Variability in the parasitoid community associated with galls of Diplolepis variabilis (Hymenoptera: Cynipidae): a test of the distance decay hypothesis

Abstract

Galls of Diplolepis variabilis (Bassett) (Hymenoptera: Cynipidae) on their host plant Rosa woodsii Lindley (Rosaceae) support a diverse community of parasitoid and inquiline wasps that exploit the gall inducer and the gall itself. Here, we studied quantitative variation in local structure of the gall community in the Okanagan Valley of southern British Columbia, Canada, from the United States border north, to test the hypothesis that dispersal limitation would generate a distance decay in gall community similarity. We also explored gall community richness in relation to latitude, as the northern range limit of the gall inducer occurs within our study area. We found that gall communities exhibited strikingly similar composition across the study region, with most of the major inquilines and parasitoids present across the gall's range. However, the increased richness of rare parasitoid taxa near the northern range limits of D. variabilis generated a marginally significant positive relationship between gall community richness and latitude. Overall, our study suggests that dispersal constraints do not influence the composition of the Diplolepis Geoffroy gall community at regional scales, and that gall communities offer useful models for studying the association between community structure and range limits.

Insect responses to host plant provision beyond natural boundaries: latitudinal and altitudinal variation in a Chinese fig wasp community

“…Within more local communities, contrary species richness patterns have nonetheless been reported among gall wasp parasitoid assemblages in Canada (Bannerman et al. ) and fig wasps in South Africa (Hawkins and Compton ). The fig wasp community associated with F. microcarpa in southwest China, where planting has extended its range northwards by about 1000 km, changes in both species richness and composition with latitude.…”

“…Apparent exceptions to global-scale declines in parasitoid species richness at higher latitudes may often be a result of sampling bias Sime and Brower 1998;Quicke 2012). Within more local communities, contrary species richness patterns have nonetheless been reported among gall wasp parasitoid assemblages in Canada (Bannerman et al 2012) (Warren et al 2010). Which stages of the insects' life cycles are particularly climate sensitive are unclear, but low temperatures will influence larval development times, the ability of the adult offspring wasps to emerge from the figs, and their ability to migrate between trees to look for oviposition sites (Yang et al 2013).…”

“…At higher latitudes, potential hosts were present at lower densities both within individual figs and in terms of the proportion of the figs that contained any fig wasps. Differences in the dispersal ability of phytophagous and parasitoid NPFW could also contribute if some species go extinct locally each winter at higher latitude sites and there are annual rescue effects from populations further south (Bannerman et al 2012). The relative dispersal ability of different groups of fig wasps is unknown, but it is possible that dispersal among parasitoid species is hampered by the long ovipositors possessed by many species.…”

“…Relatively simple spatially defined insect communities associated with a single plant resource provide good systems to try to tease apart drivers of species distribution (Hawkins and Compton ; Bannerman et al. ). Large‐scale manipulations of these communities result when the distributions of their host plants are extended beyond their natural range margins, especially where the expanded range extends into areas subject to more extreme environmental conditions.…”

“…Phylogeographic history and interactions within complex large-scale communities often make the drivers of insect distributions and responses to environmental gradients difficult to distinguish (Buckley et al 2010;Romdal et al 2013). Relatively simple spatially defined insect communities associated with a single plant resource provide good systems to try to tease apart drivers of species distribution Bannerman et al 2012). Large-scale manipulations of these communi-ties result when the distributions of their host plants are extended beyond their natural range margins, especially where the expanded range extends into areas subject to more extreme environmental conditions.…”