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.
Without a doubt, the United States has never really lived up to the ideals of the Declaration. Historians, myself included, are quick to point out that Thomas Jefferson enslaved several hundred human beings when he crafted the Declaration.
