Response of toad tadpoles to conflicting chemical stimuli: predator avoidance versus optimal foraging

Abstract

When injured by predators, Bufo tadpoles release an alarm substance from their skin which triggers conspecifics to move rapidly away from the source of the chemical. To determine whether American toad (Bufo americanus) tadpoles can balance conflicting chemical stimuli associated with avoiding predators and maximizing food intake, I manipulated levels of food and alarm substance in a farm pond in North Carolina, USA. Tadpoles quickly located and exploited food-rich patches that were created experimentally along the shoreline. Skin extracts from a single injured tadpole contained sufficient alarm substance to reduce significantly local tadpole density. Probability of vacating a local feeding area increased with predation risk: i.e., the number of crushed tadpoles used to prepare extracts. The response of tadpoles exposed simultaneously to alarm substance and food was intermediate between that of tadpoles exposed only to alarm substance or only to food. These results support the hypothesis that tadpoles can balance conflicting demands between avoiding predators and maximizing foraging rates.