Any natural assemblage of animals or plants usually contains several species of organisms. It may therefore be described as diverse. Only in the unlikely event that all the organisms in a collection belonged to the same species could one say that its diversity was zero. Diversity is thus a characteristic of biological collections. Whether the object of study be a natural community of plants, a collection of insects caught in a light trap, the microarthropods in soil samples, a population of breeding pairs of forest birds, or the plankton organisms in a sample of sea water, it will almost always exhibit diversity. A biologist will therefore wish to assign some numerical value to this property of the collection he is studying. Various methods of measuring diversity have been used in the past, the simplest being merely to count the number of species present. More precise measures take account of the fact that diversity has two quite distinct aspects. Thus, besides knowing the number of species in a collection, it is also necessary to consider how the individual organisms are apportioned among them. For a given number of species, a collection in which the species are fairly evenly rep resented has high diversity; whereas, if the bulk of the collection is made up of only a few of the species, while the remaining species are poorly represented, the diversity is lower.
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