theme five lecture 13 to 15(1)
TRANSCRIPT
NET PRIMARY PRODUCTIVITY
(NPP)
GROSS PRODUCTIVITY REFERS TO THE TEMPO AT WHICH
GREEN PLANTS PRODUCE CHEMICAL ENERGY BY MEANS OF
PHOTOSYNTHESIS AND THEN STORE THIS ENERGY IN THE
PLANT CELLS WHERE IT THEN PROVIDES FOOD FOR OTHER
ORGANISMS. THIS IS KNOWN AS GPP.
WHEN OTHER ORGANISMS EAT THE GREEN PLANTS A CERTAIN
AMOUNT OF ENERGY IS LOST BECAUSE OF RESPIRATION . THIS
IS KNOWN AS R
NET PRIMARY PRODUCTIVITY IS THEREFORE THE ENERGY
THAT IS LEFT OVER AFTER RESPIRATION HAS TAKEN PLACE
AND IS STORED IN PLANT TISSSUE THAT KEEPS THE PLANT
ALIVE.
NPP = GPP - R
NB: Natural systems vs man-made systems: e.g. agriculture
BIOMASS
BIOMASS CANNOT BE SEPARATED FROM THE CONCEPT OF
PRODUCTIVITY
BIOMASS IS THE DRY MASS OF LIVING ORGANISMS (PLANTS)
PER UNIT AREA USUALLY EXPRESSED AS KG.
IT IS INFLUENCED BY PRODUCTIVITY AND IS A FUNCTION OF
PHOTOSYNTHESIS AND DIFFERS FROM ECOSYSTEM TO
ECOSYSTEM
IN THE BIOSPHERE THE FOLLOWING APPLIES TO BIOMASS:
ANIMALS MAKE UP 3% OF THE TOTAL BIOMASS
PLANTS MAKE UP 97% OF THE TOTAL BIOMASS
THIS INDICATES THE IMPORTANCE OF GREEN PLANTS
POPULATION NUMBERS
ALL ORGANISMS HAVE THE ABILITY TO REPRODUCE AND
THEREFORE TO PRODUCE OFFSPRINGS
Birds produce 1-40 offspring per year
Amphibians produce 100 offspring per year
Fish produce 1000 offspring per year
Insects produce 1 million offspring per year
IN VIEW OF THIS IT WOULD APPEAR AS IF ORGANISMS
JUST GO ON INCREASING IN NUMBERS BUT IN REALITY
THIS IS NOT SO AS CERTAIN ENVIRONMENTAL FACTORS
ACT AS CHECKS AND BALANCES ON THESE POPULATION
NUMBERS
FACTORS CONTROLLING
POPULATION NUMBERS
FOUR MAIN FACTORS CONTROL POPULATION NUMBERS:
1. NATALITY I.E.THE NUMBER OF OFFSPRING BORN
2. MORTALITY I.E. THE NUMBER OF OFFSPRING THAT DIE
3. IMMIGRATION I.E. THE NUMBER OF ORGANISMS THAT
COME TO A REGION
4. EMIGRATION I.E. THE NUMBER OF ORGANISMS THAT
LEAVE A REGION.
THIS TIES UP WITH THE QUESTION OF SURVIVAL RATES. FOR
EXAMPLE IF THE MORTALITY RATE IS 15% THEN THE SURVIVAL
RATE WOULD BE 85% AND THE POPULATION NUMBERS WOULD
DECREASE. THE INVERSE WOULD THEN ALSO APPLY
AGE OF A POPULATION
MORTALITY AND NATALITY INFLUENCE THE
AGE/ NUMBERS OF A POPULATION
THREE GENERAL AGES CAN BE RECOGNIZED:
1. GROWING POPULATION - USUALLY HAS A
HIGH PERCENTAGE OF YOUNG ORGANISMS
2. DECREASING POPULATION - USUALLY HAS A
HIGH PERCENTAGE OF OLD PEOPLE
3. STABLE POPULATION - USUALLY HAS A HIGH
PERCENTAGE OF BOTH OLD AND YOUNG
ORGANISMS
POPULATION GROWTH
THE GROWTH OF A POPULATION CAN SHOW THREE
TENDENCIES:
1. POSITIVE GROWTH - MORE BIRTHS THAN DEATHS
2. NEGATIVE GROWTH - MORE DEATHS THAN BIRTHS
3. STABLE - EQUAL NUMBER OF BIRTHS AND DEATHS
THE POPULATION GROWTH IS USUALLY INDICATED BY TWO
TYPES OF GRAPHS:
S-SHAPED J-SHAPED
CARRYING CAPACITY
THE CARRYING CAPACITY OF AN ECOSYSTEM REFERS
TO THE TOTAL NUMBER OF ORGANISMS THAT CAN BE
MAINTAINED BY THE RESOURCES PRESENT IN THE
ECOSYSTEM
BOTH PHYSICAL AND BIOLOGICAL FACTORS CAN AFFECT
THE CARRYING CAPACITY
PHYSICAL E.G. MOISTURE , LIGHT, SHORTAGE OF FOOD,
SHORTAGE OF LIVING SPACE, UNSUITABLE SHELTER, FIRE ETC
BIOLOGICAL E.G. COMPETITION, PREDATION ETC.
THIS MAY EXHIBIT TEMPORAL AND SPATIAL VARIATIONS
BIOLOGICAL CONTROL MECHANISMS
FOR POPULATION NUMBERS
THIS RELATES TO INTERACTIONS BETWEEN ORGANISMS.
INTERACTIONS CAN BE:
1. POSITIVE - ONE SPECIES GAINS ADVANTAGE OVER
ANOTHER SPECIES BUT DOES NOT REALLY INFLUENCE
THE SPECIES OR BOTH SPECIES MAY GAIN AN
ADVANTAGE
2. NEGATIVE - BOTH SPECIES SUFFER OR ONE SPECIES
GAINS ADVANTAGE OVER ANOTHER SPECIES AND SO
HAS A DETRIMENTAL EFFECT ON THE OTHER SPECIES
THERE ARE A NUMBER OF MECHANISMS:
CONTROL MECHANISMS
PREDATISM/ PREDATION:
- ONLY OCCURS IN THE ANIMAL WORLD
- ONE ANIMAL EATS ANOTHER ANIMAL
- NEGATIVE EFFECT
- WEAKEST ANIMALS THINNED OUT
PARASITISM:
- ORGANISM THAT LIVES ON ANOTHER PLANT OR ANIMAL
- OCCURS IN BOTH PLANT AND ANIMAL WORLDS
- DOES NOT KILL BUT WEAKENS
- NEGATIVE EFFECT ON HOST
- CAN OCCUR OUTSIDE OR INSIDE BODY OF HOST
CONTROL MECHANISMS
CANNIBALISM:
- ONE ORGANISM EATS ANOTHER ORGANISM OF THE SAME
SPECIES
- USUALLY OCCURS IN THE ANIMAL WORLD
MUTUALISM / SYMBIOSIS:
- BOTH ORGANISMS GAIN ADVANGE BY ASSOCIATING WITH
EACH OTHER
- ORGANISMS DIFFER FROM EACH OTHER
COMMENSUALISM:
- ONE SPECIES GAINS AN ADVANTAGE BY LIVING IN
ASSOCIATION WITH ANOTHER
COMPETITION
COMPETITION USUALLY REFERS TO THE BATTLE FOR THE
SAME RESOURCE
IT CAN BE INTRA-SPECIFIC I.E. BETWEEN ORGANISMS OF THE
SAME SPECIES
IT CAN ALSO BE INTER-SPECIFIC I.E. BETWEEN ORGANISMS OF
DIFFERENT SPECIES
Plants usually compete for: - sunlight
- moisture
- nutrients
- may make adaptation to compete more
successfully
animals usually compete for: - space
- food
- breeding
STABILITY
THE STABILITY OF AN ECOSYSTEM REFERS TO THE
ABILITY TO MAINTAIN A CONDITION OF EQUILIBRIUM IN
SPECIES COMPOSITION
HOMEOSTASIS: THIS IS THE ABILITY OF AN ORGANISM
TO RESIST CHANGE AND TO REMAIN IN A STATE OF
EQUILIBRIUM KNOWN AS HOMEOSTASIS
DYNAMIC EQUILIBRIUM: NO ECOSYSTEM CAN REMAIN
ABSOLUTELY STABLE BECAUSE THE SYSTEM IS
CONTINUALLY AFFECTED BY FACTORS FROM OUTSIDE. AS SOON AS AN EXTERNAL FACTOR DISTURBS THE STABILITY
OF THE ECOSYSTEM A PROCESS OF RESTRUCTURING
IMMEDIATELY OCCURS. THIS MAINTAINS THE DYNAMIC
EQUILBRIUM OF THE ECOSYSTEM
ECOLOGICAL SUCCESSION
ECOLOGICAL SUCCESSION REFERS TO THE
PROCESS IN WHICH COMMUNITIES OF PLANTS
AND ANIMALS IN A PARTICULAR AREA ARE
REPLACED OVER TIME BY A SERIES OF
DIFFERENT AND USUALLY MORE COMPLEX
COMMUNITIES
SUCCESSION CAUSES AN ECOSYSTEM TO
PASS THROUGH A NUMBER OF STAGES OF
DEVELOPMENT CALLED SERAL CHANGES.
THESE ARE - THE PIONEER STATE, THE
INTERMEDIATE STAGE AND THE CLIMAX STAGE
STAGES IN SUCCESSION
PIONEER STATE:
THIS IS THE ESTABLISHMENT OF A PIONEER SPECIES ON
OR IN A NEWLY FORMED HABITAT E.G. A LAVA FLOW.
THE SPECIES ARE USUALLY VERY HARDY WITH A SIMPLE
LIFE CYCLE AND A SMALL NUMBER OF SPECIES WHERE
ONE OR ANOTHER OF THE SPECIES DOMINATES THE
OTHERS. THEY ALSO HAVE A SMALL BIOMASS, A FAST
REPRODUCTION TEMPO AND A SHORT FOOD CHAIN
PIONEER SPECIES USUALLY OCCUR BECAUSE OF A LACK
OF COMPETITION
STAGES IN SUCCESSION
INTERMEDIATE STAGE:
THE INTERACTION BETWEEN PLANSTS IS
DOMINANT, MORE ORGANIC MATTER
ACCUMULATES IN THE SOIL AND MORE HUMUS
IS PRESENT. AS A RESULT THE SOIL IS MORE
FERTILE. PLANT SPECIES THEREFORE
BECOME LARGER AND MORE ADVANCED. THE
PLANT COMMUNITIES MAY CHANGE TO MORE
COMPLEX COMMUNITIES
STAGES IN SUCCESSION
CLIMAX STAGE:
THIS IS THE FINAL OR ADULT STAGE OF PLANT
DEVELOPMENT. THE MAXIMUM AMOUNT OF
BIOMASS OCCURS UNTIL A CONDITION OF
DYNAMIC EQUILIBRIUM RESULTS
ECOLOGICAL DOMINANCE
SOME ORGANISMS COMPETE MORE SUCCESSFULLY
THAN OTHERS IN A PARTICULAR HABITAT FOR
ESSENTAIL REQUIREMENTS SUCH AS WATER, LIGHT AND
NUTRIENTS.
ECOLOGICALLY DOMINANT ORGANISMS ARE ORGANISMS
WHICH HAVE A GREATER INFLUENCE THAN OTHERS ON
THEIR HABITAT AND ON OTHER ORGANISMS WITH WHICH
THEY LIVE.
THE DOMINANT PLANT SPECIES ARE THE LARGEST OR
MOST NUMEROUS FORMS, FIXING THE MOST ENERGY
AND MAKING UP THE LARGEST PROPORTION OF
BIOMASS IN A COMMUNITY.