The non-independence of abundance and range size

Abstract

In considering the characterization and measurement of rarity (Chapters 1 and 2) it has proved convenient to treat as separate the abundance of a species and its range size. This is, nonetheless, misleading. Abundance and range size are not independent. At its crudest this is merely to state that at least one individual of a species must be present for a quadrat, site, or region to be correctly recorded as part of its area of occupancy, or as extending the limits of its extent of occurrence. The range of a species is a result of spatial variation in its abundance, with the size of the range reflecting the presence/absence component of this variation. The objective of this chapter is to explore the relationship between abundance and range size. The chapter divides broadly into two parts, concerned, respectively, with intra-specific and inter-specific interactions. The former, although in the main not explicitly about rarity, provides some important background for the latter.