A first-of-its-kind dietary study conducted in the semi-arid deciduous forests of the Aravalli mountains in Rajasthan has found that seasonal diet shifts and seed dispersal by sloth bears are helping several plant species multiply across the landscape. The research, accepted for publication in the international journal Biotropica, offers rare insight into the ecological role of large omnivorous mammals in seasonally dry forests.

What the Study Found

Researchers analysed sloth bear scat collected across winter and summer seasons to assess dietary variation and seed dispersal effectiveness. They found that the bears' diet shifts markedly with the seasons — fruits dominate winter diets, while insects and termites make up a larger proportion during summer, demonstrating considerable dietary flexibility in response to seasonal resource fluctuations.

Seeds of six plant species were found viable after passing through the bears' digestive systems. Germination success varied across species, but the results pointed to a meaningful dispersal function. Notably, the germination of the non-native invasive shrub Lantana camara occurred exclusively from scat-derived seeds — a finding that raises questions about the bear's inadvertent role in spreading an invasive species.

Species-Level Germination Outcomes

For four species, post-germination survival of seedlings from scat seeds was not significantly different from those collected directly from plants. However, seedlings of donkey berry (Grewia flavescens) from plant-collected seeds survived better, while seedlings of Coromandel ebony (Diospyros melanoxylon) from scat seeds showed higher survival — suggesting the gut-passage effect is species-specific rather than uniformly beneficial or harmful.

The study also noted that fruit consumption was selective and not consistently proportional to availability, indicating preferential foraging behaviour rather than opportunistic feeding.

Ecological Significance

'Our findings demonstrate that sloth bears function as selective seed dispersers, including enhancing the germination success of an invasive shrub in dry deciduous forests,' researcher K.S. Gopi Sundar said. 'Our findings highlight the importance of increasing focus on how large omnivores influence plant regeneration, thereby potentially affecting landscape-level vegetation dynamics in tropical seasonal ecosystems,' he added.

The study argues that in seasonal tropical systems — where resource availability fluctuates sharply — the ecological roles of mammals are tightly coupled with dietary plasticity. Such plasticity can stabilise ecological interactions but can also significantly shape patterns of plant recruitment and community composition, particularly in water-limited dry forests.

About the Sloth Bear and the Research Team

The sloth bear (Melursus ursinus), listed as 'Vulnerable' by the International Union for Conservation of Nature (IUCN) and endemic to the Indian subcontinent, was chosen as a model species for examining linkages between seasonal diet, resource availability, and seed dispersal. Although morphologically adapted for insect-feeding, the species exhibits pronounced dietary variability, incorporating fruits when available.

The study was undertaken by researchers Utkarsh Prajapati, K.S. Gopi Sundar, and Vijay Kumar Koli. Sundar is an independent researcher; Koli is affiliated with a university in Udaipur; and Prajapati conducted the research as part of his doctoral requirements. The authors note that very few prior studies have integrated diet analysis of sloth bears with experimental germination and survival tests, limiting earlier understanding of the ecological consequences of fruit consumption by the species.

As the findings make their way into peer-reviewed literature, conservationists and forest managers in the Aravalli region may need to factor the sloth bear's dispersal role — including its spread of invasive species — into landscape management strategies.