An ecosystem is a community of living organisms (populations of species) interacting with one another and its non-living physical and chemical environment. The interactions are to perpetuate the community and remain stable under varying conditions.
The concept of an ecosystem was given by Arthur George Tansley in 1935.
So, an Ecosystem is the sum of different living organisms and the non-living, physical components (such as air, soil, water, sunlight etc) of the environment. These organisms interact with one another and they also interact with the physical components. Deserts, forests, grasslands, mangroves etc. are some examples of different ecosystems.
Open ecosystem: When the different units of the ecosystem exchange energy and matter directly, it is called an open ecosystem.
Closed ecosystem: If only the exchange of energy takes place and does not matter among the different units of an ecosystem, then it is a closed ecosystem.
- Structure of an ecosystem: It is defined as the arrangement or organisation of components of an ecosystem. When this arrangement is studied through food relationships between biotic components, it is called a Trophic Structure. Thus, the trophic structure of an ecosystem is defined as an organisation of biotic components based on their feeding/food relationships.
- Functions of an ecosystem: These are the activities performed in an ecosystem to allow life to exist. There are two fundamental functions performed by every ecosystem. Flow of energy and Flow of nutrients (Biogeochemical cycling in an ecosystem)
Components of the Ecosystem
Different ecosystems have different size, structure and composition. Components of an ecosystem are two types:
- Abiotic Components
- Biotic components
Abiotic Components:
Abiotic components are the non-living components of the environment. They are classified as physical and chemical components.
- Physical components: These are the climatic factors. For example, sunlight, humidity, temperature, water availability, wind, soil etc.
- Chemical components: These are the inorganic substances like carbon, sulphur, nitrogen, phosphorus etc, and the organic substances like proteins, lipids, carbohydrates etc.
Biotic Components:
Living organisms are the biotic components of an ecosystem. For example plants, animals and microorganisms.
They can be divided into the following three groups:
- Producers: They produce their food themselves. Green plants produce food by photosynthesis in the presence of sunlight. There are certain sulphur bacteria that produce their food by oxidation of some chemicals.
- Consumers: These are those organisms that obtain their food by eating plants or other animals or their products. They are the consumers. They depend upon producers, and plants directly or indirectly. Heterotrophs can be further divided as follows:
- Herbivores: They obtain their food only from living plants.
- Carnivores: They obtain their food only from animals.
- Omnivores: They obtain their food from both plants and animals.
- Detrivores: they obtain their nutrients by detritus i.e. decomposing plant and animal parts.
- Decomposers: They eat dead decaying matter. They secrete enzymes and convert dead matter to simple compounds. Microorganisms are the decomposers.
The terms detrivores and decomposers are often used interchangeably. But there is a difference while they both get nutrition. From dead organic matter; the detrivores eat organic matter (like earthworms eating their way through soil) and decomposers secrete enzymes to digest the organic matter and then absorb the resulting molecules like bacteria or fungi do.
What are Trophic Levels?
Each organism in an ecosystem is at a specific feeding stage called the trophic level. All producers are at the first trophic level and are also called autotrophs (self-feeding organisms). All other organisms that must consume other organic matter for their survival are called heterotrophs or consumers. Consumers are classified as follows:
Primary consumers or herbivores feed directly on producers and are at the second trophic level. When we eat fruits or vegetables, we act as primary consumers.
Secondary consumers or carnivores (at the third trophic level) feed on other consumers. When we eat meat, we are secondary consumers.
Tertiary consumers eat other carnivores and are at the fourth trophic level. Again, we are tertiary consumers when we eat the fish that eats the smaller fish that eats the algae.
Omnivores eat both plants and animals and hence they feed at more than one level. Human beings, bears, and foxes are omnivores.
Detrivores are consumers that feed on detritus, which refers mainly to fallen leaves, parts of dead trees, and faecal wastes of animals. Ants, termites, earthworms, millipedes, crayfish, and crabs are examples of detrivores.
Food Chains and Food Webs
Food chains represent the feeding relationships in an ecosystem across trophic levels. In any ecosystem, there are two major types of food chains based on the source of energy for the first-level consumers,
- Grazing food Chain:- This type of food chain starts with green plants. Green plants are eaten by herbivorous animals which are in turn eaten by carnivores and omnivores. The energy for this food chain comes from the sun. This food chain contains macroscopic organisms.
- Detritus food chain: This food chain starts with dead decaying organic matter. These are eaten by some organisms which in turn are eaten by some other organisms in soil.
Organic matter is decomposed in the food chain. This food chain begins with the decomposers. Energy for this food chain comes from the dead decaying organic matter.
When we see these examples, the concept of the food chain looks very simple, but it is more complex.
Food Webs - In nature, food chains are rarely linear but form a complex network. This network of inter-connected food chains is called the Food web.
Ecological Pyramid
When the energy, number or biomass of each trophic level in an ecosystem is represented by diagram, then it is called an ecological pyramid. It can be of the following three types
- Pyramid of Number
- Pyramid of Energy
- Pyramid of Biomass
Pyramid of Number:-
We can represent the population of different biotic components of an ecosystem by the pyramid of number.
In a grassland ecosystem, grasses are eaten by herbivores such as grasshoppers, rabbits and rats. Grasses are larger in number than herbivores. Snakes and lizards eat herbivores. They are lesser in number than herbivores. They are primary consumers. Predatory birds and hawks eat both primary and secondary consumers. They are least in number. They lie on top of the trophic level. Therefore, pyramid of number in grassland ecosystem is an upright one.
The pyramid of number for parasitic food chain is inverted in nature. Birds are attacked by parasites such as lice and bugs. Microorganisms such as bacteria, viruses, fungi etc. decompose parasites. They are largest in number in an ecosystem.
Pyramid of Energy:-
In an ecosystem, green plants use energy directly from sunlight. They convert it to food by photosynthesis.
Herbivorous animals eat plants and are called primary consumers. Animals that eat herbivores only are called secondary consumers. Only a few animals form the third trophic level of carnivores at the top of the food pyramid. The energy transfer from one trophic level to the next is about 10%. For example, if there are 10000 calories at one level, only 1000 are transferred to the next. This 10% energy and material transfer rule forms the pyramid of energy in an ecosystem.
Pyramid of Biomass:-
The total dry weight of a living organism is called its biomass. Biomass decreases from one trophic level to another as we go upwards. Producers have the largest biomass in an ecosystem. Primary consumers have more biomass than secondary and tertiary consumers. Pyramid of biomass is an upright one as in case of pyramid of numbers.
If we change the size of one population in a food chain, it affects other populations. For example, if there are too many herbivorous animals, then, there will be less number of trees for all of them to eat. These animals will have no food and they will die. Then, trees will have more time to grow. Few herbivorous animals also means less food is available for carnivorous animals. Therefore, some of them will not get food and they will die. When there are few carnivorous animals, the population of herbivorous animals will again increase. Then, the balance will be maintained.
Ecosystem Productivity
The gross primary productivity (GPP) of an ecosystem is the rate at which energy is captured during photosynthesis in a given period of time. In addition, a plant respires to provide energy for its own use; this acts as a drain on photosynthesis. Energy in plant tissues after cellular respiration has occurred is net primary productivity (NPP). Both GPP and NPP are expressed as energy per unit area per unit time. Humans consume (32%) far more of earth’s resources than any other animal species, we must share terrestrial photosynthetic products with other organisms.
In environments that show variations in salinity, temperature and other environmental conditions, food webs tend to have short chains. In stable environments, such as parts of the deep ocean, food chains are longer. In addition to energy inputs, primary productivity and ecosystem structure require cycling of nutrients. Water and minerals move slowly through the physical environment, rapidly through organisms, and back to the environment in biogeochemical cycles. Water moves through a hydrological cycle. In land ecosystems, plants stabilise soil and minimise nutrient loss during the cycle as runoff. In atmospheric cycles, a nutrient prevails mainly in gaseous form (such as carbon, in carbon dioxide).
In the carbon cycle, carbon dioxide is the main gas in the atmosphere. The ocean is carbon’s main reservoir. Burning of fossil fuels, logging and conversion of natural ecosystems for farming disrupt the global carbon budget and may be responsible for global warming.
Nitrogen is a limiting factor in the total net productivity of the ecosystem on land. Gaseous nitrogen is abundant in the atmosphere. Nitrogen-fixing bacteria convert Nitrogen to ammonia and nitrates, which producers take up. Mycorrhizae and root nodules, two symbiotic interactions, enhance the hydrological cycle to move mineral nutrients to and from ecosystems.
Certain human activities are depleting minerals from ecosystems, as when the weathered soil of tropical forests is cleared for agriculture.
Some human activities are accelerating the process of eutrophication. They are adding nutrients such as nitrates and phosphates to aquatic ecosystems. This promotes the growth and decay of destructive algal blooms. The decomposition of these plants leads to the depletion of oxygen in the water, which threatens fish and other animal populations.
Types of Ecosystem
There are two types of ecosystems:
- Terrestrial Ecosystems
- Aquatic Ecosystems
Terrestrial Ecosystem:
Terrestrial ecosystems are land-based ecosystems. There are different types of terrestrial ecosystems like Forest ecosystems, Grassland ecosystems and Desert ecosystems.
Forest ecosystem
Forest is an area with a high density of plant and animal species. Forests are mainly divided into the following types-
- Boral Forests: These forests occupy the subarctic zone (latitude 53° N to 67° N). They are generally evergreen and coniferous. They are also called Taiga. The word ‘Boreal’ means northern, these forests occupy about 17% of the land. Trees like pine, spruce, fir etc. and animal species such as bats, woodpeckers, hawks deer, foxes etc., are found in these forests.
- Temperate Forests: Temperate forests can be found on both hemispheres at latitudes approximately 25° to 50°. They can be deciduous as well as evergreen. Soil of these forests is fertile. Trees of these forests are broad-leafed such as oak, maple, beech, hemlock, cottonwood, elm etc. Animals found in these forests are birds, rabbits, squirrels, wolves, black bears, mountain lions and bobcats
- Tropical and subtropical rainforests: They are mostly found near the equator. For example, southeast Brazil, parts of Africa etc. These forests are evergreen forests. They are very dense. Tropical rainforests contain many plantations.
- Plantations: Plantations are actually large farms or pieces of land. It is used for cultivation in tropical and suntropical regions. Rubber seeds, oil seeds, sugar cane, cotton, tobacco, tea, coffee etc. are grown in plantations. Plantations are sometimes grown to get large amount of wood in short time for different purposes.
Grassland Ecosystem
Grasslands are defined as areas having large amount of grasses and non-woody plants. These ae found on all the continents except Antarctica. Savanas are examples of grasslands. Grasses grow faster than other plants even if there is overgrazing or fire. Grasslands which are created and maintained by humans are called anthropogenic grasslands.
Grasslands can be divided into the following major types:
- Tropical and Subtropical grasslands: Acacia, Boabob, grass and low shrubs are the plants found in these grasslands. Acacia trees lose leaves in the dry season. Boabob trees have thick bark, long tap roots and store water in trunks. These are found in the Terai-Duars area. Grasslands are found from the belt of Uttarakhand through southern Nepal to the northern part of West Bengal.
- Temperate Grasslands: These grasslands are found in North Amaerica, Argentina, Brazil and Uruguay and the Europe. Bisons, gazelles, zebras, rhinoceroses, wild horses, lions, wolves and cheetahs and leopards etc, are found in these grasslands.
- Flooded Grasslands: These grasslands are flooded seasonally or year-round. Different migratory water birds, various reptiles and amphibians are found in these grasslands. These are warm grasslands. These have nutrient rich soil.
Desert Ecosystem:-
A desert is a region that is very dry and it receives a very low amount of rainfall. It has an annual average rainfall of less than 250 mm per year. The Atacama Desert is the driest place on earth, situated in South America. Deserts take up about 20% of the earth’s land surface. Oases are the places in deserts that support crops. People can live in such places. Deserts can be divided into the following types:
- Extremely arid lands: They have at least 12 consecutive months without rainfall.
- Arid lands: They have less than 250 mm of annual rainfall.
- Semiarid lands: They have a mean annual rainfall between 250 and 500 mm (10-20 inches)
Arid and extremely arid lands are called deserts, and semiarid areas are generally called steppes.
The major deserts of the world are following:
Antarctic Desert (in Antarctica)
Sahara Desert (in Africa)
Arctic Desert (in the Arctic region)
Arabian Desert (in the middle east)
Gobi Desert (in Asia)
Kalahari Desert (in Africa)
Patagonian Desert (in South America)
Great Victoria Desert (in Australia)
Syrian Desert (Middle East)
The Great Basin Desert (North America)
Aquatic Ecosystem
Aquatic ecosystems include different water bodies like oceans, lakes, rivers, streams, estuaries, and wetlands. Two-thirds of the earth is covered by water. The two main types of aquatic ecosystems are freshwater ecosystems and marine ecosystems.
Freshwater ecosystems:
The amount of fresh water is only 2.53% of the earth’s water and about 0.80% of the earth’s surface. The freshwater ecosystems that have running water are called lotic, for example, streams and rivers.
Ponds, tanks and lakes are ecosystems where water does not flow and are called lentic. Wetlands are special ecosystems in which the water level changes in different seasons.
Marine ecosystems
These cover approximately 71% of the Earth’s surface and contain approximately 97% of the Earth’s water. They consist of dissolved salts. Organisms found in marine ecosystems are brown algae, corals, cephalopods, echinoderms, sharks etc.
Coral reefs of marine ecosystems are very rich in plant and animal species. The Indian Ocean, the Arabian Sea and the Bay of Bengal are marine ecosystems. The shallow areas near Kutch and around the Andaman and Nicobar Islands are some of the most important coral reefs in the world. Fish, starfish, jellyfish etc are found in these coral reefs.