A biological invasion reduces rates of cannibalism by Japanese toad tadpoles

Abstract By imposing novel evolutionary pressures, biological invasions can favour rapid changes in intraspecific competitive mechanisms such as cannibalism. In their invasive range in Australia but not in their native range in South America, cane toads ( Rhinella marina ) exhibit high rates of cannibalism of embryos (eggs and hatchlings) by tadpoles. To explore the generality of such changes, we examined cannibalism in Japanese common toads ( Bufo japonicus ) on the islands of Honshu (native range) and Hokkaido (invasive range). Contrary to the Australian system, invasion has been accompanied by a reduction rather than increase in rates of cannibalism under standard laboratory conditions. That reduction in cannibalistic tendency by invasive-range toad tadpoles occurs despite an increase in the attractivity of invasive-range toad embryos as prey to other predatory amphibian larvae, including native-range conspecifics. Our data thus support the idea that biological invasions can generate rapid changes in rates of cannibalism, but also show that decreases as well as increases can occur. Future work could investigate the proximate cues and selective forces responsible for this rapid decrease in rates of cannibalism in invasive populations of Japanese common toads.