Descriptors of communities are commonly one or more of four elements below:
Some assumptions are necessary to view communities as ecosystems. One is that we know what a system of plants and animals requires to be sustained. A second is that structure and composition, which are relatively easily described, reflect function and pattern. Function especially is less easily described. A third assumption is that a description of a community can reliably provide an indication of ecosystem status. These are sometimes large assumptions. However, the jump from communities to ecosystems is shorter than the jump from species to ecosystems.