The interactions of earthworms and Robbins in a beach far is make up which ecological unit

The unit is called Ecosystem.

Ecological units comprise concepts such as population, community and ecosystem.

An ecosystem 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.