Non-native populations and global invasion potential of the Indian bullfrog Hoplobatrachus tigerinus: a synthesis for risk-analysis

Invasive amphibians have considerable ecological and socio-economic impact. However, strong taxonomic biases in the existing literature necessitate synthesizing knowledge on emerging invaders. The Indian bullfrog, Hoplobatrachus tigerinus, a large dicroglossid frog (snout to vent length: up to 160 mm), is native to the Indian sub-continent. Despite the high likelihood of invasion success for H. tigerinus, based on the species’ natural history traits and human use, the status of its non-native populations and global invasion potential has not yet been assessed. In this paper, we provide a profile of H. tigerinus as an invasive species to aid in risk analyses and management of existing populations. We review the available knowledge on non-native populations of H. tigerinus and model its potential distribution in the non-native range and globally; finally, we evaluate its ecological and socio-economic impact using standard impact classification schemes. We confirm successful invasions on the Andaman archipelago and Madagascar. The ensemble species distribution model, with ‘good’ predictive ability and transferability, predicts tropical regions of the world to be climatically suitable for the species. Considering potential for propagule pressure, we predict the climatically suitable Mascarene Islands, Malaysia and Indonesia, and East Africa to likely be recipients of bridgehead invasions. We assign the species two impact scores: both socio-economic and environmental scores were ‘moderate’ with ‘medium’ confidence levels in our assessment. Finally, this synthesis outlines the invasion process of the genus Hoplobatrachus, which is an emerging group of amphibian invaders.