Mutualist and antagonist arthropod communities of native plants are influenced by proximity to agricultural crops

Background/Question/Methods

Anthropogenic disturbances, such as urbanization, fragmentation, and introduction of invasive species, can homogenize biotic communities by reducing the variation in species composition across locations. Global agricultural intensification has produced biotic homogenization. For example, in Europe, increased pesticide use has led to increased similarities in both bee and hemipteran communities relative to non-agricultural areas. Croplands, pastures, and rangelands constituted ~50% of the global vegetated land surface as of 2005. Thus, agriculture has the potential to significantly impact diversity of natural communities. However, we do not know if agriculture has different impacts on mutualists vs. antagonists of nearby wild plants. If so, ecological and evolutionary impacts of agriculture on wild plants will hinge on differential impacts to plant mutualists and antagonists. Furthermore, plant antagonists are controlled with pesticides, while mutualists are not specifically controlled. We may gain insight into the impacts of agriculture on wild plants by understanding effects of agriculture on plant antagonists and mutualists. 

Results/Conclusions

We manipulated the proximity of wild sunflowers (Helianthus annuus texanus) to sunflower crops (H. annuus) by planting ~100 wild plants < 10 m (Near) and > 1.5 km (Far) from sunflower crops. Pollinator abundance was higher Near crops than Far from crops at some sites, but not at others. Seed predator abundance (measured as plant damage) was lower Near than Far from sunflower crops. Pollinator communities significanlty diverged both among sites and Near vs. Far from sunflower crops. In accordance with expectation, pollinator communities were more homogenous near crops  relative to far from crops. These results suggest that we should consider the separate effects of crops on mutualists and antagonists of wild plants. Ongoing work is examining how these differences in mutualist and antagonist communities translate into changes in selection on the traits of wild plants.