Food Webs

Trends in population cycles

Population cycles are especially important features in boreal forest and tundra,1 Canada’s largest terrestrial ecosystems. Herbivores are at the heart of these systems. The 10-year snowshoe hare cycle drives the cycles of many bird and mammal predators in the boreal forest,19 particularly lynx and coyote. The hare cycle itself is a result of interaction between predation and the vegetation that forms the hares’ food supply.20 In Arctic tundra, lemmings and other small rodents drive population dynamics of many predators.21

Snowshoe hare and lynx cycles, boreal forest, Kluane, Yukon

Density of hares and lynx, 1976 to 2009
Graph: snowshoe hare and lynx cycles, boreal forest, Kluane, Yukon. Click for graphic description (new window).
Source: data from Krebs, 201014

Population density peaks in 2006 in Yukon were smaller and shorter than previous peaks. Similar dampening of hare cycles is emerging in the Northwest Territories.15 Continued monitoring is needed to see if this is a change in the cycles or part of natural fluctuations.

Arctic small mammal population cycles

Long datasets are needed to detect and understand ecosystem change, especially when populations may be cyclic.16 Small- mammal monitoring programs in the Northwest Territories and Nunavut, have not been in place long enough to detect trends. Lemming cycles at Bylot Island, Nunavut, showed signs of weakening in the mid-2000s17 but high densities of lemmings in 2008 and 2010 returned the long-term trend to stable.18

Globe

Global Trends

In northern Europe, population cycles in lemmings, voles, grouse, and insects have been weakening over large areas since the early 1990s. Some studies show linkages to climate change, especially to the effects of warmer winters.22, 23
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