expressed by Aldo Leopold, that the first rule of intelligent tinkering is to save all the pieces, we are engaged in very dangerous tinkering.

Genetic diversity within species is a useful measure of biodiversity, because many species are divided into local populations that are uniquely adapted to the environments in which they live. The study of the causes and consequences of such local adaptations is an important part of population biology. Programs to restore populations in areas from which they have been almost eliminated must pay careful attention to the genotypes of the individuals to be introduced. Maintaining genetic diversity is an essential component of successful captive propagation efforts for rare and endangered species, and much valuable biodiversity can be lost when local populations are exterminated, even if the species survives.

Another important component of biodiversity is the distinctness of evolving lineages. Numbers of the higher taxonomic categories (phyla and classes) in the universally used hierarchic biologic classification system provide a rough measure of distinctness of lineages. By that measure, marine biodiversity is much greater than terrestrial biodiversity, even though there are far fewer marine than terrestrial species. Of the 32 extant phyla of multicellular animals, for example, 31 are marine, and 14 of the 31 are exclusively marine. From this perspective, preservation of marine biodiversity is more important than might be suggested if one simply compares the numbers of species in marine and terrestrial ecologic communities.

Organisms do not live in isolation, but are embedded in a physical environment and a complex matrix of interacting species; and the richness of ecosystems is another measure of biodiversity. Preservation of these systems is essential for the preservation of the species living in them. Although a rich array of terms is used to describe different ecologic communities, there is no generally accepted classification of ecosystems. Species can be defined objectively, but there is no objective basis for deciding how finely ecosystems should be divided. Efforts are under way to develop classification systems for ecosystems that can guide conservation efforts.

Where Is It?

Living species are not uniformly distributed over the surface of the globe. To describe the complex spatial patterns of biodiversity, ecologists and biogeographers have found it useful to divide diversity into two major components: α-diversity and ß-diversity. α-diversity refers to point diversity, that is, to the number of species found in a small homogeneous area. ß-diversity refers to the rate of change in species of composition across habitat

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