The coexistence of a predaceous copepod and a daphniid: Weeding and gardening in the Arctic

Summary

The predaceous copepod Heterocope septentrionalis and a prey species Daphnia middendorffiana commonly coexist in shallow arctic ponds. Ponds that lack this association are often inhabited by Daphnia pulex. Data are presented showing that Heterocope predation can eliminate or weed out D. pulex from ponds where D. middendorffiana and Heterocope exist. Heterocope predation is almost 10 times more intense on D. pulex than on D. middendorffiana. Other investigators have obtained evidence along the same lines, but they give no reports of an actual exclusion of D. pulex. In sampling a small pond during the mid to late 1970's we observed an unusual zooplankton assemblage consisting of D. middendorffiana, D. pulex, and Bosmina sp. Heterocope were inadvertently introduced into the pond in the summers of 1979 and 1980. When the pond was resampled in 1985 and 1986, Heterocope was well established, and D. pulex and Bosmina sp. were absent. Thus we believe Heterocope weeds out D. pulex from the ponds in which it exists and this eliminates D. pulex as a formidable competitor for D. middendorffiana.