In a press conference last Monday 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.
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 disproportionate 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.”