Circulation of substances and the stream of energy in ecosystem

Lecture 7. The doctrine about biosphere and biosphere - noosphere concept

Of Vernadsky. Ecosystem. Biocenosis, biotope,

Biogeocenosis and ecosystem.

Plan

1. Biocenosis, biotope and biogeocenosis.

2. The structural organization of ecosystem

3. Food chain

4. Circulation of substances and a stream of energy in the ecosystem

5. An ecological pyramid. Types of ecological pyramids

6. Biological production (efficiency) of ecosystem

7. Cyclic changes of ecosystem.

8. Succession

Biocenosis is a group of communities of the different species living in the certain territory. Biotope is the certain territory with the abiotic factors of an inhabitancy (a climate, soil). Biogeocenosis is a totality of biocenosis and biotope.

The structure of ecosystem

From the point of view of trophic structure ecosystem is divided into two circles – autotrophic and heterotrophic (Odum, 1986).

1. The top autotrophic circle, or «a green belt» is a circle of plants or their parts containing a chlorophyll where fixing of light energy, use of simple inorganic compounds and accumulation of complex organic compounds prevail.

2) The bottom heterotrophic circle, or «a brown belt» is a circle of soil and the precipitation, decompositing substances, roots and etc. in which use, transformation and decomposition of complex compounds prevail.

From the biological point of view in structure of ecosystem there are following components (Odum, 1986):

1) inorganic substances;

2) organic compounds;

3) air, water and substrate medium;

4) producers;

5) macroconsumers;

6) microconsumers.

1. Producers are the autotrophic organisms, which are capable to produce organic substances from inorganic, using photosynthesis or chemosynthesis (plants and autotrophic bacteria).

2. Consumers (macroconsumers) are the heterotrophic organisms consuming organic substance of producers or others consumers (animals, heterotrophic plants, some microorganisms). There are consumers of the first order and the second order.

3. Reducers (microconsumers, destructors) are the heterotrophic organisms, eating fossils and decomposing them to mineral substances (saprotrophic bacteria and mushrooms).

As a rule, in any ecosystem it is possible to note three functional groups of organisms: producers, consumers and reducers. In ecosystems formed only by microorganisms, consumers are absent. Each group consists of set of the populations occupying ecosystem.

In ecosystem, food and power bonds proceed in a line: producers->consumers-> reducers.

Food chain

Eating each other, alive organisms form food chain. The food chain is a sequence of organisms, on which the energy having in food is transferred (from its initial source). Each part of chain is called a trophic level. The first trophic level is producers (autotrophic organisms, mainly green plants). The second trophic level is consumers of the first level (herbivorous animals). The third trophic level – consumers of the second level (the primary predators eating herbivorous animals). The fourth trophic level is consumers of the third level (the secondary predators, eating carnivore animals). Last trophic level is reducers (saprotrophicе bacteria and mushrooms). They carry out a mineralization - transformation of fossils into inorganic substances.

There are two types of food chain. Chain of выедания (or pasturable) - the food circuits beginning alive photosynthesizing organisms. Chain of decomposition is a food chain beginning with the died rests of plants, corpses and excrement of animals. Thus, the stream of energy passing through ecosystem, is broken as though into two basic directions. Energy to consumers comes in through living tissues of plants or through stocks of dead organic substance. Chain of выедания prevails in water ecosystem, chain of decomposition is in ecosystem of land.

Circulation of substances and the stream of energy in ecosystem

In ecosystem organic substances are synthesized by autotrophic from inorganic substances. Then they are consumed by heterotrophic. Allocated during ability to live or after destruction of organisms (both autotrophic and heterotrophic) organic substances are exposed to a mineralization i.e. transformation into inorganic substances. These inorganic substances can be again used by autotrophic to synthesize organic substances. So, biological circulation of substances is carried out.

At the same time, energy cannot circulate within the limits of ecosystem. The stream of energy (transfer of energy), having in food, in the ecosystem is unidirectional carried out from autotrophic to heterotrophic.

In picture the simplified scheme of energy stream at three trophic levels of the food chain is shown. Trophic levels are shown as tanks, which size corresponds to the energy having in their biomass (B), the size of channels connecting them is equal to size of streams of energy. The stream of solar energy (L} enters in an input in the system.

At the first trophic level green plants absorb about 50 % of the solar energy (L_А.) | But, during photosynthesis, its some part will be transformed to energy of chemical bonds of organic substances. It is total primary production (P_G ). The most part of not assimilated energy disperses in an environment in the form of thermal energy. The part of the formed organic substances is oxidized, and liberated energy is consumed for maintenance of all metabolic processes. These are so-called expenses for breath (R). This energy, finally, also disperses in the form of heat. The remained part of new-formed organic substances makes up a gain of plants biomass (DB) and it is called as pure primary production (Р_N). Only 1 % of the energy absorbed by a plant is transformed into pure initial production. Thus, Р_N = P_G - R.

The scheme of an energy stream in the food chain, showing three trophic levels:

1 is an entering energy on a trophic level; L is a solar energy, get on plants; L_A- the energy absorbed by plants (nearby 0,5 L); L_U is not used part of energy of a sunlight; A is an assimilation, i.e. energy (reserved) in organic substance; R is an expense for breath; P_G is a total primary production (nearby 0,05L_N); P_N is a pure primary production; P is a secondary production (consumers); N_U is an energy not used by consumers (accumulated or exported); N_A is an energy not assimilated by consumers (allocated with excrement). Numbers below is a order of size of energy losses at each transport.

Only part of pure primary production reaches the second trophic level. Its some part (N_U) is not used by consumers of the first level. It can be collected or be exported for limits of system. That part which consumers assimilated (have consumed) (A), is partially spent for breath (Л), it is partially allocated with excrement (N_A), and the rest collects in the form of secondary production (P).

Secondary production at each subsequent trophic level of consumers (_Р2, _Р3, etc.) composites about 10 % previous (though at a level of predators it can be above 20 %). As a result, the longer the food chain the less energy (collected in the organic substances) remains by its end. Therefore the number of trophic levels never meets too greater.

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