ENVIRONMENTLECTURE-2

BY-SUMIT KONDE

BY SUMIT KONDE

14. ECOSYSTEM 14.1 Ecosystem–Structure and

Function

14.2. Productivity

14.3 Decomposition

14.4 Energy Flow

14.5 Ecological Pyramids

14.6 Ecological Succession

14.7 Nutrient Cycling

14.8 Ecosystem ServicesBY SUMIT KONDE

CLASS 12th

14.1 ECOSYSTEM–STRUCTURE AND FUNCTION In chapter 13, you have looked at the various components of the

environment- abiotic and biotic.

You studied how the individual biotic and abiotic factors affected each other and their surrounding.

Let us look at these components in a more integrated manner and see how the flow of energy takes place within these components of the ecosystem.

Interaction of biotic and abiotic components result in a physical structure that is characteristic for each type of ecosystem.

Identification and enumeration of plant and animal species of an ecosystem gives its species composition. Vertical distribution of different species occupying different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.

• The components of the ecosystem are seen to function as a unit when you consider the following aspects:

(i) Productivity;(ii) Decomposition;(iii) Energy flow; and(iv) Nutrient cycling

BY SUMIT KONDE

BY SUMIT KONDE

14.2. PRODUCTIVITY constant input of solar energy is the basic requirement for any

ecosystem to function and sustain. Primary production is defined as the amount of biomass or

organic matter produced per unit area over a time period by plants during photosynthesis.

It is expressed in terms of weight (g –2) or energy (kcal m–2). The rate of biomass production is called productivity. It is expressed in terms of g–2 yr –1 or (kcal m–2) yr–1 to

compare the productivity of different ecosystems. It can be divided into gross primary productivity (GPP) and net

primary productivity (NPP). GROSS PRIMARY PRODUCTIVITY of an ecosystem is the rate of

production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration.

Gross primary productivity minus respiration losses (R), is the NET PRIMARY PRODUCTIVITY (NPP).{GPP – R = NPP}

Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers).

• Secondary productivity is defined as the rate of formation of new organic matter by consumers.

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14.3 DECOMPOSITION Decomposers breakdown complex organic matter

into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.

Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecalmatter, constitute detritus, which is the raw material for decomposition. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humificationand mineralisation.

Detritivores (e.g., earthworm) break down detritus into smaller particles.This process is called fragmentation. By the process of leaching, watersoluble

inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.

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14.4 ENERGY FLOW Except for the deep sea hydro-thermal

ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosyntheticallyactive radiation (PAR).

We know that plants and photosynthetic and chemosynthetic bacteria (autotrophs), fix suns’ radiant energy to make food from simple inorganic materials.

Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world

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TROPHIC LEVELS IN THE ECOSYSTEM In an ecosystem, complex natural community obtain their

food from plants through one, two, three or four steps. Accordingly these steps are known as the first, second, third and fourth trophic levels or food levels. (Trophe = nourishment)

In simple terms, trophic level is the position an organism occupies in a food chain.

Trophic level 1 – Green plants (producers) – Autotrophs Trophic level 2 – Herbivores (primary consumers) –

Heterotrophs Trophic level 3 – Carnivores (secondary consumers) –

Heterotrophs Trophic level 4 – Carnivores (tertiary consumers) –

Heterotrophs Trophic level 5 – Top carnivores (quaternary consumers) –

Heterotrophs

ENERGY FLOW IN AN ECOSYSTEM The energy flows through the trophic levels from producers

to subsequent levels.

It never flows in the reverse direction.

There is loss of some energy in the form of some unusable

heat at each trophic level so that energy level decreases

from first trophic level to upwards ( 90% energy is lost so

10% energy is transferred) Energy flows from trophic level 1 (producers) to trophic

level 5 (top consumers).10% energy is transferred at each trophic level (Lindemann's rule).

The study of trophic levels helps us in understanding energy

transformation in an ecosystem.

The number of organisms at any trophic level depends

upon the availability of organism which are used as food

on lower level. So, availability of food is main factor.

14.5 ECOLOGICAL PYRAMIDS You must be familiar with the shape of a

pyramid.

The base of a pyramid is broad and it narrows down at the apex.

One gets a similar shape,whether you express the food or energy relationship between organisms at different trophic level.

Thus, relationship is expressed in terms of number, biomass or energy.

The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.

• The three ecological pyramids that are usually studied are:-(A) PYRAMID OF NUMBER (B) PYRAMID OF

BIOMASS & (C) PYRAMID OF ENERGY

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ECOLOGICAL PYRAMIDS

1. Pyramid of numbers 2. Pyramid of biomass 3. Pyramid of energy

The pyramidal representation of trophic levels of different organisms based on their ecological position (producer to final consumer) is called as an ecological pyramid.

The pyramid consists of a number of horizontal bars depicting specific trophic levels. The length of each bar represents the total number of individuals or biomass or energy at each trophic level in an ecosystem

1. PYRAMID OF NUMBERS

Represents the number of organisms in its trophic levels.

Mostly upright pyramid.

Exception: Inverted pyramid for tree and parasitic ecosystem.

Terrestrial ecosystem Aquatic ecosystem Tree ecosystem

Spindle shaped – Pyramid of numbers

2. PYRAMID OF BIOMASS

Represent the total amount of biomass of each trophic level of ecosystem.

These pyramids are mostly upright but there exceptions such as, in aquatic ecosystem it is inverted, because in this case the producers are microorganism (phytoplankton) and their biomass is very less.

The pyramid of biomass show the standing crop of the ecosystem. (standing crop – total amount of living organic matter per unit of area at that time)

3. PYRAMID OF ENERGY

Represents the amount of energy and productivity at different trophic levels.

Always upright, as there is gradual decrease in energy transfer to subsequent trophic levels.

No exceptions.

10% law of Lindemann.

Top consumers like lion are ecologically weakest.

LIMITATIONS OF ECOLOGICAL PYRAMIDS

It assumes a simple food chain, something that seldom exists in nature; it does not accommodate a food web.

Moreover, saprophytes (plant, fungus, or microorganism that lives on decaying matter) are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

Ecological pyramid does not take into account the same species belonging to two or more trophic levels.

14.6 ECOLOGICAL SUCCESSION An important characteristic of all communities is

that composition and structure constantly change in response to the changing environmental conditions.

This change is orderly and sequential, parallelwiththe changes in the physical environment.

These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.

The gradual and fairly predictable change in the species composition of a given area is called ecological succession.

During succession some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear.

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ECOLOGICAL SUCCESSION The process by which

communities of plant and animal species in an area are replaced or changed into another over a period of time.

Stability increases with complexity, but, it can never be achieved fully. Biotic communities are changing more or less over a period and space, in the presence of different type of climatic and environmental conditions.

Continuous interaction is going on between community and environment till the state of stability.

TYPES

PRIMARY SUCCESSION:

Occurs in barren area – Volcanic lava, igneous rocks, etc (1000s of years).

SECONDARY SUCCESSION:

Occurs where vegetation was present previously but was destroyed due to natural or artificial causes – fire, floods, sudden changes in climate, land slide, etc.

The soil has necessary nutrients, large pool of seeds and other dormant stages of organisms.

So comparatively, rapid 50-100 years for grasslands, 100-200 years for forests.

AUTOGENIC SUCCESSION:

During the succession, the community reacts with environment and itself.

(brought by biotic components)

ALLOGENIC SUCCESSION:

Succession brought by external conditions.

[brought by abiotic components (fire, flood, etc)]

IMPORTANT TERMS:

Pioneer community: Community that first inhabits a bare area. They will later get replaced by another community with different specie combination

Climax community: The last and stable community in an area.

Seral communities: Each transitional community that is formed and replaced during succession is called seral community.

Sere: The entire series of communities is called sere.

Pioneer Seral Climax

Sere

CAUSES OF SUCCESSION

BIOTIC FACTORS:

The action of each seral community (interaction with its environment) makes the area less favourable for itself and more favourable for next seral community in the succession.

PHYSIOGRAPHIC FACTORS:

These include climatic and other physical factors like soil erosion, soil deposition, landslide, volcanic lava.

All these factors make an area barren.

NAME OF THE SERE/SERALCOMMUNITIES

Succession in fresh water - Hydrosere

Succession in salty water – Halosere

Succession in dry region – Xerosere

Succession on rocks – Lithosere

NAME OF THE SUCCESSION

Xerach – Succession that occurs on a very moisture land – like bare rock

Hydrach – Succession that takes place in a water body.

1. Nudation – Bare area without life.

2. Invasion – Successful establishment of a species in a bare area.

a. Migration – seeds, spores.b. Ecosis/Ecesis - successful establishment of species in the new environment.c. Aggregation - species increase in number – reproduction.

3. Competition for co-action –For habitat, nutrition.

4. Reaction –Species which have survived will react with the environment and modify it (Soil, water, light, temperature) (Autogenic succession)

(The modified environment is less favourable for existing community, so it is replaced by another community)

5. Stabilisation (Climax)

Ecological succession – the process

.

14.7 NUTRIENT CYCLING organisms need a constant supply of nutrients to grow,

reproduce and regulate various body functions.

The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc. present in the soil at any given time, is referred to as the standing state.

It varies in different kinds of ecosystems and also on a seasonal basis.

What is important is to appreciate that nutrients which are never lost from the ecosystems, they are recycled time and again indefinitely.

The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling.

Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water).

Nutrient cycles are of two types: (a) gaseous and (b) sedimentary

BY SUMIT KONDE

14.8 ECOSYSTEM SERVICES Healthy ecosystems are the

base for a wide range of economic, environmental and aesthetic goods and services.

The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values.

Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a hefty price tag.

BY SUMIT KONDE

Choose the false statement among the following statements:

(a) The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton.

(b) Pyramid of numbers in a grassland ecosystem is inverted.

(c) Pyramid of energy is always upright, can never be inverted.

(d) Ecological pyramid does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain, it does not accommodate a food web.

4. Consider the following statements:1. With respect of succession of plants; Hydrarch succession takes place in wetter areas and xerarch succession takes place in dry areas.

2. The species that invade a bare area are called pioneer species.

3. All communities composition and structure constantly change in response to the changing environmental conditions. These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.

Which of the statements given above is/are correct?(a) 1 and 2 only(b) 2 and 3 only(c) 1, 2 and 3(d) 1 and 3 only

5. The pyramid of biomass in sea is also generally_______ because the biomass of fishes far exceeds that of phytoplankton.

(a) Inverted(b) Upright(c) Straight(d) Horizontal

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