Seasonal differences in diversity of macroinvertebrate and fish taxa in a Midwestern stream

Most biomonitoring projects focus on single species groups at time scales either too short or too coarse to detect intra-annual oscillations in biodiversity. Using a multifaceted approach, we compared diversity indices of larval macroinvertebrate families and fish species in a Midwestern stream during spring and fall of 2009-2013 and discovered contrasting patterns in alpha and beta diversities between the seasons for the two taxa groups. Compared with spring, both alpha and beta diversities were significantly higher during fall for macroinvertebrates; on the contrary, only alpha diversity differed between the seasons for fishes. For both taxa, we partitioned the overall beta diversity to identify contributions of temporal and spatial beta diversities on the observed differences. The observed patterns for macroinvertebrates were likely the result of season acting as environmental filter, but stochastic dispersal and recruitment processes were likely more important in driving fish diversity patterns. In light of widespread conservation and restoration efforts in the Midwestern streams, it seems prudent to study community composition frequently so that baseline alpha and beta diversities can be obtained for organisms at different taxonomic levels and during different seasons.