Biological communities in a given landscape have a history of development in that area. The gradual and progressive replacement of one community by another, till the development of a stable community in that area, or a process through which ecosystems tend to changeover a period of time is called as ecological succession. Succession can be related to seasonal environmental changes, which create changes in the community of plants and animals living in the ecosystem. The stages in succession – where different communities predominate – are called seres. Theoretically, a community will eventually form which is in complete equilibrium with its physical environment and no further changes will occur to that community – this is then known as the climax community.
The occurrence of ecological succession has following characteristics:
- It is systematic process that involves changes in species structure.
- The changes are directional and take place as a function of time.
- The succession occurs due to changes in physical environment and population of the species.
- The changes also occur due to population explosion of the species.
- The changes are predictable.
TYPES OF SUCCESSION
Primary succession is the simplest type of succession; Primary succession occurs where there was no ecosystem before, beginning with abare surface with no life or soil present. The bare surface may be rock from a recently erupted volcano or sand dunes or cliffs or even a lake surface. It starts with the arrival of living things such as lichens that do not need soil to survive. The first organisms to colonize the area are known as the pioneer species or community and usually consist of organisms such as cyanophycae, algae and lichens.Pioneer species it is the first organism to colonize any newly available area and begin the process of ecological succession. Over time, the pioneer species makes the area habitable by other species.
Secondary succession begins in a place that already has soil and was once the home of living organisms. Occurs faster and has different pioneer species than primary succession. That is, it occurs on a surface where an ecosystem has previously existed and thathave been disturbed or disrupted by animals or humans interference such as logging and clear-cutting, or by the result of natural disasters such as fires, floods, storms, earthquakes and volcanoes. Following such destruction, the process of succession will occur again from the new environmental conditions – not from a bare surface and this is known as secondary succession. eg. A natural forestdestroyed by fire or clear felling is reoccupied by herbs.
They do not require soil. They are colorful and flaky patches. Lichens composed of two species, algae and fungi. The algae photosynthesize and the fungi absorb nutrients from rocks and holds water, that is they are in symbiotic relationship. Over time, theybreak down the rock and the forces of weather and erosion help break down rocks into smaller pieces. As the rocks breaks apart, water freezes and thaws on the cracks, this breaks up the rocks further. When the lichens die, they accumulate in cracks. And theydecompose, adding small amounts of organic matter to the rock to make soil. Simple plants like mosses and ferns can grow in the new soil. Hence these simple plant die it add more organic material to the soil, which leading to the creation of fertile soil. The fertile soil is made up of the broken rocks, decayed organisms, water, and air. By this the soil layer thickens, and grasses, wildflowers, and otherplants begin to take over. These plants die, and they add more nutrients to the soil. Shrubs and trees can survive now. Insects, small birds, and mammals have begun to move in. what was once bare rock now supports a variety of life. Primary succession takes several hundred years to produce fertile soil naturally.
A climax community is a mature, stable community that is the final stage of ecological succession. In an ecosystem with a climax community, the conditions continue to be suitable for all the members of the community. Any particular region has its own set of climax species, which are the plants that are best, adapted for the area and will persist after succession has finished, until another disturbanceclears the area. eg. Pine trees in forest ecosystem.
Ecological balance is a state of dynamic equilibrium within a community of organisms in which genetic, species and ecosystem diversityremain relatively stable, subject to gradual changes through natural succession. And a stable balance in the numbers of each species.Species in an ecosystem each have a role in keeping the ecosystem running smoothly. For example, predators keep the population ofmice under control, insects pollinate flowers, and worms decompose leaf litter. All species are important and help keep the ecosystem balanced. Ecological balance is a term describing how ecosystems are organized in a state of stability where species coexist with other species and with their environment.
Even if an ecosystem is balanced, that does not mean that no changes ever occur. A windstorm might roll through wiping out a swath of trees, a predator might be overhunted, or a drought might reduce the availability of food resources. These ecological changes are called disturbances. A disturbance is any change that causes a disruption in the balance of an ecosystem.
An ecological niche is the role and position a species has in its environment (ecosystem); how it meets its needs for food and shelter, how it survives, and how it reproduces. A species niche includes all of its interactions with the biotic and abiotic factors of itsenvironment. The description of a niche may include descriptions of the organism’s life history, habitat, and place in the food chain. More formally, the niche includes how a population responds to the abundance of its resources and enemies. The abiotic or physical environment is also part of the niche because it influences how populations affect, and are affected by, resources and enemies.
If you closely look at a typical habitat in the environment, you will see many organisms living and working together, fulfilling theirecological niches. For example, in the forest where there are leaves scattered on the ground and an old rotting log sitting on the forest floor. We can see earthworms just under the soil feeding on decaying organic matter. There could also be centipedes eating small beetles and other organisms as well as a colony of ants that work and feed on dead insects. You may even find a couple of millipedesstrolling around feeding on decaying leaves. In this small section of the vast forest, all of these organisms are filling an individual ecological niche. You could think of each ecological niche as parts of a puzzle that go together to make the environment successful.
FUNCTIONS OF ECOSYSTEM
An ecosystem performs the following functions:
- It allows the flow of biological energy, controls the rate of production, respiration of community.
- It controls the rate of nutrient cycle production and consumption of minerals.
- It regulates the environment by organism and the organism by environment. For example, Nitrogen fixing by bacteria is theregulation of environment by organism and Photoperiodism (the response of an organism to seasonal changes in day length) is the process of organism regulation by environment.
- It allows the circulation of chemical elements from environment to organism and back to the environment. In this way itprovides nutrients to the producers, which build-up organic matter.