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Michigan dnr > wildlife viewing guide > ecology: carrying capacity

Carrying Capacity: How Deep is the Barrel?

The number of animals a given area of land or water can support over time is called that area’s carrying capacity. Consider this illustration representing muskrats in a marsh. The barrel represents the marsh habitat - the amount of food, water, and cover for a fixed number of muskrats. The water in the barrel is the number of muskrats the habitat can support. The pipe pouring water into the barrel represents the new muskrats that are born in the marsh or wander in from other places. The water spilling out is the number of muskrats that die each year due to starvation, predators, disease, or other factors. The barrel can only hold so much water. That is, there is a limit to the number of muskrats that can survive here from year to year unless the habitat (the size of the barrel) is changed in some way. Every parcel of land has a different carrying capacity for every different kind of wildlife that lives there. A pristine cattail marsh would be a deep barrel for muskrats, while a dune forest would hold few, if any.

Who cares how deep the barrel is?

Knowledge of carrying capacity is essential for the conservation and management of wildlife populations. For example, the wolverine requires huge tracts of wilderness to survive - the equivalent of a swimming pool in this illustration. The muskrat, on the other hand, finds everything it needs in a small marsh - a rain barrel by comparison. Biologists use the concept of carrying capacity to determine how much habitat must be conserved to maintain healthy wildlife populations.

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