BIOGEOGRAPHY
Theme 3:
THE STRUCTURE OF ECOYSYSTEMS AND THE SUSTAINABILITY OF
BIOGEOGRAPHICAL ENVIRONMENTS
Lectures 7-9
ECOSYSTEM COMPONENTS
ECOSYSTEMS CONSIST OF TWO MAIN
COMPONENTS:
- ABIOTIC (N0N-LIVING)
- BIOTIC (LIVING)
ABIOTIC COMPONENT
PLANTS AND ANIMALS ARE DEPENDENT ON
THE PHYSICAL ENVIRONMENT FOR SURVIVAL
AND CERTAIN FACTORS SET CERTAIN LIMITS
FOR SURVIVAL:
- WATER/MOISTURE
- TEMPERATURE
- LIGHT
- SOIL CONTAINING NUTRIENTS
- ATMOSPHERE CONTAINING NUTRIENTS
- TOPOGRAPHY
- FIRE
- SALINITY OF WATER
WATER
IMPORTANT FOR ALL FORMS OF LIFE
COVERS 70% OF EARTH’S SURFACE
97% OF THIS WATER OCCURS IN OCEANS
2% OCCURS AS ICE
0.2% OCCURS AS FRESHWATER WHICH
OCCURS IN RIVERS, LAKES AND DAMS
1% OF THIS FRESHWATER CIRCULATES
THROUGH THE HYDROLOGICAL CYCLE AND IT
IS THIS WATER THAT IS USED IN ECOSYSTEMS
0.5% OCCURS AS GROUNDWATER
WATER AND PLANTS
WATER IS ONE OF THE MAIN REASONS THAT
DETERMINES WHAT PLANT TYPES ARE FOUND
IN AN AREA:
HYDROPHYTES: PLANTS THAT LIVE IN WATER
XEROPHYTES: PLANTS THAT OCCUR IN DRY
AREAS AND STORE WATER IN THEIR PLANT
CELLS
MESOPHYTES: OCCUR WHERE THERE IS A
GOOD SUPPLY OF WATER OR WHERE THERE
ARE WET AND DRY SPELLS (SEASONAL
DIFFERENCES)
TEMPERATURE
FOR BOTH PLANTS AND ANIMALS THE
FOLLOWING IS IMPORTANT:
TEMPERATURE OF SOIL AND AIR
THEY EXHIBIT A LOW TOLERANCE FOR
TEMPERATURE VARIATIONS
THEY USUALLY OCCUR WHERE TEMPERATURE
LIE BETWEEN 0 °C - 50 °C BUT ARE MOST
ACTIVE BETWEEN 5 °C - 35 °C
TEMPERATURE ANIMALS ARE AFFECTED MORE THAN PLANTS BY
TEMPERATURES:
ANIMALS MAKE CERTAIN ADAPTATIONS:
ENDOTHERMS OR HOMOIOTHERMS: ANIMALS CONTROL
THEIR BODY TEMPERATURE
ECTOTHERMS OR POIKILOTHERMS: BODY
TEMPERATURE CAN CHANGE IN RELATION TO
ENVIRONMENTAL FACTORS
ORGANISMS REACT IN 4 WAYS TO CHANGES IN
TEMPERATURE:
STAY(HIBERNATE OR ESTIVATE)
MIGRATE
ADAPT
BECOME EXTINCT
Map of the principal world vegetation types
LIGHT
EXHIBITS VARIATIONS IN SPACE AND TIME
NECESSARY FOR ALL LIFE PROCESSES
ESPECIALLY PHOTOSYNTHESIS IN PLANTS
QUANTITY OF LIGHT AS WELL AS QUALITY OF
LIGHT ARE IMPORTANT
NOT ALL PLANTS NEED THE SAME QUANTITY
OR QUALITY OF LIGHT TO GROW
SUCCESSFULLY
SOIL
CHEMICAL COMPOSITION OF SOIL IS VERY IMPORTANT
VERY IMPORTANT IN TERRESTRIAL ECOSYSTEMS
SOIL IS THE GROWTH MEDIUM FOR PLANTS AND
PROVIDES PLANTS WITH NECESSARY NUTRIENTS TO
SURVIVE
CONSIDERED TO BE A MORE PERMANENT AND LESS
CHANGEABLE PART OF THE ECOSYSTEM
SOIL TEMPERATURE IS CRITICAL FOR PLANT GROWTH
ACIDITY OR ALKALINITY OF SOIL IS IMPORTANT FOR
PLANT GROWTH
SOIL AND NUTRIENTS
SOIL IS THE GROWTH MEDIUM FOR ALL
PLANTS:
o DISSOLVED INORGANIC MATERIAL
o MINERALS
o GASES
o WATER
o LIVING ORGANISMS
o DEAD PLANT MATERIAL (HUMUS)
SOIL FORMING FACTORS:
THE FOLLOWING ARE THE MOST IMPORTANT
SOIL FORMING FACTORS:
- GEOLOGICAL SUBSTRATA
- CLIMATE
- TOPOGRAPHY
- LIVING ORGANISMS
- TIME
ATMOSPHERE
CONSISTS OF A MIXTURE OF GASES
IMPORTANT FOR USE BY PLANTS:
OXYGEN FOR RESPIRATION
CARBON DIOXIDE FOR PHOTOSYNTHESIS
NITROGEN FOR THE MANUFACTURE OF
PROTEINS
WATER VAPOUR FOR CERTAIN CHEMICAL
REACTIONS
WIND ALSO PLAYS AN IMPORTANT ROLE IN
POLLINATION
TOPOGRAPHY
ORIENTATION OF SLOPES MAY INFLUENCE THE
AMOUNT OF SUNSHINE PRESENT AND ALSO
THE TEMPERATURE
THIS IN TURN INFLUENCES THE TYPE OF
PLANTS PRESENT IN AN AREA
SOUTHERN HEMISPHERE:
o WARM NORTH FACING SLOPES
o COLDER SOUTH FACING SLOPES
FIRE
FIRE IS A VERY IMPORTANT ECOLOGICAL
FACTOR AND OCCURS IN TERRESTRAIL
ECOSYSTEMS
Natural fires (Usually caused by lightning)
o not always detrimental to vegetation
o vegetation can adapt - pyrophytes
o seasonal fires in savanna grasslands
Unnatural fires (caused mainly by man):
o usually cause great damage
o can be controlled by man in burning programmes
SALINITY OF WATER
USUALLY AFFECTS MARINE AND AQUATIC
ECOSYSTEMS
OCCURS MAINLY AT RIVER MOUTHS,
ESTUARIES AND INLAND AREAS
TO SURVIVE IN SALINE CONDITIONS
ORGANISMS MUST MAKE ADAPTATIONS
VERY FEW ORGANISMS CAN LIVE IN BOTH SALT
AND FRESHWATER SYSTEMS FOR LONG
PERIODS OF TIME
BIOTIC COMPONENT
THE FOLLOWING BIOTIC ELEMENTS ARE
IMPORTANT
PLANTS
ANIMALS
MAN
THE BIOTIC ELEMENT FORMS A SORT OF CYCLE
THESE ELEMENTS CAN BE CLASSIFIED ACCORDING TO :
o THE FLOW OF MATTER THROUGH THE ECOSYSTEM IN
THE FORM OF BIOCHEMICAL CYCLING, OR
o THE FLOW OF ENERGY THROUGH THE ECOSYSTEM
BIOTIC ELEMENTS
THE FOLLOWING BIOTIC ELEMENTS ARE
IMPORTANT: AUTOTROPHS OR PRODUCERS: THESE ARE THE GREEN
PLANTS THAT PRODUCE THEIR OWN FOOD
HETEROTROPHS OR COMSUMERS: THESE ARE ORGANISMS
THAT EAT THE PLANTS OR OTHER ANIMALS. HERE WE CAN
DISTINGUISH BETWEEN:
o PRIMARY CONSUMERS = HERBIVORES
o SECONDARY CONSUMERS = CARNIVORES OR OMNIVORES
o DECOMPOSERS OR DETRIVORES FOR EXAMPLE BACTERIA,
FUNGI ETC.
BIOTIC CYCLE
IN THE BIOTIC CYCLE NO ORGANISM CAN LIVE
IN ISOLATION
THE BIOTIC ENVIRONMENT IS THEREFORE: o FIRSTLY A PRODUCT OF THE INTERACTIONS BETWEEN
ORGANISMS AND THEIR ABIOTIC HABITAT, AND
o SECONDLY A PRODUCT OF THE INTERACTIONS BETWEEN
ORGANISMS OF EITHER THE SAME SPECIES OR ORGANISMS OF
DIFFERENT SPECIES
THERE ARE THEREFORE DIFFERENT TYPES OF
BIOTIC INTERACTIONS
HIERARCHICAL NATURE OF THE
BIOTIC ELEMENT
SPECIES:
A GROUP OF PLANTS OR ANIMALS WHICH MATE
SUCCESSFULLY WITH OTHER MEMBERS OF THEIR GROUP
POPULATION:
A NUMBER OF INDIVIDUALS OF THE SAME SPECIES
WHICH OCCUR IN A CERTAIN AREA E.G. A HERD OF BUCK
COMMUNITY:
A GROUP OF PLANT OR ANIMALS POPULATIONS WHICH
LIVE IN HARMONY TOGERTHER IN A CERTAIN AREA
MAN AS AN ECOLOGICAL FACTOR:
THE ECOLOGICAL DOMINANT
MAN IS CONSIDERED TO BE THE MOST IMPORTANT
FACTOR IN THE ENVIRONMENT BECAUSE:
o HIS INFLUENCE IS NOT CONSTANT
o HIS BEHAVIOUR CANNOT BE PREDICTED
o HIS INFLUENCE IS OFTEN NEGATIVE
o HE OFTEN DESTROYS
o HE CAN CREATE NEW HABITATS OR DESTROY OTHERS
IN OTHER WORDS HE DOMINATES THE
ENVIRONMENT AND BY ASSOCIATION THE
ECOSYSTEMS WITHIN WHICH HE LIVES