PhD student University of Vermont Burlington, Vermont, United States
Communities change along elevational gradients due to local abiotic and biotic conditions, but for any given taxonomic group, the overall diversity-elevation relationship can be difficult to predict. The Nearctic solitary Hymenoptera include 14 superfamilies varying in speciosity, morphology, and functional diversity. Species energy theory predicts functional diversity will drive Hymenoptera clades’ different alpha and beta diversity patterns over elevational gradients depending on the distribution of differentially relevant resources. However, only a small portion of Hymenoptera species have definitive host associations, and the collective preferences of carnivorous clades are too complex to predict dynamics along elevational gradients. As an alternative to host availability itself, I predict the mean ability of a Hymenoptera clade to disperse to distant energy sources and the efficiency of their energy uptake decrease species turnover and increase richness, respectively. Furthermore, clades with larger global species pools are assumed to include more functional diversity, making them more likely to have niches in rare habitats. To see if these characteristics predict diversity-elevation relationships of each clade, I collected solitary Hymenoptera weekly from June to September 2020 along two replicate elevational gradients (500-1200m a.s.l.) and low elevations (May-Oct 2020) using Moericke yellow pan traps and hand-netting in Vermont, USA.
Of the five superfamilies (417 morphospecies) analyzed so far, the two clades most reliant on floral resources and least efficient clades in terms of mean effort required per progeny, Apoidea and Chrysidoidea, were almost absent from the mountain sites and entirely nested within low elevation communities. While predation, pollination, and kleptoparasitism functions were largely absent from the elevational gradients, parasitoids were plentiful. Species richness of Ceraphronoidea (~102 species in Nearctic), Cynipoidea (~104), and Ichneumonidae (~106), but not Braconidae (~105) had hump-shaped distributions over elevation, failing to indicate a connection between species pool size and modality. So far, I conclude that clades’ reliance on flowering plants and less efficient trophic interactions create steep declines in alpha diversity over elevation and a strong nestedness component of beta diversity compared to other Hymenoptera. Studies of higher-order taxa’s spatial ecology should therefore explicitly consider broadly different energy needs and acquisition efficiencies of the monophyletic clades within.