Undercover predators: Vegetation mediates foraging, trophic cascades, and biological control by omnivorous weed seed predators

Blubaugh, Carmen K. Ph.D., Purdue University, May 2015. Undercover Predators: Vegetation Mediates Foraging, Trophic Cascades, and Biological Control by Omnivorous Weed Seed Predators. Major Professor: Ian Kaplan. Weed pressure is the most costly challenge that vegetable growers face, requiring more labor investment than other production inputs. Vertebrate and invertebrate seed predators destroy a large percentage of weed propagules on the soil surface, and their ecosystem services may ease labor requirements for farmers in herbicide-free systems. Cover provided by living vegetation is an important predictor of seed predator activity, and my dissertation takes a comprehensive approach to understanding the behavior, predator, and environment-mediated mechanisms by which cover impacts weed seed predation in crop environments. First, I performed a meta-analysis of 27 studies to quantitatively evaluate what is currently known about seed predation by vertebrates and invertebrates across weed species, crop environments, and seasons (Chapter 1). I found that that seed predators impact some weed species more than others, depending on taxa-specific seed preferences, and that predation rates are minimal in environments entirely void of vegetation. Next, in Chapter 2, I examined the role of vegetative over in determining oviposition preferences of Harpalus pensylvanicus, the most common carabid seed predator in Midwestern crop systems. I found that while adult beetles were strong dispersers and foraged in a variety of habitat types, larvae were less mobile and more vulnerable to disturbance than adults. They were almost exclusively captured in environments characterized by long