Foraging traits of native predators determine their vulnerability to a toxic alien prey.
Vulnerability to toxic alien prey varies among native predator species, depending on their toxin resistance. Although foraging traits relating to the intake of prey are also likely to influence predator vulnerability to toxic alien prey, these traits have received little attention. To address this issue, we studied the toxic impacts of an alien prey species (Bufo japonicus formosus toad hatchlings) on a carnivorous and an omnivorous native amphibian species (Hynobius retardatus salamander larvae and Rana pirica frog tadpoles, respectively) that both feed on alien B. japonicus formosus toad hatchlings. First, we designed a mesocosm and an aquarium experiment to evaluate the impact of B. japonicus formosus on the survival of native amphibians under various alien prey densities and predation regimes. Second, we performed several additional laboratory experiments to clarify specific processes of native amphibian mortality in the presence of the alien B. japonicus formosus toad hatchlings. We found that both native amphibian species were impacted by the alien B. japonicus formosus toad hatchlings. Interestingly, R. pirica frog tadpoles were more affected than H. retardatus salamander larvae, partly due to their lower toxin resistance and their higher toad consumption rate. Most importantly, omnivorous foraging traits (i.e., food sharing and carcass consumption) demonstrated by R. pirica frog tadpoles, but not by the strictly carnivorous H. retardatus salamander larvae, rendered the former particularly vulnerable to the toxic B. japonicus formosus toad hatchlings. This is the first study suggesting that species-specific foraging traits such as food-sharing and carcass consumption can determine predator vulnerability to toxic alien prey. This study emphasises the importance of investigating a wider array of predator traits as factors that determine their vulnerability to toxic alien prey. By doing so, we can understand what types of native species are strongly impacted by toxic alien prey and predict the ecological consequences of toxic species invasion.