Article

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: 4.89). 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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    • "Both anuran species have primarily become established in communities that are functionally divergent to them. This is in agreement with the fact that generally, L. catesbeianus and R. marina have not caused a detectable loss of anuran diversity on the communities where they have established (Shine, 2010;Both & Melo, 2015). In some regions, alien bullfrogs do appear in communities with similar functional structures, along with other Ranidae species (Stebbins, 1985;Berroneau & Ohler, 2012). "
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    ABSTRACT: Aim Invasive species present negative impacts on native biodiversity at a global scale. A key goal of community ecology is to identify what drives invasiveness, but hypotheses relying on biotic mechanisms remain largely untested for many groups. Here we asked whether source and recipient communities of two highly successful invasive anurans (the bullfrog Lithobates catesbeianus and the cane toad Rhinellla marina) differ consistently from a taxonomic and/or functional standpoint. If affirmative, this pattern could suggest that taxonomic and/or functional distances between an invasive species and a potentially recipient community might influence the alien’s invasive potential. Location World-wide. Methods Based on co-occurrence data of 1061 amphibian species, we compared 30 source to 30 recipient communities of bullfrogs and cane toads by means of biotic metrics that summarize taxonomic and functional diversity and the relative position of the invasive species within the community. We also included environmental drivers that reportedly influence invasibility (climate, resource availability, spatial heterogeneity, and propagule pressure). Results Both invasive species were functionally distant to their respective recipient communities; in contrast, community diversity did not explain much variation between source and recipient communities. Climate matching possibly influenced cane toad’s but not bullfrog’s invasiveness, and landscape factors had little relevance overall. Main conclusion This study advances the notion that the relative position of a recently introduced species within the native functional space may help predicting its invasive potential.
    No preview · Article · Jan 2016 · Diversity and Distributions
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    • "Toads arrived in our study area in 2005 (Brown et al. 2006). Cane toads possess highly toxic defensive compounds, and many native predators (including fishes, frogs, lizards, snakes, crocodiles and marsupials) have been fatally poisoned when they have attempted to eat the invasive toads (Shine 2010). In our study area, cane toads remain active year-round but tend to be restricted to sites with permanent water during the dry season. "
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    ABSTRACT: Although generalized habitat use may contribute to the success of invasive taxa, even species that are typically described as habitat generalists exhibit non-random patterns of habitat use.We measured abiotic and biotic factors in 42 plots (each 100 × 10 m) along a 4.2-km long unpaved road in tropical Australia, at a site that had been invaded by cane toads (Rhinella marina Bufonidae) seven years previously.We also counted anurans at night in each of these plots on 103 nights during the tropical wet season, over a five-year period, beginning soon after the initial toad invasion. Spatial distributions differed significantly among adult male toads (n = 1047), adult female toads (n = 1222), juvenile toads (n = 342) and native frogs (Cyclorana australis Hylidae, n = 234). Adult male toads were closely associated with water bodies used as calling and/or spawning sites, whereas adult female toads and native frogs were most commonly encountered in drier forested areas on sloping ground. Juvenile toads used the margins of the floodplain more than conspecific adults did, but the floodplain itself was rarely used. Understanding which components of the habitat are most important to specific age and sex classes within a population, or how invasive species differ from native species in this respect, can clarify issues such as the spatial and temporal location of ecological impact by an invader, and the most effective places for control of the invader with minimal collateral effects on the native biota.
    Full-text · Article · Dec 2015 · Austral Ecology
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    • "In the case of anuran amphibians, the two most widespread taxa (the American Bullfrog Lithobates catesbeiana [5 Rana catesbeiana] and the Cane Toad Rhinella marina [5 Bufo marinus]) both possess potent chemical defenses (Kats et al. 1988; Crossland et al. 2008; Adams et al. 2011; Szuroczki and Richardson 2011). Indeed, the distinctive bufadienalide toxins (cardioactive steroids; Hayes et al. 2009) of Cane Toads have been the primary mechanism for their devastating impact on native predators in Australia (Shine 2010). The success of the Cane Toad invasion has been widely attributed to the inability of native predators to tolerate these toxins, rendering the toads invulnerable (e.g., Covacevich and Archer 1975; Burnett 1997; Letnic et al. 2008). "
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    ABSTRACT: The successful spread of invasive Cane Toads (Rhinella marina) across tropical Australia has been attributed to a lack of biotic resistance, based upon the inability of most anuran-eating vertebrate predators to tolerate the powerful chemical defenses of the toads. However, despite their high species richness, invertebrates have been much less studied than vertebrates as predators of Cane Toads. Our field and laboratory studies show that toads are killed and consumed by a phylogenetically diverse array of arthropod taxa. No arthropod predators consumed toad eggs in our laboratory experiments, but fishing spiders, water beetles, water scorpions, and dragonfly nymphs killed toad tadpoles, and ants and fishing spiders killed metamorph toads. Published accounts report predation on toads by crustaceans and hemipterans also. In our experiments, no predators showed any overt ill effects from consuming toad tissue. Dragonfly nymphs (Pantala flavescens) and fishing spiders (Dolomedes facetus) selectively took Cane Toad tadpoles at higher rates than some simultaneously offered native frog tadpoles. In combination with published data, our experiments suggest that the tadpoles and metamorphs of Cane Toads face high predation rates from the diverse and abundant invertebrate fauna of aquatic and riparian habitats in tropical Australia. The invasion of Cane Toads can potentially have positive effects on populations of many native animal species.
    Full-text · Article · Dec 2015 · Herpetological Monographs
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