The Voltage Gate

Coyote population densities are much lower in areas where their territory overlaps with wolves, according to a study done by the Wildlife Conservation Society. It's not pure numbers that they're talking about here, it's how many animals can be found within a certain area, and when there's wolves about, the density drops by about 33 - 39 percent for coyotes (percentages from different study areas). Despite the lower densities, coyotes still far outnumber wolves in these areas.

So what's going on here?

It's not predation. Wolf predation on coyotes accounts for only about 16 percent of mortality. That number is a measure of coyotes with strong connections to their pack. The so called "transient" coyotes, those that are somehow removed from a pack from old age, disease or as a yearling looking for a new pack have a much higher mortality rate due to wolf predation, about 56 percent. Transients in general have a harder time due to a lack of resources gained from being a part of a pack or a mating pair.

The researchers believe that the lower density of coyotes is due to direct, aggressive competition, usually referred to as interference competition (more precisely, interspecific interference - between species). There is an overlap in the food that coyotes and wolves eat, and the reduced densities of coyotes seem to be a reflection of that.

This is one of the most important concepts in ecology and there are a number of famous studies that have been done to analyze interference competition. One that immediately comes to mind is Grosholz's study of intraspecific competition within populations of terrestrial isopods. Grosholz stocked measured plots of soil with food and certain densities of isopods - 50 and 100 - and monitored the survival of each group. At a higher density, the isopods were less successful as a population than at a lower density. It seems like common sense; within a limited area with limited resources, you would expect that more individuals would tax those resources more heavily, leading to a lower survival rate. What Grosholz didn't expect was that the isopods living in a higher density were actually eating each other, which significantly reduced their survival rate. Little cannibals.

Studying this interaction between the coyotes and wolves has been speculated upon for a while now. Nice to see some more well-publicized results coming in.

Photo by Christopher Bruno