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The ecological impact of invasive cane toads (Bufo marinus) in Australia

School of Biological Sciences A08, University of Sydney, NSW 2006, Australia.
The Quarterly Review of Biology (Impact Factor: 5.06). 09/2010; 85(3):253-91. DOI: 10.1086/655116
Source: PubMed

ABSTRACT Although invasive species are viewed as major threats to ecosystems worldwide, few such species have been studied in enough detail to identify the pathways, magnitudes, and timescales of their impact on native fauna. One of the most intensively studied invasive taxa in this respect is the cane toad (Bufo marinus), which was introduced to Australia in 1935. A review of these studies suggests that a single pathway-lethal toxic ingestion of toads by frog-eating predators-is the major mechanism of impact, but that the magnitude of impact varies dramatically among predator taxa, as well as through space and time. Populations of large predators (e.g., varanid and scincid lizards, elapid snakes, freshwater crocodiles, and dasyurid marsupials) may be imperilled by toad invasion, but impacts vary spatially even within the same predator species. Some of the taxa severely impacted by toad invasion recover within a few decades, via aversion learning and longer-term adaptive changes. No native species have gone extinct as a result of toad invasion, and many native taxa widely imagined to be at risk are not affected, largely as a result of their physiological ability to tolerate toad toxins (e.g., as found in many birds and rodents), as well as the reluctance of many native anuran-eating predators to consume toads, either innately or as a learned response. Indirect effects of cane toads as mediated through trophic webs are likely as important as direct effects, but they are more difficult to study. Overall, some Australian native species (mostly large predators) have declined due to cane toads; others, especially species formerly consumed by those predators, have benefited. For yet others, effects have been minor or have been mediated indirectly rather than through direct interactions with the invasive toads. Factors that increase a predator's vulnerability to toad invasion include habitat overlap with toads, anurophagy, large body size, inability to develop rapid behavioral aversion to toads as prey items, and physiological vulnerability to bufotoxins as a result of a lack of coevolutionary history of exposure to other bufonid taxa.

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    • "As a case study, we used the cane toad (Rhinella marina). These invasive anurans are spreading across Australia (Urban et al., 2007), fatally poisoning native predators (Shine, 2010). Community " toad-busting " groups kill many thousands of toads annually, by a variety of methods – some of which appear to be cruel (Clarke et al., 2009) or unreliable (Sharp et al., 2011); toads are also killed for university teaching and research. "
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    • "In Australia, cane toad invasion dynamics and ecological impacts are well documented (Shine 2010; Pizzato et al. 2014). Cane toads possess highly toxic skin secretions that have caused major declines in many naïve Australian predators that die after eating them (Doody et al. 2009; Shine 2010). More recent evidence highlighting the ecological impact of cane toads on native anurans suggests that in anuran species which share micro-habitat with the cane toad, there is potential for transfer of lethal parasites by the toad, which can have devastating consequences on native species (Pizzato et al. 2014). "
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    • "Not necessarily because other factors differ also. The risk of predation may be higher at the invasion front (Phillips et al., 2008; Shine, 2010), although food is more abundant (Brown et al., 2013), parasites are rare (Phillips et al., 2010c), and low conspecific densities reduce rates of cannibalism for both larval and metamorph toads (Pizzatto & Shine, 2008; Crossland & Shine, 2012). Thus, even if invasion-front toads reproduce less often than those in long-established populations, they may achieve similar (or even greater) lifetime reproductive output because of a relative absence of density-dependent regulation. "
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