On the definition of element, chorotype and component in biogeography

Terms such as element, chorotype and component are widely used to indicate biogeographical units. As a result of variation in approaches and methodologies, these terms do not have a single definitive meaning, and similar concepts have been defined under different labels. As originally defined, element denotes a group of species that occur in previously defined biogeographical areas, while chorotype denotes a group of species with a similar distribution. The term component is widely used in ecology to denote the biotic or abiotic constituent of an ecosystem; within biogeography it has typically been used as a synonym for element. Applying the original meanings, current usage within the tradition of systematic biogeography should regard element as referring to groups of taxa defined according to the biogeographical areas they occupy. Within quantitative and evolutionary biogeography, chorotype should be used to define patterns of distribution that can be used to generate hypotheses about their causes and origins. In this paper I argue that component expresses a generic concept rather than a chorological category and should be avoided in biogeography.