EFFECTS OF CANNIBALISM AND INTRAGUILD PREDATION ON PONDSKATERS (GERRIDAE)

Gerrid-gerrid predation can limit gerrid numbers and affect phenological patterns. In a field experiment with G. pingreensis, survival of small gerrids was dramatically reduced in the presence of larger juvenile instars, and survival of larger nymphs to the adult stage was significantly greater when given access to younger stages than when held by themselves. Mass of teneral female cannibals was significantly greater than that of females not given access to younger stages, but there was no effect on male mass or on development time of either sex. Predation by G. pingreensis on G. buenoi was not consistently more common than cannibalism in either laboratory or field experiments. Thus, dominance of G. pingreensis on permanent lakes does not result from selective depredation of other species, but must relate primarily to life history traits that allow individuals to colonize, breed and develop rapidly in the spring. Intra- and interspecific predation are regulated by a mix of intrinsic and extrinsic contingencies. Starvation and habitats with low complexity were associated with increased levels of gerrid-gerrid predation. Tendency to attack other gerrids is higher in G. pingreensis than in G. buenoi but nymphs of G. buenoi have specific behaviour to avoid being captured by other gerrids. We found no differences in cannibalistic tendencies between males and females, or between pre-diapause and breeding bugs.