The influence of habitat heterogeneity on variability in stream macroinvertebrate communities

Spatial heterogeneity inherent in ecological systems impacts both diversity and community structure. However, little is known about the influence of habitat heterogeneity on temporal variability in communities. I performed several studies to examine the effects of habitat heterogeneity on variability in the benthic communities of small, New Hampshire streams. I focused on substrate heterogeneity since substrate has wide-ranging influences on population, community, and ecosystem processes in streams.;An observational study of the relationship between substrate heterogeneity and macroinvertebrate community variability found that variability decreased linearly with increasing heterogeneity. However, an experimental manipulation of substrate heterogeneity in the following year produced interesting variations. Following a large drought, community variability increased linearly with heterogeneity. However, as communities recovered through several weeks, the relationship between variability and heterogeneity progressively changed until it resembled the inverse relationship from the observational study.;I also experimentally determined whether habitat heterogeneity effects on drift and colonization could possibly generate the observed variability relationships. Habitat heterogeneity, discharge, temperature all had strong effects on drift and colonization of most functional groups. Responses of drift and colonization to heterogeneity differed widely among functional groups and suggested that high habitat heterogeneity may interfere with feeding of predators and shredding detritivores.;Finally, I examined change in benthic macroinvertebrate community composition during a flood and a drought in two streams. I found that while communities changed measurably during both disturbances, aggregate measures of community change (taxon richness and total abundance) were relatively unaffected during the drought due to functional compensation, while both aggregate and compositional measures of community change were strongly affected during the flood. In addition, there was little influence of heterogeneity on community change during the drought, but high heterogeneity buffered changes in functional group abundances during flooding. The results suggested that a community can respond uniquely to different hydrologic disturbances and that a single measure of community change, aggregate or compositional, is not appropriate for all scenarios.;One important collective result of these studies is that habitat heterogeneity had pervasive strong effects on variability in communities and should be further considered in future contemplations of community change.