Population and behavioural responses of rodents and reptiles to woody encroachment in the Thar desert

Abstract

Woody encroachment is increasingly modifying open ecosystems worldwide, often altering trophic-level interactions and species composition. In the Indian Thar Desert, Calotropis procera is rapidly expanding across grassland and scrubland habitats, but its ecological consequences for desert fauna remain poorly understood. This study assessed the effects of varying levels of Calotropis procera encroachment on habitat structure, predation pressure, and behaviour and abundance of nocturnal rodents and two diurnal lizard species in and around Desert National Park, Jaisalmer. Field surveys were conducted across no, moderate, and high encroachment levels of C. procera during 2025–2026. Responses of nocturnal rodent community were assessed through burrow counts and giving-up density (GUD) experiment. Reptile responses were assessed through abundance surveys and flight-initiation distance (FID) experiment, and clay model experiment was designed to quantify predation pressure. Rodent abundance, measured through active burrow counts, declined from no encroachment plots to moderate and high encroachment levels. Conversely, giving-up density at artificial food patches was greater in no encroached plots - indicative of greater predation risk perception - compared to moderately and highly encroached habitats. Lunar illumination interacted with encroachment level to influence rodent foraging decisions, indicating the role of habitat structure and environmental conditions in shaping behavioural responses to predation risk. Reptile species exhibited contrasting responses to woody encroachment. Acanthodactylus cantoris showed declines in abundance with increasing encroachment. Behavioural response mirrored this pattern. Flight-initiation distance of Acanthodactylus cantoris decreased substantially with increasing encroachment. In contrast, Trapelus agilis occurred at higher densities in highly encroached areas than non-encroached areas and its FID was primarily influenced by refuge availability and starting distance rather than encroachment level. Predation-risk experiment revealed context-dependent effects of encroachment. In scrubland habitat, predation was faster in moderate and high encroachment plots than in no encroachment. Habitat influenced predation pressure too, as clay models faced higher predation rate in grassland than scrubland. This study demonstrates that woody encroachment produces species-specific ecological consequences, and continued expansion of Calotropis procera has the potential to reshape community composition through behavioural responses and trophic interactions, in the Thar Desert. Management interventions aimed at maintaining and preserving open habitats may therefore be important for conserving faunal diversity in this important conservation ecosystem.