The structure of terrestrial mammal communities along an elevation gradient in the tropics

Abstract The correlates of mammal species richness and community associations along elevation gradients have resulted in conflicting results within tropical systems. We surveyed the terrestrial mammal and gallinaceous bird community (>200 g body size) along transects at 4 mountain sites in Malaysian Borneo using camera traps to assess structuring of the mammal community along the elevation gradient. Between 2015 and 2021, we surveyed Bukit Lanjak (elevation 1,300 m) in Sarawak (Lanjak Entimau Wildlife Sanctuary; LEWS) and Mts. Kinabalu, Tambuyukon, and Magdalena (up to 2,400 m) in Sabah, with a total sample effort of 20,600 camera nights. We detected 48 species of mammals and 9 species of large terrestrial birds. There was mostly a common species pool across the sites, with only 9 species detected solely in LEWS and 5 species only in Sabah. Over our limited elevation range, no species were detected across the entire elevation range and no common species were confined to the highest elevation sites in Sabah or LEWS (>1,000 m). A species richness curve for each location indicated a slight peak at ~1,000 m for LEWS, but the mid-elevation peak was not evident at Sabah. The individual response curves of relative abundance to the elevation gradient for 15 species with sufficient detections were similar across sites (1 exception—Malaysian Porcupine) with 6 species showing no correlation with elevation, while 4 species increased and 4 species decreased in detections with elevation. A multivariate analysis of species detections found herbivores at lower elevations and mesocarnivores at higher elevations, while species of the same foraging guilds differed in body size at the same elevation. As opposed to studies focused on smaller vertebrate species (i.e., rodents, songbirds), larger mammal and terrestrial bird communities in these mountains did not form unique communities along the elevation gradient but did structure according to the functional traits of foraging guilds and body size. Across 3 mountain elevations in Borneo there were distinct elevation ranges for most species but this did not result in a clear pattern of species richness along the gradients. Species traits seemed to be important with herbivores being more abundant at lower elevations and carnivores/omnivores at higher elevations.