Elevation Filters Lizard Species Occurrences and Assemblages in Chitwan Annapurna Landscape, Nepal

Understanding elevational patterns of biodiversity is essential for conservation planning. However, the spatial distribution pattern of lizards in the central Himalayan elevation gradient has rarely been investigated or is mostly from outdated literature. We carried out a study on the occurrence and associated factors of lizard species across the elevation gradients of Chitwan Annapurna Landscape (CHAL) during 2018-2019. This study was carried out by visual encounter survey along the transects (100 × 5 m) and examined the patterns of lizard species richness. We reported 23 species of lizards across our study where most observed species were Calotes versicolor (n = 405), followed by Hemidactylus flaviviridis (n = 250), and Laudakia tuberculata (n = 128), whereas the least observed species were Phrynocephalus theobaldi, Asymblepharus nepalensis, and Lygosoma albopunctata which were observed only twice. We observed that species richness varied significantly with elevation (Kruskal-Wallis χ ² = 41.29, p = 0.0076), although the monotonic relationship was weak (Spearman's ρ = 0.071, p = 0.031). Beta diversity was mostly driven by species turnover rather than nestedness. We observed significant non-linear impact of elevation on gamma diversity (edf = 2.92, p < 0.001), where terrain ruggedness positively influenced the lizard species richness (β = 0.383, p < 0.001) and canopy cover had a negative effect (β = -0.154, p = 0.033). Our study demonstrates that the lizard diversity in CHAL is structured by non-linear elevational dynamics and microhabitat heterogeneity. Also, we found a strong turnover of species across elevation bands. These results emphasize the ecological need to consider ecotonal zones and topographic complexity to conserve and maintain reptilian diversity in the Nepal Himalayas. Further, detailed and long-term studies are needed to develop conservation initiatives and fill gaps in knowledge of lizards in the human-dominated fragmented landscape of the Central Himalayas.