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Rapid expansion of the cane toad (Bufo marinus) invasion front in tropical Australia

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Abstract

Abstract  Cane toads (Bufo marinus) are large toxic anurans that have spread through much of tropical Australia since their introduction in 1935. Our surveys of the location of the toad invasion front in 2001 to 2005, and radiotracking of toads at the front near Darwin in 2005, reveal much faster westwards expansion than was recorded in earlier stages of toad invasion through Queensland. Since reaching the wet-dry tropics of the Northern Territory, the toads have progressed an average of approximately 55 km year−1 (mean rate of advance 264 m night−1 along a frequently monitored 55-km road transect during the wet season of 2004–2005). Radiotracking suggests that this displacement is due to rapid locomotion by free-ranging toads rather than human-assisted dispersal; individual toads frequently moved >200 m in a single night. One radiotracked toad moved >21 800 m in a 30-day period; the fastest rate of movement yet recorded for any anuran. Daily displacements of radiotracked toads varied with time and local weather conditions, and were highest early in the wet season on warm, wet and windy nights. The accelerated rate of expansion of the front may reflect either, or both: (i) evolved changes in toads or (ii) that toads have now entered an environment more favourable to spread. This accelerated rate of expansion means that toads will reach the Western Australian border and their maximal range in northern Australia sooner than previously predicted.

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