SPECIES INTERACTIONS

ALL POPULATION OF LIVING ORGANISMS EXISTS IN A NETWORK OF INTERACTIONS WITH OTHER POPULATION. MANY OF THESE INTERACTIONS ARE SUBTLE AND COMPLEX WHILE OTHERS ARE DIRECT. THE DEGREE OF INTIMACY IN THE RELATIONSHIPS OF THE ORGANISM INHABITING A PARTICULAR HABITAT VARIES GREATLY. THESE ASSOCIATES MAY BE EITHER BENEFICIAL OR HARMFUL TO BOTH THE PARTNERS OR BENEFICIAL TO ONE PARTNER AND HARMFUL TO THE OTHER. IF THE RELATIONSHIP IS BENEFICIAL TO ONE OR BOTH PARTNERS, IT IS CALLED POSITIVE INTERACTION OR COOPERATION. THE INTERRELATIONS OF INDIVIDUALS THAT ARE HARMFUL TO ONE OR MORE OF THE PARTICIPANTS ARE CALLED NEGATIVE INTERACTION.

INTERACTIONS BETWEEN PLANTS AND ANIMALS

IN A NATURAL ECOSYSTEM THE SUN'S ENERGY WILL BE CAPTURED BY THE TREES, GRASS OR OTHER HERBS AND CONVERTED INTO PROTEINS, CARBOHYDRATES AND OTHER FOOD COMPONENTS. THESE WILL BE CONSUMED BY PLANT EATING MAMMALS, BIRDS, INSECTS AND A GREAT VARIETY OF OTHER ANIMALS WHICH IN TURN WILL PROVIDE FOOD FOR THE MEAT-EATING ANIMAL. ALL LIVING ORGANISMS ULTIMATELY PROVIDE FOOD FOR THE ORGANISMS OF DECAY WHICH BREAKS DOWN THE PLANT AND ANIMAL MATERIALS AND RESTORE THE CHEMICAL COMPONENTS OF THE SOIL.

HERBIVORES FEED ON DIFFERENT PARTS OF A PLANT AND ALSO ON DIFFERENT PLANTS. GRAZING ANIMALS EAT UNHARVESTED HERBS AND GRASSES WHILE BROWSING ANIMALS EAT FOLIAGE OF SHRUBS AND TREES. SHEEP PREFER BROWSING ON HIGH HERBS, GOATS AND DEER ON BROAD LEAVED SHRUBS, CAMELS ON TENDER SHOOTS OF TALL TREES, WHILE HORSES AND CATTLE PREFER GRASSES.GRAZING AND BROWSING IN LIMITED NUMBERS IS BENEFICIAL BECAUSE LIGNEOUS VEGETATION BECOMES DRY AND INFLAMMABLE DURING HOT SEASONS WHEN TEMPERATURES SHOOT UP. LIGHT TRAMPLING BY ANIMALS MIXES HUMUS AND LITTER . HERBIVORES ALSO KEEP A CHECK ON PLANT GROWTH. A NUMBER OF PLANTS GIVE SHELTER TO ANIMALS, BIRDS, INSECTS, REPTILES AND MICROBES APART FROM  PROVIDING THEM PALATABLE FOOD.

PLANTS MODIFY THE PHYSICAL ENVIRONMENT AND MAKE IT MORE CONGENIAL FOR HUMAN AND LIVING . THEY ACT AS WIND BREAKERS TO STORMS AND GALES THERE BY REDUCING THEIR VELOCITY, AND THUS REDUCING ENVIRONMENTAL DAMAGE, ESPECIALLY SOIL EROSION. PLANTS ALSO HELP IN MODERATING TEMPERATURE CONDITIONS, AND THROUGH TRANSPIRATION HELP IN BRINGING LOCAL RAIN. PLANTS ABSORB LARGE QUANTITIES OF WATER WHICH IN TURN PREVENTS WATER LOGGING OR FLOODING, IN CATCHMENT AREAS THEY RETAIN LARGE AMOUNTS OF WATER WHICH BECOMES AVAILABLE TO SPRINGS AND RIVERS. THE ROLE OF PLANTS IN NATURE AND ITS INHABITANTS IS INDISPENSABLE AS THEY ARE CLOSELY RELATED TO BOTH, THE BIOTIC AND ABIOTIC COMPONENTS OF THE ENVIRONMENT.

A NUMBER OF ANIMALS, ESPECIALLY INSECTS ARE INVOLVED IN POLLINATION OF FLOWERS. THEIR BODIES HAVE BEEN FRAMED TO SUCK NECTAR, EAT/COLLECT POLLEN GRAINS AND PERFORM POLLINATION. SOME FLOWERS ARE ALSO POLLINATOR SPECIFIC. FLOWERS OF SNAP DRAGON (DOG FLOWER) HAVE CLOSED LIP-LIKE PETALS WHICH OPEN ONLY WHEN AN INSECT LANDS OVER ITS LOWER LIP. THESE ARE THE MAJOR POLLINATORS OF CROP PLANTS. FRUITS AND SEEDS OF MANY PLANTS ARE DISPERSED BY ANIMALS ESPECIALLY BIRDS AND ANIMALS. IN MANY CASES PLANTS PROVIDE FOOD TO ANIMALS FOR THIS JOB. THE GALL WASP LAYS EGGS INSIDE THE LEAVES AND YOUNG STEMS TO ENSURE THEIR PROTECTION, HATCHING AND FEEDING.

INTERDEPENDENCE BETWEEN SPECIES

NO LIVING ORGANISM EXISTS IN COMPLETE ISOLATION FROM OTHERS PLANTS AND ANIMALS THAT LIVE IN A PARTICULAR PLACE SHARE THE SAME AIR , THE SAME ROCKS AND THE SAME NEIGHBOURS. THEY LIVE TOGETHER, AND THEY LIVE IN HARMONY. SOME FEED ON OTHERS, BUT THE LARGER PICTURE IS THAT OF OVERALL BALANCE. SCIENTIFIC STUDIES HAVE SHOWN THAT THIS BALANCE IS ACHIEVED  THROUGH  AN EXTREMELY COMPLEX NETWORK OF RELATIONSHIPS IS THAT OF PLANTS AND ANIMALS . WITHOUT PLANTS, ANIMAL LIFE WOULD  BE POSSIBLE . THE LIVING ORGANISMS IN A PHYSICAL ENVIRONMENT ARE INSEPARABLY INTERDEPENDENT AND INTERACT WITH EACH OTHER.

THE BIOSPHERE AND ITS FUNCTIONING

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.

ECOLOGICAL ROLE OF BIODIVERSITY IN SHORT

ALL SPECIES PROVIDE SOME KIND OF FUNCTION TO AN ECOSYSTEM. THEY CAN CAPTURE AND STORE ENERGY, PRODUCE AND DECOMPOSE ORGANIC MATERIAL HELPS IN CYCLING WATER AND NUTRIENTS THROUGHOUT THE ECOSYSTEM, CONTROLS EROSION AND PESTS FIXES ATMOSPHERIC GASES, AND ALSO PLAYS A PIVOTAL ROLE IN REGULATING THE CLIMATE. ECOSYSTEMS ALSO PROVIDE VARIOUS SUPPORTS OF PRODUCTION, SUCH AS, SOIL FERTILITY, POLLINATORS OF PLANTS, PREDATORS, DECOMPOSITION OF WASTES, AND SERVICES SUCH AS PURIFICATION OF THE AIR AND WATER, STABILIZATION AND MODERATION OF THE CLIMATE, DECREASE OF FLOODING, DROUGHT AND OTHER ENVIRONMENTAL DISASTERS.

BEFORE WE LOOK INTO THE ECOLOGICAL ROLE PLAYED BY BIODIVERSITY IN AN ECOSYSTEM AND HOW IT HOLDS A CRUCIAL POSITION IN MAN'S OWN SURVIVAL, WE WILL BRIEFLY EXAMINE THE STRUCTURE OF THE BIOTIC COMPONENTS OF AN ECOSYSTEM.

COMMUNITIES HAVE STRUCTURES AND PROPERTIES THAT ARE ORGANIZED, AND COORDINATED IN SUCH A MANNER THAT THE SMALLER COMPONENTS ARE INSEPARABLY LINKED WITH THE LARGER COMPONENTS IN A HIERARCHY WHERE EACH LEVEL IS FORMED OF COMPONENTS OF A LOWER LEVEL WHICH IN ITSELF BECOMES A CONSTITUENT OF STILL A HIGHER LEVEL. ECOLOGICAL HIERARCHY OR ECOLOGICAL LEVELS OF ORGANIZATION ARE THE HIERARCHICAL LEVELS OF ORGANIZATION CONNECTED WITH ECOLOGICAL GROUPING OF ORGANISMS. THERE ARE NO SHARP DEMARCATIONS IN THE FUNCTIONAL SENSE AMONGST VARIOUS LEVELS OF ECOLOGICAL HIERARCHY, AS THE SAME INDIVIDUAL IS A COMPONENT OF THE POPULATION, THE BIOLOGICAL COMMUNITY AS WELL AS THE ECOSYSTEM.


THE INDIVIDUAL ORGANISM IS THE BASIC UNIT OF ECOLOGICAL HIERARCHY AS IT CONTINUOUSLY EXCHANGES MATERIALS AND INFORMATION WITH ITS ENVIRONMENT. NEW INDIVIDUALS DEVELOP FROM PRE-EXISTING ONES, AND BY THIS PROCESS HEREDITARY CHARACTERISTICS ARE TRANSFERRED. NO INDIVIDUAL CAN SURVIVE INDEPENDENTLY. POPULATIONS CONSIST OF SIMILAR INDIVIDUALS THAT INHABIT A PARTICULAR GEOGRAPHICAL AREA OR SPACE. ECOTYPES COMPRISE A LOCAL POPULATION THAT IS GENETICALLY ADAPTED TO A PARTICULAR ENVIRONMENT. A BIOTIC COMMUNITY IS ESTABLISHED WITH AN ASSEMBLAGE OF POPULATIONS COMPRISING DIFFERENT SPECIES OF PLANTS ANIMALS, BACTERIA, FUNGI WHICH LIVE IN A PARTICULAR AREA THROUGH COMPETITION PREDATION AND MUTUALISM ETC. EACH BIOTIC COMMUNITY HAS ITS OWN PECULIAR COMPOSITION AND STRUCTURE, EXAMPLE POND COMMUNITY, MARSH COMMUNITY.


A BIOTIC COMMUNITY FORMS A DISTINCT ECOLOGICAL UNIT. SUCH A UNIT MAY BE  FLORA, FAUNA OR BOTH.


COMMUNITY UNITS MAY BE VERY SMALL, LIKE THE COMMUNITY OF INVERTEBRATE. SAND FUNGI IS  A DECAYING LOG. THE EXTENT OF A COMMUNITY IS LIMITED ONLY BY THE REQUIREMENT OF A MORE OR LESS UNIFORM SPECIES  COMPOSITION. COMMUNITIES MAY BE DISTINGUISHED AS MAJOR COMMUNITIES ARE THOSE WHICH, TOGETHER WITH THEIR HABITATS, FORM MORE OR LESS COMPLETE AND SELF SUSTAINING  UNITS OR ECOSYSTEMS, EXCEPT FOR THE SUSTAINING SOLAR ENERGY. MINOR COMMUNITIES ALSO CALLED SOCIETIES, ARE SECONDARY AGGREGATIONS WITHIN A MAJOR COMMUNITY AND ARE NOT, THEREFORE, COMPLETELY INDEPENDENT UNITS AS FAR AS  CIRCULATION  OF ENERGY IS CONCERNED. THE BIOTIC COMMUNITY ALONG WITH THEIR HABITATS, FORM MORE OR LESS COMPLETE AND SELF SUSTAINING UNITS OR ECOSYSTEMS, EXCEPT FOR THE SUSTAINING SOLAR ENERGY. MINOR COMMUNITIES  ALSO CALLED SOCIETIES, ARE SECONDARY AGGREGATIONS WITHIN A MAJOR COMMUNITY  AND  ARE NOT, THEREFORE, COMPLETELY  INDEPENDENT UNITS AS FAR AS  CIRCULATION  OF ENERGY IS CONCERNED. THE BIOTIC  COMMUNITY ALONG WITH ITS HABITAT, CALLED AN ECOSYSTEM, COMPRISES  UNITS OF VARIOUS SIZES AND CHARACTERISTICS, AND ARE LIMITED  TO DISTINCTIVE COMBINATIONS OF AIR, SOIL AND WATER. THESE FUNCTIONS ARE IMPORTANT  FOR ECOSYSTEMS  FUNCTION AND HUMAN SURVIVAL.


THE PHYSICAL ENVIRONMENT IS COMPOSED OF SUNLIGHT, ATMOSPHERE, WATER AND SOIL OF ROCK. ALL THESE PHYSICAL ELEMENTS AFFECT THE LIVING ORGANISMS, AND ALL ARE  IN TURN AFFECTED  BY THEM. PLANTS  FOR EXAMPLE, OBTAIN THEIR  ENERGY  FROM THE SUNLIGHT, THEIR BASIC FOOD FROM AIR AND WATER, SUPPLEMENTED BY CHEMICALS FROM THE SOIL ROCKS. PLANTS, HOWEVER, DIFFERENTIALLY REFLECT, REFRACT OR ABSORB VARIOUS WAVELENGTHS OF SUNLIGHT, AND THUS MODIFY IT. THROUGH THE USE OF CARBON DIOXIDE AND THE GIVING OFF OF OXYGEN AND WATER VAPOUR THEY MODIFY THE ATMOSPHERE. PLANTS ALSO REMOVE AND ADD VARIOUS CHEMICALS THROUGH WHICH SOIL IS MODIFIED OR ALTERED. ALL PLANTS AND ANIMALS EXIST AS A PART OF AN ECOSYSTEM. MAN, LIKE OTHER ANIMALS, IS DEPENDENT ON THE ECOSYSTEMS IN WHICH HE EXISTS DESPITE  HIS HIGH MOBILITY WHICH ENABLES  HIM TO MOVE FROM ONE PLACE TO ANOTHER OR TO EXTRACT PRODUCTS FROM ONE ECOSYSTEM AND EXPORT THEM TO ANOTHER. DESPITE THE TECHNOLOGY WHICH PERMITS HIM TO CREATE MAJOR MODIFICATIONS IN ANY ECOSYSTEM, HE HAS NO CONTROL OVER THE NATURAL FUNCTIONING AND SUSTENANCE  OF AN ECOSYSTEM. THUS, WE SEE THAT MAN TOO IS DEPENDENT LIKE OTHER ANIMALS ON THE ECOSYSTEM FOR HIS SURVIVAL AND FUNCTIONING.

IN AN ECOSYSTEM, THE PRODUCERS ARE USUALLY THE GREEN PLANTS THAT CONVERT SOLAR ENERGY  INTO CHEMICAL OR FOOD  ENERGY. CONSUMERS MAY BE HERBIVORES, CARNIVORES OR OMNIVORES THAT DEPENDS ON THE PRODUCERS DIRECTLY OR INDIRECTLY  FOR FOOD. DECOMPOSERS TAKE THE CHEMICALS BUILT UP BY THE GREEN PLANTS AND BREAK THEM INTO SIMPLER FORMS IN WHICH THEY CAN BE REUSED. 

THE SUSTENANCE OF THE ECOSYSTEM DEPENDS UPON THE DIVERSITY OF SPECIES IN AN ECOSYSTEM AND KEEPING IN BALANCE THE MINERALS BETWEEN THE BIOTIC  AND ABIOTIC COMPONENTS OF THE ECOSYSTEM.

AN ECOSYSTEM IS A SELF MAINTAINING  SYSTEM EXCEPT THAT IT DEPENDS ON THE  SUN AS ON EXTERNAL SOURCE OF ENERGY. THE LIVING COMPONENTS OF ECOSYSTEMS ARE PLANT AND ANIMAL SPECIES  INCLUDING  MICRO-ORGANISMS  THAT MAKE UP THE BIOTIC COMMUNITY. EACH SPECIES  IS ADAPTED TO A PARTICULAR  ROLE IN THE ECOSYSTEM KNOWN AS ITS ECOLOGICAL NICHE  EACH DEPENDS  FOR ITS EXISTENCE UPON THE PRESENCE OF A SUITABLE HABITAT, COMPRISING OTHER SPECIES AS WELL AS NECESSARY  COMPONENTS OF THE PHYSICAL ENVIRONMENT. THE FUNCTIONING OF THE ECOSYSTEM IS DEPENDENT  UPON THE PRESENCE OF A SUITABLE COMBINATION OF SPECIES EACH OF WHICH PERFORMS A SPECIALIZED TASK WITHIN THE TOTAL ECOSYSTEM.

ENERGY WILL PASS THROUGH AN ECOSYSTEM IN A ONE WAY PATH OF THE SOLAR ENERGY REACHING THE EARTH, ONLY A PORTION WILL BE STORED BY PLANTS, OFTEN LESS THAN ONE PERCENT OF THE TOTAL SOLAR  ENERGY  FALLING ON A VEGETATED AREA IS RETAINED  AS CHEMICAL ENERGY BY THE GREEN PLANTS OF THE TOTAL ENERGY THUS AVAILABLE IN PLANT TISSUES FOR CONSUMPTION BY ANIMALS, USUALLY LESS THAN TWENTY PERCENT  WILL BE STORED AS CHEMICAL ENERGY IN AN ANIMAL'S BODY TISSUES.

EVENTUALLY, AFTER SUPPORTING LIFE FOR A TIME, MOST OF THE ENERGY IS LOST TO THE ECOSYSTEM. SOME HOWEVER, IS STORED IN LONG -LIVED ORGANIC MATERIALS  SUCH AS TREE TRUNKS, OR IN DEAD ORGANIC MATERIALS  PRESERVED FROM DECOMPOSITION, WHICH EVENTUALLY FORM ORGANIC DEPOSITS OF ONE OR THE OTHER, INCLUDING PEAT, COAL, OIL AND NATURAL GAS OVER LONGER PERIODS OF TIME. BY CONTRAST, CHEMICAL NUTRIENTS FLOW THROUGH  THE ECOSYSTEM IN CIRCULAR  PATHWAYS, FROM SOIL TO PLANTS AND ANIMALS AND BACK TO SOIL, BEING REUSED OR RECYCLED AGAIN AND AGAIN.