The existence of the blue whale is intimately tied to the shrimp-like krill. Few communities ever reach a perfect steady state. A biotic community and its physical environment form an ecosystem.
Ecosystems are open systems that can and do change and interact with one another.
Producers and consumers form intricate webs. Carbon isotopes can be used to trace the lines of a food web. The elements are continuously recycled through the interactions of organisms and their environments. Most organisms cannot use nitrogen directly. Phosphorus is a vital component of genetic material, ATP, and membrane phospholipids.