The food of frogs in a tropical forest

Southeast Asia is home to a highly diverse and endemic frog fauna under great threat. There is an urgent need to gather the information necessary to inform conservation efforts, but very little is known about the ecology of frogs in the region, including their diet. We used stomach flushing to obtain data on dietary composition, feeding strategies, dietary niche breadth, and overlap of nine frog species in a montane forest in Southern Vietnam. We found 31 taxonomic groups of prey in the stomach of studied species, and found that most species were generalists, consuming a wide variety of prey. Our results give us a better understand a poorly-known and highly threatened frog community and how they may respond to a changing habitat.

Frogs play an important role in food webs (who eats what) at both the larval and adult stage. Larval frogs, or tadpoles, are mostly omnivorous (feeding on both vegetables and animal materials such as algae and aquatic insects) and transfer energy from aquatic environments to the land as they metamorphose into terrestrial adults. Adult frogs then transfer energy from the invertebrates they eat to higher trophic levels (as they get eaten). Therefore, an understanding of what frogs eat in natural habitats is important in determining how they affect other organisms in a community and in development conservation plans. This is particularly important in the face of ongoing, worldwide frog declines. Despite its importance, information on the diet of frogs is limited, particularly in regions for which the threats are the greatest.

We investigated the diets and patterns of trophic niche overlap in a montane forest frog community on the Langbian Plateau, in southern Vietnam. The amphibian community of the area is threatened by ongoing habitat loss and modification, but our understanding of the basic biology, ecology, and dietary patterns of the frog fauna is deficient. Our study streams were located evergreen forest above 1,000 m elevation. We searched for frogs at night, identifying each frog found and then used stomach flushing to examine diet.

After sampling over 200 individuals of nine frog species, we detected 381 prey items belonging to 31 prey groups. Arthropods (insects) dominated in diets of all nine species. In the Belly-spotted frog (Kurixalus baliogaster), wild cockroaches were the most abundant and frequently consumed prey, while beetles, crickets, spiders and butterflies were the four main prey types in the other species.

Among the nine frog species studied, only the Vietnam Spadefoot Toad (Leptobrachium pullum) showed a high degree of specialization towards crickets, with other food categories consumed only occasionally. Being a dietary specialist and forest-dependent species, the Vietnam Spadefoot Toad may be highly sensitive to environment change and therefore more likely to suffer population declines as a result of habitat loss and modification.

Our study provides the first information on the dietary patterns of a frog community in Vietnam. Data on feeding strategies and dietary selection of the frog species of provide information useful for understanding how species co-exist in tropical habitats and may be helpful in informing conservation management of frog species in the face of habitat loss and modification.

Le Thi Thuy Duong
Faculty of Biology and Biotechnology, University of Science, Vietnam National University-HCMC
Jodi Rowley
Curator of Amphibian & Reptile Conservation Biology, Australian Museum & UNSW

More information:
Le, D.T.T., Rowley, J.J.L., Tran, T.A.D., Vo, N.T., and Hoang, H.D. (2018). Diet composition and overlap in a montane frog community in Vietnam. Herpetological Conservation and Biology. 13(1):205-215.