IMPACT OF FOOD AND PREDATION ON THE SNOWSHOE HARE CYCLE

Snowshoe hare populations in the boreal forests of North America go th rough 10-year cycles. Supplemental food and mammalian predator abundan ce were manipulated in a factorial design on 1-square-kilometer areas for 8 years in the Yukon. Two blocks of forest were fertilized to test for nutrient effects. Predator exclosure doubled and food addition tr ipled hare density during the cyclic peak and decline. Predator exclos ure combined with food addition increased density 11-fold. Added nutri ents increased plant growth but not hare density. Food and predation t ogether had a more than additive effect, which suggests that a three-t rophic-level interaction generates hare cycles.