What
Satellites Can Tell Us about How Animals Will Fare in a Changing Climate
EDITOR'S NOTE: NASA's Earth Sciences program is high on the list of programs targeted for shut-down both by Donald Trump and the Republican limate-change deniers who control the Congress in a push to end funding for research on climate change. This article is a fine example of the types of research Trump and company want to stiffle. - W. Collette
From the Arctic to the Mojave Desert, terrestrial and marine
habitats are rapidly changing. These changes impact animals that are adapted to
specific ecological niches, sometimes displacing them or reducing their
numbers.
From their privileged vantage point, satellites are particularly
well-suited to observe habitat transformation and help scientists forecast
impacts on the distribution, abundance and migration of animals.
In a press conference on December 26 at the American Geophysical
Union meeting in San Francisco, three researchers discussed how detailed
satellite observations have facilitated ecological studies of change over time.
The presenters discussed how changes in Arctic sea ice cover have
helped scientists predict a 30 percent drop in the global population of polar
bears over the next 35 years. They also talked about how satellite imagery of
dwindling plant productivity due to droughts in North America gives hints of
how both migratory herbivores and their predators will fare.
Finally, they also
discussed how satellite data on plant growth indicate that the concentration of
wild reindeer herds in the far north of Russia has not led to overgrazing of
their environment, as previously thought.
Polar bears depend on sea ice for nearly all aspects of their
life, including hunting, traveling and breeding. Satellites from NASA and other
agencies have been tracking sea ice changes since 1979, and the data show that
Arctic sea ice has been shrinking at an average rate of about 20,500 square
miles (53,100 square kilometers) per year over the 1979-2015 period.
Currently,
the status of polar bear subpopulations is variable; in some areas of the
Arctic, polar bear numbers are likely declining, but in others, they appear to
be stable or possibly growing.
“When we look forward several decades, climate models predict such
profound loss of Arctic sea ice that there’s little doubt this will negatively
affect polar bears throughout much of their range, because of their critical
dependence on sea ice,” said Kristin Laidre, a researcher at the University of
Washington's Polar Science Center in Seattle and co-author of a study on projections
of the global polar bear population. Eric Regehr of the U.S. Fish and Wildlife
Service in Anchorage, Alaska, led the study, which was published on December 7
in the journal Biology Letters.
“On short time scales, we can have variable responses to the loss
of sea ice among subpopulations of polar bears,” Laidre said. “For example, in
some parts of the Arctic, such as the Chukchi Sea, polar bears appear healthy,
fat and reproducing well — this may be because this area is very ecologically
productive, so you can lose some ice before seeing negative effects on bears.
In other parts of the Arctic, like western Hudson Bay, studies have shown that
survival and reproduction have declined as the availability of sea ice
declines.”
Regehr, Laidre and their colleagues’ results are the product of
the International Union for Conservation of Nature’s (IUCN) Red List assessment
for polar bears. To determine the level of threat to a species, IUCN requests
scientists to project what the species population numbers will be after three
generations.
Using data collected from adult females in 11 subpopulations of
polar bears across the Arctic, Regehr and Laidre’s team calculated the
generation length for polar bears—the average age of reproducing adult
females—to be 11.5 years. They then used the satellite record of Arctic sea ice
extent to calculate the rates of sea ice loss and then projected those rates
into the future, to estimate how much more the sea ice cover may shrink in
approximately three polar bear generations, or 35 years.
Lastly, the scientists evaluated different scenarios for the
relationships between polar bear abundance and sea ice. In one of them, the
bear numbers declined directly proportionally with sea ice.
In the other
scenarios, the researchers used the existing, albeit scarce, data on how polar
bear abundance has changed with respect to sea ice loss, using all available
data from polar bear subpopulations in the four existing polar bear eco-regions,
and projected forward these observed trends.
They concluded that, based on a
median value across all scenarios, there’s a high probability of a 30 percent
decline in the global population of polar bears over the next three to four
decades, which supports listing the species as vulnerable on the IUCN Red List.
“It is difficult to predict what population numbers will be in the
future, especially for animals that live in vast and remote regions,” Regehr
said. “But at the end of the day, polar bears need sea ice to be polar bears.
This study adds to a growing body of evidence that the species will likely face
large declines as loss of their habitat continues.”
Drought and mountain lions
The southwestern United States is expected to become more prone to
droughts with climate change. The resulting loss of vegetation will not only
impact herbivores like mule deer; their main predator, mountain lions, might
take an even larger hit.
To estimate the numbers and distribution of mule deer and mountain
lions in Utah, Nevada and Arizona, David Stoner, a wildlife ecologist at Utah
State University in Logan, Utah, used imagery of plant productivity from the
Moderate Resolution Imaging Spectroradiometer, flown on NASA’s Terra and Aqua
satellites, plus radio-telemetry measurements of animal density and movements.
He found that there is a very strong relationship between plant productivity
and deer and mountain lion density.
“Measuring abundance of mule deer in the western United States is
logistically difficult, hazardous and very expensive. For mountain lions, it’s
even worse,” Stoner said. “But measuring changes in vegetation is relatively
easy and more affordable. With this research, we’ve provided a model that
wildlife managers can use to estimate the density of deer and mountain lions,
two big game species of great economic importance.”
Using maps of vegetation productivity during a severe drought that
occurred in the southwestern United States in 2002, Stoner modeled what would
be the deer and mountain lion distribution and abundance, should extreme
drought become the norm.
"During 2002, there was a 30 percent decrease from the
historical record mean in precipitation,” Stoner said. “Using measurements of
vegetation stressed by drought, our model predicted a 22 percent decrease in
deer density. For mountain lions, the decline was 43 percent. Mountain lions
occur at far lower densities than deer, and so any loss of their prey can have
disporportionate impacts on their reproductive rates and overall
abundance."
Mule deer are popular game animals, bringing in hundreds of
millions of dollars to rural areas through recreational hunting and tourism.
But deer can also have adverse economic impacts; they cause vehicle collisions,
devour crops and damage gardens.
“Droughts will make human landscapes more attractive to deer,
because farms and suburban areas are irrigated and would remain fairly green,”
Stoner said. “And mountain lions will go wherever the deer are. We’re going to
lose some of the economic benefits of having those animals, because they’ll be
fewer of them, but the costs are going to increase because the remaining
animals will be attracted to cities and farms.”
Longer journeys for wild reindeer
The Taimyr reindeer herd in the northernmost region of Russia is the
largest wild reindeer herd in the world and a key of source of food for the
indigenous population of the Taimyr Peninsula.
“Reindeer populations are declining all over the world, in some
places catastrophically; in Taimyr, there has been an about 40 percent drop
since 2000 and the herd is now at 600,000 animals,” said Andrey Petrov, an
associate professor at the University of Northern Iowa, in Cedar Falls.
Petrov examined historical data going back to 1969 and determined
that there are ongoing changes in the distribution and migration patterns of
the wild reindeer due to climate change and human pressure. The reindeer have
moved east, away from human activity. At the same time, the herd is now
traveling farther north and higher in elevation during the summer, possibly to
avoid increasing temperatures and more abundant mosquitoes.
“Taimyr reindeer now have to travel longer distances between their
winter and summer grounds, and this is causing a higher calf mortality,” Petrov
said. “Other factors contributing to the higher mortality are the increased
mosquito harassment and the fact that rivers are opening earlier than before
and the animals have to cross them during their migration.”
Petrov also used imagery from the NASA/United States Geological
Survey Landsat satellite program to determine how the presence of reindeer in
their summer grounds impacts vegetation. He found that, as expected, plant
biomass decreased while the reindeer were grazing, but it bounced back a few
weeks after the animals left the area. This finding argues against overgrazing
as a possible factor for the Taimyr reindeer population decline that occurred
after 2000.
“The work discussed at today’s press conference is emblematic of
the many ways in which satellite remote sensing supports our efforts at natural
resource management and wildlife conservation,” said Woody Turner, program
scientist for NASA’s Biological Diversity Program at NASA Headquarters in
Washington.
Laidre and Stoner’s research projects received funding from NASA.
The National Science Foundation funded Petrov’s research.
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