Unpalatability in anuran larvae as a defense against natural salamander predators

Abstract

Throughout the animal kingdom, there is a general correlation between conspicuousness and qualities that are aversive to predators. The larvae of certain species of anuran amphibians form extremely large, conspicuous, aggregations composed of thousands of individuals. Members of these aggregations are not overtly attacked or eaten by vertebrate predators. The larvae of other anuran species are cryptic, form small aggregations, disperse rapidly from and are readily eaten by vertebrate predators. In conjunction with forming large, conspicuous groups, unpalatability may be one means by which larvae in conspicuous groups avoid predation. Therefore, in the laboratory, we used natural salamanders as predators to investigate relative payabilities of the larvae of three species of anurans that differ in their mode of aggregation. The larvae of the western toad (Bufo boreas) form large conspicuous aggregations and are not conspicuously attacked by most vertebrate predators. The larvae of the Cascades frog (Rana cascadae) and Pacific treefrog (Hyla regilla) form small aggregations and readily flee from and are taken by vertebrate predators. Proportionately fewer Bufo than Rana and Hyla tadpoles of similar size and same developmental stage were consumed by salamanders. Differential predation on Bufo, Rana and Hyla tadpoles was probably due to distasteful qualities of Bufo larvae as opposed to differences in prey size or escape ability. Most Bufo tadpoles captured by salamanders were rejected unharmed. Rana and Hyla tadpoles were palatable at all stages of development tested.