Concordance of taxonomic composition patterns across multiple lake assemblages: effects of scale, body size, and land use

We assessed environmental gradients and the extent to which they induced co ncordant patterns of taxonomic composition among benthic macroinvertebrate, riparian bird, sedimentary diatom, fish, and pelagic zooplankton assemblag es in 186 northeastern U.S.A. lakes. Human population density showed a clos e correspondence to this region's dominant environmental gradient. This ref lected the constraints imposed by climate and geomorphology on land use and , in turn, the effects of land use on the environment (e.g., increasing lak e productivity). For the region as a whole, concordance was highest among a ssemblages whose taxa were relatively similar in body size. The larger-bodi ed assemblages (benthos, birds, fish) were correlated most strongly with fa ctors of broader scale (climate, forest composition) than the diatoms and z ooplankton (pH, lake depth). Assemblage concordance showed little or no rel ationship to body size when upland and lowland subregions were examined sep arately. This was presumably because differences in the scales at which eac h assemblage integrated the environment were obscured more locally. The lar ger-bodied assemblages showed stronger associations with land use than the diatoms and zooplankton. This occurred, in part, because they responded mor e strongly to broad-scale, nonanthropogenic factors that also affected land use. We argue, however, that the larger-bodied assemblages have also been more severely affected by human activities.