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RESEARCH ARTICLE
Contents Vol 51(1)

Invasional meltdown-under? Toads facilitate cats by removing a naïve top predator

J. Sean Doody https://orcid.org/0000-0002-9023-6206 A * , David Rhind B , Colin M. McHenry C and Simon Clulow D
+ Author Affiliations
- Author Affiliations

A Department of Biological Sciences, University of South Florida – St. Petersburg, St. Petersburg, FL 33701, USA.

B Department of Environment, Parks and Water Security, Northern Territory Government, P.O. Box 496, Palmerston, NT 0831, Australia.

C School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.

D Centre for Conservation Ecology and Genomics, Institute for Applied Ecology, University of Canberra, Bruce, ACT 2617, Australia.

* Correspondence to: jseandoody@gmail.com

Handling Editor: Jonathan Webb

Wildlife Research 51, WR22177 https://doi.org/10.1071/WR22177
Submitted: 25 October 2022  Accepted: 13 March 2023  Published: 14 April 2023

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing

Abstract

Context

Australia has been a battleground of invasive versus native species for ~200 years. Two of the most impactful invasive species to Australian animal communities are the toxic cane toad (Rhinella marina) and the predatory feral cat (Felis catus). Australia’s native fauna is evolutionarily naïve to both invaders because neither’s taxonomic group is native to the continent. Both invaders have had severe effects on Australian native animal communities including species extinctions, extirpations, and severe population declines, but until now their effects have generally been thought to be independent of one another.

Aims

We aimed to determine the impacts of invasive cane toads on monitor lizards and feral cats by estimating changes in relative abundance before and after the toad invasion.

Methods

We studied toad impacts at three sites in the Kimberley region of northern Australia. We used two methods for estimating relative abundance: camera traps and track station data. Data included greater than 4000 trap days and included 7 years over an 11-year period.

Key results

As expected, invading cane toads rapidly decimated populations of two species of monitor lizards (97–99% declines), including the top-order predatory Varanus panoptes. Unexpectedly, this loss was associated with a >10-fold mean increase in detection rates of cats by 5 years after the loss of V. panoptes, reflecting relative increases of 3.3–8.7 individual cats per site.

Conclusions

Although some unknown factor may have caused an increase in cats, their similar trophic position and niche to V. panoptes suggests that toads facilitated cats by effectively removing the lizards from the animal community. This interaction likely reflects one type of invasional meltdown, whereby a non-native species (cane toad) facilitated any aspect of another’s (feral cat) invasion (e.g. survival, reproduction, resource acquisition), but the latter has no detected influence on the former (+/0 interaction).

Implications

Because both invaders cause declines in animal populations and are difficult to control, the potentially synergistic tandem of cane toads and feral cats could have chronic, irreversible effects on animal communities.

Keywords: cane toad, exploitation competition, Felis catus, invasive species, lethal toxic ingestion, mesopredator release, predator–prey interactions, Rhinella marina.

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