Introduction
The conceptualization of the fundamental and the realized niche
(Grinnell 1917,
Hutchinson 1957) of species has been particularly valuable to the
growth of community ecology
(Roughgarden 2009),
evolutionary biology (Sexton
et al. 2017), and in understanding distribution patterns across space
to inform conservation planning
(Pulliam 2000,
Ahmad et al. 2021, Dvořák et al. 2022). The niche mathematically
represents an n-dimensional hypervolume that describes the range of
biotic and abiotic factors in which the animal can survive and reproduce
(Grinnell 1917,
Hutchinson 1957). The width of the niche and the degree to which it can
be found in niches of other animals can be used to assess species on the
generalist-specialist continuum
(Fridley et al. 2007).
Species attributes that promote stable co-existence of ecologically
similar species in communities have intrigued researchers for a long
time, starting with competitive exclusion experiments in the 1930s
(Gause
1936, MacArthur 1958, Hardin 1960, Hutchinson 1961, Slatkin 1974, Hanski
and Ranta 1983, Nardone and Gherardi 1997, Sommer 1999). Community
assemblages or niches are known to be shaped by abiotic and biotic
filtering where physiological limits and biological interactions such as
competition for resources and predation limit species occurrence and
co-existence
(Schoener
1974,
Martin
1988, Dunson and
Travis 1991, Weiher and Keddy 1995, Weiher et al.
1998,
MacRae and
Jackson 2001, Stoks and McPeek 2003,
Cavender-Bares
et al. 2004, Dayan and Simberloff 2005, Bøhn et al. 2008, Pfennig and
Pfennig
2009,
Colman et al. 2014). In this manuscript we describe the niche
space, overlaps and partitioning between three sympatric species of
pikas (Ochotonidae ) from the high elevation trans-Himalayas
(3000m-6000m) of Ladakh, India.
Interspecific competition is known to alter the niche width of species
and affect community structuring through population sizes of different
species
(MacArthur
1958, Connell 1961, Mac Nally and Timewell 2005, Luiselli 2006, Bolnick
et al. 2010, Stellati et al. 2021). Spatially heterogeneous/patchy
environments allow for the co-existence of ecologically/closely related
species by alleviating competition through ecological specialization
(Hanski
1983, Hanski and Ranta 1983, Holt 1987, Chesson 2000, Amarasekare
2003). This is facilitated by differential habitat/microhabitat
selection or use at spatial
(Chipps
et al. 1994, Satoh and Hori 2005, Malavasi et al. 2007, Tamme et al.
2010, Sillero et al. 2020, Gurvich et al. 2022) and temporal scales
(Townsend
and Hildrew 1979, Faria and Almada 2001, Castro-Arellano and Lacher
2009, Lea et al. 2020). Although microhabitat selection between closely
related species can reduce competition
(Majumder et al.
in press, Goulart et al. 2009, Lea et al. 2020), it is often hard to
establish that competition has driven this selection over and above
other biotic and abiotic filtering mechanisms
(Shanker
2001, Zhang et al. 2006, Afonso and Eterovick 2007, Crow et al. 2010).
The trans-Himalayas of Ladakh, India, are home to asocial rock-dwelling
(Ochotona macrotis: OM ) and social burrowing species
(Ochotona ladacensis: OL, Ochotona nubrica: ON ). While OMis found in rocky talus and scree slopes in alpine deserts
(2300m-6000m), ON is a burrowing species that uses thorny
vegetation, rocks when availbale (2800m-5300m) and with
(Pfister 2004,
Wilson and Mittermeier 2016, Smith et al. 2018). OL, on the
other hand, is associated with barren xeric alpine valleys at
high elevations characterised by cushion plants and sedges
(Pfister 2004,
Wilson and Mittermeier 2016, Smith et al. 2018) (4200m-5400m). A
photographic representation of these microhabitats reveals differences
and similarities of niches of different species (Figure 1). WhileOM and OL (clade Conothoa) have diverged
~5mya, these species have diverged from ON (cladeOchotona ) 13mya
(Wang et al. 2020,
Lissovsky et al. 2022). Assuming that closely related species share
similar physiological requirements, we would expect that OM andOL use similar microhabitats when compared to ON(Dahal et al. 2020).
In this study, we describe the ecological niche space of different
species of sympatric pikas in Ladakh and address if they use different
microhabitats. In addition, we examine how various ecological factors
drive pika presence at high elevations in Ladakh, India, by documenting
microhabitat level features (variables related to rocks and vegetation)
and topographic features (elevation, slope, aspect) at different spatial
scales. Studies on Neotropical snakes
(Corrêa Nogueira et al.
2019) and Austalian songbirds
(Harmáčková et al. 2019)
found evidence for scale-dependent phenomena of niche spaces and
overlaps between species but such studies of niches at different spatial
scales are generally rare. A well-defined study at varying spatial
scales would not only provide a framework to describe niches of species,
address evolutionary drivers of such choice, but also allow for
exploration of proximate factors that drive presence and directly feed
back into conservation planning
(Lian and Jianping
2005, Edgel et al. 2014). Pikas are high-elevation specialists under
threat of extirpation due to climate change, and describing their niches
will provide baseline data for effective policy-making in the
trans-Himalayas
(Beever et al.
2010, 2011, Dahal et al. 2020).