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ECOSYSTEM

STRUCTURE & FUNCTION

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ECOSYSTEM COMPONENTS

Biotic AbioticBiotic

Producers:Plants, phytoplanktons ,macrophytes

Decomposers Fungi,bacteria

Consumers:Herbivores,carnivores

Inorganic materials

in

soil,air & water

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Ecosystem

Structure• SpeciesComposition, trophic levels &

standing crop• Nutrients standing state of of

amounts of nutrients

Functions• Productivity &energy

flow• Nutrient cycling• Development & stabilisation

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Productivity

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Laws Of Thermodynamics

• First law :Energy can neither be created nor destroyed but can be transferred or transformed.

• Second law : No energy transformation or transfer occurs spontaneously unless energy is degraded or dissipated from a concentrated to dispersed form.

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Decomposition

Hum us CO 2,H 2ONu trie n ts

D e tritu s

Environmental conditions

Fragmentation,leaching,catabolism

HumificationMineralisationNutrient immobilisation in living microbes

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Decomposition features• Decomposers break down complex organic matter into inorganic

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

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

• Humification and mineralisation occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation

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Factors affecting decomposition

• Climatic :temperature & moisture. Slow decomposition at high altitude &

latitudes• Chemical quality of detritus:propotions of

water soluble substances ,lignin,chitin ,nitrogen.

Nitrogen rich detritus with low lignin & chitin decomposes faster.

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Decomposition Cycle

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Productivity:Categories• Primary productivity is the rate at which sunlight is

being captured by producers for the synthesis of energy rich compounds.It is the dry matter produced or energy captured per unit area of land per unit time.

• Rate of total production of biomass is called as the gross primary productivity.

• Balance energy /biomass after respiration of producers is net primary productivity.

• The rate at which energy is assimilated by the consumers is called as the secondary productivity.

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Productivity• Primary production is defined as the amount 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

• Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.

• Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP

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

• PAR: Photosynthetically active radiation which caries only 50% of the incident light is available to the producers for absorption of which 2-10% is actually absorbed.

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Diagrammatic representation of trophic levels in an ecosystem

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Energy flow through different trophic levels

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Types of food chainsFood Chains

Detritus food chainGrazing food chain

Producers

Herbivores

Carnivores

Dead organic matter

Detritus feeders in soil

Organisms feeding detritus feeders

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SIMPLE FOOD CHAIN

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TERRERESTRIAL FOOD WEB

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AQUATIC FOOD WEB

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GRAZING FOOD CHAIN

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The sun is the original source of energy, in the form of light, for the food chain.(100,000 Units of Energy)

Plants capture approximately 1% of the available light energy from the sun for biomass production by way of photosynthesis. (1,000 Units of Energy)

Herbivores consume approximately 10% of the plant biomass produced in a typical food chain.(100 Units of Energy)

Carnivores capture and consume about 10% of the energy stored by the herbivores.(10 Units of Energy)

THE TEN PERCENT LAW

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Energy flow model of ecosystem.

Solar radiation

ProducersGP

HerbivoresA

CarnivoresA

Decomposers

Photosynthesis

NU NU NU NUNA NA

R R

R

R

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Ecological Pyramids

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Pyramid of Biomass(marine) and Pyramid of Energy

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.

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Ecological succession.

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

• The entire sequence of communities that successively change in a given area are called sere

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

• Primary Succession is a process that starts in areas where no living organisms ever existed e.g lava, bare rock, newly created pond or reservoir.

• Secondary succession begins in areas where natural biotic communities have been destroyed such as in aband oned farm lands, burned or cut forests, lands that have been flooded.

• Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions

• Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions

• The species that invade a bare area are called pioneer species

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Diagramatic representation of primary succession

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Carbon Cycle

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Nutrient Cycling

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

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

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

• The reservoir for gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle)exists in the atmosphere and for the sedimentary cycle (e.g., sulphur and phosphorus cycle), the reservoir is located in Earth’s crust.

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Carbon Cycle

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Review

• Pyramid of ---------is always upright.• Inverted pyramid of------ is found in -----• The most stable sere is called as-----------------.

Give reasons:• Nutrients sometimes get immobilised in soil.• Net productivity is always less than gross productivity.• Food web is more practical than food chain.• Rate of decomposition depends on quality of the detritus.