The behavioral ecology of cannibalism in cane toads (<Emphasis Type="Italic">Bufo marinus</Emphasis>) |
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Authors: | Lígia Pizzatto Richard Shine |
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Institution: | (1) School of Biological Sciences A08, University of Sydney, Sydney, New South Wales, 2006, Australia |
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Abstract: | Laboratory studies show that predatory cane toads (Bufo marinus) exhibit specialized toe-luring behavior that attracts smaller conspecifics, but field surveys of toad diet rarely record
cannibalism. Our data resolve this paradox, showing that cannibalism is common under specific ecological conditions. In the
wet–dry tropics of Australia, desiccation risk constrains recently metamorphosed toads to the edges of the natal pond. Juvenile
toads large enough to consume their smaller conspecifics switch to a primarily cannibalistic diet (67% of prey biomass in
stomachs of larger toads). Cannibalistic attack was triggered by prey movement, and (perhaps as an adaptive response to this
threat) small (edible-sized) toads were virtually immobile at night (when cannibals were active). Smaller metamorphs were
consumed more frequently than were larger conspecifics. The switch from insectivory to cannibalism reflects the high dry season
densities of small conspecifics (in turn, due to desiccation-imposed constraints to dispersal) and the scarcity of alternative
(insect) prey during dry weather. Our study pond (102 m in circumference) supported >400 juvenile toads, which consumed many
metamorphs over the course of our study. Toads appear to be low-quality food items for other toads; in laboratory trials,
juvenile toads that fed only on conspecifics grew less rapidly than those that ate an equivalent mass of insects. This effect
was not due to parotoid gland toxins per se. Thus, cane toads switch to intensive cannibalism only when seasonal precipitation
regimes increase encounter rates between large and small toads, while simultaneously reducing the availability of alternative
prey. |
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Keywords: | Anuran Feeding habits Growth rate Intraspecific predation Natural selection |
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