Interactions Between Organisms

No organism lives alone. Within an ecosystem, species constantly interact—competing, consuming, and cooperating. These interactions shape populations, drive evolution, and determine the structure of entire communities. Ecologists classify them by their effects on the species involved.

Competition

Competition occurs when organisms need the same limited resource—food, water, light, space, or mates. Both parties are harmed because the resource is shared.

• Intraspecific competition is between members of the same species and is often intense, since their needs overlap completely.
• Interspecific competition is between different species. The competitive exclusion principle states that two species competing for exactly the same niche cannot coexist indefinitely; one will outcompete the other, or th