Artificial nightlight alters the predator-prey dynamics of an apex carnivore

Artificial nightlight is increasingly recognized as an important
environmental disturbance that influences the habitats and fitness of
numerous species. However, its effects on wide-ranging vertebrates and
their interactions remain unclear. Light pollution has the potential to
amplify land-use change, and as such, answering the question of how this
sensory stimulant affects behavior and habitat use of species valued for
their ecological roles and economic impacts is critical for conservation
and land-use planning. Here, we combined satellite-derived estimates of
light pollution, with GPS-data from cougars (Puma concolor; n = 56), mule
deer (Odocoileus hemionus; n = 263), and locations of cougar-killed deer
(n = 1,562 carcasses), to assess the effects of light exposure on mammal
behavior and predator-prey relationships across wildland-urban gradients
in the southwestern United States. Our results indicate that deer used the
anthropogenic environments to access forage and were more active at night
than their wildland conspecifics. Despite higher nightlight levels,
cougars killed deer at the wildland-urban interface, but hunted them in
the relatively darkest locations. Light had the greatest effect of all
covariates on where cougars killed deer at the wildland-urban interface.
Both species exhibited functional responses to light pollution at fine
scales; individual cougars and deer with less light exposure increasingly
avoided illuminated areas when exposed to greater radiance, whereas deer
living in the wildland-urban interface selected elevated light levels. We
conclude that integrating estimates of light pollution into ecological
studies provides crucial insights into how the dynamic human footprint can
alter animal behavior and ecosystem function across spatial scales.