Compositional dynamics of the macroinvertebrate community in a Missouri prairie stream
Prairie streams often exhibit intermittency in flow, a phenomenon that is predicted to occur in many other aquatic systems with the onset of global climate change. As this flow pattern becomes more common, it will be increasingly important to study and understand the communities that are adapted to these intermittent and unpredictable habitats. Since prairies streams are among the least studied of all aquatic systems, our study aimed to expand our understanding of the community dynamics of this system and, specifically, to explore the seasonal patterns of macroinvertebrate communities and the corresponding environmental gradients in a prairie headwater stream. Macroinvertebrate samples and corresponding environmental measures were collected from two distinct mesohabitats of one headwater prairie stream from the onset of stream flow to the end of flow weekly during spring of 2014. Specimens were identified to the lowest practical taxonomic level. Nonmetric multidimensional scaling (NMS) was used to find the main gradients present in the environmental data and multi-response permutation procedure (MRPP) was used to verify the natural groupings evident in the ordination. Indicator species analysis was used to compare the abundance of taxa in these groups. Differences in various community measures were compared using ANOVA.
Preliminary NMS results from the riffle dataset revealed two strong gradients in the data that account for a total of 77% of the variation in the original data set. A joint biplot of the NMS ordination and a matrix of the environmental data revealed that one gradient was closely associated with percentage of periphyton, percentage of filamentous algae, and temperature; the other gradient was closely associated with the number of stream substrates, percentage of leaf pack, and percentage of gravel. The sampling dates separated into three natural groupings corresponding to early, mid, and late spring. This grouping was confirmed by an MRPP (p<0.0005). Indicator species analysis showed that 11 taxa had significant indicator values (p<0.05) and included Simulium sp., Culicoides sp., and non-tanypodine chironomids. These results indicate that a distinct seasonal pattern exists for both the macroinvertebrate community composition and the environmental characteristics of the prairie stream. This pattern should be taken into account when choosing sampling dates for activities such as water quality monitoring and diversity surveys when working in systems with intermittent flow.