11.4 Carrying Capacity

I would like to see more wildlife in my area. Why doesn’t the Department of Fish and Wildlife capture wildlife and release it in my area?

This always sounds like a good idea, and it seems simple enough. Capture wildlife in one area, and then take it and release it in another area so that we can increase wildlife populations. Unfortunately, this idea rarely works!

If an area has good habitat, it probably already has wildlife living in the habitat. If an area has poor wildlife habitat, then capturing and releasing wildlife in that area will not increase wildlife numbers.

You already know that good habitat contains food, water, space, and cover in the proper arrangement. But can you continue to add wildlife to good habitat without having any impact on the amount of food, water and cover? Of course, the answer is no! If you have good habitat for only 25 animals, adding another 5 animals will actually reduce the quality of the habitat for all animals. Look at the picture on the right. Think of the pail as good wildlife habitat. The pail can only hold a fixed amount of water. As more water is added to the pail, the excess water will spill out of the pail. The pail is like wildlife habitat. The habitat has enough food, water, and cover to support a fixed number of animals. When more animals are added to the habitat, they may actually damage the habitat by eating more food, using more water, etc.

Carrying Capacity: The number of animals the habitat can support throughout the year.

This picture and the story about Angel Island on the previous page help explain why we cannot simply capture and release wildlife into new areas. Biologists say that all habitats have a fixed carrying capacity. The carrying capacity of a habitat is the number of animals that the habitat can support throughout the year without damaging the habitat. Once again, look at the picture of the habitat pail. It can only hold a fixed amount of wildlife. If we add more wildlife without increasing the size of the pail, the extra animals will consume more food and water and may damage the habitat for all animals. We can’t add new animals to an area unless we know there is enough good habitat!

The carrying capacity of a habitat can change for better or for worse! Forest fires, for example, are often helpful to big game. The new vegetation that grows after a forest fire offers a ready source of food to many big game species. With enough cover and water in the right arrangement, a forest fire can actually help expand the carrying capacity of a habitat over time.

What about a new housing development that transforms 100 acres of woodlands into new homes and streets? This is an example of reducing the carrying capacity of a given habitat. Most wildlife using that 100 acres will be forced into other areas.

Sometimes biologists do live-trap wild animals and release them into new areas. Some examples of this in Washington during the past few years are with the mountain goat and the wild turkey populations.