| Fig. 1. Biological systems can be arranged in at least two nested hierarchies, one functional and the other taxonomic. The functional hierarchy reflects how researchers arrange biological material at various levels of interaction among the lower, component parts of a system. The taxonomic hierarchy provides a system for ordering and naming the diversity of life forms on Earth. To a great extent, it also reflects the suspected evolutionary relationships among the various taxa. The species concept is so important to biologists because species occur in both hierarchies. Thus, events that affect species have ramifications up and down both hierarchies. | |
