Two species occupying exactly the same niche will usually not coexist indefinitely; over time, strong competition forces a change in their populations or roles in the ecosystem. Three classic long‑term consequences are listed below.

1. Competitive exclusion (one species goes extinct)

  • If both species need the same limited resources in the same way, one will usually have even a slight advantage in survival or reproduction.
  • Over many generations, the better competitor increases, while the weaker one declines and can be driven to local extinction (disappears from that area), which is the essence of the competitive exclusion principle.

2. Niche differentiation (resource partitioning/evolutionary change)

  • To reduce intense competition, natural selection can favor individuals that use slightly different resources, habitats, or times of activity, leading to resource partitioning.
  • Over the long term, this can cause evolutionary niche differentiation, where the two species’ roles become more distinct so they can coexist with less direct overlap.

3. Stable coexistence with reduced densities

  • In some cases, both species persist in the same general habitat, but strong competition keeps each population smaller than it would be alone.
  • This coexistence is usually only possible when their niches are not perfectly identical, so each species still has some unique conditions or resources that support its continued survival.

TL;DR: Three possible long‑term consequences are:

  1. local extinction of one species (competitive exclusion),
  2. niche differentiation/resource partitioning, and
  3. coexistence with both species present but at lower population sizes due to ongoing competition.

Information gathered from public forums or data available on the internet and portrayed here.