As human populations continue to expand, many more species are affected by habitat fragmentation and urbanization. One of the most common themes in studies of fragmented habitats is finding higher rates of predation along habitat edges. However, field studies supporting this pattern are heavily influenced by avian literature and may not apply similarly to other organisms, such as invertebrates. Field studies of predation are typically performed during the day or do not distinguish between day and night; these studies therefore overlook daily fluctuations in predation and may miss important effects that occur solely at night, such as light pollution from streetlights. We tested whether predation of larval Lepidoptera differed between edge and core habitats and also whether predation along the habitat edge varied in response to light pollution from streetlights. We placed larvae in the core of suburban habitat patches and along the habitat edge, both under streetlights as well as between streetlights where it was dark. We found that predation rate increased in both edge and core habitats over the summer. Early season, we found daily fluctuations in predation dynamics with greater predation along the habitat edge than in the habitat core during the day, but not at night. Additionally, we found that streetlights did not affect predation rate along the habitat edge. Our results suggest that increased predation along habitat edges may be a diurnal effect.
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We are grateful for funding from the University of Denver’s Undergraduate Research Center Partners in Scholarship grant awarded to Bergen Tjossem for this project. We would like to thank the City and County of Broomfield, the City of Lakewood, the City of Louisville, and the South Suburban Parks and Recreation District for use of field sites. This project could not have been executed without the field help of Marianne Berge, Quyncie Grenis, Claudia Hallagan, Cheryl Harris, and Amanda Keil; Marianne Berge and Cheryl Harris were supported by a National Science Foundation Research Experience for Teachers supplement awarded to S.M.M. (Grant Number NSF-DEB 1026000). We appreciate the help of Anna Sher and Gina Wimp with statistical analyses. We would also like to thank César Nufio, the University of Denver’s Organismal Biology Group and two anonymous reviewers for helpful comments on previous drafts.
Conflict of interest
Kylee Grenis: Dieter Hochuli, John Lill; Bergen Tjossem: n/a; Shannon M. Murphy: Yan Linhart, Paul Feeny, John Lill, Gina Wimp, Danny Lewis.
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