Relationship of fish and macroinvertebrate assemblages to environmental factors: implications for community concordance

Community concordance describes similarity in distributions and abundances of organisms from different taxonomic groups across a region of interest, with highly concordant communities assumed to respond similarly to major environmental gradients, including anthropogenic stressors. While few studies have explicitly tested for concordance among stream-dwelling organisms, it frequently is assumed that both macroinvertebrates and fish respond in concert to environmental factors, an assumption that has implications for their management. We investigated concordance among fish and macroinvertebrates from tributaries of two catchments in southeastern Michigan having varied landscape characteristics. Classifications of fish and macroinvertebrate assemblages resulted in groups distinguished by differences in taxonomic characteristics, functional traits, and stressor tolerance of their respective dominant taxa. Biological groups were associated with principal landscape gradients of the study region, which ranged from forests and wetlands on coarse surficial geology to agricultural lands on finer, more impervious surficial geology. Measures of stream habitat indicated more stable stream flows and greater heterogeneity of conditions at site groups with catchments comprising forests and wetlands on the coarsest geology, but did not distinguish well among remaining site groups, suggesting that habitat degradation may not be the driving mechanism leading to differences in groups. Despite broadly similar interpretations of relationships of site groups with landscape characteristics for both fish and macroinvertebrates, examination of site representation within groups indicated weak community concordance. Our results suggest that explicit responses of fish and macroinvertebrates to landscape factors vary, due to potential differences in their susceptibility to controls or to differences in the scale at which landscape factors influence these organisms

Shifting stream planform state decreases stream productivity yet increases riparian animal production

In the Colorado Front Range (USA), disturbance history dictates stream planform. Undisturbed, old-growth streams have multiple channels and large amounts of wood and depositional habitat. Disturbed streams (wildfires and logging < 200 years ago) are single-channeled with mostly erosional habitat. We tested how these opposing stream states influenced organic matter, benthic macroinvertebrate secondary production, emerging aquatic insect flux, and riparian spider biomass. Organic matter and macroinvertebrate production did not differ among sites per unit area (m−2), but values were 2 ×–21 × higher in undisturbed reaches per unit of stream valley (m−1 valley) because total stream area was higher in undisturbed reaches. Insect emergence was similar among streams at the per unit area and per unit of stream valley. However, rescaling insect emergence to per meter of stream bank showed that the emerging insect biomass reaching the stream bank was lower in undisturbed sites because multi-channel reaches had 3 × more stream bank than single-channel reaches. Riparian spider biomass followed the same pattern as emerging aquatic insects, and we attribute this to bottom-up limitation caused by the multi-channeled undisturbed sites diluting prey quantity (emerging insects) reaching the stream bank (riparian spider habitat). These results show that historic landscape disturbances continue to influence stream and riparian communities in the Colorado Front Range. However, these legacy effects are only weakly influencing habitat-specific function and instead are primarily influencing stream–riparian community productivity by dictating both stream planform (total stream area, total stream bank length) and the proportional distribution of specific habitat types (pools vs riffles).Griffith Sciences, Australian Rivers InstituteNo Full Tex