Résumé
1) Life-history traits within ecological communities can be influenced by
regional environmental conditions (external filters) and community-wide
density-dependent processes (internal filters). While traits in a regional
context may converge to a narrow range of values because of environmental
filtering, species belonging to a guild may present contrasting traits as
a means of niche differentiation, allowing coexistence whilst exploiting
the same resources. 2) To disentangle the role of external and internal
filters on phenotypic diversity within ecological communities, we examined
the patterns of life-history trait variation within a guild of insect
parasitoids during two successive years across three contrasted regions in
relation to several ecological factors. 3) By combining a mean-field
approach and an analysis of phenotypic variance across organizational
levels (from individual to guild), we showed that the patterns of
life-history trait variation across regions are consistent with local
adaptation or adaptive phenotypic plasticity while the patterns of
phenotypic variation within regions suggested how coexistence modulates
life-history traits expression through niche differentiation. 4) Within a
given region, phenotypic pattern of parasitoid life-history traits may
also arise from bottom-up effects of trophic webs: insect host species
could also control parasitoid life-history traits in nature. Our results
also showed that parasitoid life-history traits presented contrasting
variation patterns according to the sampling year, suggesting temporal
variations in evolutionary and ecological dynamics of parasitoid species.
5) The application of such trait-based studies to insect parasitoids has
the potential to provide further insight on how agricultural environments
contribute to differential diversification among natural enemies guilds,
highlighting the main role of agricultural landscape management for
organisms' responses.