Impact of eastern mosquitofish,Gambusia holbrooki,on temporary ponds: insights on how predation may structure zooplankton communities

Ecological and evolutionary processes can conveniently be explored through the simplified communities of temporary ponds. In order to investigate the potent roles of predation in structuring zooplankton communities, we used a manipulative study to analyze the impact of eastern mosquitofish, Gambusia holbrooki, on a set of 24 temporary ponds. Fish were introduced at different densities (0, 8, 16 and 80 mosquitofish), and zooplankton assemblages were monitored monthly between January and May. Fish predation decreased markedly the overall abundance of zooplankton. Large crustaceans (Anostraca and Calanoida) were rapidly eliminated, while Cyclopoida and Cladocera peaked in March before in turn disappearing in the later stages of the hydroperiod. These results are congruent with the theory supporting the influence of both predation and competition as major interacting forces shaping freshwater communities.