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Animals often alter their behaviour, morphology and physiology in the presence of predators. These induced defences can be fine-tuned by a variety of environmental factors such as predator species, acute predation risk or food availability. It has, however, remained unclear what cues influence the extent and quality of induced defences and how the information content of these cues interact to determine the development of antipredator defences. We performed an experiment to study the significance of direct chemical cues, originating from the predators themselves, and indirect cues, released by attacked or consumed prey, for phenotypic responses in Rana dalmatina tadpoles. We reared tadpoles in the presence of caged predators ( Triturus vulgaris, Aeshna cyanea) fed either one or three tadpoles every other day outside the tadpole-rearing tanks. Fifteen hours after food provisioning, predators were put back into the tanks containing focal tadpoles either after washing (direct + digestion-released cues) or with the water containing remnants of the prey (direct + all types of indirect cues). Our results suggest that direct cues together with digestion-released cues can be sufficient to induce strong antipredator responses. Induced defences depended on both direct cues, affecting predator-specific responses, and the quantity of indirect cues, resulting in graded responses to differences in predation threat. Moreover, direct and indirect cues interacted in behaviour, resulting in predator-specific graded responses. We also observed a decrease in the extent of predator-induced responses in large tadpoles as compared to small ones. Our results, thus, suggest that prey integrate multiple cues about predators to optimize induced defences and that this process changes during ontogeny. [ABSTRACT FROM AUTHOR]

Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles. The species typically breeding in temporary or semi-permanent ponds (Rana temporaria, Rana arvalis, Rana dalmatina and Hyla arborea)--where invertebrate predator populations are predicted to vary considerably spatiotemporally--all showed marked induced increases in tail fin depth in response to predator presence. These species also tended to respond by reduced growth rates. The representative of the most ephemeral habitats, Bufo calamita, did not respond in any of these traits. Its congeneric, Bufo bufo, a toxic inhabitant of permanent ponds and lakes, tended to respond to predator presence by reducing its growth rate, though not by a tail depth increase. I argue that the rather poor swimming performance in Bufo tadpoles may opt for defenses other than locomotor ability. The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed. [ABSTRACT FROM AUTHOR]