Multiscale distribution models for conserving widespread species: the case of sloth bear Melursus ursinus in India

Abstract

Aim: Information on patterns and determinants of spatial distributions remains poorly available for many widespread species of conservation importance. The sloth bear Melursus ursinus in the Indian subcontinent exemplifies this requirement. We aimed at assessing (1) distribution patterns of sloth bears at two spatial scales, (2) ecological and anthropogenic factors that determine bear occupancy. Location: We estimated sloth bear habitat occupancy at a nationwide scale across India and at the landscape scale (38, 540 km²) in the Western Ghats of Karnataka, India. Methods: We used a grid-based occupancy approach to determine sloth bear distribution patterns. At the nationwide scale, we used data from questionnaire surveys of field experts (grid-cell size ~2818 km²; 1326 cells). At the landscape scale, we conducted field surveys of bear signs (grid-cell size = 188 km²; 205 cells). Detection/non-detection data from both surveys were analyzed using occupancy modelling methods that account for imperfect detection. We examined the influence of scale-specific ecological and social covariates on patterns of occupancy. Results: Nationwide, sloth bears occupied an estimated 67% of plausible bear habitat in contrast to 46% derived from methods that disregard detectability. Bear distribution was positively influenced by deciduous forests, scrub and barren areas, regions with high human densities and cultural tolerance. At the landscape scale, bears occupied 61% of the area versus 54% estimated from methods ignoring detectability. Occupancy probabilities increased with forest cover and topographic heterogeneity, whereas annual precipitation and human disturbance showed negative effects. Main conclusions: Our study underlines the need to integrate human-modified areas with existing conservation landscapes. Given its widespread nature, functional role, conservation status and relatively benign interactions with humans, we propose recognizing sloth bear as an umbrella species for securing unprotected habitats in India. Protection of widespread species like the sloth bear in other landscapes may complement current conservation strategies for large mammalian communities.