Habitat duration and the community ecology of temporary ponds
I have investigated the role of habitat duration following disturbance in structuring temporary pond communities. 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. Specifically, I propose that biotic interactions will mediate the relative importance of these two processes. I examine this hypothesis by first comparing data on the presencejabsence and abundance of taxa from temporary ponds along gradient of habitat duration with three simple models of community structure that incorporate random forces, life history adaptations andjor biotic interactions. I then experimentally test the ability of these processes to create the patterns observed. Comparisons of presencejabsence data to the models suggest that life history adapations are important in determining the composition of ponds. However, analysis of abundance as well as the experimental results indicate that while life history adaptations are important, the relative importance of competition and predation increases in longer-duration ponds. In intermediate-duration ponds, resource and interference competition occurs between Daphnia and rotifers. As pond duration increases, predators increase in diversity and abundance, reducing populations of most planktonic prey, releasing rotifers from competition. Predators from long-duration ponds prefer prey with which they do not typically co-occur, suggesting that predation controls their distribution. Habitat duration appears to act as a template, selecting taxa with life histories appropriate for ponds of particular duration from a pool of potential colonists. Because of correlations between life histories and trophic position or competitive ability, increasing habitat duration effects a shift in the relative importance of the processes controlling community structure, from life history adaptations in short-duration ponds to biotic interactions in long-duration ponds. These ponds are also subject to variation in the period they remain wet each year. While absolute habitat duration controls community structure in any one year, variation in habitat duration appears to control year-to-year changes in species composition. This suggests that in habitats like temporary ponds, subject to repeated disturbance, changes in species composition reflect changes in the disturbance regime, rather than the disturbance itself.