Influence of elevation gradient on Cynipid galls and their associated insect communities: the case of Quercus rugosa (Fagaceae)

The galls induced by cynipids in host oaks have been proposed as biodiversity hotspots. They constitute support for the development of arthropod communities of great diversity and functional complexity that find in them nutrition and protection from external abiotic and biotic elements which change according to environmental gradients. We characterize the abundance, richness, and diversity of gall-inducing cynipids associated with the galls of the host oak Quercus rugosa, through an elevation gradient. This study was conducted on 140 oak trees belonging to seven populations (20/site) in central Mexico. We identified 39 gall-inducing cynipid species (Cinipini), three inquiline species of galls (Synergini), and seven parasitoids of gall-inducing cynipid (Chalcidoidea), and the secondary fauna was characterized by eleven arthropod orders. We detected a positive and significant effect exerted by the altitudinal gradient on abundance, species richness, and diversity of gall-inducing cynipids, parasitoids, inquilines, and secondary fauna (order richness level). We documented positive and significant relationships between the gall-inducing cynipids and their parasitoids, inquilines, and secondary fauna in terms of species richness, diversity, and abundance of individuals. Arthropod community composition associated with gall-inducing cynipids differed among localities. This study suggests that gall-inducing cynipids in Q. rugosa act as ecosystem engineers that modify the host plant to offer a new habitat to other arthropods. Also, our results supported that Cynipid gall acts to protect the galls-associated arthropod community from unfavorable abiotic conditions throughout the altitudinal gradient.