Allelopathy between zooplankton: a mechanism for interference competition.

The filtering rate of the copepod Diaptomus tyrrelli is reduced in the presence of its potential competitor and predator, Epischura nevadensis, by as much as 60 percent. This effect is caused by a chemical released into the water by Epischura. The chemical does not pass through dialysis tubing with a pore size of 10(4) angstroms, indicating that it is a large molecular weight compound. The reduction in filtering rate is the result of interference competition between two species and may be linked to the evolution of a mechanism for avoiding predation.