The effect of container size on the feeding rate of Heterocope septentrionalis, a freshwater predaceous copepod

The feeding rates of freshwater predaceous copepods have beenmeasured many times using enclosure experiments. Typically theseexperiments involve enclosing a known number of zooplanklonprey with a known number of predaceous copepods and determiningthe number of prey remaining after a set length of time. Variousfactors such as prey species and size have been shown to influencethe feeding rate of copepods. However, little attention hasbeen paid to the influence that container size may have on feedingrates. Using previously published data and some new data itwas found that container size has a major impact on the feedingrate of Heterocope septentrionalis, a predaceous freshwatercopepod common in North American arctic waters. In experimentswith Daphnia puiex, where container size varied from 0.3 to54 l (180 times), the measured feeding rate coefficient variedfrom –0.04 to –1.7 (42.5 times). Other prey speciesshowed similar changes, but the vulnerability of particularprey species to Heterocope predation remained consistent acrossthis range of expenmental containers. The reason for the containereffect is not known, but it is postulated that edge avoidanceby Heterocope may account for the observed change in feedingrate.