Food webs

Decline of the Amphipod Diporeia in Lake Huron

Graphic thumbnail: decline of the Amphipod Diporeia in Lake Huron

This graphic consists of three maps of Lake Huron which display the distribution of densities of the amphipod Diporeia in 2000, 2003, and 2007. The year with the highest density was 2000, with densities decreasing in each subsequent study year. In 2000 Diporeia was found in the majority of the lake with the highest concentrations in the central west portion of the lake (reaching densities of 3,000 to 3,500 amphipods per square metre) and decreasing in density incrementally towards the edges of the lake (where densities were from 0 to 500 per square metre). In 2003 low densities of Diporeia were widely dispersed across a large area of the north and central lake (reaching densities from 0 to 1,500 per square metre). In 2007 a large area of low density (0 to 500 per square metre) was dispersed across the northern and central lake, with four patches of higher density (500 to 1000 Diporeia amphipods per square metre) present on the western side of the lake.

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North American range of the wolverine

Graphic thumbnail: North American range of the wolverine

This map of North America shows the historical and current distributions of the wolverine. Historically the wolverine range extended much further south than the current range. In western North America the historical range extended down the coast as far as northern California and inland to the Sierra Nevada and the American Rockies. The current range in western North America extends south just as far as Vancouver Island; inland the range extends south through the Canadian Rockies into the American Rockies, but not as far as it did in the past. Historically the wolverine range followed the Canada-U.S. border, dipping further south in places and rising north before reaching the eastern coast of the U.S., coming up to the Atlantic Maritime coast and Labrador. Currently the distribution has receded north, though it still includes areas in the following ecozones+: Pacific Maritime, Boreal Cordillera, Taiga Cordillera, Taiga Plains, and Hudson Plains. Current range also includes Alaska, and most of the Arctic Ecozone+ with only a few islands showing no historical or current distribution.

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

Graphic thumbnail: snowshoe hare and lynx cycles, boreal forest, Kluane, Yukon

This line graph displays the population rise and fall of two species in a predator-prey relationship from 1976 to 2009. Snowshoe hare populations showed cycles of steep growth and decline throughout the study period. Peaks in snowshoe hare population were: 4.4 hares per hectare in 1981, 2.5 hares per hectare in 1988, 2.7 hares per hectare in 1998, and a much lower density of 1.2 hares per hectare in 2006. The measure of lynx populations shown is the number of lynx tracks per 100 kilometres counted in transects, with data beginning in 1976. Lynx populations peaked shortly after hare population peaks. In 1990 to 1991 the mean number of tracks per 100 kilometres peaked at 53.9, in 1998 to 1999 tracks peaked at 82.4, and in 2006 to 2007 tracks peaked 39.4. The overall pattern is that the timing and the magnitude of animal population cycles of lynx followed that of snowshoe hares, and that the last peak of this cycle was smaller and shorter for both animals.

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