Cane toads (Rhinella marina) are large toxic anurans native to Central and South America, but introduced to northeastern Australia in 1935 in a futile attempt at biocontrol (Shine 2010). Behavioral plasticity has allowed toads to colonize climatic zones well outside those experienced in the native range (Brown et al. 2011a). In 1935, at the request of sugarcane plantation owners, the government released about 2,400 cane toads into north Queensland to help control cane beetles, which eat the roots of sugarcane.

2. Environmental variables

A list of the species and specimens used in this study is provided in the supplementary materials (Appendix S1). All measurements were taken by the same person (MVG) to ensure consistency in the data collection. Together these studies included comprised morphological information for 1216 specimens, 45 genera or clades (hylid clades are previously described in Vidal‐García & Keogh, 2015), and 97.5% of all Australian frog species. As there was no evidence of sexual dimorphism in any shape variable within the cane toads, sex was not taken into account when comparing morphological data to Australian clades (see Results).

Carrion removal trials

We selected eight sites in areas where toads are currently present (from 2 to 25 years postinvasion) and eight sites where toads are predicted to invade (Urban et al. 2007; Kolbe et al. 2010) but have not yet done so. Due to the patchy distribution of cane toads at the southern edge of their invasion, we were able to select interspersed study sites to minimize the confounding effects of latitude, longitude, elevation, climate, or vegetation. All campgrounds and picnic areas were adjacent to or within state forests or national parks (Fig. 1, see Supplementary Information for Table S1).

Associated Data

We also performed phylogenetic regression models using this function to test the correlation between sets of traits. We then performed a phylogenetic PCA, on all morphological variables, with phytools (Revell, 2012). Phylogenetic ANOVAs and phylogenetic PCA were also ran on the size‐corrected data set (Appendix S2). The highly invasive cane toad, Rhinella marina, is native to Central and tropical South America (Zug & Zug, 1979), but was introduced across the globe, including Australia, and has successfully invaded more than twenty countries to date (Lever, 2001). The cane toad is one of the World’s worst alien invasive species (Lowe, Browne, Boudjelas, & De Poorter, 2000) and its impact on native fauna has been studied extensively (Letnic, Webb, & Shine, 2008; Shine, 2010, 2014; van Winkel & Lane, 2012).

The fitness consequences of these divergent behavioural tactics will depend upon details of the local ecological context. For example, boldness may reduce an individual’s fitness if predators are abundant, but increase its fitness if predators are absent [45]. Our feeding competition trials suggest that bolder animals may be better competitors when prey abundance is low, but not when prey abundance is high.

  1. Unlike native Southern Toads (Anaxyrus terrestris) and American Toads (A. americanus) which have relatively small, oval paratoid glands, the paratoid glands of Cane Toads are large and triangular paratoid glands.
  2. We may see evolutionary changes in the invader, in native species directly impacted by it, and in species influenced indirectly via their interactions with affected native taxa.
  3. We also used Bartlett’s test and F‐test one‐way analysis of variance in order to test for variance differences among groups, as a proxy for environmental niche breadth differences.
  4. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information.

Extensive research in tropical Australia has demonstrated that the arrival of cane toads is consistently followed by population‐level declines of some species of large predators that are fatally poisoned when they eat the toxic toads (Letnic et al. 2008; Doody et al. 2009). However, impacts on the (virtually unstudied) southern edge of the toads’ range expansion may be very different from those in the tropics. For example, the tropical invasion front is dominated by large adult toads; any predator that consumes a large toad will be fatally poisoned (Shine 2010). In contrast, the southern front contains small as well as large toads (McCann 2014). A small toad offers a nauseating but nonfatal meal that may allow aversion learning by predators, thereby ameliorating population‐level impact (O’Donnell, Webb & Shine 2010). Yellow-spotted monitors (Varanus panoptes, Fig 1, lower panel) can grow to 7 kg and up to 2 metres, and are widely distributed through the wet/dry tropics of northern Australia [32].

In keeping with dietary analyses that report frequent consumption of small mammals by large varanids [28, 33, 35, 38], we detected a positive correlation between the relative abundances of small mammals and of lace monitors, but no correlation with yellow-spotted monitors. The pattern for yellow-spotted monitors reflects the virtual absence of records alcohol use and death by suicide of small mammals all across our transect in northern Australia. In order to compare morphological niches among Australian frogs and cane toads in a phylogenetic context, we generated a phylogenetic hypothesis for Australian hylids, Australian microhylids, myobatrachids, Rana daemeli, and Rhinella marina, using Xenopus muelleri as an outgroup.

The lace monitor inhabits forested areas, where ambient temperatures change seasonally and precipitation ranges from relatively aseasonal (southern regions) to seasonal (tropical regions). In contrast, in the areas where it is sympatric with toads the yellow-spotted monitor inhabits a monsoonal climate where daily maximum air temperatures remain high year-round but precipitation is concentrated in a brief “wet season” [34, 39]. Yellow-spotted monitors typically are found in relatively open (often, treeless) tropical floodplains, but also exploit other open habitats such as ocean beaches where they forage for the eggs of sea turtles [40, 41].

Geographic differences in the priority given to competing issues can influence funding incentives and research effort. The forests of northern NSW have been the focus of vigorous “environmental” battles over many years relating to forestry practices (Lemckert 1999; Kavanagh and Stanton 2005). That focus may have drawn public attention away from feral species impacts, but it is difficult to understand why scientific efforts were equally scarce. alcoholism recovery stages Whatever the reasons behind the disproportionate allocation of research effort toward the cane toad problem in tropical versus southern Australia, the result is clear. We have failed to recognize a major ecological problem unfolding in a place close to major cities where logistics are straightforward, and robust experimental designs are possible. If that can happen with cane toad impact, it may well happen in other ecological issues as well.

Because Australia lacks native toads, the ecological impact of cane toads has been devastating for some species of native predators (snakes, lizards, crocodiles, marsupial carnivores) that attempt to eat toads, and are killed by the toads’ powerful poisons. The process of biological invasion has imposed strong evolutionary pressures on the toads, with genes for more rapid dispersal accumulating at the invasion front; and thus the toad front is now advancing much faster than before. Vulnerable native predators have adapted to the toad’s presence, with shifts in feeding responses, physiological tolerance to toad toxins, and even body shape (relative head size).

It might seem unusual to release many thousands of baby pest toads into the environment. And importantly, we didn’t add any more cane toads into the landscape – we took female toads that were about to lay their eggs from one place, and released those eggs barbiturates: usage effects and signs of barbiturate overdose and babies into another place not too far away. Many threats imperilling ecosystems worldwide are virtually impossible to eradicate. In some cases, the only way to reduce the impacts of such invaders may be to build the resilience of native species.

For east-coast sites, bait stations and passive infrared motion sensing cameras were deployed at each site in two grids. Each grid consisted of four cameras (each was spaced 100 m apart) for a total of eight bait stations and cameras per site. One grid was placed in bushland adjacent to the focal campground and a second grid established in bushland 2 km away. Bait stations were deployed for 48 hours (total 16 camera days/nights per site) and consisted of one non-consumable chicken neck (deployed in a PVC ventilated canister to prevent predator access). An additional consumable chicken egg was placed at half of the bait stations at 13/21 sites for a concurrently run experiment. Impacts of processes such as climate change, habitat degradation, and pollution can interact with invasive species to modify the direction, magnitude or duration of invader impact.

For those of you in areas with cane toads, or areas where they expect them to invade, keep your eyes open, protect your pets, and please don’t try to lick frogs for the fun of it. Playing around with cane toads doesn’t usually work out well for those involved. With all the cane toads roaming Australia, it makes sense that researchers in the area are curious to discover whether cane toad toxins can be used as medicine. There is already evidence that this poison will kill cancer cells while leaving healthy cells alone. According to an article in The Guardian, these researchers hope to convert the toxin into a pill, despite it tasting so terrible, to make use of the overpopulated toads potentially. We’ve already mentioned that cane toads are toxic throughout all stages of their lives.

Likewise, intense selection exerted by an invader may depress population sizes of the native taxa so greatly that extinction is more likely than adaptation. Other selective forces may oppose the changes favored by the invaders’ presence. Phenotypically, plastic responses to invader cues may generate suboptimal phenotypes, curtailing effective selection (Richards et al. 2006) but potentially serving as a bridge to ultimate adaptive evolution (Ghalambor et al. 2007). Attributing a lack of evolutionary response to such mechanistic constraints is a formidable logistical challenge, requiring sophisticated experimental work to tease apart the genetic underpinnings of adaptive responses, or the lack thereof (Carroll et al. 2005). Data on the three lizard taxa were assessed independently because they were identified as having declined by SIMPER.

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