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