Species diversity of chydorid fossil communities in the Mississippi Valley

Abstract

The species diversity and equitability component were calculated for the fossil chydorid community recovered from 45 lakes in the Mississippi Valley. The lakes fall into three groups, natural lakes, artificial lakes, and oxbow lakes. Where the diversity and equitability component were low it was discovered that in nearly all cases this was due to the superabundance of Chydorus sphaericus. While the number of species present tended to be greater in the north, the species diversity was significantly greater in the southern part of the transect. The chydorid fossil populations were correlated to neither conservative parameters of the lake water nor parameters of the sediments. However, the populations recovered were significantly greater for the natural lake group compared to the other two lake groups. Species diversity was negatively correlated to population size for the natural lakes, while the opposite positive significant correlation was found for the other two lake groups. It is suggested that the correlations found between species diversity and sedimentary parameters could be caused by turbidity being high in the artificial and oxbow lakes. This could retard the cultural eutrophication of these lakes. This factor is absent in the natural lakes and has resulted in rapid eutrophication causing loss of diversity and instability in the chydorid communities in these lakes.