At the peak of the cycle, snowshoe hares can reach a density of up to animals per km 2. The habitat cannot support this many animals. As predation increases and starvation sets in, the population starts to decline. Continued predation due to high populations of lynx and other predators increases the hare population decline. When the hare population reaches a low level, it stabilizes, for several years.
The food plants slowly recover and the hare population starts to increase again. Since hares have several litters each year, the hare population increases rapidly. After a year or two at high densities, the hare cycle repeats itself.
The lynx population decline follows the snowshoe hare population crash after a lag of one to two years. As hare numbers start to decline, lynx continue to eat well because they can easily catch the starving hares.
When hares become scarce, lynx numbers also decline. Their lack of fat reserves makes them less able to live through starvation and cold temperatures. Boonstra, M. Dale, S. Hannon, K. Martin, A. Sinclair, J. Smith, R. Turkington, M. Blower, A. Byrom, F. Doyle, C. Doyle, D. Hik, L.
Hofer, A. Hubbs, T. Karels, D. Murray, V. Nams, M. Rohner, and S. Oikos 74 Keith, L. A demographic analysis of the snowshoe hare cycle. Wildlife Monographs 58 Dynamics of snowshoe hare populations. Current Mammalogy 4 Krebs, C. Boutin, R. Boonstra, A. Smith, M. Dale, K. Martin, and R. Impact of food and predation on the snowshoe hare cycle. Science When a hare happens by, the lynx makes its move, bounding from its cover and initiating an exhilarating chase in which the hare dashes one way, then another, frantically trying to evade its adversary.
And whether for the thrill of the chase, the tantalizing taste of the hare, or a combination thereof, the lynx will wait hours on end for this moment, the opportunity to pounce on an unsuspecting snowshoe hare. The relationship between the Canada lynx Lynx canadensis and the snowshoe hare Lepus americanus is considered a classic example of how interactions between a predator and its prey can influence population dynamics of the two species.
Canada lynx populations rise and fall with fluctuations in populations of snowshoe hares. Thus, when hares are abundant, lynx populations expand, and when the density of hares is reduced, lynx are forced to hunt ground squirrels , grouse , and foxes. Though they occasionally kill larger animals such as a white-tailed deer , the shift away from hares takes its toll, and lynx populations ultimately shrink.
But while it is known that the growth or reduction of Canada lynx populations is tied to the population density of snowshoe hares, why hare populations fluctuate in the first place remains a bit of a mystery. Snowshoe hares experience changes in population density in cycles spanning periods of about 8 to 11 years. During a cycle, their density may increase by as much as fold and then drop precipitously.
It was once thought that the rapid declines were mainly the result of predation by lynx, but studies of snowshoe hare populations in places where lynx are not very abundant or are absent altogether—places such as Jacquot Island in southwestern Yukon and Prince Edward Island in eastern Canada—revealed that island snowshoe hares, like their mainland counterparts, also experience cyclic fluctuations.
A snowshoe hare displaying its brown-colored summer coat.
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