Disentangling the drivers of β diversity in invertebrate communities along a latitudinal gradient

Background/Question/Methods

Quantifying variation in the composition of communities, and differences in community composition among sites (β diversity), along spatial gradients such as latitude can provide insight into the mechanisms structuring communities. β diversity can be quantified as the dissimilarity in community structure among a set of sample units within a given spatial extent. Variation partitioning of β diversity can reveal whether underlying environmental factors are associated with certain community assemblages, a concept known as environmental sorting, or that these assemblages are simply a random draw from the broader species pool. Disentangling these two possibilities is key to understanding the underlying processes that structure communities. Such insight can ultimately aid in the understanding the sensitivity of communities to variation in environmental conditions, which has many conservation implications. In this study, we quantified variation in aquatic invertebrate communities and environmental factors among freshwater lakes along a latitudinal gradient. 

Results/Conclusions

We found that β diversity increases with increasing geographic distance between sites. This pattern likely reflects differences in the regional species pools among geographic locations along the latitudinal gradient. However, β diversity does not differ within the comparisons of communities in the North and the South. Environmental variables (pH, dissolved oxygen, water temperature, and conductivity) are also associated with β diversity, but these environmental conditions varied little with latitude. Finally, both species richness and Shannon diversity show significant latitudinal patterns: both species richness and Shannon diversity increased as latitude decreased, a result consistent with previous studies. We also found that environmental factors were good predictors of species richness and Shannon diversity, but these variables differed from those that explained β diversity. Overall, our results suggest that local environmental variation is more important for explaining variation in species composition among sites than space alone. Moreover, these results suggest that different environmental factors are important for explaining species richness among sites than variation in community compositions between sites.