Oviposition sites and fish-deterrent mechanisms of two stream anurans

I studied fish-deterrent mechanisms of two coexisting anurans, Rana palustris (pickerel frogs) and Bufo americanus (American toads), from an intermittent stream in west-central Kentucky. Females of both anurans tended to oviposit in areas with few, if any fish. Pickerel frog females deposited more egg masses in upstream reaches with lower fish densities than in downstream reaches with higher fish densities. Female American toads often oviposited in fishless, isolated pools disconnected from the stream, whereas female pickerel frogs seldom used these habitats. Fish presence and habitat persistence may jointly influence oviposition site choice by females. Anticonsumption mechanisms displayed by tadpoles of both species included the use of fish-inaccessible areas (channel margins) and activity reductions elicited through detection of fish (Lepomis) chemical cues. Pickerel frog and American toad tadpoles, however, differed in susceptibility to predation by longear sunfish but not to green sunfish. Significantly more toad tadpoles were eaten by longear sunfish over 24 h than were pickerel tadpoles, suggesting pickerel frog tadpoles were less palatable than toads. Green sunfish readily consumed both species. Both anurans possess a suite of antipredator mechanisms at adult and larval stages that facilitate local coexistence with predatory fish.