Biogeochemical Cycles (Cycles of Matter): biogeochemical cycle. Sc. 2ND SEMESTER (CBCS... · A...

CORE COURSE BOTANY-PAPER II- Plant Ecology and Taxonomy (B. Sc. II Semester CBCS 2016)

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Biogeochemical Cycles (Cycles of Matter):

A biogeochemical cycle is defined as the movement of elements, like those mentioned just a

moment ago, through organisms and the environment. A way to remember this is to break

apart the word 'biogeochemical' into pieces. The first part of the word, bio, involves biological

organisms, like bacteria, plants, and animals. The next part of the word, geo, involves

geological processes, like weathering of rocks. The last part of the word indicates chemical

processes, such as the formation of molecules.

Unlike the one-way flow of energy, matter is recycled within and between ecosystems.

Elements, chemical compounds, and other forms of matter are passed from one organism to

another and from one part of the biosphere to another through cycles that connect living

things to the earth. Biogeochemical cycles connect living things to the earth.

The four chemicals that make up 95% of living things are:

carbon,

hydrogen,

oxygen and

nitrogen.

These elements are constantly being cycled through living and non-living organic matter.

Nutrient cycles within ecosystems

1. Energy flows through an ecosystem and nutrients cycle within an ecosystem. Nutrients are

substances such as water, carbon and nitrogen which are necessary for the survival of living

things. Scientists create models to represent natural interactions in the environment which

make it easier to study and understand the 'big picture' without having to physically measure

an entire ecosystem. Diagrams of the nutrient cycles could be considered models of the actual

cycles as they occur in nature. The use of models also allows scientists to

make predictionsabout how a particular event might effect an ecosystem without having to

expose the real ecosystem to that event. For example, how might the loss of trees, and

therefore transpiration, affect rainfall in a particular ecosystem?

2. In an Ecosystem the Three Primary Nutrient Cycles:

A. The Water Cycle

B. The Carbon Cycle

C. The Nitrogen Cycle


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The Carbon Cycle:

1. Together, photosynthesis and cellular respiration form the basis of the carbon cycle. Carbon

is found in all of the major macromolecules (carbohydrates, nucleic acids, proteins and lipids)

which are necessary for all living systems.

2. The Earth's atmosphere contains carbon in the form of carbon dioxide (CO2). There are five

major reservoirs of carbon:

the atmosphere

the terrestrial biosphere

oceans

ocean sediments and

the earth's interior.

3. Processes of the Carbon Cycle:

Photosynthesis: During photosynthesis, plants and other autotrophs use CO2 along with water

and solar energy, to build organic molecules (carbohydrates), thus storing the carbon for

themselves and other organisms.

Cellular Respiration: Both autotrophs and heterotrophs use oxygen to break down

carbohydrates during cellular respiration. Consumers obtain energy-rich molecules that

contain carbon by eating plants and animals.

Volcanic Eruptions and geothermal vents: carbon from deep within the earth's interior is

brought back to the surface during eruptions of steam, gasses and lava

Decomposition: Carbon is returned to the environment through decomposers and cellular

respiration (breathing releases CO2 back to the atmosphere).

Combustion: When wood or fossil fuels are burned, the chemical reaction releases carbon

dioxide back into the atmosphere

Deposition: Coal, petroleum, and calcium carbonate rock are deposited in sediment and

underground. Calcium carbonate deposits are eroded by water to form carbon dioxide. Large

amounts of carbon are tied up in wood, only returning to the atmosphere when wood is

burned.

http://www.windows.ucar.edu/tour/link=/earth/Water/co2_cycle.html&edu=high


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The black numbers in the image above indicate how much carbon is stored in various

reservoirs, in billions of tons ("GtC" stands for GigaTons of Carbon. The figures are circa

2004. The dark blue numbers indicate how much carbon moves between reservoirs each year.

The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate

rock and kerogen.


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The Nitrogen Cycle:

1. All organisms need nitrogen, an important nutrient, to make proteins and nucleic

acids.

2. Most nitrogen is found in the atmosphere (80%) as N2, and most living things cannot

use it. All organisms rely on the actions of bacteria that are able to transform nitrogen gas into

a usable form.

3. Nitrogen-fixing bacteria (Cyanobacteria and Rhizobium) play a key role in the

nitrogen cycle. They live in the soil and in the roots of some kinds of plants, such as beans,

peas, clover, and alfalfa. These bacteria have enzymes that can break the atmospheric

N2 bonds. Nitrogen atoms are then free to bond with hydrogen atoms to form Ammonia

(NH3).

Processes of the Nitrogen Cycle: Nitrogen fixation is the conversion of nitrogen gas to

ammonia; Ammonia can be absorbed by plants from the soil, and used to make proteins, and

enter the food web for consumers.

http://www.windows.ucar.edu/earth/climate/carbon_cycle.html


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Assimilation: Consumers obtain nitrogen from the plants and animals they eat by digesting

the food's proteins and using it to make their own proteins

Ammonification: Decomposers return the nitrogen from the remains of dead plants and

animals back to the soil. Nitrogen is also returned from animal and plant waste by

decomposers (dung, urine, leaves and bark). Through ammonification, nitrogen that would be

lost, is recycled back into the ecosystem.

Denitrification: Denitrification occurs when anaerobic bacteria (chemoautotrophs) break

down nitrates and release nitrogen gas back into the atmosphere.

Nitrification: Bacteria convert ammonia into nitrogen compounds that plants can utilize more

easily. Autotrophs (plants) are therefore DEPENDENT on nitrogen-fixing bacteria, and all

other organisms are DEPENDENT on autotrophs!

The Phosphorus Cycle:

The phosphorus cycle:

– Involves the movement of phosphorus throughout the biosphere and lithosphere

– Important because phosphorus is an essential element for life and often is a limiting

nutrient for plant growth.

– Phosphorus is the key to energy in living organisms, for it is phosphorus that moves

energy from ATP to another molecule, driving an enzymatic reaction, or cellular transport.


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– The keystone of getting phosphorus into trophic systems is plants. Plants absorb

phosphorous from water and soil into their tissues, tying them to organic molecules. Once

taken up by plants, phosphorus is available for animals when they consume the plants.

– When plants and animals die, bacteria decompose their bodies, releasing some of the

phosphorus back into the soil. Once in the soil, phosphorous can be moved 100s to 1,000s of

miles from where they were released by riding through streams and rivers.

– In some cases, phosphorous will travel to a lake, and settle on the bottom. There, it

may turn into sedimentary rocks, limestone, to be released millions of years later.

Phytogeography, Climate, Vegetation and Botanical Zones of India

According to Campbell (1926), the main theme of plant geography is to discover the

similarities and diversities in the plants and floras of the present and past found in widely

separated parts of the earth.

Wulff (1943) states that Phytogeography is the study of distribution of plant species in their

habitats and elucidation of origin and history of development of floras.

According to Croizat (1952), Phytogeography is the study of migration and evolution of

plants in time and space.


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Phytogeography:

There are two major divisions of Phytogeography:

(i) Descriptive or Static Phytogeography

(ii) Interpretive or Dynamic Phytogeography

Descriptive Phytogeography: This deals with the actual description of floristic or

vegetational groups found in different parts of the world. Early plant geographers described

floras and attempted to divide earth into floristic and botanical zones.

Interpretive or Dynamic Phytogeography: This deals with the dynamics of migration and

evolution of plants and floras. It explains the reasons for varied distribution of plant species in

different parts of the world. It is a borderline science involving synthesis and integration of

data and concepts from several specialized disciplines like ecology, physiology, genetics,

taxonomy, evolution, palaeontology and geology. Good (1931), Mason (1936), Cain (1944)

and some others have pointed out the factors involved in the distribution of plants.

Vegetation of any place is modified by the environmental factors; climate, geology and biotic

factors. The great area of Indian subcontinent has wide range of climate and corresponding

diversity in the vegetation.


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India has been divided into the following botanical zones by D. Chatterjee (1962) Fig.

11.4:

(1) Western Himalayas,

(2) Eastern Himalayas,

(3) Indus plain,

(4) Gangetic plain,

(5) Central India,

(6) Deccan,

(7) Western coasts of Malabar,

(8) Assam, and

(9) Bay Islands of Andaman and Nicobar.

1. Western Himalayas: The northern part of our country is bounded by highest ranges of

Himalayas and is one of the important botanical regions of the world with climate and

vegetation ranging from truly tropical near the low altitudes to temperate arctic types at the

high altitudes. The northern mountain division can phytogeographically be divided into

western, central and eastern zones.

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Western Himalayas consist of north Kashmir, south Kashmir, a part of Punjab, H.P., Garhwal

and Kumaon. This zone is wet in outer southern ranges and slightly dry in inner northern

zone. The average annual rainfall in this region is from 100 to 200 cm. Snowfall occurs in this

region during winter season. The region may be divided into three subzones (Fig. 11.5).

(i) Submontane zone or lower region or tropical and subtropical belts (up to about 1500

metres altitude from the sea level).

(ii) Temperate zone (from 1500 metres to 3500 metres altitude),

(iii) Alpine zone (above 3500 metres and up to the line of perpetual snow).

(i) Submontane or lower region or tropical and subtropical belts: It includes outer

Himalayas, particularly region of Siwaliks and adjoining areas where annual average rainfall

is over 100 cm. This zone ranges between 300 and 1500 metres above sea level. In this zone,

forests dominated by timber trees of Shorea robusta are common. Other important tree species

are Salmalia malabaricum, Butea monosperma. Acacia catachu and Zizyphus species.

In the swampy areas, Dalbergia sisso (Shisham), Ficus glomerata, Eugenia jambolana are of

common occurrence. In west dry regions sal trees are replaced by xeric plants particularly

Zizyphus, Carissa, Acacia, and thorny Euphorbias. At higher elevation, around 1000 to 1500

metre altitude, cheer (pine) forests are also found at certain places. The common species of

pine are Pinus longifolia and Pinus roxburghii. Ground vegetation is scanty.

(ii) Temperate zone: It commonly ranges at the altitudes from 1500 to 3500 metres above the

sea level. Oaks are dominant along with Populus, Rhododendron, Betula and Pyrus. Pinus

excelsa, Cedrus deodara, Picea, Abies, Cupressus and Taxus baccata are found in the heavy

rainfall region (between 1600 and 1800 m). Herbs are also common in this region. Common

herbs are Ranunculus hirtila, Polygonum, Pedicularia, Potentilla argyrophylla. Primula,

Delphinium, Clematis, crucifers and many members of asteraceae.

In cultivated drylands of Punjab, wheat and barley are main crops. In Kashmir, Betula (birch),

Salix (cane), Populus (poplar) are of common occurrence. Besides these, Quercus

semicarpifolia, Q. dilatata, Aesculus indica (chestnut) and many conifers are commonly met

within this region. In west Kashmir rice cultivation is common Sar or saffron (Crocus

sativus), apples, peaches, walnut, almonds and other fruits are important economic plants of

Kashmir region.

(iii) Alpine zone: Above the altitude of 3500 metres and up to snowline (about 5000 m) is

alpine zone. The vegetation consists of evergreen conifers and some low and broad leaved

trees. The vegetation of this region is characterized by cushion habit, dwarf nature and


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gregarious habit. In lower alpine region, shrubby forests are common which may be (a)

Birch—fir forest which is fairly dense and is mixed with evergreen shrubby Rhododendron at

higher level and (b) Birch— Rhododendron forests in which silver fir, Betula, Rhododendron

and Juniperus are common. In the upper alpine region, prominent herbaceous plants are the

species of Primula, Polygonum, Gentiana, Cassiope, Meconopsis, Saxifraga, Potentilla,

Geranium, Aster, Astragalus etc. which form alpine meadows. At about 5000 metre altitude

and above snow perpetuates round the year and plant growth is almost nil. This altitude is

called snow line or ice line.

Populations of Draba, Braya, Cortia, Leontopodium go on increasing with the increase in

altitude. Species of Ephedra, Juniperus, Berberis are also found scattered. Poa, Stipa and

Fectuca are common grasses of alpine zone.

2. Eastern Himalayas: Eastern Himalayas extend from Sikkim to upper Assam, Darjeeling

and NEFA. Vegetation of this region differs from that of western Himalayas. The chief

differences are due to changed environmental factors as heavy monsoon rainfall, less snowfall

and high temperature and humidity.

This region can also be divided into:

(i) Tropical submontane zone

(ii) Temperate or Montane zone, and

(iii) Alpine zone (Fig. 11.5).


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(i) Tropical or Submontane Zone: The tropical subzone characterized by warm and humid

conditions extends from plain up to the altitude of about 1800 m. In this zone mostly sal

forests, and mixed deciduous forests consisting of important plants, such as Sterculia,

Terminalia Anthocephalus cadamba and Bauhinia are common. In the savannah forests,

common plants are Albezzia procera, Bischofia, Salmelia, Dendrocalamus. Evergreen forests

of Dillenia indica, Michelia champaca, Echinocarpus, Cinnamon, etc. are common.

(ii) Temperate or Montane Zone: It may be further divided into upper and lower zones

Lower temperate zone is the region between 1800 and 3000 metre altitudes. In the lower

temperate zone, Oaks (Quercus). Michelia, Pyrus, Cedrela, Eugenia, Echinocarpus are

common plants. In upper temperate zone (3000-4000 metre altitude), conifers and

Rhododendrons are common. Important conifers of this region are Picea spinulosa, Abies,

Larix, Juniperus, Tsuga griffithi, Tsuga brunoniana, etc.

(iii) Alpine Zone (from 4000 metres up to snow line): Climate is humid and extremely cold.

The vegetation in the alpine zone is characterised by complete absence of trees and

predominance of shrubs and meadows. Important plants of this zone are Rhododendron and

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Juniperus. Eastern Himalayan vegetation is considered to be one of the richest vegetational

units in the world and consists of several species of plants, which are native of foreign

countries, such as, China, Japan, Burma, Malaya and European countries.

3. Indus Plains: It includes part of Punjab, Rajasthan, Cutch, Delhi, a part of Gujarat. Some

part of this plain is now in Pakistan. The climate of this zone is characterised by dry hot

summer, and dry cold winter. Rainfall is usually less than 70 cms, but in certain regions it is

as low as 10-15 cms. The soil of a wide area except cultivated land, is saline. Much of the

land has become desert due to excessive dryness.

Vegetation is mainly bushy and thorny Acacia arabica, Prosopis spicigera, Salvadora Capparis

decidua are very common plants of this region. Salsola phoetida and Lunakh grass are found

mostly in saline soils. Other plants of this botanic province are Anageissus, Eugenia, Mango,

Dalbergia sisso, Albizzia lebbek, Zizyphus nummularia, etc.

Historical evidences indicate that the area was covered by dense forest some 2000 years ago,

but gradual destruction of vegetation cover either by biotic agencies or by any other agency

led to the development of desert in this plain. Saccharum munja, Cenchrus ciliaris, Prosopis

spicigera. Acacia leucophloea, A. Senegal are the important plant species which are grown for

checking the spread of desert.

4. Gangetic Plains: This is one of the richest vegetational zones in India. This zone covers

flat land of a part of Delhi, whole of U.P., Bihar, and West Bengal and also a part of Orissa.

Rainfall in this zone is from 50 cm to 150 cm. A great part of the land is under cultivation.

The common crop plants are wheat, barley maize. Sorghum (jowar), Bajra, urad, Moong

(Phaseolus mungo), Cajanus cajan, til (Sesamum indicum), sugarcane. Pea (Pisum sp.), gram

(Cicer arietinum), potato, Brassica, rice.

In western part of U.P. annual rainfall is from 50 cm to 110 cm. Dry deciduous and shrubby

forests are common in this part. Important plants of south-western part of U.P. are Capparis,

Saccharum munja, Acacia arabica. In the north-western part of U.P. near Himalayas foothills

Dalbergia sisso. Acacia arabica are most common plants.

In eastern gangetic plain, the conditions are cold and wet (annual rainfall, 150 cm in West

Bengal). In this part evergreen forests are common. In central part, the annual rainfall is about

100 cm to 150 cm. The vegetation consists mainly of deciduous trees. Sal trees are dominant.

Other common trees are Terminalia tomentosa, T. belerica. Acacia species, Bauhinia,

Diospiros (Biri Ka patta or tendu) Eugenia sp., neem trees (margosa), Madhuca indica

(Mahua), Cordia myxa (Lasora), Tamarindus, Mango (Mangifera indica). Ficus etc.


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In Bihar and Orissa hills, Rubus, Potentilla, Fragaria (Rosaceae), Pyrus etc. are common.

Mangrove vegetation is common in tidal regions in West Bengal near Sunder-ban, and Orissa.

Rhizophora mucronata, R. conjugata, Sonneratia, Ceriops roxburghiana and Acanthus

ilicifolius, Kandelia rheedii, Bruguiera gymnorhiza are common mangrove plants in those

regions.

5. Central India: Central India covers Madhya Pradesh, part of Orissa (now Odisha), Gujarat

and Vindhya. The areas are hilly. The average rainfall per annum may be 100-170 cm. Some

places are at the altitudes of 500-700 m from the sea level. Biotic disturbances are very

common in this botanical province which have led to the development of the thorny

vegetation in open areas. In this region teak (Tectona grandis) and sal (shorea robusta) forests

are very common. Other trees are Terminalia tomentosa, Bauhinia, Mango, Phyllanthus, Ficus

glomerata, etc. Among common shrubs are Mimosa rubricaulis, Desmodium, Acacia sp.,

Zizyphus rotundifolia and other.

Entire forest vegetation of central India may be divided into:

(i) Sal forests

(ii) Mixed deciduous forests

(iii) Thorny forests.

At Sarguja (M.P.) many species have been reported to occur. Some of them are Pyrus,

Barberis asiatica, Rubus, elipticus, etc.

6. Deccan: This region comprises whole of the southern peninsular India including Satpura

and southern part of Godawari River. Average annual rainfall in this region is about 100 cm.

It may be divided into the following two subdivisions:

(i) Deccan plateau

(ii) Coromandel coast.

In Deccan plateau teak forests containing Diospiros, Acacia, Prosopis spicigera. Santalum a

hum (chandan tree) and Cedrda toona are common. On rocks, Capparis, Euphorbias,

Phyllunthus are common. Teak, Pterocarpus, Borassus, Foenix silvestris are also common in

this area In Chhota Nagpur plateau, important species are Clematis natans, Barberis,

Thallictrum and also many members of Annonaceae, Rosaceae, Compositae, Araliaceae,

Apocynaceae, Lauraceae, Amaranthaceae, Orchidaceae. Some ferns also common.

In Coromandel coast vegetation consists largely of some halophytic species.

7. Western Coast of Malabar: This is small botanical province covering Cape Comorin to

Gujarat and Western Ghats .This is a region of heavy rainfall.


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In this zone, four types of forests are common:

(i) Tropical forests (occur at 700 m altitude).

(ii) Mixed deciduous forests (found at the altitude up to 1600 m).

(iii) Temperate evergreen forests (occur above 1200 m altitude), and

(iv) Mangrove vegetation.

In tropical evergreen forest the trees are tall and they have root buttresses. Important species

are Cedrela toona Dipterocarpus. Mangifera indica, Sterculia alata, Artocarpus hirsuta. In the

mixed deciduous forests, important plants are Terminalia tomentosa, Terminalia peniculata

Tectona grandis, Dalbergia, Lagerstroemia lanceolata and bamboo species, particularly

Dendrocalamus and Bamboosa arundinacea. On the Nilgiri hills sub-tropic and temperate

conditions exist. Important plants of Nilgiri vegetation are Rubus, Rhododendron arboreum,

Barberis, Thallictrum Ranunculus, Fragaria, Potentilla. Many other herbs along with many

grasses are also common.

Temperate forests commonly called as ―sholas‖ contain Gardenia obtusa, Michelia nilgirica

Eugenia species are also common. In Malabar, plants belonging to family Dipterocarpaceae’

Tihaceae, Anacardiaceae, Meliaceae, Myrtaceae, Piperaceae, Orchidaceae and many ferns are

common. The west coast of Malabar region receives very high rainfall. In the coastal region

mangrove plants grow luxuriantly.

8. Assam: This botanical province is very rich in vegetation and covers valley of

Brahmaputra, Naga hills and Manipur. This is the region of heaviest rainfall. Cherapunji is

one of the rainiest places in the world where annual rainfall often exceeds 1000 cm. Excessive

wetness and high temperature in this zone is responsible for the development of dense forests.

Broad leaved, tall evergreen angiosperms and some conifers are very common in the forests.

Common plants occurring in this region are Ficus, Artocarpus, Michelia champaca, Sterculia

alata. Morus species. Besides these bamboos canes, climbers, and green bushes are also

common. Prominent plants in the northern forests of this zone are Alnus nepalensis, Betula.

Rhododendron arboreum. Magnolia, Michelia and Prunus. Sal also occurs at Garo hills.

Orchids and fern species are very rich in this zone.

9. Bay Islands of Andaman and Nicobar (India):

Islands: These are represented by the Andaman and Nicobar islands in the east and

Lakshadweep islands in the west. The Andaman and Nicobar islands are a group of more than

300 islands, which support many characteristic plants and animals. The forests range from

tropical evergreen to moist deciduous and even mangroves. The Lakshadweep group of


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islands comprise 36 major Islands, which together from an area of 32 sq km. Many varied

marine fauna are present here that include turtles, crabs, molluscs and fishes. Beautiful coral

reefs are also present in this part of India.

These bay islands represent elevated portions of submarine mountains. Climate is humid in

the coastal region. In Andaman, beech forests, evergreen forests, semi-evergreen forests

deciduous forests and mangrove vegetation are of common occurrence. Rhizophora

Mimusops, Calophyllum, etc. are common plants in mangrove vegetation. In the interior

evergreen forests tall trees are common. Important species of trees are Calophyllum,

Dipterocarpus, Lagerstroermia and Terminalia etc. Some part is under cultivation. The

important crops are paddy and sugarcane.

Concept of Endemism:

Endemism is an ecological word meaning that a plant or animal lives only in a particular

location, such as a specific island, habitat type, nation or other defined zone or endemism is

the association of a biological taxon with a unique and well-defined geographic area. The

opposite of endemism is cosmopolitan distribution or cosmopolitan is the antithesis of

endemic, and refers to a taxon which is extremely widespread in many world regions. Highest

numbers of endemic taxa are found in Australian region. All important islands and mountain

chain (except isolated piece of the country like Italy) from 480 N to South wards possess

endemics. Maximum proportion of endemism is found in West Australia and South Africa

regions. All the southern land masses have great number of species confined to themselves i.e.

endemism is higher in old landmasses than in young e.g. land of northern hemisphere which

are covered by the Pleistocene ice sheets have lower number of endemics. Endemics are

especially common in mountainous countries and it worth noting that most islands are also

mountainous. Botanists have long been accustomed to look upon endemic forms as the oldest.

According to Willis age-and-area hypothesis, most endemic species are considered to be

youthful i.e. youngsters rather old relic. The concept of endemism includes two types of

organisms whose areas are confined to a single regions: endemics (which are relatively

youthful species), and epibiotics (which are relatively old relic species).

Types of Endemism

There are two types of endemism - paleoendemism and neoendemism.

Paleoendemism means that a species used to live in a large area but now lives only in a

smaller area. These species are often systematically isolated taxa, whose distribution areas


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represent the remnants of originally larger distribution ranges that have been reduced due to

environmental changes.

Illustration: Formation of paleoendemic species can be understand by taking following

hypothetical example. Species A is widely distributed throughout the whole mountain range.

A change of the environmental conditions in the region leads to a reduction to the distribution

of species A. Species A does not totally distinct; it survives in a small area at the periphery of

its former distribution range. Now Species A is paleoendemic species of this area.

Neoendemic species: Neoendemism means that a species has recently appeared which is

closely related to the main species or one that has formed following hybridization and is now

classified as a separate species. This is a common process in plants especially those which

exhibit polyploidy. These species result from the divergent adaptation to differing

environmental conditions thereby leading to the formation of new species that are locally

distributed. The evolution of neoendemic plant species is often triggered by polyploids. The

endemic species may have a higher ploidy level than its related taxa (apoendemics), or it may

be diploid while its related taxa have a higher ploidy level (patroendemics). In cases where

the endemic taxon and its related taxa are of equal ploidy level, the endemic species are called

schizoendemics. Apo-, patro-, and schizoendemics are further subdivisions of neoendemic.

Illustration: Formation neoendemic species can be understand by taking following

hypothetical example. Species B is immigrates to the area and colonizes the upper region of

mountain chain. As a result, the population of species B gets separated and the two

subpopulations are isolated from each other. Since the environmental conditions of the two

subpopopulations are not identical they show different adaptations. The divergent evolution in

the subpopulation may lead to formation of new species or subspecies that are locally

distributed called neoendemic species.

Factors Responsible for Endemism

Stebbins, (1942) has given a genetical explanation for the for the endemic. He also told that

such taxa have depleted their store of genetic variation (biotype depletion) and they are unable

to expand their range. There are multiple causes of rarity and endemism. Three primary

factors i.e. geographical area, ecological breadth and isolation describe the distribution of

endemics. Endemics are found on all landmasses of the world, both continents and island, and

in all major biomes. Neither genetics, ecology, nor history alone will suffice to explain the

origin of endemic taxa. Stebbins (1980) has given the gene pool/ niche interaction theory to

explain origin of rarity and endemism. ―According to theory, the primary cause of localized or


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endemic distribution patterns is adaptation to a combination of ecological factors that are

themselves localized. Factors of soil texture and chemical composition are the most important

but by no means the only ones. Next to the climatic and edaphic factors, those inherent into

the gene pool of the population are of critical importance. They include the total amount of

variability, the amount of variability that can be released at any one time, and the amount of

variation that can be generated with respect to those particular characteristic that affect most

strongly the establishment of new population‖

The endemics have two characteristics:

May be of recent origin and have not the opportunity to occupy a large area through migration

e.g. Vernonia. Survivors of ancestor with mid range of distribute e.g. Gink biloba. A species

that is found in only a single geographical area and how where else is called endemic to that

area. When environments are damaged by human activity, the population sizes of many

species that not all species will go extinct the greatest destruction of biological communities

has occurred during the last 150 years during which human populations went from 1 billion to

7 billion. The habitat destruction, fragmentation, degradation, disease, over exploitation

causes problems to species survivals. Ecologists have observed such species for conservation

of biodiversity.

These categories are:

1. Species with a narrow geographical range.

2. Species with only one or a few populations.

3. Species in which population size is small.

4. Species with low population density.

5. Species requires a large home range.

6. Species that have large body size.

7. Species with low rates of population increase.

8. Species that are not effective dispersers.

9. Species that migrate.

10. Species with specialized niche requirements and genetic variability.

11. Species characterized to stable environment.

12. Species with aggregation or harvested by people.

To highlight the legal states of rare species for purpose of conservation the IUCN (1988) have

established main conservation strategies.


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1. Extinct: The last remaining number of the species had died or is presumed to have died

beyond reasonable doubt. In certain case captive individuals survive, but there is no free

living natural population.

2. Critical: Critically endangered, faces an extremely high risk of extinctions in the

immediate future.

3. Endangered: Faces a very high risk of extinction in the near future.

4. Vulnerable: Species that may become endangered in the near future because populations

of the species are decreasing in size throughout its ranges.

5. Rare: Species that have small total numbers of individuals after due to limited

geographical ranges or low population densities.

6. Secure or lower risk: No immediate threat to the survival of the species.

Mace & Landle (1991) have proposed a three level system of classification based on the

probability of extinction.

1. Critical species with 50% or greater probability of extinction within 5 years or 2 generation

whichever is larger.

2. Endangered: Species with 20% probability of extinction within 20 years or 10 generations.

3. Vulnerable: Species with 10% probability of extinction within 100 years.

Endangered Mammals

1. Blue Whale 2. Chimpanzee, 3. Giant Panda, 4. Fin Whale 5. Gorilla, 6. Tiger

Endangered birds

Kiwi (Apteryx anstralis)

Indian White Rumped Vulture {Gyps bengalensis)

Endangered reptile

Ripley’s Turtle

Endangered amphibians

Desert slender Salamander (Batrachoseps aridus) Palmate newt (Triturus helvenetica).

Endangered plants:

6% of identified plant species are endangered. E.g. Pinus squamata in China, Clianthus

puniceus (Lobster clow), Madonna lily (Lilium candidum).

Biogeochemical Cycles (Cycles of Matter): biogeochemical cycle. Sc. 2ND SEMESTER (CBCS... · A...

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