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Contact: Maggie MacCluskie, 907.388.8622
Scientists in Denali National Park and Preserve have published the results of long-term research on the data from plant, climate, small mammal, and golden eagle monitoring that has unique findings on how small mammals and eagles appear to be regulated by primary plant production.
“Teasing apart predator-prey relationships is a primary question in the field of ecology,” says Carol McIntyre, who collected the 29 years of golden eagle and snowshoe hare data in Denali National Park and Preserve. “First, we’re learning that eagle reproduction is directly limited by their primary prey, hares; and second, eagles are less likely to fledge young just before hare populations crash. This supports the idea that eagles are not the primary driver of hare populations.”
Overall, the recent findings are important because they suggest that fluctuations in herbivores are, at times, largely driven from the bottom-up through variation in weather conditions rather than being controlled from the top-down through predation. The findings represent a strong foundation for further investigations into how other predator-prey systems operate within Denali and throughout Alaska, and can inform resource management decisions.
The findings are the result of analyzing long-term monitoring data on weather, plant production, small mammals, snowshoe hares, and golden eagles to investigate how they interact. In Denali, both small mammal (specifically northern red-backed vole) and snowshoe hare populations are strongly cyclic, with voles peaking every three years and hares peaking every 10 years. Researchers found that after several years of favorable weather, plants had higher rates of growth and were more abundant and in turn, the peaks in the hare and vole cycles were also higher.
“Even though these two species are different biologically and cycle at different rates, the size of the response to plant production is very similar. That similarity is exciting because it suggests that plant productivity may be limiting both species in the same way,” explains Josh Schmidt, lead researcher for the project.
Both voles and hares consume plants as their main food source, but the strength of the population response to plant production in both species was marked regardless of the reproductive output of the eagle population. These insights would not have been possible without having data spanning many years, allowing researchers to observe the natural fluctuations in these species.
“Our vole monitoring began in 1992 and it took more than 20 years of data to clearly detect the cycle,” explains Melanie Flamme, the scientist in charge of the small mammal project.
The researchers agree that one of the strengths of the work in Denali is that several components have been ongoing for almost 30 years. Lengthy studies of this kind are critical for understanding complicated processes such as predator-prey dynamics, but are quite rare.