Comparison of niche overlaps and niche width between species at
broad and regional scales
At the broad scale (All of Ladakh, three species, three niches), OL
shared a substantial portion of its niche (>%40) with OM
and ON but had a small niche width given that it was elevational
restricted. ON and OM, however, shared very little of their niche with
other species and had large niche widths, given that they were found in
a diversity of microhabitats.
At the regional scale (South-East and North-West Ladakh, three species,
five niches), species shared very little of their niche with others,
suggesting that at smaller spatial scales, all species were unique in
the microhabitats they utilized, mirroring findings in Australian
songbirds (Harmáčková et al.
2019) and sharp-nosed snakes
(Corrêa Nogueira et al.
2019). OM had the largest niche width at the broad scale (generalist)
and some of the smallest niche widths in the South-East (specialists).
This is likely to have occurred due to natural variation in topography
and landscape features across sites, with the species being found in a
wide variety of microhabitats in the North-West compared to the
South-East. ON had intermediate niche width at the broad scale, while at
the regional scale, it had intermediate (North-West) and small
(South-East) niche widths. This is reflective of the exclusive
association of the species with tall mature stands of Caragana
sp. exclusively in South-East Ladakh and with Hippophae sp. in
the North-West, but inhabiting two very different microhabitats at the
broad scale (also explains slight deviation from multivariate normal
distributions in density plots at the broad scale). On the other hand,
OL had the smallest niche width at the broad scale (high elevation
specialist) and an intermediate niche width at regional scales. The
species is restricted in elevational distribution but occurs in
different microhabitats such as alpine meadows/grasslands and Caragana
scrublands at these elevations.
Identifying important ecological factors drive presence of
different species - Ecological factors contributing to different
species’ niches were used to model presence. At different spatial
scales, different variables were significant in predicting the presence
of a species. Such scale-dependent phenomena have been poorly explored
in describing niche spaces and overlaps between species
(Corrêa Nogueira et al.
2019).
At the Ladakh (broad) scale, OM was found in places with a good cover of
large-sized rocks, a high number of large-sized rocks, and a low cover
of tallgrass-reeds (Table 4).
The model suggested that presence was also driven by elevation and cover
of rocks of class size two but not those of class size three (Table 4).
This is likely an artifact of our sampling design (species found in the
elevation bands 3000m-6000m) or a problem of finely dissecting
ecological variables which doesn’t majorly affect our understanding of
how species partition microhabitats. It is worth noting that low cover
of tallgrass-reeds was the only variable related to vegetation that
appeared in the best model. This suggests that refuges are more critical
than resources for microhabitat selection for the species and agrees
with the literature on other rock-dwelling species O. roylei(Bhattacharyya et al. 2015)
and O. princeps (Hall
et al. 2016). However, it remains to be explored if refuges
associated with large-sized rocks offer thermoregulatory benefits to
animals across seasons, as shown for O. princeps(Hall et al. 2016).
At the same scale, ON was likely to occur in areas with high shrub
cover, a higher number of shrubs, and a greater height of shrubs and
other vegetation while actively avoiding areas with high rock cover
(Table 4). Our field observations indicated that ON exclusively
associates with areas with mature stands of scrub vegetationCaragana sp. at high elevations and sea buckthorn
(Hippophae rhamnoides ) at low elevations. While there are reports
of the species using rocks as refuges
(Smith et al. 2010,
Wilson and Mittermeier 2016), we failed to observe such behavior and
documented the use of forms instead (unpublished data).
OL was likely to occur at high elevations characterized by short plants
(stunted growth) on alpine meadows/grasslands, low-lyingCaragana , and cushion plants while avoiding areas with a high
cover of rocks (Table 6).
This study describes, for the first time, niche spaces and overlaps
between three sympatric species of pika from Asia. It illustrates that
sympatric pika communities in Ladakh, India, segregate into different
niches along rocks, vegetation, and elevation axes. There is a lot to
gain from measuring niche space, overlaps, and widths at different
spatial scales since it helps us understand how competition shapes
niches and communities. This also provides opportunities for
conservation planning for pikas in Ladakh’s rapidly developing
landscape.