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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    ABSTRACT: Pathways are the natural and artificial introduction processes associated to human activities that result in the introduction of exotic species. In aquatic environments, aquaculture is particularly important be- cause the species are selected for their resistance and adaptability, thus presenting a higher probability of becoming invasive. In Mexico, aquaculture relies mainly on exotic species that are grown extensively. Tila- pia, carp and rainbow trout support continental aquaculture production and their propagation is carried out by government agencies (SAGARPA). The aquarium trade is a very important pathway considering the high number of species that are traded internationally, the frequency of imports and their production. Several species that have entered through this pathway are invading the country’s water bodies (e.g., ar- mored catfish, jewel cichlid, convict cichlid, lionfish). Recreational fishing is another important pathway that primarily introduces predators (e.g., bass), plus several potential invaders used as live bait or feed (e.g., red crayfish). Moreover, ballast water is recognized as the major unintended pathway with conse- quences for the environment, economy and health. It is estimated that through this process around 12 billion m3 of water are transported per year. Virtually all marine species have planktonic stages that can be moved by this pathway and it is likely that more than 3 000 are transported daily in ballast water. Unfortunately, of the various proposed treatments for ballast water, none has proved to be completely effective, considering efficiency, environmental safety, convenience and cost. Assessing the risk for ballast water in Mexico has been difficult, and to date, the introduction of about 200 non-indigenous aquatic species by this pathway has been reported. Similarly, fouling and artificial channels are pathways that cause the unintentional introduction of a large number of species that are causing economic and ecologi- cal problems. Other pathways to consider are dams, drilling platforms, boat trailers, recreational activities, and natural dispersal of floating material.
    Especies acuáticas invasoras en México, Edited by R. Mendoza y P. Koleff, 01/2014: chapter 2: pages 43-73; Comisión Nacional para el Conocimiento y Uso de la Biodiversidad,., ISBN: 978-607-8328-04-8
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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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    ABSTRACT: Invasive species can disrupt the communication systems that native biota use for reproductive interactions. In tropical Australia, invasive cane toads (Rhinella marina) breed in many of the same waterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
    Behavioral Ecology and Sociobiology 02/2015; 69(4). DOI:10.1007/s00265-015-1879-z · 3.05 Impact Factor

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