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.
Highlights
Invasive species imperil native biodiversity (Mack et al 2000; McGeoch et al 2010), but invader impacts are highly heterogeneous (Melbourne et al 2007)
Many native taxa of this region are most active in the warmer, wetter months (September to February: Shine 1979; York et al 1991; Christian and Weavers 1996; Kavanagh and Stanton 2005; Daly and Lemckert 2011), so we confined our surveys to the spring and summer months of 2013–2014
Combining counts for all native species, toad-occupied areas contained 40% fewer animals and 31% fewer species (F1,14 = 11.82, P = 0.004; Fig. 2B) than did areas without toads
Summary
Invasive species imperil native biodiversity (Mack et al 2000; McGeoch et al 2010), but invader impacts are highly heterogeneous (Melbourne et al 2007). Impact heterogeneity necessitates studies at multiple locations throughout an invader’s range (Parker et al 1999; Melbourne et al 2007). To assess an invader’s effects, we must measure changes in abundance of native species coincident with the presence of an invader. This task may be simple in some cases (e.g., for sessile organisms), but is more challenging if the impact falls on vagile, rare predators (Caughley 1977; Woinarski et al 2001, 2004). To incorporate the influence of habitat and climate, studies of invader impacts on large, mobile vertebrates must employ multiple sites with a sampling design that captures a range of natural heterogeneity
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