Interacting Influences of Density and Preference on the Emigration Rates of Some Lotic Chironomid Larvae (Diptera:Chironomidae)

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Abstract
The effects of manipulations of density and sediment type on the emigration rates of chironomid larvae (Diptera:Chironomidae) from Hunt Creek, Montmorency County, Michigan, USA, were examined in artificial stream chambers. Both basic sediment suitability and population density were found to affect larval emigration rates. Furthermore, their interaction lead to rates of emigration not predictable from an examination of either factor alone. A simple model of habitat suitability was developed and fit to the experimental data. The fitted model provided estimates of habitat carrying capacities for two important chironomid species and for a generalized chironomid assemblage. A comparison of these estimates with observed field densities indicated that competitive displacement of individuals probably occurs regularly in sand sediments. An examination of field data from 1975—1976 revealed a suppression of species diversity and of competitor standing crops by the dominant sand species. Together these results suggest that competitive interactions have an important influence on the spatial distribution of chironomid larvae in Hunt Creek.