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).