8.2 COLONISATION & SUCCESSION IN AN ECOSYSTEM

Levels of Ecological Organization

population all the members of one species in an area

community all the members of the different interacting species in an area

ecosystem all the members of a community plus the abiotic (physical) factors influencing them

biosphere entire region of the earth where living things may be found

THINKING TIME!!!

Colonization and succession

Colonization

process : living organisms moves into newly formed area which is completely devoid of life

E.g. an environment of sand and stones

The 1st colonizers are called pioneer species

Pioneer species

Can survive on dry and nutrient poor soil

Usually are hardy plants

E.g. : lalang, grass have dense root systems

to bind sand particles, water and humus

Short life cycle

Pioneer species

› When they die, their remains add to the humus content of the soil

› establish conditions that are more conducive to other species (successor species)

Succession

takes place when successor species :› moves into the modified environment› compete & gradually replace the

pioneer species› E.g.: Herbaceous plant

Successor species bigger than the pioneer species have small wind- dispersable

seeds (enable them to spread and grow rapidly

change the structure and quality of soil, making it more conducive for larger plants to grow

plants that grow over the remaining of successor species are called dominant species

DOMINANT SPECIES grow faster and can

out-compete the pioneers which grow at a slower rate

the dominant species modify the environment which allows larger trees to grow

E.g.: Shrubs

CLIMAX COMMUNITY The stable

community undergoes little

or no change in its species composition

RAINFOREST

Colonisation and succession in a pond

groups of plants play an important roles in the colonisation & succession of newly form pond:a) Submerged plantsb) Floating plantsc) Amphibious plantsd) Land plants

Submerged plants

elodea sp

Cabomba sp

Urticularia sp

Vallisneria sp

Hydrilla sp

Floating plants

Nelumbium sp(lotus)

Pistia sp

Lemna sp(duck weed)

Eichornia sp.(Water hyacinth)

Amphibious plants

Cyperus sp.

Scirpus grossus

Scirpus mucronatus

COLONISATION & SUCCESSION IN MANGROVE SWAMPS

Pioneer Species

Sonneratia sp. (Perepat trees)

Avicennia sp. (white api-api trees)

• Thick & fleshy leaves

• Waxy cuticles

• Hydathodes

• Viviparous seedling

• Long underground cable root system

• Pneumatophores• Vertical aerial

roots

Stagnant water & reduced oxygen content

Sea currentSoft &

muddy soil

High temperatur

e(Water loss)

High Salt

Pneumatophores

Successor species

Rhizophora sp

Has prop/stilt roots These aerial roots

anchor plants to the mud and play important role in aeration

Aeration can also take place through lenticels on the tree bark.

Rhizophora sp

Rhizophora sp

Dominant sp

Dominant species

Bruguiera sp.› Has buttress root

forms loop that protrude from soil to trap more silt and mud.

› This modifies the soil structure gradually.

Buttress roots of Bruguiera sp.

Dominant species

Over time, terrestrial plants such as Nypa sp., Pandanus sp., begin to replace the Bruguiera sp.

Nypa sp.

Distribution of different mangrove species at the mouth of a river

POP QUIZ

Rhizophora sp

Avicennia sp / Sonneratia sp

Brrugeira sp

Questions 8.2

1. Which of the following describes a population? A. The function of an organism or the role it

plays in an ecosystem B. The natural environment in which an

organism lives C. A group of organisms of the same species

living in the same habitat at the same time D. A natural collection of plant and animal

species living within a habitat in an ecosystem

Answer : C

2. Phytoplankton, zooplankton and algae are often among the first species to establish themselves in a mining pond. As time passes, submerged and floating plants will grow, followed by amphibious plants, grasses, small shrubs, bushes and eventually trees.

This is an example of A. colonisation B. competition C. evolution D. succession Answer : D

3. Over many years a forest can be found on an initially barren piece of land left behind by a volcanic eruption. What is the correct sequence of ecological processes that have taken place?

A. Colonisation, succession, climax community B. Colonisation, climax community, succession C. Succession, colonisation, climax communiity D. Succession, climax community, colonisation

Answer : A

5. Diagram 1 shows the seed of Rhizophora sp. which germinates while it is still attached to the parent plant

This phenomenon is know as A. double fertilisation B. oviparity C. viviparity D. vegetative reproduction

Answer : C

REVISION