MACROINVERTEBRATE COMMUNITY STRUCTURE IN RELATION TO MEASURES OF LOTIC HABITAT HETEROGENEITY

We examined the relationship between habitat heterogeneity and benthic macroinvertebrate assemblages in thirty-two 2nd to 6th order wilderne ss streams in central Idaho. Twenty-one environmental measures were ev aluated for each stream with their heterogeneity expressed in terms of coefficients of variation (CV's). Although the annual range in water temperature was greater in the larger (5th and 6th order) streams, mos t other habitat measures showed greater variation among smaller stream s (2nd order) than larger streams. Mean habitat-CV's also were about 2 0 % greater for smaller (2nd order) than larger (5th and 6th order) st reams, suggesting a homogenizing influence of stream size on habitat h eterogeneity. Multivariate analyses of the habitat measures clearly se parated 5th and 6th order streams from less than or equal to 4th order streams, further indicating major environmental differences between l arger and smaller stream systems. Multiple regression and canonical co rrespondence analysis revealed that some biotic properties, e.g. % shr edders, were associated with stream size, reflecting longitudinal chan ges in food resource availability or annual variation in temperature, while others, e.g. Shannon's diversity, were more dependent on measure s of within-reach habitat heterogeneity.