LRES Ph.D. Dissertation Defense
- Thursday, December 7, 2017 at 1:00pm
- Animal Biosciences Building, 134 - view map
Impacts of Dryland Farming Systems on Biodiversity, Plant-Insect Interactions and Ecosystem Services
Due to agricultural intensification, biodiversity is declining globally. Farm management impacts the structure and functioning of associated biodiversity and plant-insect interactions. However, the extent and ecological role of these impacts are largely unknown in dryland agroecosystems of the Northern Great Plains, an important region for small grain, pulse, oilseed, and forage production. Using three separate studies, I compared the impacts of organic and conventional farming systems on associated biodiversity (weeds, bees, insect pests, and parasitoids), bee-forb networks, and bumblebee colony success. First, I assessed stem cuts and parasitism of Cephus cinctus in Kamut, spring, and winter wheat cultivars grown in organic and conventional fields. I found that organic fields had less C. cinctus infestation but more Braconid parasitoids. Additionally, in the greenhouse experiment, I found that C. cinctus oviposition, survival, and number of stems cut were lowest in Kamut than in Gunnison and Reeder spring wheat cultivars. Second, I assessed the impacts of conventional and organic systems on forbs, bees, and bee-flower networks. I found greater forb abundance and diversity in organic fields, but bee abundance and diversity did not differ between systems. Bee-flower networks in conventional were either absent or significantly less connected than in organic fields. Additionally, our study area contained only ~12% natural habitat within a 2000m radius of field centers, which did not affect small-bodied bees abundance but positively affected the abundance of large-bodied bees. Third, I compared Bombus impatiens colony success, worker condition, and the composition of colony-collected pollen across farming systems. I found a greater relative growth rate of colonies and more non-brood and brood cells in organic fields than in conventional fields. B. impatiens workers from conventional fields had greater wing wear and lower body lipid mass than those in organic fields. Finally, I found greater forb flower density and pollen species richness in organic fields than in conventional fields, which were positively associated with colony relative growth rate. Overall, my studies show that in dryland agroecosystems of the Northern Great Plains organically managed farms support greater associated biodiversity, more complex bee-forb networks, and better biodiversity-based ecosystem services than conventionally managed farms.
- Department of Land Resources and Environmental Sciences