Types and Components of Ecosystem/ Food Cain, Food Web

Types and Components of Ecosystem/ Food Cain, Food Web

Types of Ecosystem

• There are two types of ecosystem—Natural/Noncultivated and Artificial/Cultivated ecosystem.

1. Natural/Non-cultivated Ecosystem:

Natural ecosystem is subdivided into two categories—Terrestrial (land-related) and Aquatic (Water-related).

(a) Terrestrial (land-related): For example, Forest, Grassland, Desert etc.

(b) Aquatic (water-related): For example, Salty water (marine, estuary etc.), Fresh water (Stream, Lake, Pond etc.).

2. Artificial/Cultivated Ecosystem:

Human activities may modify or convert natural ecosystem into anthropogenic or man-made ecosystem. Generally, natural forests have been cut and land converted to agricultural system or plantation. Often, dam construction invades submergence of forests and conversion to water reservoires. For example, Crop field, Park, Spacecraft, Swimming pool, Well, Aquarium etc.

Components of Ecosystem:

An ecosystem consists of both abiotic/non-living and biotic/living components-

1. Abiotic/Non-living Component

• Abiotic components of an ecosystem consist of lithospheric, hydrospheric and atmospheric components, which are generally considered as land/ soil, water and air respectively. Actually, chemical substances (whether organic or inorganic) found in land, water and air and other climatic elements (such as light, temperature, rainfall etc.) make together aboitic components of ecosystem.
• In this way, abiotic components of ecosystem is categorized in three categories—

(i)   Inorganic Materials: For example, water, oxygen, carbon dioxide and minerals like phosphate, nitrate etc.

(ii)  Organic Materials: For example, carbohydrate, fats, proteins, vitamins etc.

(iii) Climatic Elements: For example, light, temperature, rainfall etc.

• The amount of abiotic component that is present at a particular time in a given area is known as standing state'.
• In ecosystem, abiotic matter keeps changing into biotic matter and biotic matter into abiotic matter continuously. This process is called Bio-chemical Cycle.

2. Biotic/Living Component

• Plants together with animals constitute the biotic/ living component of ecosystem.
• The biotic components are broadly divided into two major groups—the producers and the consumers.

1. Producers:

The producers are organisms which produce their own food from the physical environment. These are called autotrophic [auto (= self) + trophic (= nourishing) = self-nourishing] organisms. Green plants are Primary Producers, as they take simple inorganic substances from their abiotic environment and make complex molecules utilising Sun's radiant energy. These are the only organisms in an ecosystem that can trap energy from the Sun and make new organic materials. All other organism in this world are directly or indirectly dependent on the producers for their food. The process used by the producers to convert inorganic materials into organic matters is called photosynthesis. The green plant takes water from the soil, carbon dioxide from the atmosphere and energy from the sun to make a kind of sugar molecule. In the process, it gives out oxygen. The presence of green pigment called chlorophyll in the leaves of plants makes photosyn thesis possible. Hence, we can say that photosynthesis takes place in the leaves of the plants.

In ocean waters, phytoplanktons are primary producers as they produce their own food using solar energy.
Note: During photosynthesis process, 50% of total energy is absorbed by the plants, and at most 5% (i.e. 10% of energy absorbed) of that is converted into organic energy under the most favorable condition. Under the adverse condition, the rate of energy conversion decreases. This means 1-10% of absorbed solar energy is converted into organic energy by plants through photosynthesis.

2. Consumers:

The organisms that depend on other organisms for their food are called Consumers or heterotrophic [Haetero (- other) + trophic (= feeding) = other feeding) or Phagotrophs (phago = to devour). Consumers of an ecosystem are categorized into four catergories.

a. Primary Consumer:

An organism that feeds only on plant is called Herbivore or Primary Consumer- For example rabbit, goat, deer, cow, buffallo etc.

b. Secondary Consumer:

An organism that feeds on primary consumers is called (primary) Carnivore (meat-eater) or Secondary Consumer. For example insect eating frog, mouse eating cat, deer eating fox edible meat eating man etc.

Omnivore (Herbivore + Carnivore): Some organisms may be omnivore i.e. both herbivore and carnivore. Omnivores are able to eat both plants and animals (e.g. cockroach, rat, pig, fox, bear, human being (man) etc. Whenever they eat plants, they are treated as primary consumers and whenever they eat animals, they treated as secondary consumers. It can be seen in the case of human being (man), when he depends only on plants (such as vegetables, seeds, fruits etc.), he is herbivore or vegetarian and considered as primary consumer, but when he depends only on animals (such as chicken, mutton etc) he is carnivore (meat-eater) or non-vegetarian and considered as secondary consumer. But, when he depends on both plants and animals, he is omnivore (vegetarian + non vegetarian) and considered as primary consumer together with secondary consumer.

Note: A human being (man) may also be a tertiary consumer when he eats the big fish that eats the smaller fish that eats the algae.

c. Tertiary Consumer:

A consumer that feeds on secondary consumer is called tertiary consumer. Tertiary consumer includes top/secondary carnivore (e.g. tiger, lion etc). Which can not eat plants but depends only on meat. Top carnivore stands at top level of carnivore and they can not be eaten by other animals.

d. Decomposer or Quatemery Consumer:

A fourth group of consumer feeds on dead or decomposed tissues of plants and animals. They are called Quatemey Consumer or Decomposers or Saprotrophs (Sapro = to decompose) or Detritus feeders / Detrivoree. Example- bacteria, fungi (Hindi fa fund), termite (Hindi Deemak), maggot, ant earthworm (Hindi jonk), millipede (Hindi Kankhafura), crayfish etc. Apart from getting energy and nutrients from the plants and animals the decomposers convert organic materials into inorganic substances. They release simple substances to the environment as by-products of their metabolism. These are taken up by green plants and help in completing the cycle of soil nutrients. In this way, indefinite cycle goes on.

Note: Bacteria are both decomposer and producer Virus is not considered as a decomposer because it is neither live nor dead.

Food Chain

All organisms, including humans need food which provides energy for growth, maintenance and reproduction. In cases where some organism eat a variety of other organism food. Food energy passes from plants & planktons to animals in a chain called food chain. 

• A part of the energy provided by food is used for biological processes and the rest is dissipated to the environment as heat energy by the process of respiration. Undigest food is excreted and enters the detritus path.

On the land: Food chain is a sequence of organism in a community each of which uses the next lower member of the sequence as a food source, plants &plankons being at the base of sequence on the land surface. The starting point in a food chain is always a green plants.

In the Seas & Oceans: Similarly, there are plankons in the seas and oceans which use sunlight to help them make their food. Fish shellfish and other crustaceans eat the plankon. These animals are eaten by bigger animals such as sharks and whales. Whales are killed by man for meat.

There are two types of food chain— simple & complex food chain. Complex food chain is also called food web.

1. Simple Food Chain:

In grassland, grass is eaten by grasshopper, grasshopper is eaten by frog, frog is eaten by snake and snake is eaten by hawk. This is a simple food chain. simple food chain: Grasshopper < Frog < Snake < Hawk < Discomposed by Fungi and so on.

2. Complex Food Chain i.e. Food Web:

A food web refers to the interconnected feeding relationships between various organisms in an ecosystem. It is a graphical representation that shows how energy and nutrients move between producers, consumers, and decomposers as one organism eats another.

• A food web illustrates how energy and nutrients flow through species within an ecological community through trophic levels. It shows a network of complex, interconnected food chains.
• It consists of multiple food chains interlinked together. A single organism often belongs to multiple food chains.
• The arrows in a food web show the direction of energy transfer from one organism to another as nutrients and biomass when one organism consumes another.
• The base or bottom of the food web consists of producers or autotrophs, usually plants or algae that make their own food through photosynthesis.
• Primary consumers or herbivores like deer form the second trophic level consuming plants. Secondary and higher-level consumers subsequently follow.
• Top predators and parasites occupy the highest trophic levels at the top of the web, feeding off multiple prey lower down.
• Finally, decomposers like fungi and bacteria break down and recycle dead matter from all trophic levels back into the ecosystem to support new growth.

An ecological food web outlines complex feeding connections across organisms occupying different ecological niches within a habitat, sharing energy and nutrients facilitating the ecosystem's overall food cycle.

Aquatic Food Web

In deep sea and oceans, a different process called chemosynthesis takes place. Here specialized bacteria convert simple compounds from their surroundings into more complex compounds without sunlight. They use instead, a different source of energy. Deep in the Earth's surface, heat is generated by the decay of radioactive elements. This heat is released at hot water vents in the ocean depths. The bacteria use this geo-thermal energy for chemosynthesis. Later, these bacteria are consumed by many aquatic animals. chain becomes more complex, such complicated network of food chain is called a food web. As a variety of organism live in the ecosystem and there is competition for food among them, food webs are very complex. Realistically, almost all ecosystems have food webs, not merely food chains.

Ecological Pyramid of Trophic (Feeding) Levels

Ecological Pyramid (Producer & Consumer, Trophic Level and Usable Energy)

• Each group of organism occupies a trophic or feeding level.
• Trophic levels are classified as follows :

1. First Trophic Level: All green plants and other producers in the ecosystem occupy the first trophic level.
2. Second Trophic Level: Herbivores which feed on plants are placed at the second trophic level.
3. Third Trophic Level: (Primery) carnivores that eat herbivores occupy third trophic level.
4. Fourth Trophic Level: Top/Secondary carnivores that eat carnivore are placed at fourth trophic level.

Ecological Efficiency and 10 Percent Law (Lindeman's 10% Law)

• The different trophic levels are not equal in terms of energy available, as only a fraction of energy is transferred from lower to higher trophic level.
• The percentage of energy transferred from one trophic level to another trophic level is called Ecological Efficiency. The efficiency of energy transfer from one trophic level to another trophic level varies from 5% to 20% depending on the types of organism and environmental conditions.
• The 10% law of transfer of energy was introduced by American ecologist Raymond Lindeman (1915.42) in 1942. In the terrestrial (land-related) ecosystem, only 10% of plant material is eaten by herbivore. That means on an average only 10% of energy is transferred from one tropic level to another trophic level. This means 100 kg of grain is needed to produce 10 kg of meat.
• Such low efficiency is due to the fact that not all the organisms present at one level become easily available as food for the consumers at higher level. Predators may not able to capture all the prey available. Those organism which escape the predators eventually die and they provide food for the decomposers.
• Because ecological efficiency is low, the capacity of ecosystem to support organisms at the higher trophic level is limited.

Energy and Matter Movement

• A model of energy and nutrient movement in the ecosystem is discussed here. The sun provides radiant energy for the producer to manufacture food. The energy is transferred from producer to herbivores and then to the carnivore. Dead or decomposed remains of producers, herbivores and carnivores provide energy for the decomposers.
• While a part (10%) of the food energy consumed is assimilated by organism, rest (90%) of it is dissipated as heat by respiration. Respiration. Respiration process is the reverse of photosynthesis process. In the respiratoin process, the sugar molecule broken down in the presence of oxygen and water into carbon dioxide, energy and water is released. Sugar + Oxygen + Water -- Carbon dioxide + energy + water.
• There is uni-directional flow of energy from the sun until is dissipated as heat into space.
• The movement of nutrient element through various components of an ecosystem is called Bio-geo-cliemical cycle.
• The movement of matter in the form of mineral nutrient from the soil to the plants helps in the growth of the plants. These nutrients are consumed by herbivores and carnivores for their growth. When the plants and other organisms die, decomposers like bacteria and fungi feed on them and break then down into inorganic nutrients. These are available in the soil to be recycled by plants. The flow of mineral nutrients through the system is cyclic.
• With respect to matter, the earth is essential a closed system. Matter cannot escape from its boundries. In the words of Physics, energy can neither be created nor destroyed; it can only be transferred one form to another form (Law of conservation of Energy).
• The ecological system maintains its stability by continuous input of energy from the Sun and the cyclic movement of nutrient through the system.

Ecological Classification of Plants

• On the basis of ecology, Danish botanist Eugenius Warming (1841-1924) classified plants into five classes as follows: Hydrophytes (Hydro (- water) + phytes (= plants)], Mesophytes (Meso - middle), Xerophytes (Xero = dry), physiologically dry plants in soil and functionally dry plants in soil.

Some Specialised Plants