POPULATION STRUCTURES OF 2 SPECIES OF CAPRELLID AMPHIPODS (CRUSTACEA)

Population structures of Caprella laeviuscula Mayer and Deutella californica Mayer are compared and factors structuring the populations are discussed. Instars were determined by the number of articles in the antennules. The number of D. californica per instar continuously decreased after emergence from the brood pouch. Populations of Caprella laeviuscula had 1. 1) an initial decrease in numbers, 2. 2) an increase in cohort size at middle instars, and 3. 3) decreasing population size. For both species population declines were caused by molting-related deaths. Population structures of C. laeviuscula were also caused by selective predation, intraspecific conflict during amplexus, and by rapidly molting juveniles becoming slow molting as adults. Deviations from a 1 : 1 sex ratio in C. laeviuscula were attributed to selective predation on females. Differences in the age of becoming sexually mature reduce the probability that a chance predator would remove all mature females. © 1979.