Agonistic interactions and their implications for parasitoid species coexistence

When 2 species exploit the same limiting resource, interspecific competition may lead to the exclusion of one of them. For the 2 species to coexist, resource exploitation strategies exhibited by both species must somehow counterbalance each other. Eupelmus vuilleti and Dinarmus basalis are 2 solitary parasitoid species exploiting the same hosts (larvae and pupae of Callosobruchus maculatus) in sub-Saharan Africa. They display different strategies when in indirect (exploitative) competition situations: D. basalis females tend to avoid multiparasitism, whereas E. vuilleti females tend to accept parasitized hosts. Therefore, E. vuilleti seems dominant and potentially able to exclude D. basalis. Thus, how can D. basalis persists when in sympatry with E. vuilleti? Here, we studied the strategies adopted by females of either species when in direct (interference) competition. We investigated the effect of certain factors affecting females' competitive abilities or the value that they place on the resource such as female size, female physiological state (egg load), the quality of the habitat previously encountered by females (rich or poor in hosts), and the ownership status. This study revealed that D. basalis females tended to outcompete E. vuilleti females when competing for a given host. They were more aggressive and won most contests, whereas E. vuilleti females only won contests when being an owner with a high egg load or when having experienced high host availability. Thus, both species seem to show counterbalancing strategies when in exploitative and interference competition, which could promote their coexistence in nature. Copyright 2011, Oxford University Press.