ECOSYSTEM -STRUCTURE AND FUNCTION

Structure of Ecosystem : The structure of ecosystem depends upon following components :

(i) Species diversity (ii) Species composition

(iii) Life cycle (iv) Stratification

Component of Ecosystem

1. Abiotic components : Consists of non living substances and factors like.

(i) Climatic factors i.e. air, water, light, temperature and precipitation.

(ii) Edaphic factors like soil composition.

(iii) Topographic factors i.e. mountains, slopes.

2. Biotic components : They constitute producers or transducers, consumers and decomposers or micro-consumers or saprotrophs.

Incomplete ecosystem:

An ecosystem lacking one or more structural components e.g., deep sea, freshly formed rain water pond ecosystem.

Functions of Ecosystem :

The functional components of ecosystem are studied with following aspects like

(i) Productivity (ii) Mineral cycling

(iii) Energy flow (iv) Food chain and web

(v) Efficiency (vi) Biotic interrelationships

(vii) Homeostasis (viii) Ecoregulation

Homeostasis in ecosystem :

Ecosystem maintains functional balance or relatively stable state of equilibrium amongst its various components. It is due to

(i) Carrying capacity (ii) Nutrient cycling (iii) Self regulation (iv) Feed back

Stratification

Stratification is the structure or recognizable pattern in spatial arrangement of the members of the communities.

More specifically stratification represent vertical zonation in the community.

For example in grassland communities, there is subterranean floor containing basal portions of the vegetation.

However stratification in a forest community is most complicated where, as many as five vertical subdivisions may be recognised.

These vertical subdivisions are:

(i) Subterranean (ii) Forest floor

(iii) Herbaceous vegetation (iv) Shrubs

(v) Trees

Artificial ecosystem:

These are man-made ecosystems e.g., -Modern agriculture, dams, zoological parks, plantations, aquacultures etc.

Characteristics :

(i) Do not possess self regulatory mechanism

(ii) Have little diversity

(iii) Simple food chain

(iv) High productivity

(v) Little cycling of nutrients

Boundaries of Ecosystems

An ecosystem is generally regarded as a self-sufficient unit and a separate entity.

However, it never operates in isolation.

Boundaries between one ecosystem and another are indistinct and overlapping and all ecosystem on the earth are joined together to form a single global ecosystem known as biosphere.

Some exchange of materials and energy always occurs between different ecosystems through geological, climatic or biological processes.

STRUCTURAL ASPECT OF ECOSYSTEM

The structural aspects deal with the study of number, kinds and distribution of various types of biotic (living organisms) and abiotic (e.g., light, temperature, water, oxygen, carbon, nitrogen, minerals, etc.) components.

(I) Biotic components :

Living organisms, i.e., plants, animals and micro-organisms constitute biotic component of the ecosystem.

1. Producers:

They are green photosynthetic plants that entrap solar energy through chlorophyll to synthesise organic food from inorganic raw materials.

The green plants are thus termed autotrophs as they are capable of synthesizing their own food materials.

They are also termed transducers as they change radiant energy into chemical energy.

The complex organic substances are utilized for building up their bodies and for releasing energy required for various metabolic and physiological activites.

2. Consumers:

They are the animals that are not capable of synthesizing the food materials, but feed upon other organisms or their parts.

They are thus called heterotrophs.

They are also called phagotrophs as they ingest the solid food materials.

The consumers are mainly of two types i.e., herbivores and carnivores.

Herbivores are termed primary consumers as they obtain food directly from plants.

Cattle, deer, goat, rabbit, mouse, grasshopper, etc., are common herbivores in terrestrial ecosystem and crustaceans, molluscs and protozoans are common herbivores in aquatic ecosystems.

Some carnivores (e.g., frog, cat, jackal, fox, some fishes, etc.) feed upon herbivores and thus termed as secondary consumers.

Other carnivores feed upon secondary consumers, not eating the herbivores.

They are termed as tertiary consumers (e.g., wolf, peacock, etc).

Some carnivores are thus eaten by other larger and stronger carnivores.

However, some larger and stronger carnivores (e.g., tiger and lion) never become prey to any animal and act as predators only. They are called top carnivores.

3. Decomposers:

They are saprophytic micro-organisms (bacteria, actinomycetes and fungi) deriving their food material from organic matter present in dead remains of plants and animals.

They secrete digestive enzymes which convert complex organic substances into simpler ones.

A part of the digested organic matter is assimilated by the micro-organisms and the rest is broken down into simpler inorganic compounds for recycling.

They bring about cyclic exchange of materials between biotic community and the environment. They are thus very essential components of an ecosystem.

They are also called reducers as they are capable of degrading the dead organisms.

Some workers differentiated few other categories of living beings amongst the biotic components of an ecosystem.

They are scavengers, detrivores and parasites.

Parasites belong to diverse groups, e.g., bacteria, fungi, protozoans, worms, etc.

Every type of living being can be attacked by parasites.

Detrivores are animals which feed on detritus e.g., termites, earthworm etc.

They are helpful in quick disposal of the dead bodies.

Scavengers are animals that feed on dead or injured animals and they clean the earth of organic garbages e.g., carrion, Marabou storks, Crow, Vultures (Full time scar vengers)

(II) Abiotic Components:

Non-living factors such as temperature, water, light, etc., constitute abiotic components of the ecosystem.

They are mainly of three types, i.e., climatic, topographic and edaphic.

Different abiotic factors in an ecosystem are described below.

1. Temperature: Every organism has specific range to which it is adapted to live. There are some exceptions like prokaryotes and encysted protozoan which can withstand extremes of temperature.

2. Light: It plays, a crucial role in ecosystem as it is sunlight which is the direct or indirect source of energy for all types of living organisms. It is the driving force of an ecosystem.

3. Wind: Wind has more pronounced effect on plants than on animals.

(i) Wind velocity increases the rate of transpiration.

(ii) Wind brings about pollination in most of the gymnosperms and some angiosperms which is essential for seed formation and hence perpetuation of species.

(iii) It brings about dispersal of fruits and seeds, necessary to avoid overcrowding and competition.

(iv) Wind affects the plant and animal populations by causing soil erosion in dry areas.

4. Humidity: It refers to water vapour or moisture content of the atmosphere and affects the water loss from the body surface of terrestrial organisms that occurs through evaporation, perspiration and transpiration.

5. Precipitation: It occurs in different forms like rainfall, dew, hail, snow, etc. Rainfall is the most significant of these and is the main determinant of composition of biotic community.

6. Water: Availability of water in soil, ponds, rivers, lakes, etc., mainly depends upon rainfall which controls the distribution of animals through its effect on water availability.

7. Topography: Topography is the surface behaviour of the earth like slope, altitude, hills, plains, mountain chain, exposure, etc. These factors affect vegetation and consequently animal life indirectly through their effect on rainfall, light intensity, wind velocity, water content in soil, etc. Vegetation on two sides of a hill, one facing the sun and other away, differ because of the difference in environmental conditions, like humidity, light duration, light intensity, rainfall, etc., as two faces of hill receive different amount of solar radiations and wind action. Flora and fauna on the edge of pond and middle of pond and, on or underside of the rock are different for similar reason.

8. Soil: The edaphic factors, i.e., the factors relating to soil such as soil texture (sand, loam or clay), soil pH (acidic or alkaline), soil water, soil aeration, mineral contents of the soil, etc.,determine the distribution of plants and of animals too, which depends upon vegetation.

FUNCTIONAL ASPECT OF ECOSYSTEM

The components of the ecosystem are seen to function as a unit when following aspects are considered.

(A) Productivity

(B) Decomposition

(C) Energy flow

(D) Nutrient cycling