The effects of habitat heterogeneity on community stability and food web structure in stream benthic communities

Background/Question/Methods Previous research suggests that community stability increases with habitat heterogeneity. However, the exact mechanisms that produce this relationship. The objective of this study was to determine if high substrate heterogeneity would increase stability among a local benthic macroinvertebrate community, due to increased refugia from predators. We manipulated substrate heterogeneity in twenty enclosures placed along a 300m reach of Six Mile Creek in the Clemson University Experimental Forest. We used an analysis of covariance type design with the presence/absence of a dominant omnivore (crayfish, Cambarus bartonii) as a fixed factor, and a gradient of substrate heterogeneity as a continuous factor.  Substrate heterogeneity ranged from plots of nearly homogeneous substrate composition to plots of extremely diverse substrate composition including several different cobble classes as well as sand, gravel, and CPOM. After an acclimation period of two weeks, we sampled the macroinvertebrate community weekly (for eight weeks) to track changes in community structure.

Results/Conclusions

We predicted that stability in enclosures containing crayfish would increase with substrate heterogeneity while there would be no change in stability with habitat heterogeneity in enclosures without crayfish.  We found that community stability based on both community composition and aggregate measures of stability (e.g., total abundance) tended to increase with increasing habitat heterogeneity.  However, the presence of large, omnivorous crayfish altered the relationship between stability and habitat heterogeneity through impacts on organisms at multiple trophic levels.