Unit 2 - The Forest Ecosystem

Lesson 6: Populations

Living organisms do not exist in isolation; rather, they group together in populations. A population is a group of individuals of the same species living together in a given region at the same time.

For example, the photo to the right shows a forest that is dominated by a population of aspen trees.

A population of a certain species will occur only where their basic survival needs are met. In other words, climate, soil nutrients, and quantities of sunlight must all be appropriate — otherwise, a population of that species will not establish itself.

There are many examples of animal populations within Canada's forests. Some of these populations can affect each other. For example, one population can prey on another.
As predator populations rise, the prey species fall. Once the prey species is harder to find, the predator species does not have sufficient food and begins to die back. Those that survive may have fewer young. Thus a cycle emerges that can cause some dramatic fluctuation in numbers.

The image to the left, of a Canada Lynx chasing a snowshoe rabbit, is an example of a "predator/prey" cycle.