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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Available from: Richard Shine, Jul 28, 2015
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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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    ABSTRACT: What is the most humane way to kill amphibians and small reptiles that are used in research? Historically, such animals were often killed by cooling followed by freezing, but this method was outlawed by ethics committees because of concerns that ice-crystals may form in peripheral tissues while the animal is still conscious, putatively causing intense pain. This argument relies on assumptions about the capacity of such animals to feel pain, the thermal thresholds for tissue freezing, the temperature-dependence of nerve-impulse transmission and brain activity, and the magnitude of thermal differentials within the bodies of rapidly-cooling animals. A review of published studies casts doubt on those assumptions, and our laboratory experiments on cane toads (Rhinella marina) show that brain activity declines smoothly during freezing, with no indication of pain perception. Thus, cooling followed by freezing can offer a humane method of killing cane toads, and may be widely applicable to other ectotherms (especially, small species that are rarely active at low body temperatures). More generally, many animal-ethics regulations have little empirical basis, and research on this topic is urgently required in order to reduce animal suffering. © 2015. Published by The Company of Biologists Ltd.
    Biology Open 05/2015; DOI:10.1242/bio.012179 · 2.42 Impact Factor
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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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    ABSTRACT: Summary 1. Invasive species are amongst the most important agents of global change and understanding the mechanisms that afford them their ecological success is key to addressing their biodiversity impacts. The ecological theory of island invasion implies that small island ecosystems could permit invasive species to exploit novel ecological functions including indirect effects (such as physiological stress and reproductive failure) that diversify or intensify biodiversity impacts. Therefore, it is worthwhile to quantify the physiological mechanisms through which invasive species can exert indirect effects on the performance, and ultimately the fitness of island endemic species. 2. In this study, we used the invasive cane toad (Rhinella marina) and native Fijian ground frog (Platymantis vitiana) co-existence system on the small (60 ha) Viwa Island, Fiji to determine support for the ecological theory by quantifying the underlying physiological mechanisms that affect ground frog ecology. We used very large (4 x 10,000 m2), naturally situated and replicated enclosures to monitor ground frog stress hormone levels, reproductive hormone cycle, body-condition, breeding and survival in the presence/absence of the cane toad. We conducted monthly sampling for analyzing testosterone for males and estradiol and progesterone for females, corticosterone for both sexes and body-condition of ground frogs in replicated enclosures or natural habitats representing high/low cane toad density. We also measured the survival index and reproductive success of ground frogs in each enclosure. 3. Results showed that ground frogs living in enclosures with cane toads or natural habitats with high cane toad density had a significant reduction in body condition, increased urinary corticosterone metabolites and suppressed sex steroidal metabolites. Most importantly, annual field surveys showed significant reduction in ground frog reproductive success (fewer eggs were laid in enclosures with toads present) however survival was not severely reduced. 4. Overall, sustained pressure by the cane toad could culminate into massive population collapse or extinction of the ground frogs due to chronic stress and reproductive failure. Therefore, management actions to mitigate invasions on the islands must be both rapid and thorough to prevent establishment of invasive species and limit extinction on islands.
    Functional Ecology 03/2015; DOI:10.1111/1365-2435.12446 · 4.86 Impact Factor
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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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    ABSTRACT: The rapid evolution of increased dispersal rate during a population's range expansion provides a unique opportunity to detect trade-offs between dispersal and reproduction. If a high reproductive rate slows down an individual's dispersal, vanguard individuals should exhibit a lower reproductive output than conspecifics from long-colonized areas. In the present study, we demonstrate a reduction in reproductive rate in highly dispersive invasion-front populations of cane toads in tropical Australia.
    Biological Journal of the Linnean Society 01/2015; DOI:10.1111/bij.12618 · 2.54 Impact Factor
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