The impact of invasive cane toads on native wildlife in southern Australia

Abstract

Commonly, invaders have different impacts in different places. The spread of cane toads (Rhinella marina: Bufonidae) has been devastating for native fauna in tropical Australia, but the toads' impact remains unstudied in temperate-zone Australia. We surveyed habitat characteristics and fauna in campgrounds along the central eastern coast of Australia, in eight sites that have been colonized by cane toads and another eight that have not. The presence of cane toads was associated with lower faunal abundance and species richness, and a difference in species composition. Populations of three species of large lizards (land mullets Bellatorias major, eastern water dragons Intellagama lesueurii, and lace monitors Varanus varius) and a snake (red-bellied blacksnake Pseudechis porphyriacus) were lower (by 84 to 100%) in areas with toads. The scarcity of scavenging lace monitors in toad-invaded areas translated into a 52% decrease in rates of carrion removal (based on camera traps at bait stations) and an increase (by 61%) in numbers of brush turkeys (Alectura lathami). The invasion of cane toads through temperate-zone Australia appears to have reduced populations of at least four anurophagous predators, facilitated other taxa, and decreased rates of scavenging. Our data identify a paradox: The impacts of cane toads are at least as devastating in southern Australia as in the tropics, yet we know far more about toad invasion in the sparsely populated wilderness areas of tropical Australia than in the densely populated southeastern seaboard.

Keywords: Bufo marinus; ecological impact; invasive species; predator–prey; surveys.

Figure 1

Study site locations within the Northern Rivers region, New South Wales, Australia, depicting toad‐present (■) and toad‐absent (□) campgrounds, which were surveyed between October 2013 and February 2014.

Figure 2

Impacts of cane toad presence on (A) mean abundance per site (± SE) and (B) mean species richness per site (± SE) of native fauna encountered in campgrounds and surrounding bushland areas in northeastern New South Wales, Australia.

Figure 3

A nonmetric multidimensional scaling (nMDS) ordination plot showing the composition of faunal assemblages sampled from toad‐present (solid circles) and toad‐absent (open circles) campground sites in northeastern New South Wales, Australia (stress = 0.13).

Figure 4

Impacts of cane toad presence on the mean per site abundance (± SE) of (A) lace monitors (Varanus varius), (B) water dragons (Intellagama lesueurii), (C) land mullets (Bellatorias major), (D) black snakes (Pseudechis porphyriacus), and (E) brush turkeys (Alectura lathami) encountered during surveys of sites in northeastern New South Wales, Australia.

Figure 5

Impacts of cane toad presence and habitat type on mean number (± SE) of chicken necks removed from camera‐monitored bait stations in campgrounds and surrounding bushland areas in toad‐present and toad‐absent areas of northeastern New South Wales, Australia.