Parasitoid-mediated effects: apparent competition and the persistence of host-parasitoid assemblages.

摘要

Indirect effects such as apparent competition (in which two hosts that do not compete for resources interact via a shared natural enemy) are increasingly being shown to be prevalent in the structure and function of ecological assemblages. The empirical and theoretical evidence for these enemy-mediated effects in host-parasitoid assemblages are reviewed. Questions are addressed about the design of experiments to test for apparent competition. Factors likely to affect the coexistence of host speciesthat share a parasitoid and are involved in apparent competition are considered. It is shown that parasitoid aggregation, and the switching effect that this can generate when hosts occur in separate patches, not only promotes persistence but is also strongly stabilizing. The broader consequences of these effects are discussed.