Light pollution alters predator-prey interactions between cougars and
mule deer in western US

Date:
October 19, 2020
Source:
University of Michigan
Summary:
A new study provides strong evidence that exposure to light
pollution alters predator-prey dynamics between mule deer and
cougars across the intermountain West, a rapidly growing region
where nighttime skyglow is an increasing environmental disturbance.



FULL STORY ==========================================================================
A new study provides strong evidence that exposure to light pollution
alters predator-prey dynamics between mule deer and cougars across the intermountain West, a rapidly growing region where nighttime skyglow is
an increasing environmental disturbance.


==========================================================================
The University of Michigan-led study, published online Oct. 18 in
the journal Ecography, is the first to assess the impacts of light
pollution on predator- prey interactions at a regional scale. It combines satellite-derived estimates of artificial nighttime lights with GPS
location data from hundreds of radio- collared mule deer and cougars
across the intermountain West.

The study found that:
* Mule deer living in light-polluted areas are drawn to artificial
nighttime lighting, which is associated with green vegetation
around homes.

* Cougars, also known as mountain lions and pumas, are able to
successfully
hunt within light-polluted areas by selecting the darkest spots
on the landscape to make their kill.

* While mule deer that live in dark wildland locations are most active
around dawn and dusk, those living around artificial night light
forage throughout the day and are more active at night than wildland
deer - - especially during the summer.

The animal data used in the study were collected by state and federal
wildlife agencies across the region. Collation of those records by the
study authors yielded what is believed to be the largest dataset on interactions between cougars and mule deer, two of the most ecologically
and economically important large-mammal species in the West.

"Our findings illuminate some of the ways that changes in land use are
creating a brighter world that impacts the biology and ecology of highly
mobile mammalian species, including an apex carnivore," said study lead
author Mark Ditmer, formerly a postdoctoral researcher at the University
of Michigan School for Environment and Sustainability, now at Colorado
State University.

The intermountain West spans nearly 400,000 square miles and is an ideal
place to assess how varying light-pollution exposures influence the
behavior of mule deer and cougars and their predator-prey dynamics. Both species are widely distributed throughout the region -- the mule deer
is the cougar's primary prey species -- and the region presents a wide
range of nighttime lighting conditions.



==========================================================================
The intermountain West is home to some of the darkest night skies in
the continental United States, as well as some of the fastest-growing metropolitan areas, including Las Vegas and Salt Lake City. Between the
dark wildlands and the brightly illuminated cities is the wildland-urban interface, the rapidly expanding zone where homes and associated
structures are built within forests and other types of undeveloped
wildland vegetation.

For their study, the researchers obtained detailed estimates of nighttime lighting sources from the NASA-NOAA Suomi polar-orbiting satellite. They collected GPS location data for 117 cougars and 486 mule deer from four
states: Utah, Arizona, Nevada and California. In addition, wildlife
agencies provided locations of 1,562 sites where cougars successfully
killed mule deer.

"This paper represents a massive undertaking, and to our knowledge this
dataset is the largest ever compiled for these two species," said study
senior author Neil Carter, a conservation ecologist at the U-M School
for Environment and Sustainability.

Deer in the arid West are attracted to the greenery in the backyards
and parks of the wildland-urban interface. Predators follow them there,
despite increased nighttime light levels that they would normally
shun. Going into the study, the researchers suspected that light
pollution within the wildland-urban interface could alter cougar-mule
deer interactions in one of two ways.

Perhaps artificial nighttime light would create a shield that protects
deer from predators and allows them to forage freely. Alternatively,
cougars might exploit elevated deer densities within the wildland-urban interface, feasting on easy prey inside what scientists call an ecological trap.

Data from the study provides support for both the predator shield and ecological trap hypotheses, according to the researchers. At certain
times and locations within the wildland-urban interface, there is simply
too much artificial light and/or human activity for cougars, creating
a protective shield for deer.

An ecological trap occurs when an animal is misled, or trapped, into
settling for apparently attractive but in fact low-quality habitat. In
this particular case, mule deer are drawn to the greenery of the
wildland-urban interface and may mistakenly perceive that the enhanced nighttime lighting creates a predator-free zone.

But the cougars are able to successfully hunt within the wildland-urban interface by carefully selecting the darkest spots on the landscape to
make their kill, according to the study. In contrast, cougars living in
dark wildland locations hunt in places where nighttime light levels are slightly higher than the surroundings, the researchers found.

"The intermountain West is the fastest-growing region of the U.S.,
and we anticipate that night light levels will dramatically increase in magnitude and across space," said U-M's Carter. "These elevated levels
of night light are likely to fundamentally alter a predator-prey system
of ecological and management significance -- both species are hunted extensively in this region and are economically and culturally important."

========================================================================== Story Source: Materials provided by University_of_Michigan. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mark A. Ditmer, David C. Stoner, Clinton D. Francis, Jesse
R. Barber,
James D. Forester, David M. Choate, Kirsten E. Ironside, Kathleen M.

Longshore, Kent R. Hersey, Randy T. Larsen, Brock R. McMillan,
Daniel D.

Olson, Alyson M. Andreasen, Jon P. Beckmann, P. Brandon Holton,
Terry A.

Messmer, Neil H. Carter. Artificial nightlight alters the
predator-prey dynamics of an apex carnivore. Ecography, 2020;
DOI: 10.1111/ecog.05251 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019112158.htm

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