Identifying optimal barriers to halt the invasion of cane toads Rhinella marina in arid Australia

Abstract

Summary Spatial heterogeneity in environmental conditions may restrict the spread of invasive species to narrow corridors between extensive patches of suitable habitat; thus, we may be able to curtail invasions by identifying such corridors, and focusing control efforts in these areas. Invasive cane toads Rhinella marina have spread rapidly through northern Australia, but to invade further into Western Australia, the toads must traverse a narrow arid corridor where artificial waterbodies may serve as critical stepping stones for range expansion. We focus on the cane toads' imminent expansion into north‐western Australia and use stochastic simulation to identify areas in which removal of artificial waterbodies would be most effective at stopping their spread. Our model predicts that toads will spread from the Kimberley to the Pilbara regions of Western Australia through a narrow coastal corridor, but that they will depend upon artificial waterbodies to do so. Importantly, excluding toads from artificial waterbodies is predicted to prevent toads from colonizing c. 268 200 km2 of their potential range in Western Australia. We identified three locations where closure of a relatively small subset of artificial waterbodies is predicted to halt the spread of toads. Synthesis and applications. We present a modelling framework that can be used to focus management activities within invasion corridors. Our analyses suggest that strategic removal of potential invasion hubs along such corridors can halt the spread of an invasive species.

Invasive cane toads might initiate cascades of direct and indirect effects in a terrestrial ecosystem

“…Thus, during the wet season, encounters between cane toads and goannas could occur anywhere in the landscape, while in the dry season goannas would most likely encounter toads within 500 m of permanent water (Florance et al 2011). However, during the wet season, the density of cane toads and hence likelihood of a goanna encountering a cane toad should decrease with distance from refuges because as they disperse they are in effect diffusing away from a point source (Florance et al 2011;Tingley et al 2013). We contend then that the patterns in goanna and small lizard abundance we report are legacy effects that reflect higher encounter rates between goannas near (\ 3 km) sources of permanent water during both the wet season and dry season.…”

Invasive Aquatic Animals

“…When introduced, it spreads over wide ranges, as in Australia where it moved more than 2000 km over 75 years. Barriers to expansion of cane toad infestations include restricting access to water by fencing or draining (Tingley et al, 2013). Some Australian predators recovered 10 years or more after cane toad invasion by learning to avoid the toads.…”

The on‐ground feasibility of a waterless barrier to stop the spread of invasive cane toads in Western Australia

“…Simulation modeling has identified multiple areas within the Kimberley-Pilbara corridor where excluding toads from approximately 100 artificial water points could halt expansion of the toad front indefinitely (Southwell et al, 2017;Tingley et al, 2013). During the dry season, water sources will be crucial to toad survival in the corridor.…”

“…By managing artificial water points, we could create a "waterless barrier," protecting the biodiverse Pilbara region and up to 268,200 km 2 of mainland Australia from the toad's impact (Tingley et al, 2013). Modeling and sensitivity analyses suggest that such a barrier will hold even under a string of extremely wet years (Southwell et al, 2017;Tingley et al, 2013). In two possible locations the barrier would need to be approximately 70 km wide and, to implement, would cost approximately $4.5 million over 50 years (Southwell et al, 2017).…”