A measurable property of any collection of organisms containing more than one species is
its “species-diversity”. Methods of measuring species-diversity based on the information
content of a collection are reviewed. A collection consisting of a community of sessile
organisms, such as terrestrial plants, also has “pattern-diversity”. The pattern-diversity of a
community is high when the individuals of the various species are thoroughly mingled so
that several species are usually present in any small sub-area; it is low if the species are …