Current Biology
Volume 28, Issue 15, 6 August 2018, Pages 2474-2478.e3
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Report
Low Levels of Artificial Light at Night Strengthen Top-Down Control in Insect Food Web

https://doi.org/10.1016/j.cub.2018.05.078Get rights and content
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Highlights

  • Artificial light at night, at varying intensities, is globally widespread

  • Intensity of artificial light determines the community response in an insect food web

  • Impacts of artificial light on interactions between species may be very common

Summary

Artificial light has transformed the nighttime environment of large areas of the earth, with 88% of Europe and almost 50% of the United States experiencing light-polluted night skies [1]. The consequences for ecosystems range from exposure to high light intensities in the vicinity of direct light sources to the very widespread but lower lighting levels further away [2]. While it is known that species exhibit a range of physiological and behavioral responses to artificial nighttime lighting [e.g., 3, 4, 5], there is a need to gain a mechanistic understanding of whole ecological community impacts [6, 7], especially to different light intensities. Using a mesocosm field experiment with insect communities, we determined the impact of intensities of artificial light ranging from 0.1 to 100 lux on different trophic levels and interactions between species. Strikingly, we found the strongest impact at low levels of artificial lighting (0.1 to 5 lux), which led to a 1.8 times overall reduction in aphid densities. Mechanistically, artificial light at night increased the efficiency of parasitoid wasps in attacking aphids, with twice the parasitism rate under low light levels compared to unlit controls. However, at higher light levels, parasitoid wasps spent longer away from the aphid host plants, diminishing this increased efficiency. Therefore, aphids reached higher densities under increased light intensity as compared to low levels of lighting, where they were limited by higher parasitoid efficiency. Our study highlights the importance of different intensities of artificial light in driving the strength of species interactions and ecosystem functions.

Keywords

aphids
food webs
light pollution
parasitism rate
parasitoids

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