The importance of valuing resources: host weight and contender age as determinants of parasitoid wasp contest outcomes

When two animals compete directly for an indivisible resource, the outcome may be influenced by differences in the contestants' intrinsic contest abilities and prior owner status, collectively termed ‘resource-holding potential’, and also by any difference in the values that contestants place on the resource. Using owner–intruder contests and owner–owner contests between females of the parasitoid wasp Goniozus nephantidis, we investigated the influence of resource value asymmetries generated by differences in contestant age and by the size of the host resource, while taking resource-holding potentials into account. When owners and intruders competed, intruder success increased with both intruder age and relative body size, suggesting that larger females had greater contest ability and that older intruders valued more greatly the opportunity to obtain a host. The size of the host did not influence the outcome of owner–intruder contests but in owner–owner contests, in which asymmetries in ownership status were absent, both larger females and owners of the larger, more valued, hosts were advantaged. Overall, studies of G. nephantidis show that asymmetries in both resource-holding potentials and resource values interact to influence contest outcomes. Despite a large literature on animal contests, there have been few studies that have evaluated these influences both simultaneously and separately.