Mechanisms of Density-Dependent Population Regulation in the Marine Copepod Amphiascoides sp. (Harpacticoida)*

Amphiascoides sp. was cultured in the laboratory for the first time. Culture method and data on its life cycle are given. Reproductive potential and behaviour (pairing incidence) were studied in relation to population density (i.e. to medium conditioned by a previously dense population) and in relation to food supply. It was found that: (1) conditioned medium reduces the number of ovisacs per female by reducing its fertile period and by extending the interval between release of successive pairs of ovisacs, older females being more susceptible to this inhibition; (2) conditioned medium causes partial sterilization (nonfertilization?) of eggs; (3) these effects are partly, but not completely, reversible when females are returned to fresh medium (delayed, density-dependent effects); (4) crowding itself, but not medium conditioned by crowding, reduces the number of eggs per ovisac; (5) ovisacs are not released in absence of food, and food supply triggers the release of ovisacs; (6) mating incidence is a function of food supply; (7) mating incidence is higher in groups than in isolated pairs; (8) repeated mating is necessary for sustained fertility; (9) infertile periods in females as a result of deprivation of food or males may be compensated for by extension of the normal ( 5 0 4 0 d) fertile period to maximally 80-100 d; (10) the generation period (nauplius to fertile adult) increased by 40 '10 in the course of laboratory existence. These mechanisms of true population regulation via negative feedback are discussed in the light of the 'paradox of evolution under competition': resources are limited, yet, those genotypes that are getting more numerous than others (higher fitness) win the competition (= positive feedback).