Colonisation And Succession

Hafiz Akmal 1 BIOLOGY: Studying the process of colonisation and succession

STUDYING THE PROCESS OF COLONISATION AND SUCCESSION a)Explain the process of ecological colonization and succession The process in which living organisms arrive at new habitat, live, reproduce and take control of the habitat is known as colonisation. The first species of organisms to colonise a new habitat is called the pioneer species. The pioneer species have special adaptations to survive in unfavourable land conditions. The pioneer species gradually changes the conditions of the habitat, making it no longer suitable for itself but more suitable for other species, called the succession species. Gradually, the successor species takes over the place of the pioneer species. The process whereby a pioneer species is gradually replace by other successor species is called succession. Succession will carry on until a relatively stable community is known as the climax community. In Malaysia, the tropical rainforest is the climax community. It usually takes hundreds of years to form a climax community. After that it has little or no changes in its species structure. Therefore, we should treasures our forest.

Hafiz Akmal 2 BIOLOGY: Studying the process of colonisation and succession

b)What are the pioneer species? Pioneer species are the first living species that occupy an area previously unoccupied by living organisms. They have specialized characteristics to adapt to the area. In terrestrial sites, there are often microorganisms, mosses, lichens and some specialized flowering plants that can withstand harsh environmental conditions and very low levels of nutrients. The pioneer species add organic materials to the mineral particles. They gradually after the collisions in the habitat such that it is less suitable for the pioneer species but more suitable for other successor species.

Hafiz Akmal 3 BIOLOGY: Studying the process of colonisation and succession

c) What kind of organism is dominant at each level of succession? Colonisation takes place in newly formed areas where no life previously existed. For example, very few species can survive in an environment of sand and stones since it stores little water and has few available nutrients. The first colonizers are called pioneer species. They have special adaptations that enable them to survive on dry and nutrient-poor soil. Pioneer species are hardly plants which usually have dense root system to bind the sand particles and hold water and humus. They have a short life cycle. When they die, their remains add to the humus content of the soil. Hence, the pioneer species modify the environment, eventually creating conditions which are less favourable to themselves. Instead, they establish conditions that are more conductive to other species which are called successor species. These plants grow bigger than the pioneer species, thus reducing the amount of sunlight that reaches them and gradually replacing them. Most of these plants have small wind-dispersable seeds which are able to spread and grow rapidly. The successor species also changes the structure and quality of the soil, making it more conductive for longer plants to grow. These plants then become the new dominant species that can grow faster and so they out compete the pioneers which grow at a slower rate. As time passes, the dominant species in turn modify the environment which allows larger trees to grow. The larger trees out compete the shrubs, which are replaced by forest-floor species which require lower light intensity. The gradual process through which one community changes its environment so that it is replaced by another community is

Hafiz Akmal 4 BIOLOGY: Studying the process of colonisation and succession

called succession. Succession is a very slow and continous process which occurs in stages.

Figure 1: The process of succession

Hafiz Akmal 5 BIOLOGY: Studying the process of colonisation and succession

d)How are plants adapted at each level of succession? 1. Problem:– soft mud, strong water currents and tides. Adaptation:– Avicennia has extensive branching root system and Rhizophora has stilt roots to supports the plants and to trap the soil particles. Bruguiera has buttress roots for support. 2. Problem:– Water logged soil, less dissolve oxygen. Adaptation:– Avicennia has aerial vertical breathing roots called (pneumatophores) which grow vertically upwards. They have (lenticels for gaseous exchange). (pneumatophores) contain aerencyma tissue to facilitate oxygen transport to the parts of the roots submerged in water. Lenticels are also present on the stilt root of Rhizophora, the knee, shape aerial roots of Bruguiera and on the bark of stems of mangrove trees. 3. Problem:– Exposure to the sun and intense heat cause high transpiration rate. Adaptation:– The mangrove plants have xeromorphic features, thick succulent leaves, leaves are covered by a thick layer of cuticle and with sunken stomata to reduce the rate of transpiration.

Hafiz Akmal 6 BIOLOGY: Studying the process of colonisation and succession

4. Problem:– High salt content in sea water cause this solution surrounding the roots to be hypertonic. Adaptation:– The cell sap of the root cells has a higher osmotic pressure to absorb water from the surrounding solution. 5. Problem:– Removal of excess salts absorbed by the roots. Adaptation:– The excess salt are secreted by hydathotes found on the leaves. The crytallisle salt are washed off during high tides or by rain water. 6. Problem:– Dispetsal Adaptation:– The seed germinates while it is still attached to the parent plant. The phenomenon is known as vivipary. When the seedling is detached during low tide, it can plant itself in the salt mud below. The seedling are buoyant and can be carried by water current for several weeks and dispersed to a new suitable area to avoid overcrowding.

Hafiz Akmal 7 BIOLOGY: Studying the process of colonisation and succession

e)Explain the changes in the habitat caused by the pioneer and succession species.

Figure2: a profile transect of a mangrove swamp showing three mangrove zones and their dominant plants.

Hafiz Akmal 8 BIOLOGY: Studying the process of colonisation and succession

f) What happens to an ecosystem after a long period of time?