竞争排除原则（也称竞争排斥原理或高斯定理）在生态学里指的是，两个物种不能同时，或者是不能长时间地在同一个生态区位生存。因为两者之间会展开竞争，导致其中的一方获胜，可以留在原来的生态龛位继续生存。

另一方为了继续生存，会改变自己的居住地，或者改变饮食习惯，或者改变自身习性（如改日行性为夜行性，达到时间上和获胜的一方分离），进化适应以延续生命。相对来说，失败者一方完全灭绝是很少见的。这些改变也是促成了适应辐射：从原始的一般种类演变至多种多样、各自适应于独特生活方式的专门种类的过程。

In ecology, the competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law, is a proposition that states that two species competing for the same resource cannot coexist at constant population values, if other ecological factors remain constant. When one species has even the slightest advantage or edge over another then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolutionary or behavioral shift toward a different ecological niche. The principle has been paraphrased into the maxim "complete competitors cannot coexist".