ECOSYSTEMS OF THE EARTH COLLECTIVELY FORM THE BIOSPHERE. IT IS A NARROW ZONE WHERE LIFE EXISTS. IT INCLUDES ALL OCEANS AND FRESH WATERS, THE LOWER LAYERS OF THE ATMOSPHERE AND THE OUTER SKIN OF THE EARTH'S CRUST WHICH IS MADE UP OF ROCKS AND SOIL.
MAN IS A PART OF THE BIOSPHERE AND DEPENDS ON ITS CONTINUED FUNCTIONING FOR HIS OWN EXISTENCE. HE CANNOT, HOWEVER, RISK MAJOR MODIFICATIONS OF THE BIOSPHERE EXCEPT AT THE RISK OF HIS OWN SURVIVAL. THUS, THE CONTINUED PRODUCTION OF PLANT MATERIALS, WHETHER WILD OR CULTIVATED, IS THE BASIS FOR THE NUTRITIONAL SUPPORT OF MAN AS WELL AS ALL OTHER ANIMALS.
THE CONTINUED FUNCTIONING OF GREEN PLANTS IS THE SOURCE OF ATMOSPHERIC OXYGEN ON WHICH MAN AND OTHER ORGANISMS DEPEND . THE CONTINUED FUNCTIONING OF THE DECOMPOSERS IS THE MEANS BY WHICH THE CHEMICALS IN HUMAN WASTES OR IN THE BODIES OF PLANTS AND ANIMALS ARE MADE AVAILABLE FOR FURTHER USE BY LIVING THINGS. A BREAK DOWN IN ANY OF THESE BIOSPHERIC SYSTEMS WOULD ENDANGER HUMAN SURVIVAL.
MANY SCIENTISTS BELIEVE THAT SPECIES DIVERSITY IS ESSENTIAL FOR THE PROPER FUNCTIONING OF COMMUNITIES AND FOR THE EMERGENCE OF COMMUNITY LEVEL PROPERTIES. JUST AS MANY DECODED DNA-ENCODED ENZYMES ARE NEEDED FOR A COMPLEX ORGANISM TO FUNCTION PROPERLY. SCIENTISTS BELIEVE THAT MANY KINDS OF SPECIES ARE NECESSARY TO MAINTAIN COMMUNITY STRUCTURE. BUT IS ANY DIVERSITY SUFFICIENT, OR ARE SPECIFIC MIXES OF SPECIES NECESSARY FOR THE COMMUNITIES AND ECOSYSTEMS TO FUNCTION ? THIS IS A VERY OLD QUESTION IN ECOLOGY AND TWO OPPOSING VIEWS EXIST. ONE VIEW IS THAT A COMMUNITY IS FORMED BY THE SPECIES THAT HAPPENED TO ARRIVE FIRST- THAT THE MIX OF SPECIES IN A COMMUNITY IS A MATTER OF CHANCE. THE VEGETATION OF AN AREA IS MAINLY THE RESULTANT OF TWO FACTORS, THE FLUCTUATING AND VARIABLE ENVIRONMENT. ACCORDING TO THE OPPOSING VIEW, IN A FAIRLY LIMITED AREA, ONLY A FRACTION OF THE FORMS THAT COULD THEORETICALLY DO SO ACTUALLY FORM A COMMUNITY AT ANY ONE TIME. THE COMMUNITY IS REALLY AN ORGANIZED COMMUNITY IN THAT IT HAS A LIMITED MEMBERSHIP.
ARE THESE TWO VERY DIFFERENT VIEWS REALLY IRRECONCILABLE ? NOT NECESSARILY, IF THE COMMUNITY IS DEFINED AS THE SUM OF ALL THE PLANTS AND ANIMALS THAT GROW TOGETHER IN AN AREA, CERTAIN PATTERNS CAN BE OBSERVED; AREAS WITH MORE THAN 1000 mm OF EVENLY DISTRIBUTED RAINFALL ALWAYS CONTAIN A WOODLAND; CONIFERS OCCUR IN AREAS OF EXTREMELY LOW WINTER TEMPERATURES ; TREES IN WARM MOIST CLIMATE HAVE BROAD LEAVES; AND SUCCULENT PLANTS ARE FOUND IN ARID CLIMATES. THE SAME IS TRUE FOR ANIMALS. THE MIX OF SPECIES ENCOUNTERED IN A COMMUNITY IS NOT A RANDOM SAMPLE OF ALL PLANTS AND ANIMALS IN THE WORLD.GREATER DIVERSITY IN PLANT COMMUNITY WILL RESULT IN A GREATER DIVERSITY OF ANIMAL SPECIES. THE HEALTH AND REGENERATION OF THE ECOSYSTEMS GETS BETTER WITH SPECIES DIVERSITY.
IN A COMMUNITY TWO TYPES OF PROCESSES ARE AT WORK AND NEITHER OF THEM IS DOMINANT. FIRST, THERE IS NATURAL SELECTION SPECIES IN THE COMMUNITY ARE CONSTANTLY EVOLVING TO INCREASE THEIR ABILITY TO WITHSTAND THE RIGOURS OF ENVIRONMENT. THIS PROCESS ACCOUNTS FOR THE COLD-HARDY SPECIES NEAR THE POLES, FOR GRASS- EATING RUMINANTS NEAR THE SAVANNAS, AND FOR FRUIT-EATING BATS IN THE FORESTS. THE INDIVIDUAL THAT ESCAPES ITS PREDATORS AND IS ABLE TO SURVIVE OTHER ENVIRONMENTAL CHALLENGES PASS ON THEIR CHARACTERISTICS IN THE COMMUNITY THAT WERE ONCE ADVANTAGEOUS CAN BECOME A BURDEN. DISEASE MIGHT BE INTRODUCED , SUCH AS DUTCHELM DISEASE FOR WHICH LOCAL SPECIES HAVE NO DEFENCE. HURRICANES, TORNADOES, FLOODS AND DROUGHTS ARE UNPREDICTABLE AND THEIR FREQUENCY CHANGES WITH TIME . CHANCE ALSO PLAYS A ROLE IN DISPERSAL. FOR EXAMPLE, A SPECIES MIGHT BE ABSENT FROM A COMMUNITY PURELY BY CHANCE. THUS, BOTH NATURAL SELECTION AND CHANCE RESULT IN THE STEADY COMING AND GOING OF SPECIES THROUGH IMMIGRATION, EXTINCTION AND GENE MUTATION.
A LARGE NUMBER OF QUESTIONS EXIST REGARDING THE ECOLOGICAL ROLE OF BIODIVERSITY IN COMMUNITIES. FOR EXAMPLE, CAN MORE AND MORE SPECIES BE PACKED INTO A COMMUNITY, OR ARE THERE UPPER AND LOWER LIMITS ? A RELATED QUESTION CONCERNS OPTIMAL LEVELS OF DIVERSITY AND THE FACTORS THAT CONTROL THEM. OTHER ISSUES INCLUDE THE ROLE OF DIFFERENT INDIVIDUALS WITHIN A POPULATION, DIFFERENT POPULATIONS WITH A SPECIES AND SO ON.
IN A VARIABLE ENVIRONMENT, THE EXISTENCE OF INDIVIDUALS WITH DIFFERENT CHARACTERISTICS MAY INCREASE IN WAYS IN WHICH THE POPULATION CAN RESPOND TO CHANGE. FOR EXAMPLE, IF ALL PLANTS OF A SPECIES HAD SIMILAR WATER REQUIREMENTS, ALL OF THEM WOULD SUFFER WATER STRESS IN ANY YEAR THAT WAS DRIES THAN NORMAL; AND SUCH PERIODS WOULD RESULT IN SIGNIFICANTLY REDUCED SEED PRODUCTION ON THE OTHER HAND, IF THERE IS GENETIC VARIATION, SOME INDIVIDUALS MIGHT PERFORM ABOVE AVERAGE EACH YEAR WITHIN CERTAIN LIMITS OF ENVIRONMENTAL VARIATION. THEREFORE, SEED PRODUCTION WOULD BE SATISFACTORY IN BOTH WET AND DRY YEARS. MOREOVER, GENETICALLY ADAPTABLE ORGANISMS SHOULD SURVIVE IN MORE ENVIRONMENTS THAN THE GENETICALLY UNIFORM POPULATIONS. EXPERIENCE WITH CROPS SHOWS THAT HIGHLY PRODUCTIVE BUT GENETICALLY UNIFORM VARIETIES HAVE MORE RESTRICTED ENVIRONMENTAL REQUIREMENTS THAN THE LESS PRODUCTIVE BUT MORE VARIABLE VARIETIES. PLANTATIONS FORMED BY UNIFORM VARIETIES ARE MORE SUSCEPTIBLE TO DISEASE OUTBREAKS.
THUS WE SEE THAT VARIABILITY WITH A SPECIES SEEMS TO BE IMPORTANT FOR LONG TERM SURVIVAL. DOES THE SAME HOLD FOR A COMMUNITY, WHICH IS FORMED OF SPECIES THAT LIVE TOGETHER BUT DO NOT HAVE A COMMON GENE POOL? COMMUNITIES WITH HIGH SPECIES DIVERSITY MAY ALSO COPE WITH LONG TERM ENVIRONMENTAL FLUCTUATIONS BETTER THAN THE COMMUNITIES WITH SPECIES. HOWEVER, THE EVIDENCE IS CONTRADICTORY. TERRESTRIAL COMMUNITIES WITH FEW SPECIES. HOWEVER, THE EVIDENCE IS CONTRADICTORY. TERRESTRIAL COMMUNITIES IN THE CLIMATICALLY VARIABLE MID-LATITUDES ARE LESS DIVERSE THAN TROPICAL COMMUNITIES IS MORE UNIFORM ENVIRONMENTS. DEEP BENTHIC COMMUNITIES ARE AMONG THE MOST VARIABLE COMMUNITIES ANYWHERE EVEN THOUGH THEY EXIST IN POSSIBLY THE MOST UNIFORM ENVIRONMENT OF THE PLANT.
THE STEADY INCREASE IN HUMAN PRESSURE ON THE EARTH'S SURFACE IS DRIVING ON EXTINCTION SPASM THAT SEEMS LIKELY TO RIVAL OR SURPASS IN RATE FAR BEYOND NATURAL PRECEDENT. IN THE PERIOD SINCE 1600, 171 BIRD AND 115 MAMMAL SPECIES ALONE ARE KNOWN TO HAVE BECOME EXTINCT THROUGH HUMAN ACTION. THESE FIGURES, FOR THE KNOWN AND LABELLED EXTINCTIONS OF THE KIND, DO NOT COUNT FOR THE SPECIES THAT MAY HAVE OCCURRED UNNOTICED. IT IS ESTIMATED THAT ABOUT 1 PERCENT OF ALL SPECIES PRESENT IN 1600 HAVE BECOME EXTINCT, HALF OF THEM SINCE 1881 CURRENT HUMAN ACTIVITY IS EXPECTED TO RESULT IN THE LOSS OF GENETIC DIVERSITY WITHIN THE SPECIES AND A THREAT TO ITS SURVIVAL OF ITS GEOGRAPHICAL RANGES. MAN'S ACTIVITIES HAVE TRANSFORMED THE EARTH INTO A LESS HOSPITABLE PLACE FOR MANY LIVING ORGANISMS, THROUGH MORE INVITING FOR A FORTUNATE FEW.
HABITAT CHANGE LIKE WISE AFFECTS THE DIVERSITY OF WILDLIFE IN AN ECOSYSTEM. EVEN SMALL LANDSCAPE TRANSFORMATION CAN OBLITERATE THE HOME OF AN ENDEMIC SPECIES. DRAINAGE OF WETLANDS; THE PLOUGHING OF GRASSLANDS AND DEFORESTRATION HAVE GREATLY REDUCED THE NUMBERS AND NARROWED THE RANGE , EVEN OF WIDELY DISPERSED SPECIES. THE COUPLED EFFECT OF HABITAT LOSS AND HUNTING HAS GREATLY SHRUNK THE RANGE OF MANY SPECIES, AS A RESULT DISRUPTING THE ECOLOGICAL FUNCTIONING OF ECOSYSTEMS.POLLUTION, A SPECIAL CASE OF HABITAT CHANGE REPRESENTS AN ADDED FORM OF IMPACT ESPECIALLY IN HIGHLY DEVELOPED AND INDUSTRIALIZED REGIONS.
RESEARCH SUGGESTS THAT A MORE DIVERSE ECOSYSTEM IS BETTER ABLE TO WITHSTAND ENVIRONMENTAL STRESS AND CONSEQUENTLY IS MORE PRODUCTIVE . THE LOSS OF A SPECIES IS THUS LIKELY TO DECREASE THE ABILITY OF THE SYSTEM TO MAINTAIN ITSELF OR TO RECOVER FROM DAMAGE OR DISTURBANCE. JUST LIKE A SPECIES WITH HIGH GENETIC DIVERSITY, AN ECOSYSTEM WITH HIGH BIODIVERSITY MAY HAVE A GREATER CHANCE OF ADAPTING TO ENVIRONMENTAL CHANGE. IN OTHER WORDS, THE MORE SPECIES COMPRISING AN ECOSYSTEM, THE MORE STABLE THE ECOSYSTEM IS LIKELY TO BE . THE MECHANISMS UNDERLYING THESE EFFECTS ARE COMPLEX AND HOTLY CONTESTED. IN RECENT YEARS, HOWEVER, IT HAS BECOME CLEAR THAT THERE ARE REAL ECOLOGICAL EFFECTS OF BIODIVERSITY.
NATURE CERTAINLY HAS SOME BUILT DEDUN DANCY, AND SOME DIVERSITY COULD BE LOST WITHOUT BEING NOTICED. NEVERTHLESS, FEW DATA ARE AVAILABLE ON WHICH GENES OR SPECIES ARE PARTICULARLY IMPORTANT IN THE FUNCTIONING OF ECOSYSTEMS, SO IT IS DIFFICULT TO ESTIMATE THE EXTENT TO WHICH SOCIETY IS SUFFERING FROM THE LOW OF BIODIVERSITY. THE IMPACT OF THE LOSS OF TOP PREDATORS MAY BE OBVIOUS ENOUGH, BUT THE ECOLOGICAL ROLES PLAYED IN MANY SPECIES OR POPULATIONS ARE STILL ONLY PARTLY KNOWN. DUE TO THIS UNCERTAINTY ABOUT THE ROLES OF DIFFERENT COMPONENTS IN DETERMINING THE FUNCTIONING OF ECOSYSTEMS, THE WISEST COURSE IS TO APPLY PRECAUTIONARY PRINCIPLES AND VOID ACTIONS THAT NEEDLESSLY REDUCE BIOLOGICAL DIVERSITY.
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