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Resource Overlap and Competition in Pond Snails: An Experimental Analysis
Author(s) -
Brown Kenneth M.
Publication year - 1982
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1938959
Subject(s) - interspecific competition , biology , competition (biology) , ecology , habitat , fecundity , niche , generalist and specialist species , ecological niche , niche segregation , detritivore , intraspecific competition , periphyton , invertebrate , population , biomass (ecology) , demography , sociology
Several ponds were quantitatively sampled in northeastern Indiana, and the relative abundances of pulmonate snails were determined. Feeding preferences, on several natural food types, were estimated in feeding trials in the laboratory. The two main objectives of the study were to determine (1) which species pair had the highest resource overlap along the habitat and food dimensions of the niche, and (2) whether these species actually suffered decreased growth or fecundity due to competition. Sampling data and feeding trials indicate that Aplexa hypnorum is a specialist in both habitat and food use, and is a 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 in this study only in a permanent pond. These data, and niche overlap estimates based on them, predict that L. elodes and P. gyrina should have the greatest overlap on resources. Manipulative field experiments, in three different ponds, 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, in two separate experiments. 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. Data on size—specific reproductive rates suggest that the earlier reproducing P. gyrina may be able to exploit more ephemeral habitats as refuges.