Effects of light environment on behavior in prairie butterfly communities

Butterflies are highly visual insects that have species specific responses to qualities in ambient light. Even in open habitats, ambient light varies in the environment due to seasonal changes and amount of cloud cover. With increased cloud cover, the relative amount of ultraviolet light in the environment increases compared to the human visible spectrum of light. Butterflies use ultraviolet light and other colors to inform mating and feeding behaviors. We examined if a change in light environment in open habitats translates to changes in behavior at the community level in butterflies. From May to November in 2018, 2019, and 2020 we surveyed butterflies and light environments every 2 weeks in 3 Northwest Arkansas prairie sites. Butterfly behavior and numbers were surveyed during transect walks and point counts. Irradiance was measured at point count locations with a spectrometer. Data were analyzed with nominal logistic regression models in R. We found that butterfly behavior depended on taxonomic family status, time of day, time of year, and total irradiance. The interaction between time of year and relative amount of ultraviolet light present compared to total irradiance also affected butterfly behavior. Our results show that prairie butterfly communities are sensitive to changes in light environment. As light environments shift due to human activity and global warming our findings suggest that understanding the role of light environment may play an important in pollinator conservation.