Competition can either have direct or indirect effects on individuals. Indirect effects occur through the depletion of a limiting resource; this is often called exploitation competition. In this situation, individual fitness is reduced due to a lack of resource availability.

Individuals may also interact directly with each other, called interference competition. A common case of this type of interaction occurs when animals fight over territory. Another example of direct competition is the use of toxins by one of the competitors. For example, black walnuts release quinine into the soil, killing other individual plants and thereby limiting the amount of competition (Mackenzie et al. 1998).

The effects of competition may differ for the individuals involved. Often, the cost for one of the individuals is much greater than the other. For example, one individual may die while the other one lives