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From Individuals to Ecosystems 4th Edition - Chapter 21

Chapter 21 Patterns in Species Richness Why the number of species varies from place to place, and from time to time, are questions that present themselves not only to ecologists but to anybody who observes and ponders the natural world. They are interesting questions in their own right . | Chapter 21 Patterns in Species Richness hot spots of species richness biodiversity and species richness 21.1 Introduction Why the number of species varies from place to place and from time to time are questions that present themselves not only to ecologists but to anybody who observes and ponders the natural world. They are interesting questions in their own right - but they are also questions of practical importance. A remarkable 44 of the world s plant species and 35 of vertebrate species other than fish are endemic to just 25 separate hot spots occupying a small proportion of the earth s surface Myers et al. 2000 . Knowledge of the spatial distribution of species richness is a prerequisite for prioritizing conservation efforts both at a large scale setting global priorities and at a regional and local scale setting national priorities . This aspect of conservation planning will be discussed in Section 22.4. It is important to distinguish between species richness the number of species present in a defined geographical unit - see Section 16.2 and biodiversity. The term biodiversity makes frequent appearances in both the popular media and the scientific literature - but it often does so without an unambiguous definition. At its simplest biodiversity is synonymous with species richness. Biodiversity though can also be viewed at scales smaller and larger than the species. For example we may include genetic diversity within species recognizing the value of conserving genetically distinct subpopulations and subspecies. Above the species level we may wish to ensure that species without close relatives are afforded special protection so that the overall evolutionary variety of the world s biota is maintained as large as possible. At a larger scale still we may include in biodiversity the variety of community types present in a region - swamps deserts early and late stages in a woodland succession and so on. Thus biodiversity may itself quite reasonably have a diversity .