Death by a thousand cuts: the role of pesticides, predators, and habitat patch characteristics on wild bee and insect communities

Habitat degradation, loss, and fragmentation are some of the primary drivers of species loss globally. These processes occur mainly because of human actions and disproportionately impact ecologically and economically important taxa such as bees. This dissertation aims to address how habitat degradation in the form of pesticide pollution and altered trophic interactions impact bee biology and how patch physical characteristics affect the persistence and movement of beetles (Order: Coleoptera), bees (Clade: Anthophila), and thrips (Order: Thysanoptera) in a fragmented landscape. Most bee species nest below ground in soils where some pesticides, such as the neurotoxic neonicotinoids, have long half-lives and can accumulate in agrolandscapes. However, risk assessments for pesticides on bee health currently ignore the role of chronic contact with contaminated soils. In Chapter 1, I assess the sublethal effects of chronic contact exposure to realistic soil concentrations of imidacloprid - a commonly used neonicotinoid pesticide - during the immature life stages on adult movement and brain development. While I did not detect an effect on adult female Osmia lignaria or Megachile rotundata adult brain development, significant changes in the movement characteristics of female O. lignaria and male M. rotundata could have negative consequences for bee populations. Female O. lignaria exposed to moderate (15 ppb) and high (100 ppb) concentrations of imidacloprid did not move faster with age compared to the control (0 ppb) and low (7.5 ppb) imidacloprid treatments. This could lead to a 25% reduction in nest provisioning efficiency over the first 14 days of adulthood. Conversely, young male M. rotundata moved more quickly (7.5 and 100 ppb) and further (100 ppb) when treated with imidacloprid. This may increase access to mates for exposed males. If these males also live longer and have reduced sperm quality, as reported elsewhere, the number of effective matings may decline, resulting in a more male-skewed sex ratio. Consequences for bee populations in pesticide-degraded habitats are discussed in light of recent field observations. Research concerned with the impact of habitat degradation on bee communities typically focuses on bottom-up mechanisms such as access to floral and nesting resources. However, recent sub-community studies have described important, yet inconsistent, top-down effects on bees. In Chapter 2, I simultaneously evaluate the roles of top-down and bottom-up forces on bee communities and foraging behavior using the ongoing reintroduction of a top predator. The top-down forces of eastern collared lizards (Crotaphytus collaris; ECL) explained a similar amount of the variation in bee community structure as floral resources and habitat spatial characteristics. Additionally, there was a significant interaction between floral quality and the presence of ECLs on bee species richness. In habitats with ECLs, increasing floral resource quality lead to greater bee species richness while in areas without ECLs, changes in floral resource quality did not affect bee species richness. The effects of ECLs on bees were mediated via changes in spider communities. Habitat with ECLs had higher abundances of on-flower ambush hunters, particularly in the family Salticidae. This, in turn, shifted bee foraging behavior to avoid warmer afternoon hours when spiders hunt more aggressively. This research highlights the potential importance of the top-down effects of predators for bee communities and, more specifically, their conservation in a naturally fragmented landscape. Species, landscape, and patch characteristics are thought to influence the direction and magnitude of the effects of habitat fragmentation on organisms. The role of species and landscape traits on persistence and movement and patch traits on persistence within fragmented landscapes are well described. Conversely, while all dispersal movements start and, if successful, end at a habitat patch, there has been relatively little attention on the roles of patch physical characteristics on movement. In Chapter 3, I investigated the independent contributions of patch area, perimeter-area ratio, and shape on the persistence and movement of beetles, bees, and thrips. These taxa were selected based on their different dispersal abilities and resource requirements. Beetles, which have diverse dispersal abilities and resource requirements, were primarily affected by patch area; however, the direction of this effect differed by family. Bees, which rely on patch resources for food and have strong dispersal abilities, had increased persistence and movement across patch-matrix borders in patches with a more complex shape. Thrips rely on patch resources for food and are weak fliers. They exhibited increased persistence in patches with high perimeter-area ratios, regardless of area or shape. Taken together, patch physical characteristics play taxon-specific roles in the movement of insects across patch-matrix borders. Conservation and restoration plans can use this information to improve outcomes for species in fragmented landscapes.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste