Habitat duration and community structure in temporary ponds

Models of the factors affecting community structure following a disturbance differ in the emphasis placed on adaptations to the physical environment and to biotic interactions. We investigated the hypothesis that the duration of a habitat following disturbance mediates the relative importance of physical and biotic control. We combined detailed information on natural populations in a series of temporary ponds with small-scale experiments on specific processes. We compared data on presence/absence and abundance of taxa from temporary ponds showing a gradient of habitat duration with 3 simple models of community structure that incorporate random forces, life history adaptations, and biotic interactions, respectively. Different scales of resolution in describing community structure provide different emphases on which processes are important in these communities. The Life History Model explained patterns of presence/absence in the ponds, but not patterns of abundance of many taxa which best fit a model in which the importance of predation and competition in structuring communities increases with increasing duration. Experimental studies confirmed that the effect of predation and competition in temporary pond communities depends on habitat duration. Predation on all prey species examined increased with increasing pond duration. Predators were more diverse and more abundant in long-duration ponds where effects of their consumption on the abundance of prey taxa were greater than in shorter-duration ponds. Predators from long-duration ponds fed preferentially on prey taxa that predominate in shorter-duration habitats such as Aedes mosquitoes and the fairy shrimp Eubranchipus. Competition between Daphnia and rotifers occurred primarily in intermediate-duration ponds, where Daphnia at typical densities was capable of drastically reducing abundances of Keratella cochlearis in cultures. However, at densities found in both short- and long-duration habitats, Daphnia had no effect.