Ecosystem hero and villain: Native frog consumes rice pests, while the invasive cane toad feasts on beneficial arthropods

Abstract

Lowland irrigated rice fields serve the dual purpose of providing an essential food crop to the world’s most populous regions and functioning as man-made wetlands that harbor a diversity of organisms. Amphibians occupy rice fields throughout Asia and South America, but little is known about their functional role in the rice ecosystem. We conducted field surveys in Los Baños, Philippines over two separate rainy seasons (2015 and 2017) to determine whether native Luzon wart frogs and invasive cane toads consume rice pests, and if so, which species was more effective in doing so. We also examined diet composition to test whether the two species compete for food resources in rice fields. We found that despite smaller body sizes, the Luzon wart frog consumed the same total mass of prey as the cane toad (although it consumed fewer total prey items), and that pests made up the largest proportion (54.1%) of its total diet. In contrast, the majority (89.4%) of the cane toad’s diet consisted of beneficial arthropod predators. Taxonomic analyses of diet composition and breadth revealed that the diet of Luzon wart frog was distinct from that of the cane toad, although there was overlap, and that both species consumed diverse array of prey. Taken together, these data suggest adult Luzon wart frogs may provide effective pest control services, and that they may not be in direct competition over food resources with adult cane toads in rice fields. We also present the first evidence suggesting that cane toads may indirectly damage rice crops by consuming beneficial predators integral to the function of lowland rice ecosystems. We suggest that rice agro-ecosystems should be managed to promote species such as the native Luzon wart frog, and to reduce populations of the introduced cane toad in order to safeguard native biodiversity while simultaneously improving yields and reducing insecticide input.