Urbanization is a dominant form of land-use change driving species distributions, abundances, and diversity. Previous research has documented the negative impacts of urbanization on the abundance and diversity of many groups of organisms. However, some organisms, such as bees, may benefit from moderate levels of development, depending on how development alters the availability of foraging and nesting resources. To determine how one type of low-intensity human development, suburbanization, affects bee abundance and diversity and the mechanisms involved, we surveyed bees across suburban and natural forests in the Raleigh-Durham area of North Carolina. We sampled for bees using a combination of bee bowls and hand-netting from March through July of 2008 and 2009. We found higher bee abundance in suburban than natural forests, and although observed species richness was greater in suburban than natural forests, there were no significant differences in rarefied richness or evenness estimates in either year. In addition, the effects of suburbanization were similar across bee species of varying ecological and life-history characteristics. At the local scale, bee abundance and species richness were both positively related to the abundance and richness of flowering species within forests, while the proportion of surrounding developed open areas, such as yards and roadsides, was a strong positive predictor of both bee abundance and richness at the landscape scale. These results suggest that open habitats and the availability of floral resources in suburban sites can support abundant and diverse bee communities and underscore the potential for native bee conservation in urban habitats.

Defense against natural enemies constitutes an important driver of herbivore host range evolution in the wild. Populations of the Baltimore checkerspot butterfly, Euphydryas phaeton (Nymphalidae), have recently incorporated an exotic plant, Plantago lanceolata (Plantaginaceae), into their dietary range. To understand the tritrophic consequences of utilizing this exotic host plant, we examined immune performance, chemical defense, and interactions with a natural entomopathogen (Junonia coenia densovirus, Parvoviridae) across wild populations of this specialist herbivore. We measured three immune parameters, sequestration of defensive iridoid glycosides (IGs), and viral infection load in field‐collected caterpillars using either P. lanceolata or a native plant, Chelone glabra (Plantaginaceae). We found that larvae using the exotic plant exhibited reduced immunocompetence, compositional differences in IG sequestration, and higher in situ viral burdens compared to those using the native plant. On both host plants, high IG sequestration was associated with reduced hemocyte concentration in the larval hemolymph, providing the first evidence of incompatibility between sequestered chemical defenses and the immune response (i.e., the “vulnerable host” hypothesis) from a field‐based study. However, despite this negative relationship between IG sequestration and cellular immunity, caterpillars with greater sequestration harbored lower viral loads. While survival of virus‐infected individuals decreased with increasing viral burden, it ultimately did not differ between the exotic and native plants. These results provide evidence that: (1) phytochemical sequestration may contribute to defense against pathogens even when immunity is compromised and (2) herbivore persistence on exotic plant species may be facilitated by sequestration and its role in defense against natural enemies.

Plant interactions with mutualists and antagonists vary remarkably across space, and have played key roles in the ecology and evolution of flowering plants. One dominant form of spatial variation is human modification of the landscape, including urbanization and suburbanization. Our goal was to assess how suburbanization affected plant-animal interactions in Gelsemium sempervirens in the southeastern United States, including interactions with mutualists (pollination) and antagonists (nectar robbing and florivory). Based on differences in plant-animal interactions measured in multiple replicate sites, we then developed predictions for how these differences would affect patterns of natural selection, and we explored the patterns using measurements of floral and defensive traits in the field and in a common garden. We found that Gelsemium growing in suburban sites experienced more robbing and florivory as well as more heterospecific but not conspecific pollen transfer. Floral traits, particularly corolla length and width, influenced the susceptibility of plants to particular interactors. Observational data of floral traits measured in the field and in a common garden provided some supporting but also some conflicting evidence for the hypothesis that floral traits evolved in response to differences in species interactions in suburban vs. wild sites. However, the degree to which plants can respond to any one interactor may be constrained by correlations among floral morphological traits. Taken together, consideration of the broader geographic context in which organisms interact, in both suburban and wild areas, is fundamental to our understanding of the forces that shape contemporary plant-animal interactions and selection pressures in native species.