Predator behaviour and morphology mediates the impact of an invasive species: cane toads and death adders in Australia

Abstract

The arrival of an invasive species can have severe impacts on native species. The extent of the impact, as well as the speed at which native species may mount an adaptive response, depend upon the correlation between impact and the individual phenotypes of the native species. Strong correlation between phenotype and impact within the native species raises the possibility of rapid adaptive response to the invader. Here, we examine the impact of a dangerous newly arrived prey species (the highly toxic cane toad Bufo marinus) on naı¨ve predators (death adders Acanthophis praelongus) in northern Australia. During laboratory trials and field radiotracking, toads killed 48% of the adders we studied. Long-term monitoring of the population also suggests a massive decline (489%) in recent years concurrent with the arrival of toads. Variation in snake physiology (resistance to toad toxin) had little bearing on snake survival in the field. Snake behaviour (tendency to attack toads) and morphology (body size and head size), however, were strong predictors of snake survival. Smaller snakes with relatively small heads, and snakes that were unwilling to attack toads in the laboratory, had much higher survival rates in the field. These results show that toads have a massive impact on death adder populations, but that snake phenotypes strongly mediate this impact. Thus natural selection is operating on these adder populations and an adaptive response is a possibility. If these adders can rapidly shift toad-relevant morphological and behavioural traits (either through plastic or evolved means), they will ultimately face a lowered impact from this toxic invader.

Islands and scales: a biogeographic survey of reptiles on Kimberley islands, Western Australia

“…Death Adders (Acanthophis praelongus), Blue-tongue Skinks (Tiliqua scincoides) and a number of goannas, especially Varanus p. panoptes and V. mertensi, are known to be particularly susceptible to toxic poisoning following the ingestion of toads (Smith and Phillips 2006;Doody et al 2009;Price-Rees et al 2010;Shine 2010). Although some population recoveries on the mainland have been noted (Phillips et al 2009), recovery in island populations, with their small population size and limited genetic variation, may be less likely.…”

Sunning themselves in heaps, knots, and snarls: The extraordinary abundance and demography of island watersnakes

“…Adult survival was also associated with prey availability in Liasis fuscus (Water Python, Madsen, Ujvari, Shine, & Olsson, 2006; Ujvari, Brown, Shine, & Madsen, 2016) and Vipera berus (European Adder, Forsman & Lindell, 1997). Changes in adult survival were associated with the arrival of nonnative toxic toads in the Tropidonophis mairii (Common Keelback) and Acanthophis praelongus (Northern Death Adder) but not Stegonotus cucullatus (Slatey‐grey Snake; Brown, Ujvari, Madsen, & Shine, 2013; Phillips, Greenlees, Brown, & Shine, 2010). Other variables associated with variation in survival included degree of habitat fragmentation ( Drymarchon couperi , Indigo Snake, Breininger et al., 2012), fire ( Vipera ursinii , Ursini’s Viper; Rhinoplacephalus nigrescens, Small‐eyed Snake; Webb & Shine, 2008; Lyet, Cheylan, Prodon, & Besnard, 2009), color morph ( Vipera berus, European Adder; Crotalus horridus, Timber Rattlesnake; Forsman, 1995; Brown, Kery, & Hines, 2007; Brown, 2008), and possibly, disturbance by researchers ( Crotalus oreganus, Pacific Rattlesnake; Diller & Wallace, 2002).…”

A new species of death adder (Acanthophis: Serpentes: Elapidae) from north-western Australia

“…Lethal ingestion of the cane toad (Rhinella marina) has been documented in previous studies on Acanthophis specimens from the Kimberley region and Northern Territory (Phillips & Shine 2007;Hagman et al 2009;Phillips et al 2010;Pearson et al 2014) indicating the species is likely to be at risk of significant decline as cane toads continue to move west across the Kimberley region. A detailed assessment on potential threats to the species including cane toads will identify the need for listing as a species requiring protection under state or federal legislation.…”