Predator-induced changes in life history in two anuran tadpoles: effects of predator diet

We studied effects of the non-lethal presence of a predator on behaviour and larval life history of two species of anuran tadpoles, common frog, Rana temporaria, and common toad, Bufo bufo. We manipulated predator diet to study whether differences in chemically perceived predation risk affect the tadpoles. Tadpoles of both species were raised at two food levels either in the absence of the predator or in the presence of an insect-, frog- or toad-fed larval dragonfly Aeshna juncea. R. temporaria tadpoles lowered their activity in the presence of a predator and also avoided the predator spatially. Furthermore, they showed the strongest response to tadpole-fed predators. The number of days elapsed since the last provisioning of food affected the behaviour of both species. In R. temporaria, differences in activity level between predator treatments vanished as the food resources were depleted. In B. bufo, activity was lower in the presence of a toad-fed predator shortly after food had been added to the containers. Spatial avoidance of predators by B. bufo was stronger in the presence of a load-fed predator than when an insect- or frog-fed predator was present. In both tadpole species growth rate was higher at the high food level but remained unaffected by the predator treatments. In both species individuals at higher food level metamorphosed earlier and at larger size. The metamorphic responses to predator treatments differed between the species. R. temporaria metamorphosed later and at larger size in the presence of tadpole-fed predators than in the control treatment or in the presence of an insect-fed predator. B. bufo metamorphosed earlier in the presence of a toad-fed predator, but this was only slightly correlated to metamorphic size. Manipulations of predator diet affected tadpole life history in both species. However, predator effects on larval life history were not mediated by tadpole behaviour in either species.