What's for dinner? Diet and potential trophic impact of an invasive anuran Hoplobatrachus tigerinus on the Andaman archipelago

Abstract

Amphibian invasions have considerable detrimental impacts on recipient ecosystems. However, reliable risk analysis of invasive amphibians still requires research on more non-native amphibian species. An invasive population of the Indian bullfrog, Hoplobatrachus tigerinus, is currently spreading on the Andaman archipelago and may have significant trophic impacts on native anurans through competition and predation. We carried out diet analyses of the invasive H.Tigerinus and native anurans, across four habitat types and two seasons; we hypothesized that (i) small vertebrates constitute a majority of the H.Tigerinus diet, particularly by volume and (ii) the diet of H.Tigerinus significantly overlaps with the diet of native anurans, thereby, leading to potential competition. We assessed the diet of the invasive H.Tigerinus (n = 358), and individuals of the genera Limnonectes (n=375) and Fejervarya (n=65) and found a significant dietary overlap of H.Tigerinus with only Limnonectes. Small vertebrates, including several endemic species, constituted the majority of H.Tigerinus, diet by volume, suggesting potential impact by predation. Prey consumption and electivity of the three anurans indicated a positive relationship between predator-prey body sizes. Individuals of H.Tigerinus and Fejervarya chose evasive prey, suggesting that these two taxa are mostly ambush predators; individuals of Limnonectes chose a mixture of sedentary and evasive prey indicating that the species employs a combination of active search' and 'sit and wait' foraging strategies. All three species of anurans mostly consumed terrestrial prey. This intensive study on a genus of newly invasive amphibian contributes to knowledge of the impact of amphibian invasions, and elucidates the feeding ecology of H.Tigerinus, and species of the genera Limnonectes and Fejervarya. We also stress the necessity to evaluate prey availability and volume in future studies for meaningful insights into diet of amphibians.