STRUCTURE AND FUNCTION OF ECOSYSTEM
Ecosystem is an assemblage of organisms and the environment. It includes the living and non-living components. To understand the structure and function of ecosystem, you must be familiar with some basic terminologies in ecology.
1. Species: It is a unique organism with similar genetic identity. For example, all humans form a species called Homo sapiens
2. Population: It is a group of individuals of same species. For example, a population of humans or cows.
3. Community: It refers to the populations of animals, plants and other organisms living in a specific region under similar environmental conditions. For example, mammals and plants in a forest, fishes and algae in a pond.
4. Ecosystem: It is a biological community of interacting organisms and their physical non-living environment. For example, a pond ecosystem.
Species --> Population ---> Community ---> Ecosystem
The concept of ecosystem was first introduced by A G Tansley (1935). According to Woodburry (1954) ecosystem is a complex in which habitat, plants, animals and other organisms are considered as one interesting unit, the materials and energy of one passing in and out of the others.
Structure of Ecosystem
All ecosystems consist of the following basic components
1. Abiotic Component
The abiotic component includes all non-living components of the ecosystem. For example, soil, water, air, calcium carbonate, phosphates etc.
2. Biotic Component
The biotic component include all living organisms. For example, animals, plants and microbes.
The biotic component can be grouped into two categories-
2.1. Autotrophic component/ Producers : These are organisms which can synthesize their own food using non living molecules. All green plants come under this category, they can fix radiant energy of sun and manufacture food in the form of molecules such as glucose and starch.
2.2. Heterotrophic component/ Consumers: These are organisms which are unable to synthesize their food and depend on autotrophs. All non-green plants and all animals come under this category.
2.3. Decomposers: These are organisms which perform the role of decomposing all dead and decaying matter, there by ensuring the smooth function of bio-geo-chemical cycle. For example, fungi and bacteria. These are also known as Scavengers of Earth.
Producers
Any ecosystem is founded by the producers, which are capable of making their on food. They perform the one of the most fundamental reactions for sustaining on earth, called photosynthesis, that is synthesizing food using sun light. The green algae and cyanobacteria are assumed to be the first photosynthesizing organisms on earth. All other organisms depend on producers such as herbs, shrubs and trees.
Consumers
Members of the ecosystem which consume the food synthesized by the producers are called consumers. For example, all animals. Deer, cow, goats etc eat the leaves of grasses and other plants. Birds, monkeys etc eat fruits of the plants. Humans eat rice, wheat, ragi etc They provide carbohydrates (Rice, wheat), fats (Nuts), proteins (green gram, bengal gram etc) and form steady source of food for all animals.
Consumers are classified as follows
1. Primary consumers: These are pure herbivores, which eat only plants or plant parts. eg: rabbit, deer, cow, buffalo, goat etc.
2. Secondary consumers: These are animals which eat herbivores. They include carnivores and omnivores. They are basically flesh eating animals, but they also eat plant parts. eg: crow, sparrow, fox, dog, cat, snake etc.
3. Tertiary consumers: They are the top carnivores which prey upon other carnivores, omnivores and herbivores. eg; tiger, lion, hawk, vulture etc.
Decomposers
Decomposers feed on dead and decaying matter. Imagine how the world would look if all the dead organisms remained without decaying! The decomposers recycle minerals back to earth. Hence they are called 'scavengers of earth'. Examples- Fungi and bacteria.
Functioning of Ecosystem and energy transfer
Abiotic components such as air, water and soil provide the matrix for the synthesis and perpetuation of organic components. This process involves energy exchange and the energy comes from the sun in the form of light. The green plants convert inorganic matter to organic molecules such as glucose, starch, proteins and fatty acids. Hence they are called as producers. Photosynthesis and nitrogen fixation play a crucial role in fixing atmospheric carbon dioxide and nitrogen. Carbon is used to make glucose and nitrogen is used to make amino acids, which are very essential for sustaining life on earth.
Energy gathered from sunlight by the producers in transferred to next levels such as herbivores which eat the plants. The energy transfer mainly occurs through food chains and food webs. It is a process of '
'eating and being eaten'. The energy received by herbivores from the producers is transferred to carnivores and omnivores. Finally the energy is transferred to top carnivores such as tiger and lion. When all the organism die, the dead matter is decomposed and recycled back to earth by the fungi and bacteria which also releases energy.
On average, only about 10% of energy stored as biomass in a trophic level is passed from one level to the next. This is known as ''the 10 percent rule''.
Functions of Ecosystem
There are mainly four functions of the ecosystem
1. Productivity
2. Decomposition
3. Energy flow
4. Nutrient cycling
1. Productivity
It is the rate of biomass production by any trophic level per unit area in unit time. It is measured as Weight (g/m2/year) or energy (kcal/m2/year).
Productivity is of two types- Primary productivity and secondary productivity.
Primary productivity
Primary productivity is the amount if biomass produced per unit area over a time of period by plants during photosynthesis. It is divided into gross primary productivity (GPP) and net primary productivity (NPP).
The rate of production of TOTAL biomass by green plants during photosynthesis per unit area per unit time is known as gross primary productivity (GPP). Organisms use energy for their daily activities (respiration) from the energy synthesized during photosynthesis. The energy level remaining after respiration is known as net primary productivity (NPP) and this energy will be stored for future activity.
NPP= GPP- Respiration
Secondary Productivity
The rate of assimilation of organic matter at the level of consumers. It is the amount of energy available at the level of consumers.
2. Decomposition
It is the physical and chemical break down of complex organic matter formed when organisms die. It is performed by fungi and bacteria. Termites, earth worms etc also feed on dead and decaying matter. Such organisms are called detrivores.
Humification leads to the formation of soil. A dark colored organic substance called humus rich in cellulose and lignin. Humus is further degraded by microbes.
3. Energy flow
Plants capture sunlight, but they are able to capture only 2% of sunlight. The energy captured by the plants are transferred to next trophic levels. Only 10% of energy is transferred from one trophic level to the next.
4. Food Chain
Food chain is the process of eating and being eaten. Herbs are eaten by herbivores, herbovores are eaten by carnivores. Food chains form food webs, which in turn becomes a path for energy transfer from one trophic level to the next.
Grass--> Grass hopper--> Frog--->Snake
Alexander Von Humboldt is known as 'Father of Ecology'. Read more about Alexander Von Humboldt.
Eugene P Odum is known as Father of Modern Ecology'. Read more about Eugene P Odum.
Ramdeo Misra is known as Father of Indian Ecology'. Read more about Ramdeo Misra.
Prepared by Shijith Puthan Purayil
