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Study of vertical segregation, seasonal separation and size differences as mechanisms for the coexistence of Diaptomus minutus, D. oregonensis, and D. sanguineus (Calanoida: Copepoda) Sandercock, Gail Ann

Abstract

Three species of Diaptomus (D. minutus. D. oregonensis and D. sanguineus, in order of increasing size) occur in Clarke Lake, Ontario. The following mechanisms have been suggested in the literature to explain the occurrence of congeneric Diaptomus species; vertical segregation, seasonal separation and size differences. In Clarke Lake D. minutus was found in the upper five metres, separated from D. sanguineus which occurred below the six metre level. A distinct size difference with no overlap was observed between D. minutus and D. sanguineus. D. minutus was also distinctly different from D. oregonensis in size. The seasonal maxima of these two species were distinct, that of D. minutus was in the spring, and of D. oregonensis in the summer months. D. oregonensis was separated seasonally from D. sanguineus. The latter species had a seasonal maximum in the spring. D. oregonensis was found above five metres and so was segregated vertically from D, sanguineus. A combination of two mechanisms seems to enable the coexistence of each of the three Diaptomus species-pairs in Clarke Lake. It is suggested that in general two or more mechanisms must be operative for the co-occurrence of Diaptomus species.

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