The unit is called Ecosystem.
Ecological units comprise concepts such as population, community and ecosystem.
<em>An ecosystem</em> is a community of plans and animals interacting with each other in an particular area. They also interact with their non-living environments (water, earth, sun, soil, climate and atmosphere).
The robins are in relationship with the earthworms because the robins eat them in order to survive and as a part of the food chain. The food chain is a linear sequence of organism through which nutrients and energy pass as one organism eats another. Ecosystems consist of creatures that mutually benefit from each other.
