Thesis Defence: Ground-Dwelling Natural Enemies Across Vineyards and Semi-Natural Habitats in the Okanagan Valley

Hannah Friesen, supervised by Dr. Lael Parrott, will defend their thesis titled “Ground-Dwelling Natural Enemies Across Vineyards and Semi-Natural Habitats in the Okanagan Valley” in partial fulfillment of the requirements for the degree of Master of Science in Earth and Environmental Sciences.

An abstract for Hannah Friesen’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

Abstract 

Perennial agroecosystems such as vineyards may be able to support biodiversity by managing non-crop vegetation and retaining semi-natural habitats (SNH). However, biodiversity responses to local and landscape factors vary by region and taxa, and few studies have compared communities within vineyards to those in SNH. Ground-dwelling natural enemies, such as carabid beetles and spiders, are important generalist predators and indicators of biodiversity. My MSc research integrates field sampling, geospatial analysis, and statistical modelling to explore communities of ground-dwelling natural enemies across vineyard and SNH in the Okanagan Valley, British Columbia. Specifically, I investigate (1) how carabid and spider abundance and taxonomic richness vary in relation to vineyard management, local vegetation and landscape heterogeneity and (2) variation in carabid and spider diversity, community composition and functional traits across vineyards and SNH. I sampled 22 vineyards in 2024 and 37 in 2025 (21 sites sampled both years) from Osoyoos to Lake Country, representing both organic and conventional management. At each site, I deployed pitfall traps in vine rows, inter-rows, and adjacent SNH where possible (14 SNH sites in 2024, 31 SNH sites in 2025). Within vineyards, organic management was associated with over two times higher spider abundance and 19% higher family richness than conventional management, while there was no evidence of carabid abundance or richness varying systematically with organic management. Both taxa increased in abundance by 15-30% with increasing vegetation height, but there was no evidence that spider or carabids abundance or richness varied with landscape heterogeneity. Spider and carabid abundance were higher in vineyards; however, SNH supported 35-46% greater spider diversity across all Hill diversity orders than vineyards. SNH had 20% lower carabid species richness but 80% higher Simpson diversity than vineyards, indicating more even communities. Vineyards were generally dominated by introduced carabid species adapted to agricultural environments. This is the first region-wide study to explore ground-dwelling natural enemies in vineyards in the Okanagan and provides insight into how vineyards can be managed to support biodiversity. My findings suggest that while vineyards can support abundant populations of carabids and spiders, SNH remain important for maintaining diverse and even communities.