The role of geography, environment, and genetic divergence on the distribution of pikas in the Himalaya.

Nishma Dahal,Barry R Noon,Uma Ramakrishnan,Sunil Kumar,Rinzin Phunjok Lama,Rajat Nayak

doi:10.1002/ece3.6007

Abstract

Pikas (Ochotona Link, 1795) are high‐altitude specialist species making them a useful bioindicator species to warming in high‐altitude ecosystem. The Himalayan Mountains are an important part of their range, supporting approximately 23%–25% of total pika species worldwide, yet we lack basic information on the distribution patterns. We combine field‐based surveys with genetics‐based identification and phylogeny to identify differences in species‐environment relationships. Further, we suggest putative evolutionary causes for the observed niche patterns.LocationHimalayan high‐altitude region.MethodsWe sampled 11 altitudinal transects (ranging from ~2,000 to 5,000 m) in the Himalaya to establish occurrence records. We collected 223 species records using genetic analyses to confirm species' identity (based on some invasive and mostly noninvasive biological samples). Niche and geographic overlap were estimated using kernel density estimates.ResultsMost pikas in the Himalaya span wide elevation ranges and exhibit extensive spatial overlap with other species. However, even in areas of high species diversity, we found species to have a distinct environmental niche. Despite apparent overlapping distributions at broad spatial scales, in our field surveys, we encountered few cases of co‐occurrence of species in the sampled transects. Deeply diverged sister‐species pair had the least environmental niche overlap despite having the highest geographic range overlap. In contrast, sister‐species pair with shallow genetic divergence had a higher environmental niche overlap but was geographically isolated. We hypothesize that the extent of environmental niche divergence in pikas is a function of divergence time within the species complex. We assessed vulnerability of species to future climate change using environmental niche and geographic breadth sizes as a proxies. Our findings suggest that O. sikimaria may be the most vulnerable species. Ochotona roylii appears to have the most unique environmental niche space, with least niche overlap with other pika species from the study area.

Highlights

Ochotona sikimaria has least geographic breadth, and as expected, the estimated niche breadth was minimum for O. sikimaria despite having a broad elevational range (Table 2)
Niche overlap (D) patterns among pika species from the Himalaya and surrounding ranges are presented in Figure 3 along with two estimates of geographic overlap and genetic distance
Comparisons of niche overlap values among two pair of congeneric species, O. roylii and O. macrotis and, O. sikimaria and O. nubrica, showed contrasting result with higher overlap for the first pair with higher genetic distance compared with the latter conger pair with low genetic distance

Summary

Introduction

Occurrence records of species from less than two localities in the sampled transects (O. ladacensis and O. curzoniae) were excluded for niche analyses as these would capture a limited environmental range of species. Four out of six species, O. sikimaria, O. roylii, O. nubrica, and O. macrotis, had wide altitudinal ranges varying from 2,500 to 4,700 m, 2,800 to 4,900 m, 2,800 to 4,600 m, and 3,000 to 4,800 m, respectively (Supplementary Figure 2).

Results

Conclusion