Data from: Stacking the odds: light pollution may shift the balance in an ancient predator-prey arms race

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.