Evaluating the effects of climate change and pathogens on pollinator health using plant functional traits and longitudinal monitoring

Abstract

Pollinators are essential for the maintenance of biodiversity, ecosystem function, and economic productivity. In particular, bee pollinators are required for plant reproduction and pollination of agricultural crops. However, land use change, climate change, pathogens, pesticide exposure, among other factors likely act alone and in combination to negatively impact bee pollinators and the services they provide. Further resolution of the effects of these stressors, both individually and combined, on bee pollinators is important to understand the global decline of pollinator health. Abiotic conditions associated with climate change may alter plant traits important for pollinator attraction leading to in shifts in plant-pollinator communities. Floral visual and chemical traits were measured in four species of forbs subjected to elevated or ambient concentrations of carbon dioxide, and decreased or normal water availability in a fully factorial crossed design. Treated plants were observed for pollinator visitation rates and community composition to better understand the mechanisms by which climate change can influence pollinator attraction. Results indicate that changes in both visual and chemical cues of plants will alter plant-pollinator interactions. Furthermore, plant functional trait responses to climate change increase competition for pollinators in forbs with overlapping flower types, while facilitating pollinator visitation to forbs with dissimilar flower types. Pathogens contribute to annual honey bee colony losses and the declining populations of some wild bee species. Bee pathogens, including viruses, fungi, microparasites and ectoparasites, can vary across geographic location and season. To examine the impact of pathogens on honey bee colony health, using colony size as a proxy for health, we longitudinally monitored pathogen prevalence and abundance of pathogens in honey bee colonies involved in California almond pollination. Individual honey bee associated pathogens varied throughout the one year monitoring period, but Deformed wing virus in parallel with increasing levels of Varroa destructor mite infestation predominated shifts in honey bee pathogen profiles by the end of the sampling period. Our results indicate that bee populations experience multiple concurrent threats operating at multiple scales to affect pollinator health. Continued investigation into factors affecting pollinator health both independently and in concert are needed to develop strategies mitigating declines in pollination services.