Host-Mediated Competition in a Bloodsucking Insect Community

Abstract

(1) Communities of adult bloodsucking insects utilize host blood as a common resource, and often exhibit niche partitioning suggestive of interspecific competition. To investigate competition in parasite communities, a field study was made of horsefly species (Diptera:Tabanidae) attacking Camargue horses. (2) The fitness of a fly in the presence of potential competitors of the host (other flies) was measured in terms of this residence time, the duration of a single visit to the host. Longer residence times were associated with larger bloodmeals. (3) Evidence for intra- and interspecific competition was found for two tabanid species, and was associated with parasite density and host defensive behaviour. At higher overall rates of fly landing, the residence times of individual flies decreased as a result of increased host grooming. (4) A simple model of host-mediated competition is presented, and its implications for the evolution of community structure are discussed.