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2.1 Ecosystem -living things in a given area, non-living chemical and physical
factors of their environment, linked together through nutrient cycle and energy

Types of Ecosystem

Natural Artificial/Man-made

Terrestrial Aquatic

Marine Fresh water

Lotic -river, stream or spring. Lentic -lake, pond or swamp.

2.2.1 Ecology – Study of the distribution and abundance of organisms, the flows of energy and
materials between abiotic and biotic components of ecosystems.

2. Ecosystem Structure: The living components of an ecosystem

• The roles of organisms in an ecosystem:

• Producer (autotrophy): make food; plants, algae

• Consumer (heterotrophy): eat other organisms

• Decomposer: eat dead organic matter; bacteria and fungi

1. Classes of Consumers

Herbivore – primary consumer – eats plants

Carnivores – secondary – meat eaters; eat herbivores

Tertiary – feed on carnivores

Omnivores – eat plants/animals.

2. Role of Organisms

Scavengers – feed on dead organisms (vultures, flies, crows, lobsters)

Detritus feeders – organisms that extract nutrients from fragments of dead organisms into more
simple organic waste (termites, earthworms, crabs)

Decomposers – organisms that digest parts of the dead organisms into simplest chemicals (bacteria,



Fig. 2.2.2 Role of organisms


1. Introduction

❖ A forest is an area with a high density of trees.

❖ World’s total land area is 13,076 million hectares – (Source: FAO; 1989)

❖ Of which total forests account for about 31% of the world’s land area.

❖ In India, the forest cover is roughly 19% of the total land area.

❖ The forest ecosystems are of great concern from the environmental point of view.

❖ It provides numerous environmental services like;

➢ Nutrient cycling,

➢ Maintaining biodiversity

➢ Providing wildlife habitat

➢ Affecting rainfall patterns

➢ Regulating stream flow

➢ Storing water

➢ Reducing flooding

➢ Preventing soil erosion

➢ Reclaiming degraded land & many more….

❖ Apart from environmental values, forest ecosystems have some traditional values as well.

❖ Examples are:

➢ Fire Wood & Timber.

➢ Fruits.

➢ Gums.

➢ Herbs & drugs.



2.3.2 Structure and Function of Forest Ecosystem

I. Biotic components

❖ The various biotic components, representatives from the three functional groups, of a
forest ecosystem are:

1) Producer Organisms

❖ In a forest, the producers are mainly trees.

❖ Trees are of different kinds depending upon the type of forest developed in that climate.

❖ Apart from trees, climbers, epiphytes, shrubs and ground vegetation.

❖ Dominant species of trees in major types of forest ecosystems are:

❖ Tectona grandis, Acer, Betula, Picea, Pine, Cedrus.

2) Consumers

❖ In a forest, consumers are of three main types;

a) Primary Consumers

❖ These are Herbivores which feed directly on producers.


❖ Ants, Beetles, Bugs, spiders etc. feeding on tree leaves.

❖ Larger animals such as Elephants, Deer, giraffe etc. grazing on shoots
and/or fruits of trees.

a) Secondary Consumers

❖ These are carnivores and feed on primary consumers.

Eg: Birds, Lizards, Frogs, Snakes and Foxes.

c) Tertiary Consumers

❖ These are secondary carnivores and feed on secondary consumers

❖ These include top carnivores like Lion, Tiger.

3) Decomposers

❖ These include wide variety of saprotrophic micro- organism like;

❖ Bacteria (Bacillus Sp., Clostridium sp., pseudomonas.

❖ Fungi (Aspergillus sp., Ganoderma sp., Fusarium.

❖ Actinomycetes (Streptomyces).

❖ They attract the dead or decayed bodies of organisms & thus decomposition takes place.

❖ Therefore, nutrients are released for reuse.

II. Abiotic components

❖ These include basic inorganic & organic compounds present in the soil & atmosphere.

❖ In addition dead organic debris is also found littered in forests.



Fig.2.3 Forest Ecosystem


1. Introduction

❖ Grasslands (also called Greenswards) are areas where the vegetation is dominated
by grasses and other herbaceous (non-woody) plants.

❖ Grasslands occupy about 24% of the earth’s surface.

❖ Grasslands occur in regions too dry for forests and too moist for deserts

❖ The annual rainfall ranges between 25- 75 cm, Usually seasonal

❖ The principal grasslands include:

➢ Prairies (Canada, USA),Pampas (South America),Steppes (Europe & Asia)

Veldts (Africa)

❖ The highest abundance & greatest diversity of large mammals are found in these ecosystems.

❖ The dominant animal species include

❖ Wild horses, asses & antelope of Eurasia,

❖ Herds of Bison of America; and

❖ The antelope & other large herbivores of Africa.

2.4.2 Structure and functions of Grassland Ecosystems

I. Biotic components

1) Producer Organisms



❖ In grassland, producers are mainly grasses; though, a few herbs & shrubs also contribute to
primary production of biomass.

❖ Some of the most common species of grasses are:

❖ Brachiaria sp., Cynodon sp., Desmodium sp., Digitaria sp.

2) Consumers

❖ In a grassland, consumers are of three main types;

a) Primary Consumers

❖ The primary consumers are herbivores feeding directly on grasses. These are grazing animals
such as

❖ Cows, Buffaloes, Sheep, Goats, Deer, Rabbits etc.

❖ Besides them, numerous species of insects, termites, etc are also

b) Secondary Consumers

❖ These are carnivores that feed on primary consumers (Herbivores)

❖ These include;-Frogs, Snakes, Lizards, Birds, Foxes, Jackals etc.

c) Tertiary Consumers

❖ These include hawks etc. which feed on secondary consumers.

1) Decomposers

❖ These include wide variety of saprotrophic micro- organism like: Bacteria; Fungi;

❖ They attract the dead or decayed bodies of organisms & thus decomposition takes place.

❖ Therefore, nutrients are released for reuse by producers.

II. Abiotic components

❖ These include basic inorganic & organic compounds present in the soil & aerial environment.

❖ The essential elements like C, H, N, O, P, S etc. are supplied by water, nitrogen, nitrates,
sulphates, phosphates present in soil & atmosphere.



Fig.2.4 Grassland Ecosystem


1. Introduction

❖ A desert is a landscape or region that receives almost no precipitation.

❖ Deserts are defined as areas with an average annual precipitation of less than 250 millimeters
per year.

❖ It occupies about 17% of the earth’s surface.

❖ Deserts are characterized by hot days & cold nights.

❖ The deserts of the world are mainly located in the

South- western United States, Mexico, North

America, Asia (Thar, Gobi, Tibet) & west Asia.

❖ Deserts are characterized by scanty flora & fauna.

❖ Soils of deserts often have abundant nutrients but little or no organic matter.

2. Sturucture and Functions of Desert Ecosystms

I. Biotic components

1) Producer Organisms

❖ In a desert, producers are mainly shrubs/bushes; some grasses & a few trees.

❖ Dominant plant species include: Succulents (water – retaining plants adapted to arid climate
or soil conditions) & hardy grasses.



❖ Besides some lower plants such as lichens & xerophytic mosses are also present.

2) Consumer Organisms

These include animals such as insects, reptiles which are capable of living in xeric conditions

❖ Besides some nocturnal rodents, birds & some mammalians like camel etc are also found.

3) Decomposers

Due to poor vegetation with very low amount of dead organic matter, decomposers are poor in
desert ecosystem.

❖ The common decomposers are some bacteria & fungi, most of which are thermophillic.

II. Abiotic components

Due to high temperature & very low rainfall, the organic substances are poorly present in the soil.

Fig. 2.5 Forest Ecosystem


1. Introduction

❖ Aquatic ecosystems deal with biotic community present in water bodies.

❖ In terrestrial ecosystem, carbon dioxide & oxygen are present in gaseous form whereas in
aquatic ecosystem, these are available in dissolved state.