Abstract
Artificial lights may be altering interactions between bats and moth prey. According to the allotonic frequency hypothesis (AFH), eared moths are generally unavailable as prey for syntonic bats (i.e., bats that use echolocation frequencies between 20 and 50 kHz within the hearing range of eared moths) due to the moths’ ability to detect syntonic bat echolocation. Syntonic bats therefore feed mainly on beetles, flies, true bugs, and non-eared moths. The AFH is expected to be violated around lights where eared moths are susceptible to exploitation by syntonic bats because moths’ evasive strategies become less effective. The hypothesis has been tested to date almost exclusively in areas with permanent lighting, where the effects of lights on bat diets are confounded with other aspects of human habitat alteration. We undertook diet analysis in areas with short-term, localized artificial lighting to isolate the effects of artificial lighting and determine if syntonic and allotonic bats (i.e., bats that use echolocation frequencies outside the hearing range of eared moths) consumed more moths under conditions of artificial lights than in natural darkness. We found that syntonic bats increased their consumption of moth prey under experimentally lit conditions, likely owing to a reduction in the ability of eared moths to evade the bats. Eared moths may increase in diets of generalist syntonic bats foraging around artificial light sources, as opposed to allotonic species and syntonic species with a more specialized diet.



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Acknowledgements
Brad Sharp and Robert White kindly allowed the use of Kleinrivier and Table Farm as respective study sites. Dion Marais kindly set up the equipment at Kleinrivier. Alyssa Stulberg assisted in equipment collection and initial setup. Anne Brigham and Emma Sydie photographed the experimental area. Additionally, Anne Brigham, Emma Sydie, Devin DeWet, Malcolm Bailey and Nita Pallet assisted with netting efforts and data collection. Eero Vesterinen and two anonymous reviewers provided comments on improving the manuscript.
Funding
Research funding was provided by the National Research Foundation Thuthuka Grant (Grant no. 106958 [BS]) and the Natural Sciences and Engineering Research Council, Canada (RMB).
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SJB, RMB, JGB and BS conceived and designed experiments. LAB performed experiments. LAB and BS analysed data. LAB wrote manuscript; all other authors provided editorial advice.
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Communicated by Thomas Lilley.
Our study is of the first to compare allotonic and syntonic bat diet shifts under a priori field manipulative light experiments, in comparison to previous observation studies.
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Bailey, L.A., Brigham, R.M., Bohn, S.J. et al. An experimental test of the allotonic frequency hypothesis to isolate the effects of light pollution on bat prey selection. Oecologia 190, 367–374 (2019). https://doi.org/10.1007/s00442-019-04417-w
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DOI: https://doi.org/10.1007/s00442-019-04417-w