CONGENERIC OCCURRENCES OF SPECIES OF DIAPTOMUS IN SOUTHERN ONTARIO LAKES

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Abstract
The vertical distribution of adult calanoid copepods was studied in 100 lakes in southern Ontario. In addition to Epischura lacustris, Limnocalanus macrurus, and Senecella calanoides, seven species of Diaptomus were recorded. Diaptomus minutus and D. oregonensis, the commonest species, coexisted in 45% of the lakes. In 9% a third species was also present. Coexisting populations of D. minutus and D. oregonensis were not well separated by their vertical distribution, but a third species, if present, occurred in deeper water than these two. Size displacement does not contribute to the ecological separation of D. minutus and D. oregonensis. The difference in size between populations coexisting in the same lake is less than between populations living in separate lakes.