Researchers from Oregon State University have reviewed fur trap data for the entire Canadian provinces of Saskatchewan and Manitoba — an area covering nearly 1.3 million square kilometers of land. Their study focused on the relationship between populations of wolves, coyotes, and foxes.
Wolves are known to kill coyotes, and coyotes are known to kill foxes — therefore, introducing wolves in an area should reduce the population of coyotes, and increase the population of red foxes. In the absence of wolves, coyotes flourish, and red fox populations are reduced. In the first pass through the data, that’s exactly what the researchers found.
However, due to the size of the area they were examining, the scientists were able to see that coyote populations are not reduced evenly over wolf territory. Wolves spend more time at the center of their territories than at the perimeter. This leaves the edges of wolf territory open for partial utilization by coyotes. Coyotes thus dominate local fox populations when far away from wolf territory, but their influence on foxes is reduced in areas closer to wolf territory.
This explains why the reintroduction of wolves into Yellowstone National Park had the expected result of reducing coyote numbers, but did not actually change the coyote population in the greater Yellowstone ecosystem. When the wolves moved in, the coyotes simply packed up and moved next door, into the open area on the perimeters of the wolf territories.
This study highlights wolves’ need to occupy large, contiguous areas in order to properly interact with their environment, and control other species such as coyotes.
Original article available here.
Source: Newsome T.M. & Ripple W.J. (2014). A continental scale trophic cascade from wolves through coyotes to foxes., The Journal of animal ecology, PMID: 24930631