An example of niche partitioning in three coexisting freshwater cyclopoid copepods

Vertical distributions at noon and midnight of copepodites,males and females of three coexisting species of freshwatercyclopoid copepods, Cyclops vicinus (a cold-water form), Thermocyclopscrassus and Mesocyclops leuckarti (warm-water forms), were studiedin Dreiangel Lake, a small eutrophic gravel pit. The largestspecies, C. vicinus, inhabits deep water layers, both at noonand midnight, while the smaller species, T.crassus and M.leuckarti,inhabit upper water layers. In all three species, copepoditesand males live closer to the water surface than females. Insummer, abundance of the smallest species (T.crassus) is highest,although finite birth rates are lowest. The distribution patternsand population characteristics suggest that the vertical distributionof cyclopoid copepods in Oreiangel Lake is mainly governed byfish predation; different temperature tolerances and preferencesof the three species may also be of significance.