Analysis of a Predator-Prey Relationship Ecological Study at Isle Royale, Michigan, U.S.
Michigan Can you name the Great Lakes?
Isle Royale National Park • Established April 3, 1940 • Designated as Wilderness Area 1976 • International Biosphere Reserve 1980 • 894 square miles 209 square miles above water • 17 smaller islands part of park
Ecology of Isle Royale • Known for its wolf and moose populations • Celebrating 50 years of study of closed system predator-prey relationship • On average: • Wolf population: 25 wolves • Moose population: 1000 moose • Population fluctuations (1980 wolf – 50; 1995 moose – 2422)
Wolf - Moose Moose first arrived ~ 1900 via swimming(?) from Canada Wolf first arrived in 1950 via ice bridge from Canada
Moose • During summer, moose eat ~30-40 pounds of vegetation each day, increase body weight by 25% • Winter feeding is difficult, eat twigs and balsam fir / cedar needles; snow depth makes foraging difficult
Wolf • Complex pack behavior with alpha male and alpha female • http://isleroyalewolf.org/overview/overview/wolves.html
Other Wildlife on Isle Royale There are not many species living on the Isle • Loons, osprey, beaver, red fox, squirrels • Will not find porcupine, coyote, white-tailed deer, black bear, chipmunk, skunk
Causes of Fluctuations • Moose population tends to increase in mild winters, early spring green-up, abundant winter forage, low wolf numbers, low tick infestation – wolf is the only predator • Wolf population tends to decrease due to disease, starvation, injury - ~90% of wolf diet is moose (few other species available)
Simplicity of the Chain Isolation of these species from others makes it ideal to study the direct predator-prey relationship Isle Royale’s simplified wolf food chain compared to Yellowstone’s more complex wolf food web.
Impact of Global Warming(?) • Five of last six summers hottest in past 50 years • Both moose and wolf populations declining • Increased temp. → moose rest more, eat less (heavy foraging in summer helps moose survive winters) • Increasingly warm summers cause increase in tick populations; weaken moose → easy prey • As moose populations decrease, what happens to the wolf population?
Changing Fortunes of Wolf And Moose Moose and wolf population fluctuations on Isle Royale depend on factors like weather, disease and possibly genetic problems. Scientists are trying to sort out reasons for the current wolf resurgence. j