J. Zool., Lond. (2004) 262, 57–63
C 2004 The Zoological Society of London
Printed in the United Kingdom
DOI:10.1017/S0952836903004394
Habitat segregation between sympatric Tibetan argali
Ovis ammon hodgsoni and blue sheep Pseudois nayaur
in the Indian Trans-Himalaya
Tsewang Namgail1,2 , Joseph L. Fox1 ∗ and Yash Veer Bhatnagar 2
1
2
Department of Biology, Faculty of Science, University of Tromsø, N-9037 Tromsø, Norway
Wildlife Institute of India, P.O. Box 18, Dehradun – 248 001, Uttaranchal, India
(Accepted 18 June 2003)
Abstract
Tibetan argali Ovis ammon hodgsoni and blue sheep Pseudois nayaur have almost completely overlapping
distributions encompassing most of the Tibetan plateau and its margins. Such a sympatric distribution of related
species with similar ecological requirements implies that there is some degree of resource partitioning. This may
be accomplished on the basis of habitat and/or diet separation. This study evaluated such ecological separation on
the basis of physical habitat partitioning by these two sympatric ungulates in Hemis High Altitude National Park,
Ladakh, India, in an area where the argali established a small new population in 1978. Such separation was tested for
on the basis of expected difference between the species in their proximity to cliffs, associated with species-specific
anti-predator behaviour. Tibetan argali selected habitats away from cliffs while blue sheep selected habitats close
to cliffs. Blue sheep also selected steep slopes whereas argali selected gentle slopes. The two species did not differ
in their use of habitats in terms of elevation. They did, however, differ in their use of plant communities; blue
sheep selected sub-shrub and grass-dominated communities whilst argali selected forb-dominated communities.
We suggest that the two species coexist in this site as a result of the differential use of habitat associated with their
species-specific anti-predator strategies.
Key words: argali, Ovis ammon hodgsoni, blue sheep, Pseudois nayaur, habitat selection, resource partitioning,
niche relationship
INTRODUCTION
The pattern of resource partitioning in ungulate
communities is widely studied (Jarman, 1974; Jarman &
Sinclair, 1979; Gordon & Illius, 1989; Voeten & Prins,
1999; Forsyth, 2000), but the mechanisms which produce
such partitioning remain elusive. The observed pattern of
resource partitioning or niche differentiation in ungulate
communities could be attributed to both ecological
forces (i.e. current competition and/or predation) and
evolutionary history (i.e. ghost of competition past)
(Connell, 1980). In coevolved communities, the extant
species may have competed in the past and developed
different morphological and/or behavioural characteristics
through evolutionary time, thus accomplishing resource
partitioning. There is however an inherent problem in
invoking the so-called ‘ghost of competition past’, as we
cannot in retrospect determine the past processes and
check whether they competed in the past or not (Begon,
Harper & Townsend, 1996). Therefore, the pattern of
*Corresponding author: Joseph L. Fox.
E-mail: joe.fox@ib.uit.no
resource partitioning in ungulate communities can only
be tested and interpreted in terms of current ecological
forces.
Resource partitioning studies have addressed mountain
ungulate–livestock interaction for the Asiatic ibex Capra
ibex sibrica (Bhatnagar et al., 2000) and blue sheep
Pseudois nayaur (Mishra, 2001) in the relatively dry
areas of the Indian Himalayan region, but other than
theoretically (Mishra et al., 2002) niche separation
among wild species has not been addressed in this
area. Study of ecological separation among musk deer
Moschus chrysogaster, goral Nemorhaedus goral, serow
Capricornis sumatraensis and sambar Cervus unicolor
has indicated that, in the moist and productive areas of
the Greater Himalaya, these dissimilar sympatric species
apparently partition the abundant resources (Green, 1987).
Ungulates in the drier Trans-Himalayan region, however,
live in a relatively impoverished environment (Mishra,
2001), where they are expected to compete for common
resources, and coexist either by geographical or resource
partitioning (Schaller, 1977). In recent years, there has
been a great controversy on the relative importance
of competition and predation in structuring ecological
communities (see reviews by Sih et al., 1985; Gurevitch,
58
T. NAMGAIL, J. L. FOX AND Y. V. BHATNAGAR
Morrison & Hedges, 2000). Much of the literature
has focused on competition as a plausible factor
influencing differential use of resources by coexisting
species (MacArthur, 1972; Pianka, 1976; Fritz, de GarineWichatitsky & Letessier, 1996), while importance of
predation in resource partitioning is little understood.
Predation may lead to resource partitioning provided the
species are safest from predators in different habitats
(Sih et al., 1985; Repasky, 1996).
The Tibetan argali Ovis ammon hodgsoni, henceforth
‘argali’, and the blue sheep P. nayaur are two wild
ungulates of the Bovidae subfamily Caprinae, with almost
completely overlapping distributions (see Shackleton,
1997) that encompass the Tibetan plateau and its peripheral areas. Although other subspecies of O. ammon
occur in areas without blue sheep, where overlap occurs as
with O. a. hodgsoni such sympatric distribution of related
species with similar ecological requirements implies that
they avoid any high degree of competition, and that there
is some degree of resource partitioning. This may be
accomplished on the basis of habitat and/or diet separation. Initial food habit studies of argali and blue sheep
on the Tibetan plateau (Harris & Miller, 1995; Miller &
Schaller, 1998) have shown a considerable overlap in diet,
suggesting that they accomplish the resource partitioning
primarily by habitat separation.
Various anecdotal reports on argali and blue sheep
habitat utilization suggest that although both species
are denizens of mountainous areas, blue sheep prefer
steep terrain near cliffs whereas argali prefer open and
rolling terrain away from cliffs (Fox, Nurbu & Chundawat,
1991; Schaller, 1977, 1998). The biological basis for
this difference in habitat use is explained in terms of
contrasting predator avoidance strategies associated with
morphological differences between the two species (Geist,
1971; Main, Weckerly & Bleich, 1996). Thus, the long
slender legs of argali enhance its cursorial strategy of
out-running predators on the open and rolling terrain of
its preferred habitat. In contrast, the relatively short and
muscular legs of the blue sheep support its agility in
steep and rugged terrain (i.e. cliffs) where it retreats to
avoid predators, which are generally less agile in such
habitat (Bleich, 1999; Geist, 1999). Thus, based on this
difference, the blue sheep and argali are expected to show
some differences in their use of habitat in terms of their
proximity to cliffs related to the respective anti-predator
strategies. This expected difference provides the basis for
the present study, especially so because no studies have
hitherto actually measured argali habitat use in relation to
escape terrain.
Although the species argali is widely distributed in
mountainous regions of central Asia, the Tibetan argali
is one of the two subspecies of Ovis ammon that are
listed as endangered on Appendix I of the Convention
on International Trade in Endangered Species of Wild
Fauna and Flora (CITES). The most recent estimates
suggest that, although other subspecies are much more
numerous, there are < 7000 Tibetan argali left in the wild
(Shackleton, 1997; Schaller, 1998). Within India there are
only c. 200 argali remaining, mostly in Ladakh and a few
in Sikkim (Fox & Johnsingh, 1997). The small population
(c. 20 individuals) of argali within the Hemis High
Altitude National Park in Ladakh presents an interesting
case where three individuals established a new population
in 1978 (Fox et al., 1991). The fact that these argali
have not greatly increased in number since their arrival
concerns the park managers.
Relying on theoretically-based expectations regarding
niche (in this case habitat) separation, we have initiated
an investigation of habitat use differences between this
argali population and the blue sheep that share its range.
This has clear implications for conservation efforts in
the Hemis population, and perhaps with other argali
populations. If predation was important in shaping their
niche relationship, we expected blue sheep to use steep
habitats near the cliffs and argali to use moderate slopes
away from cliffs. Current predation does appear to be
an important ecological factor in the study area, as
several large predators are known to prey on these
wild ungulates (Chundawat, 1992; Fox & Chundawat,
1995). Thus, we hypothesized that ecological separation
between argali and blue sheep exists on the basis of
physical habitat (escape terrain), and tested for this on
the basis of expected difference in distance to cliff, with
possible additional influences related to slope angle and/or
elevation.
The study was carried out in summer (July–August) as
the blue sheep, mostly males, migrate to higher elevations,
where the argali occur, during this season (Chundawat,
1992). Although difference in the diet was not addressed
in this summer season study, easily obtainable data on
plant community type were also gathered to assess the
differences in vegetation use that could be related to
the aforementioned habitat differentiation.
METHODS
Study area
Our study was carried out in the north-western part
of Hemis High Altitude National Park (34◦ N, 77◦ E) in
the Ladakh Province of Jammu & Kashmir State, India
(Fig. 1). The known range of the small argali population
in the Park was delineated from local knowledge and past
studies (e.g. Fox et al., 1991). The entire argali range
currently used encompasses c. 10 km2 in the headwaters
of the Shingo and Rumbak streams, and is situated in
the Zanskar Range near the confluence of the Indus and
Zanskar rivers about 20 km from Leh, the principal town
of Ladakh.
Elevation within the area used by argali ranges from
4000 to 5500 m. The argali range is relatively higher than
the overall blue sheep range in the whole of the Rumbak
catchment (Chundawat, 1992). Within the small area of
argali use, topography varies from steep, rocky slopes
along the highest ridgelines to gently rolling in the midelevation zone and steeper again at the lowest sites. Hemis
National Park is situated in the rain shadow of the Great
Habitat segregation between argali and blue sheep
59
5335 m
5367 m
N
Indus River
Leh
Zhingchen (20 km)
Rumbak
Study area
Shrub
Sedge
Sub-shrub
Forb
Grass
Barren
0
INDIA
2 km
6123 m
Fig. 1. Distribution of vegetation communities in the study area, north-western Hemis National Park, Ladakh, India.
Himalaya; hence the climate is characterized by cold and
arid conditions, with low plant productivity confined to
the 3-month growing season in summer (June–August).
Diurnal temperatures in the Park in summer range from
15 ◦ C to 35 ◦ C (Chundawat, 1992). Annual precipitation in
the Indus Valley at Leh is c. 100 mm, increasing somewhat
south-westward and altitudinally to 500–1000 mm in
valleys at the northern base of the Himalaya (Hartmann,
1983), and is probably c. 500 mm in the study area.
Vegetation of Hemis National Park is characterized by
dry alpine steppe. Within the study area there are no
trees, and vegetation consists of small shrubs, sub-shrubs,
grasses, sedges and forbs (Fig. 1; see Namgail (2001) for
a complete description of the vegetation). Predators of the
argali and blue sheep include snow leopard Uncia uncia,
wolf Canis lupus chanko, and wild dog Cuon alpinus, with
red fox Vulpes vulpes montana and golden eagle Aquila
chrysaetos a threat only to the young lambs.
Habitat use
Data were collected by searching for argali and blue
sheep from selected trails and ridges, all with good
vantage points. Observations were conducted using 8 × 40
binoculars and a 15–45X spotting scope. Records were
made of species type, group size, sex, age, date and
time. Individuals were considered to be solitary or
belong to different groups when they stood 50 m away
from another group. Observations on argali and blue
sheep were taken between 06:00 and 20:00, but most
of the observations were obtained from 06:00 to 12:00,
when animals were active, and effects of human-related
disturbance minimal. Although not distributed evenly
throughout the day, these observations can reasonably
be considered a representative sample for anti-predator
related habitat use. All observations were made by
1 person, thus there was no inter-observer bias.
The locations of the blue sheep and argali groups were
plotted on 1:50 000 topographic sheets with elevation
contour intervals of 40 m. Elevation, distance to cliff,
slope angle and vegetation type (plant community) at the
animal locations were recorded. Elevation was determined
from the topographic sheet, and slope angle calculated
from the measured distance between the nearest contour
lines. Distance to cliff was determined by measuring the
distance between the animal location and the nearest cliff
on the map. Cliffs, very steep slopes (> 45◦ ) on an area
of >30 m diameter with vertical drops of >3 m, were
identified and mapped in the field. The vegetation was
classified into 5 communities, based on physiognomy
and dominant species, and mapped on the topographic
sheet (Fig. 1). Subsequently, the mapped blue sheep and
argali locations were classified as to different vegetation
communities.
As there were only 20 argali present in the area
(Namgail, 2001), pseudo-replication was inevitable
60
T. NAMGAIL, J. L. FOX AND Y. V. BHATNAGAR
5335 m
5367 m
Rumbak
Shingo
N
Indus River
Zhingchen
Leh
(20 km)
Blue sheep
Cliff
Tibetan argali
Village
INDIA
Rumbak
0
Study area
2 km
6123 m
Fig. 2. Locations of Tibetan argali Ovis ammon hodgsoni and blue sheep Pseudois nayaur and cliffs in the upper Rumbak and Shingo
catchments of Hemis National Park, Ladakh, India.
(Machlis, Dodd & Fentress, 1985), although frequent regrouping lessened the dependency. Owing to the high
fluidity of group membership for blue sheep, and
movements in and out of the study area (Namgail, 2001), it
is difficult to demonstrate that the same groups shared the
argali range throughout the study period. Nevertheless,
a group of c. 27 males was frequently observed in the
area through the entire study period. Blue sheep nursery
groups used lower and more rugged areas in the vicinity
of the study area, where they may be more secure from
predators, similar to that observed for bighorn sheep Ovis
canadensis (Bleich, Bowyer & Wehausen, 1997).
angle and elevation) at 366 points were sampled. These
variables were determined in the same way as described
for the animal habitat use.
To assess the vegetation availability, a reconnaissance
survey of vegetation was conducted in the area during the
study period. The plant identification was carried out in the
field, using Polunin & Stainton (1985) as a reference. Once
the 5 plant communities were mapped on the topographic
sheet (Fig. 1), a systematic sample at the same 366 points
was taken to determine their availability.
Data analysis
Available habitat
Availability of a habitat is the quantity of that habitat
accessible to the population of animals during the study
period (Manly, McDonald & Thomas, 1993). The animals
were assumed to have equal access to all the available
habitats as they could move across the study area within
a day, and sometimes did. For availability of habitat, a
systematic sample of habitat characteristics was obtained
from a 1:50 000 topographic sheet of the study area. For
this purpose, a point grid was overlaid on the topographic
sheet and the habitat variables at the location of each point
were recorded. Habitat characters (distance to cliff, slope
Habitat preference was determined by relating use of
a habitat to its availability. When resources are used
disproportionately to their availability, use is said to
be selective (Manly et al., 1993). Since individual
animals were not identified and were assumed to be
randomly sampled, and available population proportion
of habitat characteristics was assumed to be known,
the habitat selection data conformed to Design 1 with
sampling protocol A, according to Manly et al. (1993).
Although availability was sampled, since it was a systematic and intensive sampling with a point grid overlaid
on the small study area, we assume that the sample available proportion represents the population proportion.
Habitat segregation between argali and blue sheep
61
Table 1. Estimated habitat use for Tibetan argali Ovis ammon hodgsoni and blue sheep Pseudois nayaur in Hemis National Park, India.
πi , proportion of available resource units in category i; ui , number of used resource units in category i; oi , proportion of used units in
category i and si , selection of habitat category i
Tibetan argali
Variable
Distance to cliff (m)
Very close to cliff (< 50)
Close to cliff (51–250)
Away from cliff (251–450)
Farther away (> 450)
Total
Slope angle (degrees)
Flat (< 10)
Moderate (11–30)
Steep (31–50)
Very steep (> 50)
Total
Elevation (m)
Low (< 4300)
Middle (4301–4600)
High (4601–4900)
Very high (> 4900)
Total
Vegetation type
Shrub
Sub-shrub
Grass
Sedge
Forb
Barren
Total
Blue sheep
πi
ui
oi
si
ui
oi
si
0.119
0.374
0.336
0.171
1.000
6
39
47
11
103
0.058
0.379
0.456
0.107
1.000
–
0
+
0
11
43
20
8
82
0.134
0.524
0.244
0.098
1.000
0
+
0
0
0.014
0.437
0.522
0.027
1.000
1
64
40
0
105
0.010
0.610
0.381
0.000
1.000
0
+
0
–
0
22
57
3
82
0.000
0.268
0.695
0.037
1.000
–
–
+
0
0.075
0.242
0.372
0.311
1.000
4
15
31
55
105
0.038
0.143
0.295
0.524
1.000
0
–
0
+
2
6
33
41
82
0.024
0.073
0.402
0.500
1.000
–
–
0
+
0.383
0.186
0.077
0.038
0.071
0.246
1.000
27
19
1
0
57
1
105
0.257
0.181
0.010
0.000
0.543
0.010
1.00
–
0
–
–
+
–
18
35
17
4
1
7
82
0.220
0.427
0.207
0.049
0.012
0.085
1.000
–
+
+
0
–
–
+, Selection; −, avoidance; 0, use: in proportion to availability based on Bonferroni-adjusted 95% confidence intervals for habitat
use.
For the determination of habitat selection, the variables
were classified into distinct categories. To statistically
test significant departures of use from availability, the
modified χ 2 : log-likelihood chi-square test (χ L2 ) was calculated (see Manly et al., 1993). If the χ L2 was significant, the null hypothesis: all habitats are used in
proportion to their availability (no selection) was rejected.
Subsequently, for each habitat category, the Bonferroniadjusted 100 (1 – α)% confidence intervals for habitat use
were constructed. A habitat category was selected if the
lower confidence interval for that category was greater
than the corresponding population proportion. Similarly,
a habitat category was avoided when the upper confidence
interval for that category excluded the corresponding
population proportion.
RESULTS
A total of 82 observations on blue sheep and 105
observations on argali was recorded during the 2-month
study period (Fig. 2). The argali population was composed
of three adult males, 11 adult females, one yearling and
five lambs (Namgail, 2001). Eighty five percent of blue
sheep observations were of all-male groups, with 6%
mixed groups, and 9% nursery groups.
Argali selected the habitat category ‘away from
cliff’, and avoided the category ‘very close to cliff’
(χ L2 = 19.53, P < 0.01). Blue sheep in contrast selected
the category ‘close to cliff’ (χ L2 = 9.7, P < 0.05), and
its use of other categories were in proportion to the
respective availabilities (Table 1). Argali also selected
‘moderate’ slopes, and avoided ‘very steep’ slopes
(χ L2 = 9.26, P < 0.05). Blue sheep use of ‘steep’ slopes
was significantly higher than expected, and they avoided
‘moderate’ slopes (χ L2 = 29.80, P < 0.01).
Argali used the ‘very high’ elevation category more
than expected from its availability, and avoided the middle
elevation habitats (χ L2 = 21.56, P < 0.01), while it used
the other two categories as expected (Table 1). Blue sheep
also exhibited a similar pattern of habitat use (χ L2 = 29.80,
P < 0.01). Regarding vegetation, argali selected forb
communities (dominated by Potentilla spp., Oxytropis
spp., Astragalus spp., Thermopsis sp., Delphinium sp.,
Dracocephalum sp. and Saussurea spp.), and avoided
shrub (mainly Caragana spp. and Artemisia spp.), grass
(mainly Festuca sp., Poa spp. and Elymus spp.), and sedge
(Carex spp. and Kobresia spp.) (χ L2 = 189, P < 0.0001)
(Table 1). Blue sheep, however, avoided forb communities,
and selected sub-shrub (dominated by Aconogonum sp.
and Stachys sp.) and grass communities (χ L2 = 55.0,
P < 0.001).
62
T. NAMGAIL, J. L. FOX AND Y. V. BHATNAGAR
DISCUSSION
Our results support the hypothesis that ecological
separation between argali and blue sheep exists on the
basis of physical habitat selection. Observations of the
two species showed a distinct niche divergence, with
argali using relatively open terrain, and blue sheep
using more rugged terrain, which conforms to previous
anecdotal reports (Fox et al., 1991; Schaller, 1977,
1998). Ecologists have long considered that habitat
segregation serves to reduce both interference and
exploitation competition, and facilitates coexistence of
ecologically similar species (Pianka, 1978). Thus the
habitat segregation, in terms of proximity to cliff and
slope steepness, by blue sheep and argali in Hemis
National Park may minimize competition and facilitate
their coexistence. Although the species also differed in
their association with different vegetation communities,
implications regarding diet are speculative.
As there is evidence of substantial predation pressure
in the study area (Chundawat, 1992), prey species may
actively lower risk of predation by selecting habitat that
serves as effective refuge against predators (Houtman &
Dill, 1998). During the present investigation, 65% of the
sightings of blue sheep were within 250 m from cliffs
(escape terrain). Such high affinity by blue sheep toward
cliffs, which generally support less vegetation, suggests
that forage is not the only constraint in their habitat use.
In contrast, 64% of the argali observations were beyond
250 m from cliffs, which illustrates the importance of open
terrain in the determination of habitat use by argali. This
difference in the use of habitat, in terms of proximity to
cliff can be attributed to the species-specific anti-predator
behaviour.
Various studies (Belovsky, 1978; Sih, 1980; FestaBianchet, 1988; Houtman & Dill, 1998) with their
implications to the ‘optimal foraging theory’ suggest that
an animal should forage in areas where its intake rate is
highest and predation risk lowest. Although the blue sheep
may be safer in the cliffs (escape terrain), there is generally
less forage available in them (Namgail, 2001). Therefore,
they move out of such escape terrain for feeding (Wegge,
1979). Blue sheep probably need to strike a balance
between food acquisition and predator avoidance, while
feeding outside the escape terrain. Their high affinity for
the neighbourhood of cliffs may thus minimize overlap
with argali.
Although diet competition was not addressed in this
summer season study, as food is not likely to be limiting
during this season (Miller & Schaller, 1998), association
with plant communities was assessed. Blue sheep selected
grass and sub-shrub communities, which were more
abundant in vicinity of the cliffs. Argali, on the other hand,
showed higher affinity for forb-dominated communities,
which were more abundant in the open areas. Assuming
that each species feeds on the dominant plants, such a
selection pattern is at least consistent with the results of
some diet-based studies (Koirala & Shrestha, 1997; Miller
& Schaller, 1998) that record a preponderance of forbs in
argali diet, and graminoids in blue sheep diet.
As for the nutritional relationships associated with
interspecific differences in body size (Bell, 1971; Gagon
& Chew, 2000), one would expect blue sheep (relatively
smaller) to show a forb-dominated diet and argali a
graminoid-dominated diet. The converse relationship
observed in this study could be dictated by the plant
community use associated with anti-predator habitat
selection. In any case, because forage is not limiting at
this time of year, such expectation for diet differences
may not be appropriate.
The study has shown that despite the sparse vegetation
(Chundawat, 1992), argali and blue sheep coexist in Hemis
National Park, apparently by differential anti-predator
habitat selection by the two species. The differential use
of habitat as well as vegetation communities suggests
little overlap on these dimensions, and presumably a
reduced possibility of competition between argali and
blue sheep. Although the continued presence of argali
in the area thus seems possible, the slow growth of this
new population may simply be the result of the limited
amount of appropriate habitat here for this species. Other
factors, such as possible competition with livestock may
be important (Namgail, 2001); a threat that should also be
assessed soon because of the precarious overall status of
argali in India.
Acknowledgements
Financial support for this study was provided by the
Department of Biology and the Centre for Environment
and Development Studies, University of Tromsø, Norway
and the Earthwatch Institute, USA. We express gratitude
to Richard B. Harris and an anonymous reviewer for
their helpful comments. We are grateful to Mr. Abdul
Rauf Zargar, Wildlife Warden, Department of Wildlife
Protection, Leh, for granting permission to work in Hemis
High Altitude National Park.
REFERENCES
Begon, M., Harper, J. L. & Townsend, C. R. (1996). Ecology:
individuals, populations and communities. Oxford: Blackwell
Scientific Publications.
Bell, R. H. V. (1971). A grazing ecosystem in the Serengeti. Sci.
Amer. 255: 86–93.
Belovsky, G. E. (1978). Diet optimisation in a generalist herbivore:
the moose. Theor. Popul. Biol. 14: 105–134.
Bhatnagar, Y. V., Rawat, G. S., Johnsingh, A. J. T. & Stüwe, M.
(2000). Ecological separation between ibex and resident livestock
in a Trans-Himalayan protected area. In Grassland ecology and
management in protected areas of Nepal: 71–84. Richard, C.,
Basent, K., Sah, J. P. & Raut, Y. (Eds). Kathmandu: International
Centre for Integrated Mountain Development.
Bleich, V. C. (1999). Mountain sheep and coyotes: patterns of
predator evasion in a mountain ungulate. J. Mammal. 80: 283–
289.
Bleich, V. C., Bowyer, R. T. & Wehausen, J. D. (1997). Sexual
segregation in mountain sheep: resources or predation. Wildl.
Monogr. 134: 1–50.
Chundawat, R. S. (1992). The ecological studies of snow leopard
and its associated prey species in Hemis National Park, Ladakh,
India. PhD thesis, University of Rajasthan.
Habitat segregation between argali and blue sheep
Connell, J. H. (1980). Diversity and the co-evolution of competitors,
or ghost of competition past. Oikos 35: 131–138.
Festa-Bianchet, M. (1988). Seasonal range selection in bighorn
sheep: conflicts between forage quality, forage quantity, and
predator avoidance. Oecologia (Berl.) 75: 580–586.
Forsyth, D. M. (2000). Habitat selection and coexistence of
the Alpine chamois (Rupicapra rupicapra) and Himalayan
tahr (Hemitragus jemlahicus) in the eastern Southern Alps,
New Zealand. J. Zool. (Lond.) 252: 215–225.
Fox, J. L. & Johnsingh, A. J. T. (1997). Country report for India. In
Wild sheep and goats, and their relatives: 215–231. Shackleton,
D. M. (Ed.). Cambridge: IUCN.
Fox, J. L., Nurbu, C. & Chundawat, R. S. (1991). Tibetan argali
(Ovis ammon hodgsoni) establish a new population. Mammalia
55: 448–451.
Fox, J. L. & Chundawat, R. S. (1995). Wolves in the Transhimalayan
region of India; the continued survival of a low-density
population. In Ecology and conservation of wolves in a changing
world: 95–103. Carbyn, L. N., Fritts, S. H. & Seip, D. R. (Eds).
Edmonton: University of Alberta Press.
Fritz, H., de Garine-Wichatitsky, M. & Letessier, G. (1996). Habitat
use by sympatric wild and domestic herbivores in an African
savanna woodland: the influence of cattle spatial behaviour.
J. Appl. Ecol. 33: 589–598.
Gagon, M. & Chew, A. E. (2000). Dietary preferences in extant
African Bovidae. J. Mammal. 81: 490–511.
Geist, V. (1971). Mountain sheep: A study of behaviour and
evolution. Chicago: University of Chicago Press.
Geist, V. (1999). Adaptive strategies in American mountain sheep:
effects of climate, latitude and altitude, ice age evolution, and
neonatal security. In Mountain sheep of North America: 190–
208. Valdez, R. & Krausman, P. R. (Eds). Tucson: University of
Arizona Press.
Gordon, I. J. & Illius, A. W. (1989). Resource partitioning by
ungulates on the Isle of Rhum. Oecologia (Berl.) 98: 167–175.
Green, M. J. B. (1987). Ecological separation in Himalayan
ungulates. J. Zool. (Lond.) 1: 693–719.
Gurevitch, J., Morrison, J. A. & Hedges, L. V. (2000). The interaction
between competition and predation: a meta-analysis of field
experiments. Am. Nat. 155: 435–453.
Harris, R. B. & Miller, J. D. (1995). Overlap in summer habitats and
diets of Tibetan Plateau ungulates. Mammalia 59: 197–212.
Hartmann, H. (1983). Pflanzengesellschaften entlang der
Kashmirroute in Ladakh. Jb. Ver. Schutz der Bergwelt: 131–137.
Houtman, R. & Dill, L. M. (1998). The influence of predation risk on
diet selectivity: a theoretical analysis. Evol. Ecol. 12: 251–262.
Jarman, P. J. (1974). The social organisation of antelope in relation
to their ecology. Behaviour 48: 215–267.
Jarman, P. J. & Sinclair, A. R. E. (1979). Feeding strategy and
the pattern of resource partitioning in ungulates. In Serengeti,
dynamics of an ecosystem: 130–166. Sinclair, A. R. E. & NortonGriffiths, M. (Eds). Chicago: University of Chicago Press.
Koirala, R. A. & Shrestha, R. (1997). Floristic composition of
summer habitats and dietary relationships between Tibetan
63
argali (Ovis ammon hodgsoni), naur (Pseudois nayaur) and
domestic goat (Capra hircus) in the Damodar Kunda region of
Upper Mustang in Nepal Himalaya. MSc thesis, Agricultural
University of Norway.
MacArthur, R. H. (1972). Geographical Ecology: Patterns in the
distribution of species. Princeton: Princeton University Press.
Machlis, L., Dodd, P. W. D. & Fentress, J. C. (1985). The pooling
fallacy: problems arising when individuals contribute more than
one observation to the data set. Z. Tierpsychol. 68: 201–214.
Main, M. B., Weckerly, F. W. & Bleich, V. C. (1996). Sexual
segregation in ungulates: new directions for research. J. Mammal.
77: 449–461.
Manly, B. F. J., McDonald, L. L. & Thomas, D. L. (1993). Resource
selection by animals. London: Chapman and Hall.
Miller, J. D. & Schaller, G. B. (1998). Rangeland dynamics in the
Chang Tang Wildlife Reserve, Tibet. In Karakorum-HindukushHimalaya: Dynamics of Change: 125–147. Stellrecht, I. (Ed.).
Koln: Rudiger Koppe Verlag.
Mishra, C. (2001). High altitude survival: conflicts between
pastoralism and wildlife in the Trans-Himalaya. PhD thesis,
Wageningen University.
Mishra, C., Van Wieren, S. E., Heitkönig, I. M. A. & Prins,
H. H. T. (2002). A theoretical analysis of competitive exclusion in
a Trans-Himalayan large-herbivore assemblage. Anim. Conserv.
5: 251–258.
Namgail, T. (2001). Habitat selection and ecological separation
between sympatric Tibetan argali and blue sheep in northern
India. MPhil thesis, University of Tromsø.
Pianka, E. R. (1976). Competition and niche theory. In Theoretical
ecology: 167–196. May, R. M. (Ed.). Oxford: Blackwell
Scientific Publications.
Pianka, E. R. (1978). Evolutionary ecology. 2nd edn. New York:
Harper & Row.
Polunin, O. & Stainton, A. (1985). Flowers of the Himalaya. Oxford:
Oxford University Press.
Repasky, R. R. (1996). Using vigilance behaviour to test whether
predation promotes habitat partitioning. Ecology 77: 1880–
1887.
Schaller, G. B. (1977). Mountain monarchs. Chicago: University of
Chicago Press.
Schaller, G. B. (1998). Wildlife of the Tibetan steppe. Chicago:
University of Chicago Press.
Shackleton, D. M. (1997). Wild sheep and goats, and their relatives.
Cambridge: IUCN.
Sih, A. (1980). Optimal behaviour: can foragers balance two
conflicting demands? Science 210: 1041–1043.
Sih, A., Crowley, P., McPeek, M., Petranka, J. & Strohmeier, K.
(1985). Predation, competition, and prey communities: a review
of field experiments. Ann. Rev. Ecol. Syst. 16: 269–311.
Voeten, M. M. & Prins, H. H. T. (1999). Resource partitioning
between sympatric wild and domestic herbivores in the Tarangire
region of Tanzania. Oecologia (Berl.) 120: 287–294.
Wegge, P. (1979). Aspects of the population ecology of blue sheep
in Nepal. J. Asian Ecol. 1: 10–20.