Polymorphism and predation: The effect of invertebrate predation on the distribution of two varieties of Daphnia carinata in South India ponds 1

Two varieties of Daphnia carinata showed a disjunct distribution in four ponds in South India: an exuberant variety, cephalata, was generally restricted to those ponds that did not contain a more usual morph, forma typica, and vice versa. The ponds studied were quite similar except for the presence of large Anisops spp. in the two ponds containing cephalata and their absence or low abundance in those containing forma typica. Experiments showed that the exuberant cephalata form was frequently able to evade capture and thus was preyed upon at a much lower rate than forma typica. In the absence of such predation, however, forma typica had the competitive advantage: its survivorship and rate of increase were higher and its feeding rate more rapid. Thus the exuberant morphology of D. carinata var. cephalata appears to be an adaptation that reduces invertebrate predation.