Resource overlap and competition in pond snails: an experimental analysis.

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Aplexa hypnorum studied in NE Indiana is a specialist in both habitat and food use, and is detritivore in heavily wooded, temporary ponds. Lymnaea elodes is more common in partially wooded, temporary ponds, and specializes on periphyton and carrion. Physa gyrina has a broad utilization of both the habitat and food dimensions of the niche. Helisoma trivolvis is a generalist in food preference, but was common only in a permanent pond. These data, and niche overlap estimates, predict that L. elodes and P. gyrina should have the greatest overlap on resources. Field experiments suggest that high overlap along the habitat and dietary dimensions of the niche results in competition in these freshwater snails. Interspecific competition decreased fecundity in P. gyrina, but not in L. elodes. For both species, interspecific competition had less of an effect than increased conspecific densities on growth rates. Physa generally did better in the less productive, temporary ponds, while L. elodes had higher fecundities and growth rates in a permanent, more productive pond. Lymnaea elodes was considered the better competitor because interspecific competition had smaller effects on growth and reproduction than intraspecific competition. The earlier reproducing P. gyrina may be able to exploit more ephemeral habitats as refuges. -from Author

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