IS PREDATION BY TURTLES SUFFICIENTLY STRONG TO AFFECT BIODIVERSITY WITHIN FISHLESS PONDS?

Abstract

Ecologists have long known that predation can have a strong effect on the diversity and abundance of prey in ecological communities. Much evidence on the importance of predation in aquatic systems has stemmed from studies involving manipulations of abundance or occurrence of predator species thought to play an important role. In freshwater aquatic systems, fish often are considered as the most important predators in permanent ponds; in contrast, salamanders and insects are often considered to be the most important predators in ephemeral ponds. Freshwater turtles are a group that often is overlooked in studies assessing the importance of predation, yet turtles often are locally abundant and can consume a wide array of prey species. I conducted an exclosure experiment in a fishless ephemeral pond to assess whether turtles play an important role in controlling the distribution and abundance of amphibian and invertebrate prey. The ability of turtles to access and feed in certain experimental plots but not others did not alter the number of prey species present within study plots or the evenness of prey species present within study plots. A comparison of species accumulation curves revealed that turtles tended to reduce the total number of prey species found across all study plots where turtles had the ability to feed. Areas in which turtles were excluded had higher total number of prey species across all study plots. I found that scale dependent differences in the effect of turtles on species richness are the result of turtles homogenizing the kinds of prey species present in areas where they could graze. My results demonstrate that turtles may have an important effect on the diversity within fishless ponds, possibly by homogenizing species composition of different localities.