Abstract

Climate change is causing species to expand their ranges poleward into new locations. Since diversity decreases towards the poles, they will move into less diverse recipient communities, losing interactions with species that fail to follow and gain new interactions with species with which they are not coevolved or coadapted. A loss of or less effective interactions with competitors and enemies may provide high “niche opportunities” and result in “ecological release.” High niche opportunities for range-expanding species can result from mismatched traits among antagonistically interacting species in recipient communities. Here, we study a poleward range-expanding oak gall wasp, Neuroterus saltatorius (NS) (Hymenoptera: Cynipidae), which occurs on Quercus garryana, and is experiencing ecological release in its expanded range of Vancouver Island, BC. We measured morphological characteristics of co-occurring cynipid hosts and interacting parasitoid wasps to examine if community traits of interacting species vary along a latitudinal gradient, and between the native and expanded range of NS. We measured morphological traits of 23 cynipid morphospecies and their associated parasitoids collected from 540 trees at 18 sites in 6 regions along the range of Q. garryana (northern California, US to Vancouver Island, BC). We predict that community traits of the recipient community in the expanded range will be less specialized and more divergent from the range-expanding host than community traits in the native range. Trait-mismatching between NS and recipient communities of interacting host and parasitoids may facilitate high niche opportunities at higher latitudes where NS is outbreaking.