Owing to their important and conspicuous role as pollinators, bee communities have traditionally been thought to be structured by access to floral and, more recently, nesting resources. However, the role of higher tropic levels on bee populations is gaining attention. Recent work on "bee hotels" (human-provided nesting resources for above-ground, cavity-nesting bees) has suggested that these apparently good resources also lead to increased densities of pathogens, parasites, and predators. Additionally, pathogen spillover from managed pollinators has been implicated in the decline of some native bee species. Using a naturally fragmented ecosystem with high levels of endemism in southeast Missouri, we investigated how bee communities are impacted by conservation efforts to reintroduce a top predator (eastern collared lizard, Crotaphytus collaris) that is known to influence spider communities - likely the primary bee predators in a system that does not support insectivorous grassland birds. Spider, bee, and plant communities and nesting resources were characterized in 24 habitat patches across 6 mountains. Additionally, we quantified changes in bee foraging behavior in response to a predation threat (i.e., a crab spider model) by observing 40 flower patches within each habitat patch.
Results/Conclusions
We found that bee community composition was significantly affected by the presence of collared lizards, habitat area, flower community composition, and the mountain of the habitat patch. Nesting resources and spider community composition did not help to explain our observed bee communities. The effect of collared lizards is not mediated through changes in floral or nesting resources in response to management activities or spider abundances as there were no differences across these measures between areas with and without this predator. However, bee foraging behavior did differ. In areas where eastern collared lizards have been reintroduced, approximately half as many bees approached and visited observed flower patches. For bees that did visit a flower patch, the duration of their visit was twice as long in habitat patches with eastern collared lizards. The observed changes in bee foraging behavior may suggest increased anti-predator foraging behavior in which bees are more cautious in the flowers they visit, but once they identify a "safe" flower, they forage longer to collect the necessary resources to provision their nests. The results of this study illustrate the complex assemblage of factors that influence bee community composition and the importance of considering top-down effects in pollinator conservation.