Richness and size distribution of large herbivores in the Himalaya

Species diversity across several taxa ranging from plants to vertebrates isreported to decrease with altitude, or to show a mid-elevation peak in mountainsystems. Plant biomass availability for herbivores is similarly expected to declinewith altitude as temperature becomes limiting. However, the relationship betweenherbivore species richness and altitude has not been examined in detail. We showthat while the overall regional pattern (gamma-richness) for 25 large-herbivorespecies (56 % grazers, 44 % browsers/mixed feeders) in the Western Himalayasshows a mid-elevation peak, the species richness of grazers increases nearlymonotonically with altitude peaking at 4000–5000 m. Median body mass of herbivores decreased with altitude, suggesting greater suitability of higher elevationsfor smaller bodied herbivores. We propose that seasonal altitudinal migrationpatterns, biogeographic influences, increases in the abundance of graminoids, andan increase in plant nutrients with altitude might explain the unusual high grazerspecies richness at higher altitudes in the Himalayan Mountains.