Here's why:

* Interdependence: Each organism in an ecosystem relies on others for survival. This can include food sources, shelter, pollination, decomposition, and more.

* Food Webs: Ecosystems are made up of intricate food webs where energy and nutrients flow through various organisms.

* Competition and Cooperation: Organisms compete for resources like food, water, and space, but they also cooperate in ways like mutualism (both species benefit) or commensalism (one species benefits, the other is unaffected).

* Habitat: Organisms share the same environment with its abiotic (non-living) factors like climate, soil, and water.

* Balance: Changes in one population can have ripple effects throughout the ecosystem.

While organisms in the same ecosystem share a common environment, they are not necessarily all the same species or even the same type of organism.