CHAPTER 8

8.2 : THE PROCESSES OF

COLONISATION & SUCCESSION IN AN ECOSYSTEM

Ecosystem, Community & Population

• Ecosystem : natural system formed by the interaction of plants & animals between one another & also with their environment.

• Interaction between biotic & abiotic components balanced ecosystem balanced environment

• 1 of components is disturbed whole ecosystem upset not in balance

• Ecosystem = niche + habitat + population + community

• Niche : the status / role of an organism in its environment

• Each species has its own niche in an ecosystem• The types of food it consumes & the activity it carries

out• Examples : aphids, grass, ringed plover (kedidi

gelang) - picked food from the surface of the shore, curlew – probe deep into the mud (long, curve beak)

• Habitat : the natural place in which an organism lives

• A Population : a group of organisms from the same species living in certain area

• A community : the plants & animals that live in a certain habitat

Process of Colonisation & Succession

• The process of colonisation : plants start to inhabit an uninhabited place & form a colony in the place

• Pioneer species – 1st plant species to inhabit a new place

• Has special adaptive characteristics to adapt to the new environment

• Change the new habitat gradually to make the habitat more suitable for another species New habitat not suitable for the pioneer species replaced by another species succession begins

• The process of succession : a certain dominant plant species in a habitat is gradually replaced by another plant species (successor species)

• Proceed stage by stage until a stable & matured community climax community (Eg. : tropical rain forest in M’sia)

Process of Colonisation & Succession in a Pond

• In an unused mining pond• The plants involved :

– Submerged water plants (pioneer)– Floating water plants– Amphibious plants– Land plants

• Colonisation by pioneer species• Unused & abandoned mining pond is not fertile & not suitable

for any organism to live• Pioneer species : phytoplankton (microscopic algae),

submerged water plants (Hydrilla sp., Elodea sp., Utricularia sp., Cabomba sp.)

• These pioneer organisms carry out photosynthesis to provide food for other organisms

• Pioneer die & decompose organic substance produced will be deposited at the bottom of the pond

• The banks of the pond are eroded & the soil settles the bottom of the pond more shallow, not suitable for the submerged water plants, phytoplankton.

• Succession by floating water plants• the successor – replace the pioneer species 1st

succession occurs• Duckweed (Lemna sp. – kiambang), water lettuce

(Pistia sp.), water hyacinth (Eichornia sp. – keladi bunting) & lotus (Nelembium sp.) grow rapidly cover the surface – prevent sunlight from penetrating into the pond

• The pioneer species cannot carry out photosynthesis die

• The decayed organic substance from the pioneer species continued to be deposited ponds becomes too shallow for the floating water plants

• Succession by amphibious plants• 1st successor are replace by amphibious plants

(2nd successor) that live in marshes (paya)• Initially grow at the side of the ponds spread to

the centre of the pond• The plants died more decayed organic substance

is deposited at the bottom of the pond• The pond become more shallow & dried up

suitable for other land plants

• Succession by land plants• 2nd successors are replaced by land plants –

shrubs & woody plants• The process of succession continues to occur until

a climax community is formed (tropical rain forest) take long time to complete

Colonisation & Succession in a Mangrove Swamp

• Mangrove swamp – can be found at river mouth that are sheltered from strong wave

• The mangrove swamp environmental condition (unsuitable for habitation) :

• Soft muddy soil• Waterlogged soil which lacks of O2• Seawater with high salinity (high salt content)• Strong sunlight & extreme heat

• 3 types of mangrove trees are involved in the process of colonisation & succession :

• Avicennia sp. & Sonneratia sp. (pioneer)• Rhizophora sp. (successor)• Bruguiera sp. (successor)

• Mangrove trees adaptive characteristics to overcome the problems it faces in the environment :

• A root system that spread out widely provide support in soft muddy soil

• Pneumatophores breathing roots, protrude out of the soil – enables gaseous exchange (waterlogged soil lack of O2)

• The roots of mangrove trees can withstand the highly saline seawater by having the higher osmotic pressure of the cell sap than the surrounding water osmosis occurs [hydathode in the epidermis of leaves secrete excess salts from the plants – to control the osmotic pressure]

• Leaves : have thick cuticle & sunken stomata to reduce transpiration, thick & succulent to store water

• Have viviparity seeds begin to germinate while still attached to the parent tree. the seeds will get sufficient O2 from the atmosphere during germination & will not suffocated for lack of air in a waterlogged environment. Also prevent dehydration of seed

Avicennia sp. & Sonneratia sp. Zone

• The adaptations of pioneer :• A root system that spread out widely• Have asparagus-shaped pneumatophores very

spongy & take air for respiration of the root system

• The widely spread roots trap mud accumulate the bank slowly raised, less water

• More suitable for Rhizophora sp. As the successor

Rhizophora sp. Zone• Higher & less waterlogged• The adaptations :

• Has prop roots to support & anchor the tree in the soft muddy soil

• Has viviparity seeds to ensure the seedlings can grow, not carries away by the seawater

• The prop roots are able to trap mud. The pioneer species & the Rhizophora sp. die & decay, adding humus to the soil

• The banks are raised up even higher more solid/ compact, fertile & less saline

• Not suitable for Rhizophora sp. replaced by the Bruguiera sp.

Bruguiera sp. Zone• Grow well in hard clay soil• Have buttress roots for support & knee-shaped

pneumatophores – for gaseous exchange• More sedimentation of decayed substances

new bank are being build up seawards, old banks move further inland, away from the sea soil becomes harder, dry land is formed

• Bruguiera sp. are replaced by other types of plants (coconut trees, Pandanus sp.) climax community (a few hundred years)