Abstract:
1. Artificial night-lighting threatens to disrupt strongly conserved light-dependent processes in
animals and may have cascading effects on ecosystems as species interactions become altered.
Insectivorous bats and their prey have been involved in a nocturnal, coevolutionary arms race for
millions of years. Lights may interfere with anti-bat defensive behaviours in moths, and disrupt a
complex and globally ubiquitous interaction between bats and insects, ultimately leading to
detrimental consequences for ecosystems on a global scale. 2. We combined experimental and mathematical approaches to determine effects of light
pollution on a free-living bat–insect community. We compared prey selection by Cape serotine
bats Neoromicia capensis in naturally unlit and artificially lit conditions using a manipulative
field experiment, and developed a probabilistic model based on a suite of prey-selection factors
to explain differences in observed diet. 3. Moth consumption by N. capensis was low under unlit conditions (mean percentage volume ±
SD: 5.91 ± 6.25%), while moth consumption increased six-fold (mean percentage volume ± SD:
35.42 ± 17.90%) under lit conditions despite a decrease in relative moth abundance. Predictive
prey-selection models which included high-efficacy estimates for eared-moth defensive
behaviour found most support given diet data for bats in unlit conditions. Conversely, models
which estimated eared-moth defensive behaviour as absent or low, found more support given diet
data for bats in lit conditions. Our models therefore suggest the increase in moth consumption
was a result of light-induced, decreased eared-moth defensive behaviour. 4. Policy implications. In the current context of unyielding growth in global light pollution, we
predict that specialist moth-eating bats and eared-moths will face ever-increasing challenges to
survival through increased resource competition and predation risk, respectively. Lights should
be developed to be less attractive to moths, with the goal of reducing effects on moth behaviour.
Unfortunately, market preference for broad-spectrum lighting and possible effects on other taxa
make development of moth-friendly lighting improbable. Mitigation should therefore focus on
the reduction of temporal, spatial, and luminance redundancy in outdoor lighting. Restriction of
light inside nature reserves and urban greenbelts can serve as dark refugia for moth-eating bats
and moths, and may become important for their persistence.
