Growth and voltinism of lotic midge larvae: Patterns across an Appalachian Mountain basin

Abstract

The influence of thermal regime upon community-level growth rates and voltinism was estimated for larval Chironomidae inhabiting litter accumulations in four streams located in an Appalachian Mountain basin. Groups of larvae were confined in growth chambers and incubated in situ at time intervals representing the observed range of annual thermal variation. Estimates of daily growth rates (g) were derived from change in average length over the incubation period. Using multiple regression, I found temperature and larval size to have significant positive and negative effects on g, respectively. Equations derived for each stream described a substantial proportion of the variance among observed g values (R² = 0.71–0.82) but did not differ significantly. Therefore, the data from all streams were combined to derive a single general equation which, along with larval size distribution, biomass, and temperature data, was used to model the variation in annual biomass turnover (G) and hypothetical size-dependent voltinism among the study streams. Size distribution of larvae did not differ significantly among streams and variation in G (range = 12.8–18.6) was attributed primarily to variation in thermal regime. Differences in voltinism were predicted to be minor but were closely dependent on both terminal size of larvae and thermal regime. The model provides evidence that spatial variation of G on the order of 31% can be expected for midge communities within a 2 area of this Appalachian Mountain basin.