Behaviour and growth of southern leopard frog (Rana sphenocephala) tadpoles: effects of food and predation risk

Abstract

I examined the effects of a nonlethal predator, larvae of the odonate Anax junius, and food-resource level on behaviour and growth of larval southern leopard frogs (Rana sphenocephala) to test whether the strength of effects of a nonlethal predator was influenced by background resource level. I crossed two levels of food resources, growth-limiting and non-growth-limiting, with the presence or absence of A. junius. Tadpoles responded to predators by altering spatial distribution and activity. When predators were present, tadpoles on both food treatments had similar low levels of activity, but tadpoles on the nonlimiting food treatment showed a much larger reduction in activity than tadpoles on the growth-limiting treatment. Tadpoles on both food treatments delayed metamorphosis when exposed to predators. Growth and size at metamorphosis were affected significantly by food treatment but not by predator treatment. However, the direction of response to predators differed. Tadpoles on the growth-limiting treatment were larger at metamorphosis and grew faster when exposed to predators; the opposite was true for tadpoles on the non-growth-limited food treatment. This raises the interesting possibility that for some species experiencing low resource availability, predators may induce a behaviourally mediated positive effect on growth.