Factors Influencing Cannibalism, a Mechanism of Population Limitation in the Predator Notonecta hoffmanni

Factors influencing cannibalism rates in the freshwater insect predator Notonecta hoffmanni were analyzed in a series of field and laboratory experiments. Starvation was rejected as a cause of nymphal mortality. Cannibalism was related to both the relative and absolute abundances of alternative food, the cannibal's age, and the presence of refuges for the vulnerable nymphs, although the predator's state of hunger also influenced cannibalism rates. Cannibalism occurred when there was physical proximity between different age—classes even if alternative food were abundant. Long—term feeding history had no effect on cannibalism, which is a rapid response to rapid response to immediate food availibility. The population consequences of cannibalism seem analogous to those of dominance and spacing behavior, causing a decline in population size before animals are actually killed by the limiting resource, and increasing the chances that at least some relatively well—fed individuals will survive and reproduce successfully.