The idea that no two species can occupy the same ecological niche for long in a given ecosystem is summarized in the principle of exclusion.

The principle of competitive exclusion, often referred to as Gause's Law, posits that two species competing for the same limited resources cannot coexist at constant population values. This principle is particularly significant in ecology and helps explain the observed distribution and abundance of species within ecosystems.

To elaborate, when two species share the same niche—the specific area or environment where a species operates and gathers resources—they will inevitably compete for resources (such as food, light, or space). This competition can lead to one species outcompeting the other, ultimately resulting in the local extinction of the weaker competitor, or it may force one of the species to adapt to exploit different resources (resource partitioning).

In sum, this principle reinforces the importance of biodiversity in ecosystems, illustrating how niche differentiation and species diversity contribute to ecological stability. It highlights that maintaining a balance of species is essential for the health and function of ecosystems.