Predation of two common native frog species (Litoria ewingi and Crinia signifera) by freshwater invertebrates

Abstract

The primary aim of this study was to identify aquatic invertebrate predators of amphibian eggs and tadpoles in an area of South Australia. The presence and abundance of aquatic invertebrates was monitored at four field sites for a period of 5–6 months; this revealed notonectids, freshwater crayfish and odonates to be amongst the most common invertebrate predator types. The ability of these predators to consume eggs and tadpoles of the native Australian frogs Litoria ewingi and Crinia signifera was then investigated. Freshwater crayfish (Cherax destructor) were the most prolific consumers of frog eggs and tadpoles. The notonectid Enithares woodwardi significantly impacted tadpole survivorship for both species while Anisops sp. was less successful at capturing and consuming these tadpoles. Caddisfly nymphs (Lectrides varians and Leptorussa darlingtoni) reduced egg survivorship but not to the same extent as C. destructor. Unlike some predators, which prey upon particular life stages, freshwater crayfish are large, polytrophic omnivores that can act as important predators of both anuran eggs and tadpoles. Given that predation is a key source of mortality in juveniles, identification of likely common predators is useful for understanding the regulation of amphibian populations.