e h a b i t s o f e l k
o v e r l a p t h o s e of d e e r on one hand and c a t t l e on t h e
o t h e r . F u r t h e r , e l k c l e a r l y tend t o avoid c a t t l e
whenever p o s s i b l e and s e e k t h o s e a r e a s where no c a t t l e
o c c u r ( S k o v l i n e t a l . 1968, Lonner 1975, Komberec
1 9 7 6 ) . Thus t h e p r e s e n c e of c a t t l e t e n d s t o i n t e n s i f y
o p p o r t u n i t i e s f o r c o n f l j c c between e l k and mule d e e r
and, p e r h a p s between mule d e e r and c a t t l e a s w e l l .
E l k withdraw i n t o a r e a s l e a s t g r a z e d by c a t t l e a n d / o r
c o n c e n t r a t e i n a r e a s where no c a t t l e o c c u r , p o s s i b l y
c a u s i n g o r i n c r e a s i n g t h e i n t e n s i t y of i n t e r a c t i o n
where none o r l e s s o c c u r r e d w i t h o u t c a t t l e . A l s o ,
r e d u c t i o n s i n c a t t l e numbers on many r a n g e s , removal
from o t h e r s inclucling many w i n t e r d e e r and e l k r a n g e s ,
and more r e s t r i c t i v e + a n a g e m e n t of e l k on m u t u a l l y
used a r e a s have a l l s e r v e d t o f a v o r e l k and i n t e n s i f y
p o t e n t i a l c o n f l i c t w i t h mule d e e r .
PROBLEMS I N ASSESSING INTERSPECIFIC COMPETITION
As t h e p r e c e d i n g d i s c u s s i o n s i n d i c a t e , i t i s n o t
especially d i f f i c u l t to obtain data indicating the
p o s s i b l e o c c u r r e n c e of some i n t e r a c t i o n a n d f o r e x p l o i t a t i o n - t y p e c o m p e t i t i o n among v a r i o u s s p e c i e s o r
s p e c i e s populations of l a r g e r herbivores.
Clearly,
mule d e e r may i n t e r a c t i n c o m p e t i t i v e r e l a t i o n s h i p s
w i t h e a c h of t h e o t h e r u n g u l a t e s w i t h which they
a s s o c i a t e . O p p o r t u n i t y , however, need n o t p r e s c r i b e
t h e f a c t ; a n d , by i t s e l f , h a s l i t t l e p r e d i c t i v e v a l u e .
Yet, e x i s t i n g s t u d i e s , even w i t h c a r e f u l d e s i g n , cont i n u e d measurement and o b s e r v a t i o n o v e r s e v e r a l y e a r s ,
and e x h a u s t i v e a n a l y s i s , have n o t produced s u b s t a n t i v e
e v i d e n c e f o r t h e e x i s t e n c e o f c o m p e t i t i o n nor more
than very g e n e r a l conclusions about i t s e x a c t n a t u r e
and importance.
The l a c k of a d e q u a t e means of
measuring t h e b i o l o g i c a l and e c o l o g i c a l e f f e c t s of
c o m p e t i t i o n o r o t h e r i n t e r a c t i o n s and d i s t i n g u i s h i n g
t h e s e e f f e c t s from t h o s e of o t h e r p o p u l a t i o n r e g u l a - t i n g mechanisms and f a c t o r s which e x p r e s s themselves
i n t h e same way may b e a m a j o r r e a s o n f o r t h e f a c t
t h a t few f i r m c o n c l u s i o n s have emerged.
In addition,
we may l a c k e i t h e r a d e q u a t e means o r s u f f i c i e n t
p e r s p e c t i v e t o i n t e r p r e t e x i s t i n g d a t a on h a b i t a t
r e q u i r e m e n t s and r e l a t i o n s h i p s . Because o f t h i s ,
b o t h t h e k i n d s of d a t a and t h e c r i t e r i a which we
commonly employ i n a s s e s s i n g i n t e r a c t i o n s p r o b a b l y
have some i m p o r t a n t l i m i t a t i o n s .
The e x p e c t e d e f f e c t s of i n t e r s p e c i f i c c o m p e t i t i o n
among u n g u l a t e s a r e t h o s e which d i r e c t l y o r i n d i r e c t l y
depress carrying capacity, c r e a t e o r i n t e n s i f y intras p e c i f i c c o m p e t i t i o n , and u l t i m a t e l y r e s u l t i n changes
i n numbers o r d i s t r i b u t i o n , o r b o t h . Most w i l d
u n g u l a t e s , i n c l u d i n g mule d e e r , a p p e a r t o b e f a i r l y
a d a p t a b l e i n t h e i r c h o i c e of Food and h a b i t a t r e q u i r e ments. Thus, under n a t u r a l c o n d i t i o n s t h e y occupy a
r a t h e r wide r a n g e of h a b i t a t s wherein c a r r y i n g
c a p a c i t i e s and s p e c i e s d e n s i t y v a r y n a t u r a l l y i n
r e l a t i o n t o t h e k i n d s , q u a l i t y , and amounts of food
and c o v e r a v a i l a b l e i n l o c a l a r e a s . I n t y p i c a l rangel a n d s i t u a t i o n s , i n which p o p u l a t i o n d e n s i t i e s of
e i t h e r o r both competitors a r e a t o r close t o t h e i r
carrying capacities, it is d i f f i c u l t to distinguish
t h e a d d i t i o n a l e f f e c t s , i f a n y , of i n t e r s p e c i f i c
c o m p e t i t i o n from t h o s e of i n t r a s p e c i f i c c o m p e t i t i o n .
I t is a l s o d i f f i r u l t t o d i s t i n g u i s h e f f e c t s of i n t e r s p e c i e s i n t e r a c t i o n s and c o m p e t i t i o n from t h o s e of
v a r i o u s o t h e r e n v i r o n m e n t a l f a c t o r s which s i m i l a r l y
Interspecific Competition
i n f l u e n c e c a r r y i n g c a p a c i t i e s . Normal f l u c t u a t i o n s
i n w e a t h e r and snow c o n d i t i o n s , f o r a g e p r o d u c t i o n ,
p r e d a t i o n , h u n t i n g , and o t h e r f a c t o r s may e l i c i t
changes i n c a r r y i n g c a p a c i t i e s o r c e r t a i n s p e c i e s
r e s p o n s e s and p o p u l a t i o n consequences e s s e n t i a l l y
i n d i s t i n g u i s h a b l e from i n t r a - o r i n t e r - s p e c i f i c
competition.
S i m i l a r i t i e s and/or differences i n d i s t r i b u t i o n ,
r a n g e u s e , and food h a b i t s a r e n o t e v i d e n c e a p r i o r i
f o r o r a g a i n s t a c o m p e t i t i v e r e l a t i o n s h i p . There
may b e s e v e r a l r e a s o n s f o r t h i s .
Only r a r e l y , i f e v e r , h a v e we had o p p o r t u n i t y
t o r e c o r d t h e s e k i n d s of d a t a f o r mule d e e r ( o r any
o t h e r s p e c i e s ) i n a s i t u a t i o n where no o t h e r s p e c i e s
o c c u r r e d . Thus, most e x i s t i n g i n f o r m a t i o n h a s been
c o l l e c t e d i n p l a c e s o r under c o n d i t i o n s when i n t e r a c t i o n was a m a t t e r of f a c t . Because o f t h i s , we
u s u a l l y f i n d o u r s e l v e s u s i n g d a t a , which i n thems e l v e s r e f l e c t e f f e c t s of i n t e r a c t i o n , t o d e t e r m i n e
whether i n t e r a c t i o n and c o m p e t i t i o n a r e o c c u r r i n g .
Secondly, n o t a l l i n t e r a c t i o n s need t o b e comp e t i t i v e . T h e r e a r e numerous r e p o r t s i n r a n g e and
w i l d l i f e l i t e r a t u r e suggesting increased availa b i l i t y , p a l a t a b i l i t y , o r p r o d u c t i o n of f o r a g e p l a n t s
f o r o n e animal a s a r e s u l t of g r a z i n g o r browsing
a c t i v i t i e s of a n o t h e r . B e l l (1971) d e s c r i b e d s i t u a t i o n s i n t h e S e r e n g e t t i P l a i n s of A f r i c a i n which
s e v e r a l s p e c i e s of h e r b i v o r e s g r a z e d t h e same a r e a
and, t o a c e r t a i n e x t e n t , t h e same p l a n t s i n a
m u t u a l i s t i c o r c o m m e n s a l i s t i c r e l a t i o n s h i p . On some
w e s t e r n r a n g e l a n d s a t l e a s t , t h e c o n v e r s i o n of
perennial grasslands to shrub and/or annual grassf o r b t y p e s a s a r e s u l t of heavy e a r l y l i v e s t o c k
g r a z i n g i s b e l i e v e d t o have improved f o r a g e condit i o n s f o r mule d e e r . R e d u c t i o n s i n d e n s i t i e s of
n a t i v e p e r e n n i a l g r a s s e s paved t h e way f o r t h e subs e q u e n t abundance of p a l a t a b l e s h r u b s a n d / o r i n t r o duced g r a s s e s and f o r b s which a r e more d i g e s t i b l e
t h a n n a t i v e p e r e n n i a l s (Longhurst e t a l . 1968,
1976). A s i m i l a r r e l a t i o n s h i p i s i m p l i c i t i n t h e
c o n c e p t t h a t "sound g r a z i n g p r a c t i c e s p l a y a n
i m p o r t a n t r o l e i n m a i n t a i n i n g a d e q u a t e browse s t a n d s
e s s e n t i a l f o r a h e a l t h y p o p u l a t i o n of b i g and upland
game (Clawson and Lesperance 1 9 7 3 ) . "
F u r t h e r m o r e , o u r p r e o c c u p a t i o n w i t h more
p r e f e r r e d and i m p o r t a n t f o r a g e p l a n t s i n a s s e s s i n g
c o m p e t i t i o n may have i g n o r e d v i t a l r o l e s of l e s s e r
s p e c i e s i n t h e d i e t s of g r a z i n g a n i m a l s and p e r h a p s
more s u b t l e c o m p e t i t i v e r e l a t i o n s h i p s w i t h r e s p e c t
t o t h e i r u s e and a v a i l a b i l i t y . B i o l o g i s t s have
lung r e c o g n i z e d a n a p p a r e n t r e q u i r e m e n t f o r a v a r i e t y
of f o r a g e i t e m s i n t h e d i e t of l a r g e h e r b i v o r e s ;
and b o t h Smith (1959) and Longhurst e t a l . (1968)
h a v e i n d i c a t e d t h a t t h e r e may be p h y s i o l o g i c a l l i m i t s
a s t o t h e amount of c e r t a i n s p e c i e s , e . g . b i g sageb r u s h , t h a t d e e r c a n consume. Longhurst e t a l .
(1968) r e l a t e d t h i s t o i n h i b i t o r y e f f e c t s of e s s e n t i a l o i l s on rumen f u n c t i o n . S i m i l a r l y , F r e e l a n d
and J a n z e n (1974) p o i n t o u t t h a t many p l a n t s n o r m a l l y
f e d upon by h e r b i v o r e s c o n t a i n t o x i c m a t e r i a l s which
can have d e t r i m e n t a l e f f e c t s u n l e s s consumed w i t h
o t h e r k i n d s of p l a n t s which e i t h e r o f f s e t o r n e u t r a l ize their toxicity.
F i n a l l y , c o m p e t i t i o n f o r f o r a g e may b e g i n long
b e f o r e p r e f e r r e d f o r a g e p l a n t s used i n common a r e
"overused".
L i v e s t o c k g r a z i n g t r i a l s have shown
r e p e a t e d l y t h a t r a t e s of weight g a i n i n h e a v i l y stocked p a s t u r e s d e v i a t e from t h o s e under l i g h t e r s t o c k i n g
almost from t h e time c a t t l e a r e placed i n t h e p a s t u r e s
( c f . Woolfolk and Knapp 1949, Kipple and C o s t e l l o 1960,
Reed and P e t e r s o n 1961). The r a t e a t which a n animal
can f i n d food depends upon t h e d e n s i t y of food i n i t s
environment, t h e amount of time and e f f o r t s p e n t i n
looking f o r food, and i t s e f f i c i e n c y i n feeding a l l
may be i n f l u e n c e d by preemption o r common usage w e l l
b e f o r e t o t a l u t i l i z a t i o n reaches a "proper" l e v e l .
Dusek, G. L. 1971. Range r e l a t i o n s h i p s of mule deer
i n t h e p r a i r i e h a b i t a t , n o r t h c e n t r a l Montana.
M.S. Thesis, Mont. S t a t e Univ., Bozeman. 63p.
Firebaugh, J . E. 1969. R e l a t i o n s h i p s of mule d e e r
t o l i v e s t o c k on summer range i n t h e Pryor Mount a i n s , Montana. M.S. Thesis. Mont. S t a t e Univ.
Bozeman. 55p.
Freeland, W. J. and D. H. Janzen. 1974. S t r a t e g i e s
i n herbivory by mammals: The r o l e of p l a n t
secondary compounds. Am. Nat. 108(961):269-289.
CONCLUSIONS
G e i s t , V. 1970. A b e h a v i o r a l approach t o t h e
management of wild ungulates. pp413-424.
In
E. Duffey and A. S. Watt ( e d ) . The s c i e n t i f i c
management of animal and p l a n t communities f o r
conservation. The 1 1 t h Symposium of t h e B r i t i s h
E c o l o g i c a l S o c i e t y . Blackwell S c i e n t i f i c Publ.,
Oxford.
The f a c t t h a t we must admit t o knowing l i t t l e
about t h e e x a c t n a t u r e and importance of competition
e s s e n t i a l l y precludes any f i r m conclusions a s t o i t s
p o s s i b l e s i g n i f i c a n c e i n t h e c u r r e n t t r e n d s and
s t a t u s of mule deer populations i n Western North
America. This does n o t mean t h a t competition i s n o t
o r has not been of some o r even c o n s i d e r a b l e i n f l u e n c e .
Rather, i t s e r v e s t o p o i n t o u t t h a t much remains t o
be accomplished i n t h e way of f i n d i n g ways and means
of more e f f e c t i v e l y a s s e s s i n g i n t e r s p e c i e s r e l a t i o n s h i p s and applying our c u r r e n t knowledge t o s i t u a t i o n s
of p o t e n t i a l competition on rangelands. Since e x i a t ing d a t a do n o t o r cannot s a t i s f y t h e demands of
m u l t i p l e use land managers attempting t o accommodate
a l l uses, i t seems imperative t h a t we r e d i r e c t our
t h i n k i n g and e f f o r t s t o e s t a b l i s h v a l i d d a t a and
conclusions a s r a p i d l y a s p o s s i b l e . U n t i l we can
f u l l y document t h e b i o l o g i c a l and e c o l o g i c a l s i g n i f i cance of i n t e r s p e c i e s competition we can only cont i n u e t o say maybe t o t h e q u e s t i o n s of whether
competition i s o c c u r r i n g o r important.
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Hunter, G. N. and R. G . Kinghorn. 1950. Mountain
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J e f f e r y , D. E. 1963. F a c t o r s i n f l u e n c i n g e l k
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