Stream community structure in relation to spatial variation: the influenceof mesohabitat characteristics

Community structure of benthic macroinvertebrates was studied in six first- through fourth-order streams in northeast France, to elucidate changes in richness, abundance, diversity and evenness of mesohabitat assemblages as a function of environmental conditions. Patch samples were subjected to mult ivariate analyses to determine: (i) relationships among seven indices descr ibing community structure (structure parameters); (ii) relationships among seven environmental variables; (iii) the relationship between community str ucture and environmental characteristics of patches. Faunal data showed tha t indices measuring the distribution of individuals among taxa (evenness, d ominance) and richness are prominent in describing the structure of macroin vertebrate communities of mesohabitats. The analysis of environmental data demonstrated a major differentiating ability of current velocity and strong inter-relations among in-stream hydraulic-dependent parameters in structur ing the mesohabitat environment. The co-structure (= relationship) between community organization and environmental variables indicated that substrate may be a primary determinant of community structure. Current velocity and water depth emerged as secondary factors. Trends in community structure wer e closely related to the spatial variability of mesohabitats. Species richn ess increased with habitat heterogeneity. Total abundance increased with tr ophic potentialities of patches. Equitability and diversity seemed to incre ase with patch stability.