Sloth bears shape dry forests by dispersing seeds, study finds

A study conducted in the Kumbhalgarh and Todgarh-Raoli wildlife sanctuaries in Rajasthan's Aravalli hills has found that sloth bears act as significant seed dispersers in dry deciduous forests. Researchers collected 180 scat samples across winter and summer seasons between November 2021 and July 2022, identifying 38 dietary items. The analysis revealed a strong seasonal diet shift: plant material dominated in winter, while insects such as termites became the primary food source in summer, a pattern the authors suggest may have been influenced by wetter-than-normal summer conditions associated with La Niña.

The bears showed distinct fruit preferences rather than consuming fruits solely based on availability. Grewia flavescens was the most important fruit species in both seasons, while Ziziphus nummularia featured heavily in winter and Cassia fistula in summer. Ants appeared in over 80% of winter scats, and termites in over half of summer scats, indicating high adaptability in foraging behavior.

To test seed dispersal effectiveness, researchers selected the eight most consumed plant species and compared germination of seeds recovered from bear scats with seeds collected directly from trees. Seeds from six species remained viable after gut passage. For several species, including Ziziphus nummularia, scat-derived germinated earlier — around 50 days versus 100 days for tree-collected seeds. Seedling survival rates were broadly similar between the two sources, though Diospyros melanoxylon seedlings from bear-dispersed seeds survived better, while Grewia flavescens seedlings from tree seeds showed higher survival.

A striking finding involved the invasive shrub Lantana camara. In the experiment, lantana seeds germinated only after passing through a sloth bear's digestive tract; none of the 25 seeds collected directly from fruits germinated. Three of 25 scat-derived lantana seeds sprouted, suggesting bears may contribute to the plant's spread across large home ranges, though birds likely remain the primary dispersers.

The researchers emphasize that omnivores like sloth bears play understudied ecological roles in Indian forests, where conservation focus often centers on predators and herbivores. The findings highlight the need for long-term research to understand whether the observed patterns hold across other regions and years, and to quantify the relative contributions of different animal taxa to forest structure.

Co-author K.S. Gopi Sundar noted that dry deciduous forest plant compositions appear to be a function of sloth bear presence, movement, and dietary habits. The study underscores the importance of maintaining species diversity so that ecological benefits are distributed across a variety of species, not only flagship predators.