Direct and indirect effects of fish predation on freshwater littoral benthos.

摘要

Predictions of direct and indirect consequences of predation by large and small sunfish were tested in a 2 X 2 factorial experiment conducted in large in situ enclosures. These predictions were: (1) large fish will reduce densities of large invertebrates, (2) small invertebrate densities will be enhanced by the removal of their predators and competitors, (3) small fish will compete with large invertebrate predators and deplete shared prey, (4) large and small fish will interact to produce lower survival and growth of invertebrate predators than would be predicted from an additive model, and (5) predation from large fish on fast growing Epitheca cynosura and competition with small fish will reduce the proportion of the cohort that develops in a univoltine manner.; The presence of large fish produced a statistically significant decrease in the density of large gastropods, but not in densities of large odonates or large chironomids. Trichoptera and small chironomid densities were higher in the presence of large fish.; The small fish imposed a surprisingly severe recruitment bottleneck on odonates and gastropods. Thus, expected negative direct effects on small invertebrates were potentially ameliorated, or reversed, by the removal of larger invertebrates.; Large fish did not produce a statistically significant effect on E. cynosura densities. But the presence of small fish resulted in reduced proportions of univoltine individuals, presumably due to competition. Counts of exuviae recovered from enclosure walls the following spring were reduced in the presence of both large and small fish. These exuviae could only have come from univoltine individuals, thus both large and small fish reduced the number of successfully emerging univoltine Epitheca cynosura.; At the end of the experiment, samples of periphyton and macrophytes were recovered to test for indirect effects of fish predation on these groups. Periphyton abundance and cell biovolume were increased in the presence of fish, presumably due to the removal of gastropods by the fish. Macrophyte dry weight was very reduced in the presence of fish, suggesting a chain of strong interactions from fish to snails to periphyton to macrophytes.