The effects of hydroperiod and predator density on growth, development, and morphology of wood frogs (Rana sylvatica)

Accelerated development and metamorphosis allow tadpoles to escape death by leaving the aquatic habitat before it dries. Phenotypic plasticity in response to predators typically includes development of physical and behavioral traits, including changes in tail coloration, activity rate, and tail shape and body size. Responding to predators increases the probability of survival, but lowers growth rate. Responses to two common stressors in ephemeral aquatic habitats appear to be in direct opposition to one another. In this study, we examined the individual and interactive effects of hydroperiod and predator density on the life history, morphology, and metamorphosis of wood frog (Rana sylvatica) tadpoles in an outdoor mesocosm study. Tadpoles were exposed to three hydroperiods (constant, intermediate, and short) and three predator densities (zero, four, and eight Anax junius naiads) using a complete block design. The threat of habitat desiccation resulted in increased developmental rate and shorter larval periods. Increased predator densities resulted in increased size at metamorphosis and development of the induced morphology. Although the threat of predation precluded growth and developmental responses to shortened hydroperiod in tadpoles, it did not negate the metamorphic responses to hydroperiod. It appears that, at least at the treatment levels imposed in this experiment, the interaction between these multiple stressors is complex, with the stressors acting both individually and together on different aspects of tadpole ecology.