food chain
1. A hierarchy of organisms that transfer food energy between them. The smallest organisms are at the bottom—and they are preyed upon by the larger ones above them in the food chain. Grizzly bears are at the top of the food chain.
2. A hierarchy of people in a group or organization. Often used in the phrases "at the top of the food chain" and "at the bottom of the food chain." As a medical intern, I'm at the bottom of the food chain, but I'll move up soon enough. It will take a while to move up the food chain in such a large company, but you'll make manager soon enough.