Chydorid (Cladocera) Ecology: Seasonal Patterns and Abundance of Populations in Elk Lake, Minnesota
1974
Population dynamics of chyorids from Elk Lake, Minnesota, were followed from May through October 1971 by means of three collecting methods. Emphasis was placed on data obtained by use of artificial substrate. This method was found to collect most species of chydorids living in the underlying substrate. A second method, funnel trapping, collected animals that migrated 10—20 cm vertically from their substrate into the funnel traps. Funnel trapping was found to be not very efficient at collecting all chydorid species, but to be useful for following overall population trends and for exploring the vertical movements of some species. A third method, called pattern sampling, was tried experimentally. It appears to collect most chydorid species, and also shows the mocro—distributions (or spatial arrangements) associated with population densities. Most chydorid species increase in population numbers during spring and fall, and decrease during midsummer. Chydoris have clumped or contagious patterns that fit the negative binomial distribution. A log/log relationship exists between estimates of the mean and variance over the sampling interval, May–October; this relationship establishes a relatively constant structural arrangement of patterns as reflected by the exponent k of the negative binominal, and by b of Taylor's power law. There are several possible explanations for chydorid clumping–heterogeneous habitat, aggregation about food sources, predation, lack of dispersal, and behavior. Future studies will be directed at evaluating the relationships between spatial patterns and population densities.
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