Genetic, species, and ecosystem diversity
           Item Type           article
           Download date       20/01/2023 11:11:35
           Link to Item        http://hdl.handle.net/1834/34701
            BACKGROUNDER
            Genetic, species, and ecosystem diversity
                    Biological diversity or biodiversity is gen­            isolated 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 ecosys­               ronment,  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  that               km of coastline, but migrates to the Sargasso 
            determines the characteristics of all species and               Sea to reproduce as one massive population. As 
            individuals that make up the diversity of the living            a result, individual eels inhabiting streams many 
            world.  The number of possible combinations of                  miles apart do not demonstrate any geographic 
            genes and of the molecules making up genes is                   differentiation.  However, other species such as 
            immense -   much  larger than the  number of                    salmon, 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 differences              marked 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 characteris­                 to a given area -  from a small field to the entire 
           tics of individuals within the species.  In simple               planet.     It  can  be  assessed  in  terms  of  the 
           terms, genetic material dictates whether we have                 number of species or the range of different types 
            blue or brown eyes, blond or black hair, and are                of 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 sur­              described  worldwide.          Estimates  of  the  total 
           vive in a particular habitat or under particular                 number of species on Earth range from 5 to 100 
            environmental  conditions.           Some plants, for           million --12.5 million being a conservative work­
            example, are able to grow in saline water as a                  ing  estimate.  Although  most  of  the  Earth’s 
            result of genetic variation.                                    species are insects and microorganisms, this is 
                    Genetic variation occurs to varying  deg­               not 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.  Further­                those 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 of              most closely resembling humans (vertebrates, 
            both internal and external factors.                             especially  mammals),  and those that  have  a 
                   This variety of genetic material within spe­             direct impact on human activities (such as pests). 
           cies  has  enabled  distinct  species  to  evolve                Organisms that can be studied without complex 
           through  natural  selection.  Broadly  speaking,                 procedures or expensive equipment have also 
            species that inhabit large areas and interbreed                 taken  precedence,  as  have  those  which  are 
           throughout the whole area have a high rate of                    relatively easy to locate.
            gene flow and show few or no localized char­                            This, however, underestimates the impor­
            acteristics;  however, species living in small or               tance of microorganisms including algae, bacte-
            2   Aqua Farm News Vol. XII (No. 3) May-June 1994
         ria, fungi, protozoa and viruses,  which are vital       fied into a number of ecosystems.  Major habitat 
         to life on Earth.  So far, less than 3-5 percent of      types include tropical  rain forests,  grasslands, 
         microorganisms have been described.  Yet the             wetlands, coral reefs and mangroves.  Measur­
         very  existence  of  larger  organisms  depends          ing    changes in the  extent of ecosystems  is 
         upon the continued availability of the microor­          difficult,  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 ecosystem         are often variable and elusive. Species contained 
         level,  the  greatest  biomass  in  soil  is  micro­     within 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 dead           to  an  entire  region  containing  many  different 
         plant and animal remains.  Clearly, the loss of          ecosystems.  Regions containing a great variety 
         micro-organisms can lead to major changes in             of ecosystems are rich in biodiversity, but indi­
         ecosystems.                                              vidual ecosystems containing endemic species 
                Biologists  are  currently  studying  both        also  make a significant  contribution  to  global 
         species-rich groups (such as insects) and spe­           biodiversity.
         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 spe­         tropical moist forests.  Although they cover only 
         cies richness patterns and a basis for estimating        7 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 classi­
                                                                   Nations Environment Programme, Nairobi, Kenya.
                                                                     Aqua Farm News Vol. XII (No. 3) May-June 1994    3