In many species of anurans, tadpoles adjust their behavior in the presence of fish or fish cues, in many cases reducing their activity. Tadpoles may also adjust their activity or behavior in response to group size. We examined the effects of predator cues (bluegill sunfish, Lepomis macrochirus) and group size on the behavior of Wood Frog (Rana sylvatica) tadpoles in a factorial laboratory experiment. Wood Frog tadpoles were less active and used the vegetated side of the experimental aquaria more in the presence of fish. Group size alone had no effect on the behavior of the Wood Frog tadpoles in our experiments. Our experiment shows that cues from fish predators have a greater influence on the behavior of Wood Frog tadpoles than does group size, at least in the range of group sizes used in this experiment.
INTRODUCTION
The number of conspecifics in an area (group size) can influence perceptions of predation risk and influence the behavior of individuals. One might expect individuals in larger groups to perceive lower predation risk and to engage in “riskier“ behavior compared to individuals that are alone or in smaller groups. Such a pattern has been demonstrated in a variety of animals, including mammals, fish and lizards , but not all (e.g., primates).
Tadpoles appear to adjust their activity or behavior in response to the number of conspecifics in a group, at least in some species, suggesting that tadpoles may use group size as a cue to assess predation risk. Indeed, some species respond to increased predation risk by forming larger or more cohesive aggregations. Alternatively, the increased activity in larger groups may reflect a response to increased numbers of conspecifics (i.e., potential competitors)
Fish are frequently major predators on anuran tadpoles and can have impacts on amphibian populations and communities. Thus, there may be strong selection on the ability of anuran tadpoles to be able to detect and respond to cues from potential fish predators. Indeed, in several species of anurans, tadpoles adjust their behavior in the presence of fish, in many cases reducing their activity.
We examined the effects of predator cues and group size on the behavior of wood Frog (Rana sylvatica) tadpoles in a factorial laboratory experiment. Based on previous work, we predicted that the presence of fish would cause a reduction in the activity of the tadpoles, as well as an increase in the use of vegetated habitats. We also predicted that group size would increase tadpole activity. both alone and in the presence of predator cues (is, tadpoles in larger groups would engage in "riskier" behavior than tadpoles in smaller groups). In particular, we expected that tadpoles in the larger group would be less affected by the presence of the predator than would tadpoles in the smallest groups or alone.
