EcosystemThe term ecosystem was coined by A.G. Tansley (1953). Ecosystem is defined as a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment.

An ecosystem is a self regulating group of biotic communities of species interacting with one another and with their non-living environment exchanging energy and matter.

The term Ecology was coined by Earnst Haeckel (1869). The term ecology is derived from Greek words Oikos (home) and Logos( study). So it deals with the study of organism in their natural home interacting with their environment. The Ecology is also defined as study of the structure and functions of an ecosystem.

The ecosystem can be Natural such as forests, grasslands, deserts, and aquatic ecosystems such as ponds, rivers, lakes, and the sea and human modified such as agricultural fields and aquarium.

• Structure and function of ecosystem:

1) Structural features of Ecosystem: Composition and organization of biological communities and abiotic components constitute the structure of an ecosystem.

(A)Biotic component: The plant, animal and microorganism present in an ecosystem forms the biotic component. They are divided based on the way they get their food

1) Producers: They generate food by their own. They can be Photo autotrophs( mainly green plants) which produces organic matter in presence of sun light through photosynthesis and chemo-autotrophs ( produce organic matter through chemical reaction) such as sulphur oxidizing or reducing bacteria, nitrifiers , methanogens.

2) Consumers: They get their food by feeding upon either plants or other organisms. They can by divided into

a) Herbivores (plant eaters): They feed directly on producers for their food and also known as primary consumers. Ex- rabbit, insects, man.

b) Carnivores ( meat eaters) : They feed on consumers and can be called secondary consumers ( if feeds on herbivores . Example: frog) or tertiary consumers( feeds upon secondary consumers, example: snake, big fish).

c) Omnivores: They feed on both plants and animals. Example: Humans, rat, many birds.

3) Decomposers or Saprotrophs: They derive their nutrition by breaking down the dead organic material to simpler organic compounds and ultimately into inorganic nutreints. Examples: Bacteria, fungi and actinomycetes are decomposer. Decomposition is a vital function in nature as without this all the nutrient would be tied up in dead matter and no new life will be produced.

Most ecosystem are highly complex and consist of an extremely large number of individuals of a wide variety of species. Some species of plant and animals are extremely rare and may occur only at a few locations. These are said to be endemic to these area.

Biotic component of an ecosystem

B) Abiotic component: It include air, water, soil and can be divided into:

1) Climatic component: include, sunlight and shade, average temperature, rainfall, wind pattern, humidity of a particular area. Most of the climatic parameters occurs in the lower atmosphere known as troposphere.

2) Edaphic component: Soil is the major source of mineral nutrients for plants and other organisms. Soil fertility is determined by nutrient availability, the water holding capacity and aeration of the soil.

Soil profile: It is the sequence and nature of the horizons (layers) superimposed one above the other and exposed in a pit section dug through the soil mantle. In a longitudinal section of soil, three distinct layers (A, B and C horizons) can be seen. Sometime we also observe O layers which is present above the surface of mineral matrix and mainly composed of fresh or partially decomposed organic matter.

The uppermost A : horizon is the most important one in which seeds are grown and from which plants derive nutrition. These are rich in organic matter and show downward loss of soluble salts, clay, iron and know as zone of eluviations.

B- horizon : it contains less organic matter and is hence less fertile as compared to horizon A. The chemical leached from A horizon , collects in this zone. Also know as zone of illuviations.

C – horizon : which is a mineral layer made of incompletely weathered large masses of rocks.

A horizon: Organic matter, roots, worms, insects, small rockand mineral fragments. Dark in color.

B horizon: Some roots and other living organisms, materials leached by water from the A horizon, clay, rock fragments, minerals. Lighter in color than topsoil.

C horizon: Weathered parent rockmaterials leached by water from the B horizon, partly weathered rock fragments. yellowish color.

So overall abiotic component can be divided into:

1) Physical factors: It include climatic, edaphic, geographical factor such as latitude and altitude, Soil type, water availability, water current etc. The variation in these physical parameter decide the type of ecosystem characteristics. The solar flux, temperature and precipitation pattern shows mark difference in a desert ecosystem, tropical or tundra ecosystem.

2) Chemical factors: Availability of major essential nutrient such as carbon, nitrogen, phosphorous, level of toxic substances, salts affects the functioning of an ecosystem.

Function attributes of an ecosystem: The major functional attributes of an ecosystems are as follows:

a) Food chain, food webs and trophic structure b) Energy flow

b) Cycling of nutrients (Biogeochemical cycles)

c) Primary and secondary production

d) Ecosystem development and regulation

Food chains: The sequence of eating and being eaten in an ecosystem is known as food chain. All organism, living or dead are potential source of food for some other organism and thus there is essentially no waste in the functioning of a natural ecosystem.

Example of food chain:

Grass grasshopper Frog Snake Hawk ( Grassland ecosystem)

Phytoplankton water fleas small fish Tuna ( Pond ecosystem)

Lichens reindeer Man ( Arctic tundra)

Each organism in the ecosystem is assigned a feeding level or trophic level depending upon its nutritional status. So in grassland ecosystem grass constitute the 1st trophic level, grasshopper 2nd, frog 3rd and snake and hawk occupy the 4rd and the 5th trophic levels, respectively.

The decomposer consume the dead matter of all these trophic level.

In nature we come across two type of food chain in ecosystem:

1) Grazing food chain: It starts with green plants( primary producer) and culminates in carnivores. Examples:

Grass Rabbit Fox

Phytoplankton water fleas small fish Tuna ( Pond ecosystem)

2) Detritus food chain: It start with dead organic matter which the detritivores and decomposer consumes. Partially decomposed dead organic matter and even the decomposers are consumed by detritivores and their predators. Example:

Leaf litter algae crabs small carnivorous fish large carnivorous fish

(Mangrove ecosystem)

Dead organic matter fungi Bacteria ( Forest ecosystem)

Food web: Food chain in ecosystem are rarely found to operate in isolated linear sequence. Rather they are found to be interconnected and usually form a complex network with several linkages and are known as food web. Food web is a network of food chain where different types of organisms are connected at different trophic levels, so that there are number of option of eating and being eaten at each trophic level.

Food webs give greater stability to the ecosystem, as if one species become extinct or suffers then the species in the subsequent trophic level are also affected in food chain, however in case of food web effect will be reduced due to presence of other food options.

Significance of food chains and food webs:

1) Plays significant role in ecosystem as flow of energy and nutrient cycling take place through food chain and food webs.

2) Food chain and food webs also help in the maintaining and regulating the population size of different animals thus maintain the ecological balance.

3) Food chain shows a unique property of biological magnification of some chemicals. Pesticides for examples DDT or other chemical which are non-biodegradable in nature. Such chemicals are not decomposed or excrete out so their concentration keep on increasing at each successive trophic level. This phenomenon is know as biomagnification or biological magnification.

Trophic structure: The producer and consumer are arranged in the ecosystem in a definite manner and their interaction along with population size are expressed together as trophic structure. Each food level is known as trophic level and the amount of living matter at each trophic level at a given time is known as standing crop or standing biomass.

Ecological Pyramids: Ecological pyramids were first devised by British ecologist Charles Elton(1927). Ecological pyramids is graphical representation of trophic structure and function of an ecosystem, starting with producers at the base and successive trophic level forming the apex is known as an ecological pyramid. It is of three types:

1) Pyramid of numbers: It represent the number of individual organisms at each trophic level. It may be upright or inverted pyramid of number depending upon the type of ecosystem and food chain. Example:

Producers

Herbivores

Carnivores

Top carnivores

Hawks, otherbirds

Frogs, birds

Insects

Grasses

Herbivores

Carnivores

Tree

Top carnivores

Producers

Insects, birds

Snakes, Foxes

Lion, Tigers

Grassland ecosystem ( upright)Forest ecosystem ( narrow on both end and broader in the

middle

Hyper parasite

Parasite

Herbivores

Producer

Fleas, microbes

Lice, bugs

BirdsTrees

Parasitic food chain( Inverted)

2) Pyramid of Biomass: It is based upon the total biomass (dry weight) at each trophic level in a food chain. It can be upright or inverted. Example:

Producer

Herbivores

Carnivores

Tree, herbs, grasses

Squirrel, rabbit, insect

Snake, frog, birds

phytoplankton

Forest ecosystem

Tertiary Carnivores

Carnivores

Herbivores

producer

Big fish

Small fish

insect

Pond ecosystem

3) Pyramid of energy: The amount of energy present at each trophic level is considered for this type of pyramid. It is always upright, because there is huge loss of energy (about 90%) in the form of heat and respiration at each successive trophic level. Thus at each energy level only 10% of the energy passes on.

Producer(100)

Herbivores(10)

Carnivores(1)

0.1 Top carnivores

Pyramid of energy