PS 8-109 - Wasp community changes across the growing season in Mid-Columbia Basin Oregon white oak (Quercus garryana) habitat fragments

Abstract: Land use change represents the leading cause of biodiversity decline worldwide. Conversion of natural habitats to agricultural uses often leaves small remnants of the original habitat where agriculture is not feasible (e.g., steep slopes). Habitat conversion and subsequent fragmentation not only reduces biodiversity, but also negatively affects numerous ecosystem services. Wasps represent an important component of invertebrate diversity, yet knowledge about their diversity and community composition within these systems is lacking. As land conversion continues, it is increasingly important to understand if habitat fragments may serve as biodiversity reservoirs for beneficial taxa, such as wasps. To this end, we sought to describe the diversity and life history traits of wasp communities within Oregon white oak (Quercus garryana) habitat fragments in The Dalles, Oregon. We also aimed to quantify changes in wasp community composition to better understand potential changes in ecosystem services across the growing season. We sampled wasps in five oak fragments monthly from April to August 2021 using a combination of yellow sticky cards and plant volatile-baited delta traps. All study sites were situated within an agricultural matrix dominated by cherry production. Traps were left in the field for a minimum of three days per site, then collected for further processing in the lab. Larger wasps ( > 5 mm) were identified to subfamily and smaller wasps (< 5 mm) were simply counted. Shannon diversity of larger wasps was calculated for each site for each month. We compared abundance for small wasps and abundance, subfamily richness, and subfamily diversity for larger wasps between months using ANOVA. Changes in monthly community composition were analyzed visually using NMS ordination and MRPP. We collected 18,754 wasps over the course of the study including 11,421 sawflies and 7,333 predatory or parasitoid wasps. There was a striking mid-season depression in abundance, followed by a shift in community composition which may mirror food resource phenology. Earlier season communities were dominated by social predators and various parasitoids, while later season communities contained virtually none of these taxa and had a notable increase in solitary spider-hunting wasps. Another noteworthy trend is that nearly all of the sawflies were collected in May. Wasp-mediated services are not only intrinsically valuable within ecosystems, but also benefit local agricultural producers (e.g., biological pest control). An increased awareness of the biodiversity and ecosystem services provided by these natural habitat fragments is crucial to promoting their conservation.