Community concordance among fish, aquatic invertebrates, and submerged aquatic plants in shallow lakes

Background/Question/Methods

Community concordance is the degree to which patterns in community structure are similar among different taxonomic groups across different ecosystems. Concordance analysis can provide insight into environmental factors associated with both strong and weak concordance in communities, clarifying overall patterns of ecosystem structure. The goal of this study was to test for community concordance among aquatic invertebrates and fish, aquatic invertebrates and submerged aquatic plants, and fish and aquatic plants in shallow lakes. In 2010 we sampled communities in 104 lakes dispersed across five ecoregions in Minnesota, USA. We used procrustes rotation analysis to test for significant community concordance among pair wise-comparisons of aquatic invertebrates, submerged plants, and fish. We also determined the average residual for each lake across the three concordance tests, and used an information-theoretic approach to assess the most parsimonious model for predicting weak community concordance in lakes. Candidate models were constructed from ecosystem state (turbid versus clear), nutrient levels, ecoregion, biomass of fish and aquatic plants, and species richness of plants, invertebrates, and fish.

Results/Conclusions

We found significant concordance between aquatic invertebrates and fish (P = 0.013), aquatic invertebrates and submerged plants (P < 0.001), but not between fish and aquatic plants (P = 0.481). A model using macrophyte biomass and summed biomass of planktivores and benthivores was the most parsimonious for explaining residuals from the concordance tests, and indicated the weakest concordance among invertebrates, fish and submerged plants occurred in lakes with high biomass of both submerged plants and fish. Shallow lakes exist as two alternative stable states of domination by submerged plants or phytoplankton, and high abundance of planktivores and benthivores generally favors the turbid state. However, relationships between submerged plants and fish are nonlinear due to time lags and other influences on plant abundance such as water depth. We suspect these nonlinear dynamics are responsible for both the absence of concordance between plants and fish and the reduced concordance among all three communities in lakes with high biomass of macrophytes and fish.