Genetic, species, and ecosystem diversity

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Genetic, species, and ecosystem diversity

Biological diversity or biodiversity is gen­isolated areas have low rates of gene flow and, erally divided into three fundamental categories:as they adapt over time to their particular envi­ genetic diversity, species diversity, and ecosys­ronment, they develop into distinct, localized tem diversity. populations. Behavioral traits can also influence the Genetic diversity geographical distribution of genetic characteris­ tics within a given species. For example, the The genetic material of microorganisms,North American eel inhabits streams along 4000 plants and animals contains information thatkm of coastline, but migrates to the Sargasso determines the characteristics of all species andSea to reproduce as one massive population. As individuals that make up the diversity of the livinga result, individual eels inhabiting streams many world. The number of possible combinationsmiles of apart do not demonstrate any geographic genes and of the molecules making up genesdifferentiation. is However, other species such as immense - much larger than the numbersalmon, of breed in different streams, but spend individuals making up a species. most of their life at sea; these species develop Genetic diversity refers to the differencesmarked genetic variations between populations. in genetic make-up between distinct species and to genetic variations within a single species.Species diversity Individuals belonging to a species share, by definition, certain characteristics, but genetic Species diversity is measured in relation variation determines the particular characteris­to a given area - from a small field to the entire tics of individuals within the species. In simpleplanet. It can be assessed in terms of the terms, genetic material dictates whether we havenumber of species or the range of different types blue or brown eyes, blond or black hair, andof are species an area contains. tall or short. It also determines whether an So far, 1.7 million species have been individual animal or plant has the ability to sur­described worldwide. Estimates of the total vive in a particular habitat or under particularnumber of species on Earth range from 5 to 100 environmental conditions. Some plants, million for --1 2 .5 million being a conservative work­ example, are able to grow in saline water asing a estimate. Although most of the Earth’s result of genetic variation. species are insects and microorganisms, this is Genetic variation occurs to varying deg­not reflected in the types of species that have rees in most species of plants and animals.been described to date. There has been a There is high genetic variation in Indian rhinos,definite bias towards describing large organisms, for example, but little among cheetahs. Further­those that are considered attractive or appealing more, the genetic make-up of an individual(such as flowering plants and butterflies), those species is not static -- it changes as a result mostof closely resembling humans (vertebrates, both internal and external factors. especially mammals), and those that have a This variety of genetic material within spe­direct impact on human activities (such as pests). cies has enabled distinct species to evolveOrganisms that can be studied without complex through natural selection. Broadly speaking,procedures or expensive equipment have also species that inhabit large areas and interbreedtaken precedence, as have those which are throughout the whole area have a high raterelatively of easy to locate. gene flow and show few or no localized char­ This, however, underestimates the impor­ acteristics; however, species living in small ortance of microorganisms including algae, bacte-

2 Aqua Farm News Vol. XII (No. 3) May-June 1994 ria, fungi, protozoa and viruses, which are vitalfied into a number of ecosystems. Major habitat to life on Earth. So far, less than 3-5 percenttypes of include tropical rain forests, grasslands, microorganisms have been described. Yet wetlands,the coral reefs and mangroves. Measur­ very existence of larger organisms dependsing changes in the extent of ecosystems is upon the continued availability of the microor­difficult, because there is no globally agreed ganisms they require. Coral reefs, for example,classification of ecosystems, and boundaries could not exist without algae. At the ecosystemare often variable and elusive. Species contained level, the greatest biomass in soil is micro­within a given ecosystem also vary over time. organisms, especially fungi. These maintain soil Studies of ecosystem diversity are car­ structure and composition through, for instance,ried out on different scales: from one ecosystem the biodegradation and incorporation of to dead an entire region containing many different plant and animal remains. Clearly, the lossecosystems. of Regions containing a great variety micro-organisms can lead to major changesof in ecosystems are rich in biodiversity, but indi­ ecosystems. vidual ecosystems containing endemic species Biologists are currently studying bothalso make a significant contribution to global species-rich groups (such as insects) and spe­biodiversity. cies-rich areas (such as moist tropical forests) in Some of the world's richest habitats are order to provide a more reliable picture of spe­tropical moist forests. Although they cover only cies richness patterns and a basis for estimating7 percent of the world’s surface, these areas the number of species on Earth. contain at least 50 percent, and possibly up to 90 percent of all plant and animal species. Isolated Ecosystem diversity islands are often rich in endemic species.

The enormous range of terrestrial and Reference:Global Biodiversity.1993. United aquatic environments on earth has been classi­Nations Environment Programme, Nairobi, Kenya.

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