Competitive exclusion is a principle in ecology that states two species competing for the same resources cannot coexist indefinitely. When two species have similar needs, one will typically outcompete the other, leading to the latter's decline or extinction in that environment. This concept helps explain biodiversity and species distribution. The principle was first articulated by ecologist G.F. Gause in the 1930s through experiments with protozoa. It highlights the importance of resource availability and niche differentiation, where species adapt to utilize different resources or habitats to reduce competition and coexist more effectively.