Net Accumulation Rates and the History of Cladoceran Communities

Calculation of net accumulation rates for microfossils in Frains Lake, Michigan, reveals that (1) Daphnia has been an important competitor most of the time, except during the last 140 years; (2) when Daphnia was rare, Bosmina was abundant, and vice versa; (3) extinction of larger species of Daphnia, reduced abundance of Daphnia, and simultaneous increases in Bosmina and Chydorus, all coincide with forest clearance 140 years ago. Man's activities at that time appear to have caused either directly or indirectly a major increase in the number of planktivorous fish in Frains Lake, and the changes seem associated with the extension of littoral vegetation.