One situation where breeding pressure may occur is on an island. In ecological terms the word ``island'' means not only a piece of land isolated from other land masses by a large body of water, but any ecosystem isolated from similar ecosystems. For example, a mountainous region that is heavily forested would be an island as far as a cougar is concerned if the cougar had to cross farmland or urban areas to get to a different high altitude forest.
An important attribute of an island ecosystem is its carrying capacity, which is the number of individuals it can support. In the cougar example, a region of 100 square miles may support only a few dozen cougars since they would have to compete with one another for food, shelter, and so on.