The addition of non-native species and loss of native species has modified the composition of communities globally. Although changes in β-diversity over time have been well documented, there is a need for studies incorporating multiple time periods, more than one dimension of biodiversity, and inclusion of nestedness and turnover components to understand the underlying mechanisms structuring community composition and assembly. Here, we examined temporal changes in functional dissimilarity of fish communities of the Laurentian Great Lakes and compared these changes to those of taxonomic dissimilarity by decade from 1870 to 2010. We used Jaccard-derived functional dissimilarity index to quantify changes in functional β-diversity within communities, between all possible pairs of communities, and across all communities through time.
Results/Conclusions
Similar to patterns in taxonomic dissimilarity, each community differentiated over time, with Lake Superior changing the most (~24%) and Lake Ontario the least (~14%) compared to the historical community of 1870. However, while communities have become taxonomically homogenized, functional differentiation has occurred between communities over time. This is likely due to historically high functional similarity between the communities. The higher taxonomic turnover relative to functional turnover indicates that the species being replaced are functionally redundant, and this could be the result of the relatively harsh environmental conditions of the Laurentian Great Lakes region and/or the glacial history of the region. The biotic differentiation observed is likely due to the addition of non-native species with functional traits unique to the region or the loss of functionally redundant native species. This study is the first to comprehensively examine changes in patterns of taxonomic and functional β-diversity between the historical and present-day community, as well as continuously examine the dynamics between those two points in time.