BIOLOGICAL HOMOGENIZATION OF FRESHWATER MUSSELS FROM HUMAN ACTIVITIES

Freshwater mussels are among the most heavily impacted groups of living organisms from anthropogenic activities. This group has extremely high rates of extinction and threat because of their typically narrow geographic range and freshwater habitats which are dramatically altered from dams, water pollution and many other human activities. Mussels are also being highly affected by invasive mussels such as the zebra mussel and the Asian clam. We hypothesize that this combination of high rates of extinction and invasion of non-native species may be causing biological homogenization, which is driven by the replacement of distinctive native species by widespread non-native species. To examine this hypothesis, we collected data from many published freshwater mussel surveys (including relict shell remains) in various parts of the U.S. including the Midwest and Southeast. We focused on surveys that included data collected at different time intervals at each locality so that we could compare the mussel species composition among different localities at different time intervals to determine if there was any change (increase or decrease) in the similarity of mussel communities through time. Our metric was the Jaccard Index (JI) and we analyzed changes in the JI among sites at different time intervals. Our preliminary results indicate that there is no simple pattern of increasing homogenization through time. While there is a tendency for many mussel communities to increase in similarity, we also found many cases where the communities became more dissimilar. This latter occurred because of the extinction of native species that were shared among sites but are no longer present at one or both localities. Our findings are consistent with findings in other taxa, such as plants and birds, where human activities have been found to increase community similarity in some cases and decrease similarity in others.