Ecosystem

Ecosystem:

Meaning and Definition of Ecosystem:

An ecosystem is the basic functional unit in ecology since it includes both- the biotic and environment component influencing each other for the maintenance of life. The term ‘ecosystem’ was proposed by A.G. Tansley (1935), who defined it as “the system resulting from the integration of all the living and nonliving factors of the environment.” Whereas, Odum (1962) defined the ecosystem “as the structural and functional unit of ecology.” Interdependence is the important basic of an ecosystem. Ecosystems include interacting and interdependent components that are open and linked to each other. An ecosystem may be as small as a drop of pond water (micro-ecosystem) or as large as an ocean. It can be temporary (for example- a field of cultivated crops) or permanent (for example- a forest or ocean). The earth itself is a vast ecosystem (biosphere) where abiotic and biotic components are constantly acting and reaching upon each other. The biosphere has various smaller ecosystems, for example- forest, desert, grassland, cropland, freshwater, marine, etc. An ecosystem represents the highest level of ecological integration, which is an energy processing unit that is restrained or limited by the number of nutrients and water available to it.

Definition- An ecosystem may be defined as a structural and functional unit of the biosphere, comprising living organisms and their nonliving environment that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity, and material cycling to form a stable, self-supporting system.

Types and Examples of Ecosystems:

(1) Natural and Artificial Ecosystem- Natural ecosystem is one that develops under natural conditions without any human support. For example- forest, grassland, desert, lake, river, and sea. An artificial ecosystem is created and maintained by human beings. Instances of artificial ecosystems are a manned spaceship, garden, poultry, piggery, and apiary. The agroecosystem is the largest man-made ecosystem.

(2) Large and Small Ecosystem- A very large ecosystem is known as a mega ecosystem. For example- sea. A large ecosystem like the forest is called a macro ecosystem. An ecosystem restricted to a small area like a valley and a pond is called a micro ecosystem. The term nano ecosystem is used where the area is very small, like a wooden log, aquarium, or kitchen garden.

(3) Temporary and Permanent Ecosystem- A temporary ecosystem is short-lived and may be natural or man-made. Common examples include a rainfed pond and laboratory culture of protozoans. A permanent ecosystem is a self-supporting natural ecosystem that maintains itself for a relatively long duration. For example- a forest or a lake.

(4) Complete and Incomplete- An ecosystem that has all the components is known as a complete ecosystem. Example- forest. An ecosystem that is deficient in one or more components is known as an incomplete ecosystem. Example- rainwater pond (without consumers), sea bottom (without producers).

Components of an Ecosystem:

An ecosystem comprises of two parts- biotic and abiotic.

Biotic Components (Living):

The living organisms in an ecosystem form the biotic component. These include producers, consumers, and decomposers.

(1) Producers- These are green plants of the ecosystem. With the help of chlorophyll, green plants entrap the light energy of the sun and bind it in the form of carbohydrates produced by them from simple inorganic compounds like carbon dioxide and water. This process is called photosynthesis.

From the basic simple organic material, i.e. glucose, plants form complex organic compounds like starches, proteins, and lipids. As green plants, cyanobacteria and photosynthetic bacteria prepare their own food from simple inorganic substances such as water and CO₂, they are called photoautotrophs. Since the energy trapped in photosynthesis is the radiant energy of the sun and is changed into chemical energy, producers are also called transducers. The producers include herbs, shrubs, large-size tres, and microscopic free-floating phytoplankton.

Some bacteria, such as colorless sulfur bacteria, iron bacteria, and nitrifying bacteria, capture the energy released during certain inorganic chemical reactions and prepare organic food with it. They are chemoautotrophs, and the process is termed chemosynthesis.

Importance of Producers- These pick up carbon dioxide from the atmosphere and release oxygen during the process of photosynthesis. All other organisms depend upon the producers for organic food. Producers also maintain the CO₂ – O₂ balance in nature.

(2) Consumers- These are heterotrophic organisms (animals) which are also called macro consumers. Since consumers ingest their food, they are also called phagotrophs. Consumers are of the following types:

(a) Herbivores or Primary or First Order consumers- These animals are the primary consumers of the ecosystem. A deer or rabbit is a primary consumer in a forest and a rat in the gardens. Protozoans, crustaceans, and mollusks are the primary consumers of the pond or lake, or sea and feed upon the floating algae. Herbivores were called “key industrial animals” by Elton (1927) because they change the plant material into animal material.

Rabbit, goat, cattle, deer, grasshoppers, etc. are the herbivores of the terrestrial ecosystem, and crustaceans, mollusks, protozoans, and many fishes are the herbivores of an aquatic ecosystem.

(b) Secondary or Second Order Consumers or Primary Carnivores- They are animals that prey on herbivores. For Example- water insects, Hydra, frog, some fishes like Roach (aquatic ecosystem), centipedes, spiders, toad, insectivorous birds, snake feeding on rats, fox feeding on rabbits, and wild cat preying on squirrels (terrestrial ecosystem).

(c) Tertiary or Third Order Consumers or Secondary Carnivores- The animals feed on primary carnivores. For example- larger fishes like Pike, wolf feed on foxes, and snake feed on frogs.

(d) Quaternary or Fourth Order Consumers- These are the largest carnivores that take tertiary consumers. They are not eaten by other animals. Tigers and lions are examples on land and dolphins and whales in water. They are also called top carnivores.

(3) Decomposers or Reducers- Bacteria, fungi, and molds are the decomposers or reducers of the ecosystem. These obtain their food by breaking the dead plants and animals into simple compounds. These are released into the atmosphere and are utilized by producers for the synthesis of organic food. The decomposers are also called micro consumers or saprotrophs. These are also called mineralizers and the breaking down of complex organic compounds into simpler ones as mineralization.

Importance of Decomposers- Sun is an endless source of energy, but the chemical materials of the environment are not inexhaustible. Decomposers return chemical nutrients to the environment by decomposing the dead bodies of plants and animals. These nutrients are reused by the producers. The decomposers are present in the soil and at the bottom of ponds, lakes, and oceans. Thus decomposers play an important role by recycling the materials in the biosphere.

Though most of the ecosystems have micro consumers as their integral part but these are not essential.

(4) Other Heterotrophs-

(a) Scavengers or Detrivores- They feed on corpses. For Example- Vultures, Carrion Beetle. They help in the quick disposal of dead bodies. In the process, they also leave small fragments for decomposers.

(b) Parasites- They obtain nourishment from a living host without capturing or killing the same. Parasites obtain food from all categories of organisms. Common parasites are bacteria, fungi, some worms, and some insects.

Abiotic components (Nonliving):

The abiotic component can be grouped into the following three categories:-

(1) Physical factors: Sunlight, temperature, rainfall, humidity, and pressure. They sustain and limit the growth of organisms in an ecosystem.

(2) Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulfur, water, rock, soil, and other minerals.

(3) Organic compounds: Carbohydrates, proteins, lipids, and humic substances. They are the building blocks of living systems and therefore, link the biotic and abiotic components.

Difference Between Autotrophs and Heterotrophs:

Following are the points of difference between Autotrophs and Heterotrophs-

Functions of the Ecosystem:

Ecosystems are complex dynamic systems. They perform certain functions. These are:-

Energy flow through the food chain:

The flow of energy in an ecosystem takes place through the food chain and it is this energy flow that keeps the ecosystem going. The most important feature of this energy flow is that it is a unidirectional or one-way flow. Unlike the nutrients (like carbon, nitrogen, phosphorous, etc.) which move in a cyclic manner and are reused by the producers after flowing through the food chain, energy is not reused in the food chain. Also, the flow of energy follows the two laws of Thermodynamics.

First Law of Thermodynamics: States that energy can neither be created nor be destroyed but it can be transformed from one form to another. The solar energy captured by the green plants (producers) gets converted into the biochemical energy of plants and later into that of consumers.

Second Law of Thermodynamics: States that energy dissipates as it is used or in other words, it gets converted from a more concentrated to dispersed form. As energy flows through the food chain, there occurs dissipation of energy at every trophic level. The loss of energy takes place through respiration, loss of energy in locomotion, running, hunting, and other activities. At every level there is about 90% loss of energy and the energy transferred from one trophic level to the other is only about 10%.

Nutrient cycling (Biogeochemical Cycles):

It involves the storage and transfer of nutrients through various components of the ecosystem so that the nutrients are repeatedly used. The biogeochemical cycle also denotes the nutrient cycle but it is generally considered in a regional or global context. Following are the basic characteristics of the nutrient cycle.

• It is a cycle where the nutrients are not lost from the system but are recycled again and again.
• It operates through the soil, water bodies, air, and living organism.
• It converts nutrients into usable form with the help of decomposers. So, the decomposers help in the recycling of nutrients.
• It helps in maintaining the nutrient pool of the earth.

Ecological succession or Ecosystem Development:

Biotic communities are dynamic in nature and change over a period of time. The process by which communities of plant and animal species in an area are replaced by another over a period of time is known as ecological succession. Both the biotic and abiotic components are involved in this change. This change is brought about both by the activities of the communities as well as by the physical environment of that particular area.

The physical environment often influences the nature, direction, rate, and optimal limit of changes. During succession both the plant and animal communities undergo change. There are two types of succession (i) Primary succession and (ii) Secondary succession. If succession begins on a newly constructed deposit of mineral sediment, it is called primary succession. Primary succession could happen on a sand dune, a sand beach, the surface of a new lava flow, a freshly fallen layer of volcanic ash, or the deposits of silt on the inside of a river bend that is gradually shifting. The sequence of successional stages of primary succession is called prisere. Primary succession takes a very long time to reach the climax stage.

If succession occurs on a previously vegetated area that has been recently disturbed, perhaps by fire, flood, windstorm, or human activity, it is referred to as secondary succession. The sequence of successional stages of secondary succession is called subsere. Secondary succession takes comparatively much less time to reach the climax stage.

Homeostasis (or Cybernetic) or Feedback Control Mechanisms:

Ecosystems are capable of maintaining their state of equilibrium. They can regulate their own species’ structure and functional processes. This capacity of an ecosystem of self-regulation is known as homeostasis. The plants (producers) provide food and oxygen to animals (herbivores). The animals provide CO₂ to the producers and help in the pollination of flowers and the dispersal of plants and other animals. Microorganisms reduce the waste materials of animals and the dead bodies of plants and animals into simple inorganic materials. These materials are reused by plants. The minerals circulate in the ecosystem through the environment, plants, and animals. Thus abiotic and biotic components are in a dynamic state.

Carrying capacity is the ability of an ecosystem to provide enough food and space to the organisms. In a stable ecosystem, the carrying capacity of the ecosystem keeps the populations of different species more or less constant.

An increased population of herbivores puts pressure on the producers. Predation keeps the prey population in check. But, uncontrolled hunting of large predators or carnivores such as tigers may result in a rapid increase in herbivores’ populations such as rabbits, deer, etc. These herbivores destroy vegetation which creates an imbalance in the ecosystem.

Importance of the Study of Ecosystem:

• It tells us about the availability of solar energy and the efficiency of an ecosystem to trap the same.
• It gives information about the essential minerals present and their recycling period.
• It tells us about the gross and net productivity of an ecosystem.
• It gives information about the interactions and inter-relations amongst different food chains operating in the ecosystem.
• It helps to know about the conservation of resources and inputs required to increase productivity.

Boundaries of Ecosystems:

An ecosystem is a separate entity but its boundaries are not that distinct. A pond may be separated from a grassland but birds from the grassland visit the pond to feed on crabs and fishes. At times, inhabitants of one ecosystem move to other ecosystems. The migration of birds from colder areas to warmer ones during severe winters is an example of the movement from one ecosystem to the other.

In addition to the interaction of the biotic community of different ecosystems, physical factors of the environment also act. We see that ecosystems are not isolated units but are joined directly or indirectly to form the largest global ecosystem, the biosphere.

FAQs on Ecosystem:

Describe briefly the structure of the Ecosystem.

Biotic and abiotic components are well organized to give a characteristic structure to the ecosystem. Its important structural features are species composition and stratification. Some ecosystems like tropical rainforests show tall plant canopy with numerous biological species. Similarly, desert ecosystems show a low, discontinuous herb layer consisting of fewer species and bare patches of soil.

Ecosystem structure can also be depicted on the basis of the food relationships of producers and consumers. The producer form the first trophic level, herbivores the second and carnivores constitute the third, and so on. A trophic structure may be described in terms of the amount of living materials, called a standing crop, present in different trophic levels at a given time. The standing crop is commonly expressed as the number or biomass of organisms per unit area. The biomass of a species is expressed in terms of either fresh or dry weight. Dry weight is preferred to avoid variations in weight due to seasonal moisture differences in biomass. Nutrients that remain necessary for the growth of living organisms are accumulated in the biomass and that abiotic components like soil. The amount of nutrients present in the soil at any given time is called the standing state which remains different from one ecosystem to another.

What is Food Chain?

The movement of energy from producers up to top carnivores is known as the food chain, i.e., in any food chain, energy flows from producers to primary consumers, then from primary consumers to secondary consumers, and finally secondary consumers to tertiary consumers. Hence, it shows linear network links. In other words, the sequence of eating and being eaten in an ecosystem is known as the food chain.

What is Food Web?

A food web is a network of food chains where different types of organisms are connected at different trophic levels so that there are a number of options for eating and being eaten at each trophic level.

What is an Ecological Pyramid?

A graphic representation of the trophic structure and function of an ecosystem, starting with producers at the base and successive trophic levels forming the apex is known as an ecological pyramid.

What is the Ten Percent Law?

After studying energy transfer in different food chains in a large number of ecosystems, Lindermann in 1942 gave a generalized law, called the 10 percent law. According to the 10 percent law, only 10 percent of the energy entering a particular trophic level is available for transfer to the next higher trophic level.

It means that the energy available at each successive trophic level is 10 percent of the previous level. Thus there is a gradual decline in the amount of energy available from the producer level to the higher trophic level. For Example, if plants receive 1000 J of energy, 990 J of this energy is lost as heat to the environment and only 10 J of it is available as food to the next trophic level. Out of this 10 J of energy 9 J is lost to the environment and only 1 J of energy is available as food to the next trophic level. Thus, if a food chain has more than steps then the energy available at the last step would be negligible to sustain the life processes.

What is the Trophic Level?

A trophic level refers to the position of an organism in the food chain. The number of trophic levels is equal to the number of steps in the food chain. The green plants (producers) occupying the first trophic level (T₁) are called producers. The energy produced by the producers is utilized by the plant eaters (herbivores) they are called primary consumers and occupy the second trophic level (T₂).

Herbivores are eaten by carnivores, which occupy the third trophic level (T₃). They are also called secondary consumers or primary carnivores. Carnivores are eaten by the other carnivores, which occupy the fourth trophic level (T4). They are called tertiary consumers or secondary carnivores. Some organisms which eat both plants and animals are called omnivores (Crow). Such organisms may occupy more than one trophic level in the food chain.