1. INTRODUCTION
Differential resource use allows for diverse species to specialize in
ecological niches and thus coexist in a particular area and this theory
has been stimulated one of the most fertile fields in ecology (Chase and
Leibold, 2003). The requirement-based concept of the ecological niche
(Grinnell, 1917; Hutchinson, 1957) defines it as a function that links
the fitness of individuals to their environment. Whenever several
species co-exist, biotic interactions (like competition, predation,
parasitism, mutualism) affect their fitness and behavior and may
drastically affect their niches (Pearson and Dawson, 2003).
Morphologically and phylogenetically, similar sympatric species are
expected to have niche overlap and competitive interactions under
conditions of limited resources (Schoener, 1974; Putman, 1996). Hence,
potentially competing sympatric species are expected to develop niche
differentiation to avoid or decrease competition (Pianka, 1974;
Schoener, 1974; Putman, 1996). The spatial aspect of niche (habitat) is
the most commonly partitioned resource followed by food (Schoener, 1974,
1983; Toft, 1985). Habitat selection and the niche theory explains that
similar species with similar niches should be allopatric or possess some
of their behavioral aspects that separate them spatially or temporally
within the same range. The coexistence of competitive species co-occurs
in the same habitat as a result of the resource partitioning (Hardin,
1960). Niche breadth can be measured by observing the distribution of
individual organism within a set of resource states. Some plants and
animals are more specialized than others and measure of niche breadth
attempt to measure this quantitatively.
Swamp deer (Cervus duvaucelii ) has been enlisted as the
“vulnerable” in the red list of International Union for Conservation
of Nature (IUCN) (Duckworth et al., 2015b) and is listed on Appendix I
of Convention on international trade in endangered species of wild fauna
and flora (CITES) (CITES, 2019). This deer was extirpated from Chitwan
National Park of Nepal during the 1960s, possibly due to a combination
of factors (e.g. poaching, disease and habitat loss) (Duckworth et al.,
2015b). Swamp deer is one of 27 mammal species strictly protected by the
National Parks and Wildlife Conservation Act 2029 (1973) of Nepal. Swamp
deer mortality is largely by predation, flooding (for R. d.
duvaucelii and R. d. ranjitsinhii ) and poaching. Tiger
(Panthera tigris ) is a major predator of this deer and there are
few reports of kills by leopard (P. pardus ) and dhole (Cuon
alpinus ) (Qureshi et al., 2004). Swamp deer is predominantly a grazer
(Qureshi et al., 2004), but at least R. d. duvaucelii is known to
feed occasionally on aquatic plants, and aquatic plants contribute
significantly to the diet of R. d. ranjitsinhi during the monsoon
and winter (Qureshi et al., 1994).
Spotted deer (Axis axis ) has been enlisted as the “least
concern” in the red list of International Union for Conservation of
Nature (IUCN) (Duckworth et al., 2015a). Spotted deer is a plastic
species capable of considerable adaptive response. This characteristic
is well reflected through its wide-ranging distribution in India and
even where it is an exotic (Dave, 2008). Also, most of the natural
ranges of spotted deer are shared with livestock (Dave, 2008).
In Nepal, out of four localities reported by Schaller (1967), only two
of them hold the species at present. Thus, there are ongoing plans in
Nepal to translocate some of the deer from Suklaphanta National Park
(SNP) to boost the smaller population of Bardia National Park (BNP)
(Duckworth et al., 2015b). The Department of National Parks and Wildlife
Conservation is also looking at the feasibility of re-introducing the
species to Chitwan National Park (CNP) (Duckworth et al., 2015b). At the
same time it is essential to know about the competitive behavior of this
species at its natural habitat. Intensive grazing by large number of
cattle have created severe condition in SNP (Bhattarai, 2012). Domestic
cattle grazing and other disruptions may affect the nutritional
stability of wild animals because they expend additional energy moving
away from the disruptions and may be forced to forage in poor habitats
instead of high-quality patches, and consequently may be competitively
excluded from better habitats (Schaller, 1977). Quantitative studies on
these aspects are required in order to understand the relationships
between domestic cattle and herbivores, which are crucial to
understanding the major factors limiting wild ungulates densities and
formulation of a meaningful conservation plan for the region and
species.
Thus, this study tried to quantify the potential competition based on
overlap in two dimensions, habitat and space, between the indigenous and
domestic species. We focused on swamp deer and spotted deer, living
sympatrically in SNP along with the domestic cattle. This study assessed
the vulnerability of species by determining the niche breadth regarding
habitat use by the species, assessed the habitat overlap among wild and
domestic herbivores and explored whether the potential exists for direct
interspecific competition.