VARIABILITY IN PARASITOID COMMUNITY STRUCTURE

1. Two data sets were compiled, the first representing the parasitoids known from 381 well-studied host species in 56 genera and the second representing the parasitoids from 389 populations of 66 host species, to examine between- and within-host-species variability in parasitoid complexes and to estimate levels of guild occupancy in parasitoid comm unities. Analyses were based on assigning parasitoids to each of nine guilds distinguished by the host stage attacked, mode of parasitism, a nd the host stage from which parasitoids emerge. Host taxonomy and hos t feeding type were used to evaluate the relative influence of histori cal and ecological processes on parasitoid guild structure. 2. The num ber of parasitoid guilds that hosts support was highly variable both a mong host species and among populations within host species, Guild num bers were strongly associated with host taxonomy but weakly with host feeding type, suggesting that historical patterns of host and parasito id evolution are much more important determinants of parasitoid guild structure than are current biological and ecological characteristics o f hosts. The bulk of the variability in the number of parasitoid guild s occurred among host orders and among host species within genera. Dif ferences among host families within orders, and among genera within fa milies, contributed relatively little variance. 3. Summing levels of o ccupancy by parasitoid guilds within host genera indicated that a maxi mum of 69% of the potential parasitoid guilds that hosts could support are actually present. Using data from multiple populations within eac h host species indicated a maximum guild occupancy rate of 73%. Thus, we estimate that at least 25% of the parasitoid functional groups that could persist are absent from communities, suggesting that parasitoid communities are infrequently saturated with species. Across all paras itoid guilds, distributions of host utilization were not associated wi th either host taxonomy or host feeding type. However, levels of host utilization by specific guilds were associated with both variables. 4. Our results are concordant with those arising from similar analyses o f the guild structure of the insect herbivores of British trees, sugge sting that undersaturation is widespread in insect communities at all trophic levels, and the functional structure of communities is largely due to chance historical events.