In ecology, the species-area curve is a graph showing the number of species foun in a defined area of a particular habitat or of habitats of different areas. It is related to, but not identical with, the species discovery curve. The species-area relationship is usually constructed for a single type of organism, such as all vascular plants or all species of a specific trophic level. It is rarely, if ever, constructed for all types of organisms if simply because of the prodigious data requirements. The species-area relationship is sometimes called as species-area theory.