Deserts are formed in regions with less than 25 cm of annual rainfall, .or sometimes in hot regions where there is more rainfall, but unevenly distributed in the annual cycle.

Lack’ of rain in the mid latitude is often due to stable high pressure zones; deserts in temperate regions often lie in “rain shadows”, that is where high mountains block off moisture from the seas.

The climate:of these biomes is modified by altitUde and latitude. At greater distance from the equator the deSerts are cold and hot near equator and tropics.

As the large volume of water passes through the irrigation system, salts may be left behind that will gradually accumulate over the years until they become limiting, unless means of avoiding this difficulty are devised

Adaptations

(i)  These plants conserve water by following methods:

They are mostly shrubs. Leaves are absent or reduced in size.

Leaves and stem are succulent and water storing.

In some plants even the stem contains chlorophyll for photosynthesis.

Root system is well developed and spread over large area.

The annuals wherever present germinate, bloom and reproduce only during the short rainy season, and not in summer and winter.

(ii) The animals are physiologically and behaviorally adapted to desert conditions.

They are fast runners.

They are nocturnal in habit to avoid the sun’s heat during day time.

They conserve water by excreting concentrated urine.

Animals and birds usually have long legs to keep the body away from the hot ground.

Lizards are mostly insectivorous and can live without drinking water for several days.

Herbivorous animals get sufficient water from the seeds which they eat.

Mammals as a group are poorly adapted to  deserts

Indian Desert — Thar desert (hot)

The climate of this region is characterised by excessive drought, the rainfall being scanty and , irregular.

The winter rains of northern India rarely penetrate into the region.

The proper desert plants may be divided into two main groups.

1. i) depending directly upon on rain and
2. ii) those depending on the presence of subterranean water.

The first group consists of two types:

the ‘ephemera’s’ and the rain perennials’.

The ephemera’s are delicate annuals, apparently free from any xerophilous adaptations, having slender stems and root-systems and often large Flowers.

They appear almost immediately after rain, develop flowers and fruits in an incredibly short   time, and die as soon as the surface layer of the soil dries up.

The rain perennials are visible above the ground only during the rainy season, but have a perennial underground stem.

The second group – depending on the presence of subterranean water

By far the largest number of indigenous plants are capable of absorbing water from deep below the surface of the ground by means of a well-developed root system, the main part of which generally consists of a slender, woody tap root of extraordinary length.

Generally, various other xerophilous adaptations are resorted to such as reduced leaves, thick hairy growth, succulence, coatings of wax, thick cuticle, protected stomata, etc., all having for  their object of reduction of transpiration.

 

Fauna

It is home to some of India’s most magnificent grasslands and sanctuary for a charismatic bird, the Great Indian Bustard. Among the mammal fauna, the blackbuck, wild ass, chinkara, caracal, Sandgrouse and desert fox inhabit the open plains, grasslands, and saline depressions.

The nesting ground of Flamingoes and the only known population of Asiatic wild Ass lies in the remote part of Great Rarm, Gujarat.

It is the migration flyway used by cranes and flamingos.

Some endemic flora species of Thar Desert includes Calligonum Polygonoides, Prosopis cineraria, Tecomella undulate, Cenchrus biflorus and Sueda fruticosa , etc

 

found where rainfall is about 25-75 cm per year, not enough to support a forest, but more than that of a true desert.

vegetation formations that are generally found in temperate climates.

In India, they are found mainly in the high Himalayas. The rest of India’s grasslands are mainly composed of steppes and savannas.

Steppe formations occupy large areas of sandy and saline soil; in western Rajasthan, where the climate is semi-arid,

The major difference between steppes and savannas is that all the forage in the steppe is  provided only during the brief wet season whereas in the savannas forage is largely from grasses that not only grow during the wet season but also from the  smaller amount of regrowth in the dry season.

 

Types of Grasslands

1. semi-arid zone (The Sehima-dichanthium type)

It covers the northern portion of Gujarat, Rajasthan (excluding Aravallis), western Uttar Pradesh, Delhi and Punjab.

The topography is broken up by hill spurs and sand dunes.

senegal, Calotropis gigantia, Cassia auriculata, Prosopis cineraria, Salvadora oloides and zizyphus Nummularia which make the savanna rangeland look like scrub.

2. dry sub humid zone (The Dichanthium- cenchrus-lasitrrus type)

It covers the whole of peninsular India (except Nilgiri).

The thorny bushes are Acacia catechu, Mimosa, Zizyphus (ber) and sometimes fleshy Euphorbia, along with low trees of Anogeissus latifolia, Soymida febrifuga and other deciduous species.

Sehima (grass)is more prevalent on gravel and the cover maybe 27%. Dichanthium (grass) flourishes on level soils and may cover 80% of the ground.

3)  moist subhumid zone(The Phragmities- sacchrum-imperata type)

It covers the Ganga alluvial plain in Northern India.

The topography is level, low lying and ill-drained.

Bothriochloa pertusa, Cypodon dactylon and     Dichanthium annulatum are found in transition zones.

The common trees and shrubs are Acacia arabica, hogeissus, latifolia, Butea monosperma,

Phoenic sylvestris and Zizyphus nummularia.

Some of these are replaced by Borassus sp in the palm savannas especially near Sunderbans.

4) The Themeda – Arundinella type

This extends to the humid montane regions and moist sub-humid axeas of Assam, Manipur,West Bengal, Uttar Pradesh, Punjab, Himachal Pradesh and. Jammu and Kashmir.

The savanna is derived from the humid forests on account of shifting cultivation and sheep grazing.

Indian Grasslands and Fodder Research Institute, Jhansi and Central Arid Zone Research institute, Jodhpur

Role of fire

fire plays, an important role in the management  of grasslands.

Under moist conditions fire favours grass over trees, whereas in dry conditions fire is often necessary to maintain grasslands against the invasion of desert shrubs.

Burning increases the forage yields, e.g. Cynodon daotylon

 

Forest types in India are classified by Champion and Seth into sixteen types.

 

Tropical Wet evergreen forests

are found along the Western Ghats, the Nicobar and Andaman Islands and all  along the north-eastern region.

It is characterized by tall, straight evergreen trees.

The trees in this forest form a tier pattern:

Beautiful fern of various colours and different varieties of orchids grow on the trunks of the trees.

Among the following States, which one has the most suitable climatic conditions for the cultivation of a large variety of orchids with minimum cost of production, and can develop

Tropical Semi-evergreen forests

found in the Western Ghats, Andaman and Nicobar Islands, and the Eastern

Himalayas.

Such forests have a mixture of the wet evergreen trees and the moist

deciduous trees. The forest is dense

Tropical Moist deciduous forests

found throughout India except in the western and the north -western regions.

The trees are tall, have broad trunks, branching trunks and roots to hold them firmly to the ground.

These forests are dominated by sal and teak, along with mango, bamboo, and rosewood.

Littoral and swamp

found along the Andaman and Nicobar Islands and the delta area of the Ganga and the Brahmaputra.

They have roots that consist of soft tissue so that the plant can breathe in the water.

Tropical Dry deciduous forest

The northern part of the country except in the North-East. It is also found in Madhya Pradesh, Gujarat, Andhra Pradesh, Karnataka, and Tamil Nadu. The canopy, of the trees does not normally exceed 25 metres.

The common trees are the sal, a variety of acacia, and bamboo.

Tropical Thorn forests

This type is found in areas with black soil: North, West, Central, and South India. The trees do not grow beyond 10 metres. Spurge, caper, and cactus are typical of this region.

Tropical Dry evergreen forest

Dry evergreens are found along Tamil Nadu Andhra Pradesh and Karnataka coast. It is mainly hard-leaved evergreen trees with fragrant flowers, along with a few  deciduous trees.

Sub-tropical Broad-leaved forests

Broad-leaved forests are found in the Eastern Himalayas and the Western Ghats, along the Silent Valley.

There is a marked difference in the form of vegetation in the two areas.

In the Silent Valley, the  poonspar, cinnamon, rhododendron, and fragrant grass are predominant.

In the Eastern Himalayas, the flora has been badly affected by the shifting cultivation and forest fires.

There are oak, alder, chestnut, birch, and cherry trees. There are a large variety of orchids, bamboo and creepers.

Sub-tropical Pine forests

found in Shivalik Hills, Western and Central Himalayas, Khasi, Naga, and Manipur Hills.

The trees predominantly found in these areas are the chir, oak, rhododendion, and   pine as well as sal, amla, and laburnum are found in the lower regions.

 

Sub-tropical Dry evergreen forests

hot and dry season and a cold winter. It generally has evergreen trees with shining

leaves that have a varnished look.

found in the Shivalik Hills and foothills of the Himalayas up to a height of 1000 metres.

Montane Wet temperate forests

In the North, found in the region to the east of Nepal into Arunachal Pradesh, receiving a minimum rainfall of 2000 mm. In the North, there are three layers of    forests: the higher layer has mainly coniferous, the middle layer has deciduous trees such as the oak and the lowest layer is covered by rhododendron and champa.

In the South, it is found in parts of the Niligiri Hills, the higher reaches of Kerala.

The forests in  the northern region are denser than in the South. Rhododendrons and a

variety of ground flora can be found here.

Himalayan Moist temperate Forest

This type spreads from the Western Himalayas to the Eastern Himalayas. The trees

found in the western section are broad-leaved oak, brown oak, walnut,

rhododendron,

Eastern Himalayas, the rainfall is much heavier and therefore the vegetation is also more lush and dense. There are a large variety of broad-leaved trees, ferri, and  bamboo.

Himalayan Dry temperate Forest

This type is found in Lahul, Kinnaur, Sikkim, and other parts of the Himalayas.

There are predominantly coniferous trees, along with broad-leaved trees such as the oak, maple, and ash. At higher elevation, fir, juniper, deodar, and chilgoza are found.

 

Sub alpine forest

Sub alpine forests extend from Kashmir to Arunachal Pradesh between 2900 to 3500 metres.

In the Western Himalayas, the vegetation consists mainly of juniper, hododendron, willow, and black currant.

In the eastern parts, red fir, black juniper, birch, and larch are the common trees.

Due to heavy rainfall and high humidity the timberline in this part is higher than that in the West.

Rhododendron of many species covers the hills in these parts.

Moist Alpine scrub

Moist alpines are found all along the Himalayas and on the higher hills near the Myanmar border. It has a low scrub, dense evergreen forest, consisting mainly of rhododendron and birch. Mosses and ferns cover the ground in patches. This region receives heavy snowfall.

Dry alpine scrub

Dry alpines are found from about 3000 metres to about 4900 metres. Dwarf plants predominate, mainly the black juniper, the drooping juniper, honeysuckle, and willow.

Forest ecosystem includes a complex assemblage of different kinds of biotic communities. Optimum conditions such as temperature and ground moisture are responsible for the establishment of forest communities.

Forests may be evergreen or deciduous which are distinguished on the basis of leaf into broad-leafed or needle leafed coniferous forests in the case of temperate areas. classified into three major categories: coniferous forest, temperate forest and tropical forest.

All these forest biomes are generally arranged on a gradient from north to south latitude or from high to lower altitude

 

Coniferous forest (boreal forest):

Cold regions with high rainfall, strong seasonal climates with long winters and short summers

evergreen plant species such as Spruce, fir and pine trees, etc and by animals such as the lynx, wolf, bear, red fox, porcupine, squirrel, and amphibians like Hyla, Rana, etc.

Boreal forest soils are characterized by thin podozols and are rather poor. Both because, the weathering of rocks proceeds slowly in cold environments and because the litter derived from conifer needle (leaf  is decomposed very slowly and is not rich in nutrients.

These soils are acidic and are mineral deficient.

This is due to movement of large amount of water through the soil, without a significant counter-upward movement of evaporation, essential soluble nutrients like calcium, nitrogen and potassium which are leached sometimes beyond the reach of roots. This process leaves no alkaline oriented cations to encounter the organic acids of the accumulating litter.

The productivity and community stability of a boreal forest are lower than those of any other forest ecosystem.

Temperate deciduous forest:

The temperate forests are characterised by a moderate climate and broad-leafed deciduous trees, which shed their leaves in fall, are bare over winter and grow new foliage in the spring.

The precipitation is fairly uniform throughout.

Soils of temperate forests are podozolic and fairly deep.

Temperate evergreen forest:

Parts of the world that have Mediterranean type of Climate are characterised by warm, dry summers and cool, moist winters. low broad leafed evergreen trees.

Fire is an important hazardous factor in this ecosystem and the adaptation of the plants enable them to regenerate quickly after being burnt.

Temperate rain forests:

seasonality with regard to temperature and rainfall

Rainfall is high, and fog may be very heavy. It is the important source of water than rainfall itself

The biotic diversity of temperate rain forests is high as compared to other temperate forest.

the diversity of plants and animals is much low as compared to the tropical rainforest.

 

Tropical rain forests:

 

Near the equator.

Among the most diverse and rich communities on the earth.

Both temperature and humidity remain high and more or less uniform.

The annual rainfall exceeds 200 cm and is generally distributed throughout the year.

The flora is highly diversified The extreme dense vegetation of the tropical rain  forests remains vertically stratified with tall trees often covered with vines, creepers,   lianas, epiphytic orchids and bromeliads.

The lowest layer is an understory of trees,  shrubs, herbs, like ferns and palms.

Soil of tropical rainforests are red latosols, and they are very thick

Tropical seasonal forests:

also known as monsoon forest occur in regions where total annual rainfall is very high but segregated into pronounced wet and dry periods.

This kind of forest is found in South East Asia, central and south America, northern Australia, western Africa and tropical islands of the pacific as well as in India.

Subtropical rain forests:

Broad-leaved evergreen subtropical rain forests are found in regions of fairly high rainfall but less temperature differences between winter and summer

Epiphytes are common here.

Animal life of subtropical forest is very similar to that of tropical rainforests.

 

a universal process of directional change in vegetation, on an ecological time scale. occurs when a series of communities replace one another due to large scale destruction either natural or manmade.

continously -one community replacing another community, until a stable, mature community develops.

The first plant to colonise an area is called the pioneer community. The final stage of succession iscalled the climax community.

The stage leading to the climax community are called successional stages

or seres. characterised by the following: increased productivity, the shift of nutrients from’ the reservoirs, increased diversity of organisms with increased niche development, and a gradual increase in the complexity of food webs.

Primary Succession

In primary succession on a terrestrial site the new site is first colonized by a few hardy pioneer species that are often microbes, lichens and mosses.

The pioneers through their death any decay leave patches of organic matter in which small animals can live.

The organic matter produced by these pioneer species produce organic adds during decomposition that dissolve and etch the substratum releasing nutrients to the substratum. Organic debris accumulates in pockets and crevices, providing soil  in which seeds can become lodged and grow.

As the community of organisms continues to develop, it becomes more diverse and competition increases, but at the same time new niche opportunities develops.

The pioneer species disappear as the habitat conditions change and invasion of new species progresses, leading to the replacement of the preceding community.

Secondary Succession

Secondary Succession occurs when plants recognize an area in which the climax community has been disturbed.

Secondary Succession  is the sequential development of biotic communities after the complete or partial destruction of the existing community.

This abandoned farmland is first invaded by hardy species of grasses that can survive in bare, sun-baked soil. These grasses may be soon joined by tall grasses and herbaceous plants.

These dominate the ecosystem for some years along with mice, rabbits, insects and seed- eating birds.

 

Eventually, some trees come up in this area, seeds of which may be brought by wind or animals. And over the years, a forest community develops. Thus an abandoned farmland over a period becomes dominated by trees and is transformed into a forest.

The differences between primary and secondary succession, the secondary succession starts on a well-developed soil already formed at the site. Thus secondary succession is relatively faster as compared to primary succession which may often require hundreds of years.

Autogenic and Allogenic Succession

When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession, while change brought about by outside forces is known as allogenic succession.

Autotrophic and Heterotrophic succession

Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession;  and the ones in which the heterotrophs are greater in quantity is known as heterotrophic succession.

Succession would occur faster in area existing in the middle of the large continent. This is because, here all prop gules or seeds of plants belonging to the different seres would reach much faster, establish and ultimately result in climax community.

The elements or mineral nutrients are always in circulation moving from non-living to living and then back to the non-living components of the ecosystem in a more or less circular fashion. This circular fashion is known as biogeochemical cycling (bio for living; geo for atmosphere).

1. Nutrient Cycling:

The nutrient cycle is a concept that describes how nutrients move from the physical environment to the living organisms, and subsequently recycled back to the physical environment.

It is essential for life and it is the vital function of the ecology of any region. In any particular environment, to maintain its organism in a sustained manner, the nutrient cycle must be kept balanced and stable.

 

Types of Nutrient Cycle

Based on the replacement period a nutrient cycle is referred to as Perfect or Imperfect cycle.

A perfect nutrient cycle is one in which nutrients are replaced as fast as they are utilised.

Most gaseous cycles are generally considered as perfect cycles.

In contrast sedimentary cycles are considered relatively imperfect, as some nutrients are lost from the cycle and get locked into sediments and so become unavailable for immediate cycling.

Based on the nature of the reservoir, there are two types of cycles namely Gaseous and sedimentary cycle

Gaseous Cycle — where the reservoir is the atmosphere or the hydrosphere, and

Sedimentary Cycle — where the reservoir is the earth’s crust.

 

2. Gaseous Cycles:

Water Cycle (Hydrologic)

The hydrologic cycle is the continuous circulation of water in the Earth-atmosphere system which is driven by solar energy.

Water moves from one reservoir to another by the processes of evaporation,

transpiration, condensation, precipitation, deposition, runoff,

infiltration, and groundwater flow.

 

3. The Carbon Cycle

without carbon dioxide life could not exist, because it is vital for the production of carbohydrates through photosynthesis by plants. It is the element that anchors all organic substances from coal and oil to DNA(deoxyribonudeic acid: the compound that caries genetic information) Carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. Carbon from the atmosphere moves to green plants by the process   of photosynthesis, and then to animals. By process of respiration and decomposition of dead organic matter it returns back to atmosphere.

 

4. The Nitrogen Cycle

an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins.

There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms needs to be ‘fixed’, that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. on earth it is accomplished in three different ways:

(i) By microorganisms (bacteria and blue-green algae)

 

(ii) By man using industrial processes (fertilizerfactories) and

(iii) To a limited extent by atmospheric phenomenon such as thunder and lighting

The amount of Nitrogen fixed by man through industrial process has far

exceeded the amount fixed by the Natural Cycle.

As a result Nitrogen has become a pollutant which can disrupt the balance of

nitrogen. It may lead to Acid rain, Eutrophication and Harmful Algal Blooms.

Certain microorganisms are capable of fixing atmospheric nitrogen into

ammonium ions. These include free living nitrifying bacteria (e.g. aerobic

Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in  association with leguminous plants(pulse etc) and symbiotic bacteria    living in non leguminous root nodule plants (e.g. Rhizobium) as well as blue green algae (e.g. Anabaena, Spirulina).

Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria:

Nitrosamines bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.

The nitrates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins.

These then go through higher trophic levels of the ecosystem.

During excretion and upon the death of all organisms nitrogen is returned to the soil in the form of ammonia.

Certain quantity of soil nitrates, being highly soluble in water, is lost to the system by being transported away by surface run-off or ground water. In the soil as well as oceans there are special denitrifying bacteria (e.g. Pseudomonas), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus  completing the cycle.

The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth’s surface through precipitation and then into the soil to be utilized by plants.(Better if You Check Diagram)

5. Sedimentary Cycle

Phosphorus, calcium and magnesium circulate by means of the sedimentary cycle.

(a) Phosphorus Cycle

Phosphorus plays a central role in aquatic ecosystems and water quality.

Phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and minning activities.

This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants in lakes.

The main storage for phosphorus is in the earth’s crust.

On land phosphorus is usually found in the form of phosphates.

By the process of weathering and erosion phosphates enter rivers and streams that transport them to the ocean.

In the ocean once the phosphorus accumulates on continental shelves in the form of insoluble deposits

After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land.

After more time, weathering will release them from rock and the cycle’s

geochemical phase begins again.

(b) Sulphur Cycle

The sulphur reservoir is in the soil and sediments where it is locked in organic

(coal, oil and peat) and inorganic deposits (pyrite rock and sulphur rock) in the

form of sulphates, sulphides and organic sulphur.

 

It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.

The sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide

(H2S) and sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.

Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid.

sulphur in the form of sulphates is take up by plants and incorporate through a series of metabolic processes into sulphur bearing amino acid which is incorporated in the  proteins of autotroph tissues. It then passes through the grazing food chain.

Sulphur bound in living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excretion and decomposition of dead organic material.

 

The interaction between the organisms is fundamental for its survival and functioning of ecosystem as a whole.

Type of Biotic Interaction

1. Mutualism:

both species benefit.

Example: in pollination mutualisms, the pollinator gets food (pollen, nectar), and the plant has its pollen transferred to other flowers for cross-fertilization (reproduction).

 

2. Commensalism:

one species benefits, the other is unaffected.

Example: cow dung provides food and shelter to dung beetles. The beetles have no effect on the cows.

 

3. Competition:

both species are harmed by the interaction.

Example: if two species eat the same food, and there isn’t enough for both, both may have access to less food than they would if alone. They both suffer a shortage of food

 

4. Predation and parasitism:

one species benefits, the other is harmed.

Example : predation—one fish kills and eats ..parasitism: tick gains benefit by sucking blood; host is harmed by losing blood.

 

5. Amensalism :

One species is harmed, the other is unaffected.

Example: A large tree shades a small plant, retarding the growth of the small plant. The small plant has no effect on the large tree.

 

6. Neutralism :

There is no net benefit or harm to either species. Perhaps in some interspecific interactions, the costs and benefits experienced by each partner are exactly the same so that they sum to zero

 

Movement of these pollutants involves two main processes:

 

1. Bioaccumulation

refers to how pollutants enter a food chain. there is an increase in concentration of a pollutant from the environment to the first organism in a food chain.

 

2. Biomagnification

refers to the tendency of pollutants to concentrate as they move from one trophic level to the next.  there is an increase in concentration of a pollutant from one link in a food chain to another.

In order for biomagnification to occur, the pollutant must be: long-lived, mobile, soluble in fats, biologically active.

If a pollutant is not active biologically, it may biomagnify, but we really don’t worry about it much, since it probably won’t cause any problems Examples : DDT.

 

ENERGY FLOW- Energy is the basic force responsible for all metabolic activities. The flow of energy from producer to top consumers is called energy flow  which is unidirectional.

Energy flows through the trophic levels: from producers to subsequent trophic levels. There is a loss of some energy in the form of unusable heat at each trophic level.

The trophic level interaction involves three concepts namely :-

1. Food Chain
2. Food Web
3. Ecological Pyramids
4. FOOD CHAIN- A food chain starts with producers and ends with top carnivores. The sequence of eaten and being eaten, produces transfer of food energy and it is known as food chain.

Grazing food chain-The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain.

This food chain begins from green plants at the base and the primary consumer is herbivore

For example, In terestrial ecosystem, grass is eaten up by caterpillar, which is eaten by lizard and lizard is eaten by snake.

In Aquatic ecosystem phytoplanktons (primary producers) is eaten by zoo planktons which is eaten by fishes and fishes are eaten by pelicans

Detritus food chain- The food chain starts from dead organic matter of decaying animals and plant bodies to the micro-organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.

 

Litter —■Earthworms —■Chicken—■Hawk

Detritus food chain

The distinction between these two food chains is the source of energy for the first level consumers.

2. FOOD WEB

“A food web illustrates, all possible transfers of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces only one pathway of the food”.

3. ECOLOGICAL PYRAMIDS

The steps of trophic levels expressed in a diagrammatic way are referred as

ecological pyramids.

 

The food producer forms the base of the pyramid and the top carnivore forms the tip. Other consumer trophic levels are in between.

The pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producer level through herbivore, carnivore onwards.  The length of each bar represents the total number of individuals at each trophic level in an ecosystem.

The ecological pyramids are of three categories-

1.Pyramid of numbers,

2.Pyramid of biomass, and

3.Pyramid of energy or productivity

1. Pyramid of Numbers

This deals with the relationship between the numbers of primary producers and consumers of different levels. Depending upon the size and biomass, the pyramid of numbers may not always be upright, and may even be completely inverted.

(a) Pyramid of numbers – upright

In this pyramid, the number of individuals is decreased from lower level to higher trophic level.

This type of pyramid can be seen in grassland ecosystem.

(b) Pyramid of numbers – inverted

In this pyramid, the number of individuals is increased from lower level to higher trophic level.

A count in a forest would have a small number of     large producers, for e.g. few number of big trees.   This is because the tree (primary producer) being

few in number and would represent the base of the pyramid and the dependent herbivores  (Example – Birds) in the next higher trophic level and it is followed by parasites in the next trophic level. Hyper parasites being at higher trophic level represents higher in number.

A pyramid of numbers does not take into account the fact that the size of organisms being counted in each trophic level can vary

the pyramid of number does not completely define the trophic structure for an ecosystem.

2. Pyramid of Biomass

In this approach individuals in each trophic level are weighed instead of being counted. This gives us a pyramid of biomass, i.e., the total dry weight of all organisms at each trophic level at a particular time.

Biomass is measured in g/m2.

 

(a) Upward -pyramid For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level perched on top

 

(b) Inverted pyramid-In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form

3. Pyramid of Energy

To compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is most suitable.

An energy pyramid, reflects the laws of thermodynamics, with conversion of solar energy to chemical energy and heat energy at each trophic level and with loss of energy being depicted at each  transfer to another trophic level.

Hence the pyramid is always upward, with a large energy base at the bottom.

Biosphere is a part of the earth where life can exist.

represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land) Life in the biosphere is abundant between 200 metres (660 feet) below the surface of the ocean and about 6,000 metres (20,000 feet) above sea level. absent at extremes of the North and South poles. Living organisms are not uniformly distributed  throughout the biosphere