Predaceous diving beetles (Coleoptera : Dytiscidae) may affect the success of amphibian conservation efforts

Jose W Valdez

doi:10.1071/zo19039

Abstract

The role of invertebrate predation in shaping vertebrate communities is often overlooked. This is evident with predaceous diving beetles (Coleoptera: Dytiscidae), which are often the top predator in many aquatic freshwater habitats. During weekly monitoring of a reintroduction for an endangered frog, a group of a dozen adult diving beetles were encountered attacking and quickly dismembering and consuming a tadpole. A single adult diving beetle was also discovered burrowing its head inside and consuming a tadpole approximately 3–4 times its size by seemingly piercing its prey to suck out its liquefied remains. This is in contrast with the well known behaviour of adult dytiscids, which involves tearing prey into small pieces with their chewing mouthparts. Although dytiscids are known to occasionally consume vertebrates such as tadpoles, adults are typically considered scavengers, and this communal predatory behaviour and feeding method have not previously been documented. Moreover, over 80% of the tadpoles in the monitored site were found in ponds with no beetles and despite representing only a quarter of all ponds, half of the tadpoles across the landscape were in ponds free of diving beetles, demonstrating a possible influence of diving beetles on tadpoles. These observations may have implications for amphibian conservation since management efforts are not typically concerned with naturally occurring ubiquitous threats such as those from small invertebrate predators, as it has rarely been observed in nature. Although amphibian conservation plans expect some losses from natural predation, diving beetles may affect conservation efforts such as captive breeding and reintroductions with populations where every individual is critical to success.

Highlights

In-situ and ex-situ conservation programs, including reintroductions to formerly occupied sites and translocations to compensatory habitats, have emerged as key management tools to mitigate the global decline of amphibians (Biega et al 2017; Harding et al 2016; Heatwole et al 2018; Zippel et al 2011)
Besides the novelty of these behaviors, it was concerning how vicious and quickly the adult diving beetles consumed their much larger tadpole prey, especially considering that predation occurred within a managed compensatory habitat enclosed by predator-proof mesh designed to protect the managed sympatric species from large vertebrate predators
Diving beetles were not observed predating on tadpoles of the reintroduced L. aurea species, it is possible that this interaction could at least partly explain the few remaining adults and lack of recruitment after only three years, despite being one of, if not the largest, amphibian reintroductions in Australia with 10,000 tadpoles originally released (Valdez et al 2017)

Summary

Introduction

In-situ and ex-situ conservation programs, including reintroductions to formerly occupied sites and translocations to compensatory habitats, have emerged as key management tools to mitigate the global decline of amphibians (Biega et al 2017; Harding et al 2016; Heatwole et al 2018; Zippel et al 2011). Recent evidence suggests that adults have the capability to predate on larger vertebrates but that their predatory behavior can have drastic effects on populations of endangered species (Bittel 2019).

Results

Conclusion