Environmental biology
A. Ecology.
Ecologydeals with the various principles, which govern the relationships between organisms and their environment. Reiterfirst used the term ecology in 1868. Ernst Haeckel(1886) first correctly defined ecology as “the science dealing with reciprocal relationship of organisms and the external world”. Prof. R.Misrais known as “Father of ecology in India”. Other famous Indian ecologists include G.S.Puri, S.C.Pandeya.Dudgeon (1921) started ecological studies in India.
Branches of ecology
❒ Autecology:Ecology of individuals.
❒ Synecology:Study of relationships between communities and environment.
❒ Genecology:Study of ecological adaptations in relation to genetic variability.
❒ Paleoecology:Study of relationship between organisms and environment in the past.
❒ Applied ecology:Application of ecological concepts for human welfare.
❒ Systems ecology:Interpretation of ecological concepts in terms of mathematical principles.
Units
❒ Individual 
❒ Individual is most concrete and observable unit which carry out life processes within its body as an entity.
(1)Species : It is unit of classification and can be defined as sum total of all populations of the same kind / form of a species.
(i) Exceptions to species concept
(a) Difference in the morphology of developmental stages of an individual.
(b) Sexual dimorphism :Occurrence of two forms among the organisms of the same species is known as dimorphism. Plants such as the date plam have male and female individuals which bear different types of flowers. Man and woman, peacock and pea hen are two sexual forms of same species. They show sexual dimorphism.
(ii) Polymorphism : The occurrence of many forms of individuals within the same kind of organism (species) is known as polymorphism. e.g. :
(a) Colonies of social insects.
(b) Colonies of coelentrates and Volvox.
(c) Different human races (Negraoids, Caucasoids, Mongoloids, Indian, Australoid, Polynesian).
(iii) Speciation or Origin of species :May be
(a) Due to physical barrier (Allopatric)
(b) Due to reproductive barrier (Sympatric)
(c) Mutation
(d) Polyploidy
(e) Genetic (Wright effect)
(iv) Home range :A space to live is a basic need of an organism. Several members of a species may cover a defined area in search of food and mates, which is called home range.
(2)Population : Geographically localised group of individuals of the same kind at a particular time represents population e.g., Population of Delhi in 2000 year.
Population density (D) = 
N= Total no. of individuals, S= No. of units of space
(i) Factors affecting population
(a) Natality :Birth rate.
(b) Mortality :Death rate.
(c) Population growth :Shows two types of curve :
❒ S. shaped curve.
❒ J. shaped curve.
(d) Emigration :Permanent outward movement. Decreases population.
(e) Immigration : Permanent inward movement. Increases population.
(f) Migration :Two way movement of entire population. Does not change the size of population.
(g) Biotic factors :Growth rate of certain population decreases with the increase in density (density dependent) before the carrying capacity of the environment is reached, predators also keep the size of a population under check.
(h) Carrying capacity :of an environment is the maximum number of individuals of a population which can be provided with all the necessary resources for their healthy living.
(i) Biotic potential :Maximum capacity of a population to reproduce under ideal conditions (environmental).
(ii) Control of population :It is by three factors :
(a) Geographic factors (b) Demographic factors (c) Socioeconomic factors.
(3)Community : An association of a number of different interrelated populations belonging to different species in a common environment, which can survive in nature, is known as biotic community (e.g. different species of organisms occurring in a pond constitute the pond community. The members of a community have different type of inter relationship.
B. Environment.
The environment is the aggregate of all those things and set of conditions which directly or indirectly influence not only the life of organisms but also the communities at a particular place. The environmental conditions which influence the life and development of plants are grouped into four main classes (ecological factors) which are as follows :
(1)Climatic factors : The study of climatic factor is known as climatology. The chief climatic factors are :
(i) Water : Rainfall is the chief source of soil moisture. Water exchange between earth surface and atmosphere is called hydrological cycle. Humidity of the air is expressed in terms of relative humidity. It is measured by hygrometer(Psychrometer). Epiphytes and cryoptogamic plants grow in those regions where relative humidity is high.
Annual rain fall determines the types of vegetation in any region such as :
(a) The area where rainfall is scanty are seen with deserts and xerophytic vegetation.
(b) The tropical area with heavy rainfall throughout the year consists of evergreen forests.
(c) The area with heavy rainfall during summer and low during winter consists of grasslands.
(d) The area with heavy rainfall during winter and low during summer consists of sclero-phyllous forests(The plants are shrubs stunted in height with leathery, thick evergreen leaves).
(ii) Light : The radiant energy of sunlight carries out all important functions, without this life except few bacteria would disappear. On this basis of relative light requirements and the effect of light on the overall vegetative development, plants are classified ecologically into following categories :
(a) Heliophytes : These plants grow best in full sunlight. In these plant internodes are short, leaves are small narrow, thick and with cuticle and hair.
(b) Sciophytes : These plants grow best in lower light intensity. In these plant internodes are long, leaves are large broad and thin, leaf surface is dull.
The plants grow in total darkness are called etiolated (Long thin, weak and yellow in colours).
(iii) Temperature : Temperature had a marked effect on the growth of plants. Due to high temperature plants suffer solarization and due to low temperature plants suffer freezing or frost injury.
On the basis of temperature the plants are classified as below :
(a) Megatherms or Climate or Tropical : The vegetation growing in the condition in which high temperature prevails throughout the year (30-40°). The dominant vegetation is tropical rain forest. They are in South America (on the side of Amazon river), Middle Africa (on the side of Congo River) and S.E. Asia.
The effect of altitude and latitude is similar upon plant vegetation. It is due to similar change of temperature is these two places.
The tropical rain forests are the most dense forests of the world.
(b) Mesotherms : Climate-subtropical, the high and low temperature alternates. The dominant vegetation is tropical decidous forest type. Those plants in which leaf fall takes place once in a year are called decidous plants e.g.Ficus religiosa(Sacred tree).
(c) Microtherms :The vegetation growing in the low temperature (10-20°C) condition. (The temperature remains low throughout the year). The vegetation is mixed coniferous forests type (Teiga).
(d) Hekistotherms : The vegetation growing in the very low temperature (0-10°C) conditions. The dominant vegation is Alpine vegetation (Tundra).
The plants growing at very low temperature are called cryophytesor psychrophytes.
(iv) Wind : High wind velocity causes soil erosion, breakage and up rooting of trees. Most of the pollutants are dispersed through the medium of air. Wind do harm is blossom trees because it prevents working of insects.
Wind modifies the humidity. Dry winds cause dwarfing of plants. Wind helps in pollination, dispersal of fruits and seeds and prevents frost damage. If the areas subjected to strong winds the leaves of plants become small and rolled and these plants develop an overall shape that offer resistance to wind.
Sometimes shrubs and trees are planted to protect the field against wind. Such structures are known as wind breaks or shelter belts. These plants (Trees) are planted at 90° to the wind velocity.
Absolute and relative humidity vary with changes in temperature. Absolute humidity is maximum near equator and gradually decreases towards the poles. This indicates that relative humidity is affected by temperature as well as latitude. Temperature, rainfall and humidity are three major factors which effect and control the climate.
(2)Topographic or Geographic factor : Topographic factors are concerned with the physical geography of the earth in an area. The chief topographic factors are as follows :
Micro climate refers to local combinations of factors such as wind, rate of evaporation, humidity, temperature which differ from regional climate.
(i) Altitude : Height of mountain chains. With the increase in altitude climate changed as decrease in temperature, increase in humidity, increase in precipitation and increase in wind velocity.
Earth’s vegetation can be divided into different zones based on altitude :
(a) Upto 1800 feet :Tropical rain forest.
❒ Tropical moist deciduous with 1000-1500 mmrainfall.
❒ Tropical moist evergreen with 2500 mmrainfall.
(b) 1800-4000 feet : Grassland or desert, savanna.
(c) 4000-7500 feet :Temperate deciduous forest. Oak is common.
(d) 7500-12000 feet :Coniferous forest (Temperate evergreen forests) e.g., Pinus, Abies, Picea.
12000 feet is regarded as tree or timber line. Above this height of plants decreases.
(e) 12500-14500 feet :Alpine vegetation (tundras) Rhododendron, Betulla. Cushion shaped dwarf shruby vegetation.
(f) 145000 upward :Snow line.
Generally the vegetation that develops on base of mountain to top is Tropical → Temperate → Taiga → Tundra. Species diversity generally increase as one proceeds from high altitude to low altitude and from high latitude to low latitude.
(ii) Steepness of the slopes : Steep slopes cause fast running of water which result in erosion and do not permit the accumulation of humus so the soil becomes denuded. In such soil plants can not grow properly and vegetation changes to xerophytic plants.
(iii) Exposure of slopes : Exposure of slope to sun and wind affects very much the kind of plants growing there. Generally the slopes exposed to sun and wind supports vegetation. That’s why green houses and hot beds are always built in a way to face sun or southern slopes which receive greater amount of solar energy.
(iv) Direction of mountains chain : Mountains steer or deflect winds into different dierctions. Outer Himalayas show frequent rains with luxurient vegetations while the middle and inner Himalayas are dry with poor vegetation. The southern slopes of Himalayas e.g.Kullu valley are directly exposed to sunlight and has luxurient mesophilous vegetation due to mansoon wind. Where as Northern slopes of Himalayas e.g.Lahul valley exposed to weak light and strong dry wind, thus they have xerophilous vegetation.
(3)Edaphic factor : The study of soil is called edaphologyor pedology. The soil can be defined as “the upper crust of earth surface in which plants roots are anchored.” The term soil is derived from the Greek work solum.
(i) Soil formation : It is derived from rocks by weathering which is of three types :
(a) Chemical weathering : It is caused by oxidation, hydrolysis or carbonation.
(b) Mechanical weathering : It is caused by living organisms, e.g.lichens, grazing animals or earthworm.
Weathering results into conversion of rocks to small fragments. Humus accumulated and now this can be called as soil. The development of soil is called pedogenesis. Soil is of two types :
❒ Residual soil : If the soil remain at the same place where it is formed.
❒ Transported soil : This soil brought from their place of origin to other place by some agents. It may be :
Alluvial soil : Carried by running water (rivers).
Colluvial soil : Carried by gravity.
Eolian soil : Carried by wind.
Glacial soil : Carried by glacier.
The soils of planes of India is mainly alluvial. In India the principal residual soil types are :
❒ Reddish soil of Vindhyas and South.
❒ Black soils of South West India.
❒ Calcareous soil :With 20% CaCO3.
❒ Laterite soil :Oxides of iron and aluminium.
❒ Peat soil :With high percentage of humus 90%.
❒ Black soil : Predominantly with clay and humus (very fertile because most of minerals are present in it).
(ii) Soil profile :A fully formed soil shows different layers called horizons. The sequence and nature of these layers is called soil profile (Cross section of soil) which consist of following horizons.
(a) Horizon ‘O’ : It is uppermost horizon made of organic matter. It has both fresh or nondecomposed as well as partially decomposed matter. It consist of following two sub-layers :
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❒ O1 region (Aoo) : It is uppermost layer which consists of freshy added organic matter such as dead leaves, branches, flowers and fruits.
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❒ O2 region (Ao) : It is present below O1region. It consists of organic matter which is in different stages of decomposition.
(b) Horizon ‘A’ : It is rich in mineral elements. A large amount of completely decomposed organic matter is present in this region. It shows downward loss of soluble salts clay, aluminium and iron. So this region is called zone of leaching or zone of eluviation.
(c) Horizon ‘B’ : It is dark in colour due to accumulation of leached substances like clay, iron and aluminium from horizon. So it is called as zone of accumulation or zone of illuviation.
Horizon ‘O’, A and B are together called as top soil.
(d) Horizon ‘C’ : It consists of partially weathered parental rock material. It is called as sub soil.
(e) Horizon ‘R’ : It is the lowermost layer of soil which consist of bed rocks (unweathered).
(iii) Composition of soil : The garden soil is made up of :
(a) Mineral matter (40%) :They are derived from rocks (by disintegration). The soil, derived from lime stone, is called chalky soil.
❒ Size of mineral particles :Depending upon their size, the mineral particles are of following types :
❒ Coarse gravel : More than 5.0 mm.
❒ Fine gravel : 5.0 to 2.0 mm.
❒ Coarse sand : 2.0 to 0.02 mm.
❒ Slit : 0.02 to .002 mm.
❒ Clay : Less than 0.002 mm.
Sandy soils have more coarser particles and lower water holding capacity and better aeration. Sand is most porous. Clayey soils have fine particles which have high water holding capacity and very poor aeration. Clay is least porous (water logged). Loam (50% sand + 25% clay + 25% slit) are best for plant growth.
The best apparatus used to analyse the soil is sieving.
(b) Organic matter : Humus is total organic matter in the soils. It is rich in N P K. The humus is formed from decay and decomposition of dead plant and animal matter. It is in colloidal state and increase water holding capacity of the soil. The formation of humus is called humificationwhich is caused by microbial activity. The humus soil is the best soil as it has got high water holding capacity, high porocity, aeration and high organic matter content. The complete decomposition of humus forms minerals. The formation of minerals is called mineralization. So, humus is the secondary source of minerals in the soil.
The three distinct layers of humus in soil of forests are :
❒ Litter :All dead fresh organic matter fallen (undecomposed) recently to the ground is called litter.
❒ Duff :The layer, where decomposition is just started, is called as duff as duff layer. Partially decomposed litter is called duff.
❒ Leaf mold or Real humus : When the litter is modified into dark, finely divided, amorphous organic matter by the activities of micro-organisms living in soil is called humus. Humus is maximum in peat soil (90%).
(c) Soil solution : The soil solution is the primary source of inorganic nutrients for plants. Soil solution helps in exchange of ions. pH of fertile soil is 6 to 7. pHbelow 5 inhibits bacterial activity. The plants prefer to grow in acidic soil are called oxylophytes e.g.Drosera. The plants prefer to grow in alkaline soil are called halophytes.
The soil rich in nutrients is called eutrophicand soil with less amount of minerals is called as oligotrophic.
(d) Soil air : 20-25% air or O2is necessary for proper growth of plants. The well aerated soil support the plant growth well because :
❒ Root respiration increases.
❒ The capillary potential of the soil increases.
❒ The accumulation of CO2could not take place.
❒ The root growth increases.
❒ Poor soil aeration supresses root hair development and may reduce the rates of absorption of water and minerals.
(e) Soil micro-organims : Soil has its own distinctive flora and fauna (bacteria, algae, fungi, protozoans, nematods, earth worms, molluscs, insects etc.) which make the biological system of the soil complex.
These organisms play following important roles in the soil :
❒ Nitrogen fixation
❒ Mycorrhizal association
❒ Soil borne diseases
❒ Decomposition of organic matter.
C. Biotic factor :
Biotic factor means the effect of living organism upon other living organism.
In natural conditions organisms live together and influence each others life i.e.show interactions. Interactions may be :
(i) Positive interactions
(a) Mutualism or Symbiosis : An association of two organism in which both partners are benefitted, (but can not live separately) e.g.lichens, mycorrhiza, symbiotic nitrogen fixers, pollination, Zoochlorellaand Zooxanthallae. Ruminant mammals have flagellates and bacteria for cellulose digestion which obtain food and shelter.
(b) Commensalism : It is the relationship between two living individuals of different species in which one is benefitted while the other is neither harmed nor benefitted except to negligible extent. e.g.epizoic algae, epiphytes and parasitic vascular plants. Jackals follow a lion or tiger while arotic fox follows a seal for obtaining food from pieces or bits left by the predators.
(c) Protoco-operation : It is interaction between two living organism of different species in which both are mutually benefitted but they can live without each other. e.g.tick bird ox pecker and Rhinoceros.
(ii) Negative interactions
(a) Deforestation : By deforestation the land is exposed to erosion and desertification. Deforestation in catchment areas causes floods in plains. Deforestation reduces the chances of rainfall.
(b) Competition : Competition can be defined as the rivalry between two or more organism for obtaining the same resources. Competition is greatest between the individual of the same species (intraspecific) which make similar demands upon the same supply at the same time in same area (niche).
❒ Gause’s hypothesis or Principle of competitive exclusion : Gause noted that out of two species of Parameciumgrown together, one is eliminated. It is called Gause’s hypothesis.
(c) Grazing : Constant grazing does not permit the plants to grow. Heavy grazing results in soil erosion (sheet erosion). Selective grazing and browsing a responsible for marked changes in vegetation. The only way grazing animals help vegetation is that they add their excrete to the soil.
(d) Fire : Most of the fires are of biological origin. Fires are mostly man caused. Sometimes fire develops due to mutual friction between tree surfaces in forests.
Fire destroy plant communities. A number of grasses are stimulated by a fire or in a burnt forest the grasses first and luxuriently.
(e) Exploitation : One species harm another species by making its direct or indirect use.
❒ Parasitism :The parasite grow on other living organism for food and support called host e.g.Cuscutta, Orobanche.
❒ Predation : It is an association between members of two species in which members of one species capture, kill and eat up members of other species. The former is called predator and later is called prey. A predator is a free living animal which catches and kills another species for food. Most of the predators are animals but sometimes some plants such as insectivorous plants and some fungi (predaceous fungi or animal traping fungi) e.g.Datylella, Arthrobotrys. They feed on small insects, protozoans and nematodes.
(f) Antibiosis or Amensalism : One organism inhibits the growth of other organisms through the secretion of antibiotics. It is common in micro-organism. This is based on biological antagonism. It is also called allelopathy. Smoother crops (e.g.Barley, rye, millets, alfalfa sun flower) are those which do not allow weeds to grow near by.
D. Ecological plants groups.
On the basis of requirements Warmingclassified plants into following categories :
(1)Hydrophytes :They live in abundance of water. They are of following types :
(a) Rooted submerged : Roots in the soil and submerged in water e.g.Hydrilla, Vallisnaria.
(b) Submerged floating : They are not rooted in the soil but completely submerged and floating e.g.Ceratophyllum, Utricularia.
(c) Rooted with floating leaves : They are rooted in the soil but the leaves are floating on the surface of water e.g.Nelumbo, Trapa, Victoria.
(d) Free floating : They float on the surface of water e.g.Wolfia(Smallest angiosperm), Lemna, Spirodella, Pistia, Azolla, Salvinia.
(e) Rooted emergent : Roots are in soil shoots or leaves are partly outside and partly inside the water. Plants show heterophilly(Amphibious plants) e.g. Typha, Ranunculus, Sagittaria, Cyperus.
E. Morpholigical adaptations
❒ Roots of hydrophytes are poorly developed or completely absent in Wolfia, Ceratophyllumetc. Root hair absent but root pockets may be present e.g.Pistia, Eichornia, Trapa.
❒ Stem is reduced in free floating plants e.g. Pistia,narrow and slender in submerged plants e.g. Hydrilla, Ceratophyllumand well developed in amphibious plants e.g.Typha.
❒ Petioles become long, swollen and spongy for floating.
❒ Leaves are usually long ribbon like e.g.Potamogeton, or finely divided e.g.Ranunculus or thin and broad e.g. Nelumbo, Victoria.
❒ In some hydrophytes leaves of different forms are produced by same plant. Aerial leaves are not dissected but submerged leaves dissected (Heterophilly) e.g.Ranunculuc, Limnophila.
Anatomical adaptations
❒ Cuticle absent or poorly developed.
❒ Stomata are absent in submerged plants. Floating hydrophytes have stomata on upper surface e.g. Lotus (epistomatic).
❒ Air spaces are extensively developed in root, stem and leaves. Well developed aerenchymahelps in buoyancy and gaseous exchange.
❒ Leaves have spongy tissues and palisade is poorly developed. As light difuses from all palisade and spongy tissue. Epidermal cells contain chloroplasts for maximum capturing of difused light.
❒ Mechanical tissues like sclerenchyma (lignified tissues) and collenchyma are poorly developed or absent.
❒ Vascular tissues are poorly developed.
Physiological adaptation
❒ Water and mineral nutrients are absorbed through general body surface.
❒ Osmotic concentration or osmotic potential of cells is equal to or is slightly higher than external water.
(2)Xerophytes :They are adapted to grow in dry habitats. On the basis of pattern of life cycle, xerophytes are of three types :
(i) Ephemerals : They complete their life cycle in a very short period, evade dry season by disappearing, leaving their seeds. They are referred as drought escapersor drought evaderes e.g. Cassia toria, Argemone maxicana, Solanum xanthocarpum.
(ii) Succulents (Fleshy xerophytes) :They absorb large quantities of water during rainy season and store water in different body parts. They are common in deserts and referred as drought avoiding xerophytese.g. Opuntia, Bryophyllum, Euphorbia, Mesembryanthemum (ice plant).
(iii) Non succulents : They are true xerophytes and called as drought resistant. They can with stand long drought periods e.g. Acacia, Calotropis, Casuarina, Nerium, Capparis, Prosopis.
Morphological adaptations
❒ Roots of xerophytes are extensively developed to increase water absorption. Roots are much more longer than the shoots. Root hairs and root caps are well developed. The roots reach to great depth.
❒ Stems of xerophytes is usually stunted (dwarf), woody, dry, hard and covered with thick bark. Stem is modified into flat leaf like phylloclades or cladodes e.g. Opuntia, Ruscus, Asparagus.
❒ Leaves of xerophytes are usually thick may be reduced to spines e.g.Opuntia, scales e.g.Casuarinaor may become needle like e.g.Pinus(Microphyllous) or may absent e.g.Capparis. Leaves and stem become fleshy (Malacophyllous) e.g. Bryophyllum.
Anatomical adaptations
❒ Stomata are sunken and generally on the lower surface of leaves.
❒ Epidermal cells thick walled and covered by hairs (Trichophyllous). e.g.Calotropis. Epidermis may be multilayered (Multiple epidermis) e.g. Ficus, Nerium.
❒ Palisade generally on both sides (surfaces) of leaves e.g. Nerium.
❒ In leaves spongy parenchyma are absent.
❒ Water storing parenchyma, conducting tissues and mechanical tissues are well develop.
❒ Bulliform or motor cells are found in between the cells of upper epidermis. These cells cause rolling and unrolling of leaves e.g. Poa, Amnophila(grasses).
❒ In Neriumleaf, upper as well as lower epidermis are multiseriate or multiple and are covered with thick cuticle. Mesophyll is different into palisade and spongy parenchyma palisade tissue occurs near both the epidermis while spongy parenchyma is located in between the palisade.
❒ In Ficusleaf, upper epidermis is multiseriate and is thickly cuticularised. Cystoliths are present is the cells of inner layers of this epidermis.
Physiological adaptations
❒ Osmotic concentration or osmotic potential of cell sap is high.
❒ They have resistance to dessication and mucilage to hold water.
❒ They show less transpiration.
(3)Halophytes :They are special types of xerophytic plants which grow on saline soils with high concentrations of salts like NaCl, MgCl2, MgSO4(Physiologically dry soil). Most of these are succulents. They have negatively geotropic roots for gaseous exchange called Pneumatophores. Halophytes show Vivipary(germination of seeds inside the fruits).
Halophytic communities growing on swamps are called helophilous halophytes which are of two types :
❒ Salt swamp and salt desert.
❒ Littoral swamp forests which are most extensive in all tropical areas.
❒ Swamp forest forms a characteristic vegetation called mangrovese.g. Rhizophora, Sonneratia, Avecenia, Heritiera, Salsola.
In India mangroves are quite common in sea shores of Bombay and Kerala, an in Andamans and Nicobar Islands.
(4)Epiphytes :They are special type of xerophytic plants which grow on other plants only for physical support or shelter. They do not suck the food material from the plant. They are common in Tropical rain forests.
They have aerial hanging hygroscopic roots which have special tissues Velamento absorb moisture from atmosphere. Seeds of epiphytes are very light. They are also known as aerophytes. e.g.Vanda, Dendrobiumus, Dischidiaor Orchids.
F. Succession.
Every community undergoes a series of changes until a group of organisms is established which can live and reproduce most successfully in the area. This is called biotic succession. The term succession was coined by Hult (1885). A biotic community normally undergoes continuous changes. Generally, definite and orderly sequences of communities gradually appear in an area over a period of time. A specific sequence of development of a community is related to particular set of physical and chemical conditions. This is known as sere. The last succession in a sere is called climax or a climatic climax.
Types : Succession is of two types :
(1)Primary succession : It includes changes which occur when living things become established on a previously uninhabited area such as a newly exposed sea floor, lake sediments or sand dunes.
(2)Secondary succession : It occurs where early communities have been damaged, leaving a few organisms and considerable organic matter. These remnant species, along with some new ones, regenerate a new community. Ecological succession on dry habitat, bare rock, sandy soils and aquatic habitats are called xerosere, lithosere, psammosere and hydrosere, respectively. The first plants to appear in an area are called pioneer plants. In hydrosere (or hydrach), pioneers are phytoplanktons; in lithosere, the pioneers are crustose (Saxicolous) lichens and mosses.
(3)Life forms : Raunkiaer(1934) has distinguished plants into five forms on the basis of size, shape, branching, crown, life span and perennation.
(i) Therophytes : Annual plants which perennate in the form of seeds.
(ii) Cryptophytes : Buds are occurs very deep in the soil e.g.Bulbs, rhizomes, corm, tubers etc.
(iii) Hemicryptophytes : Perennating structures occur at ground level. Aerial shoots die in the onset of winter, e.g. rosette plants.
(iv) Chemaephytes : Small plants of cold areas where perennating buds or shoot apices lie at or above the ground level.
(v) Phanerophytes : Perennial herbs, shrubs and trees, epiphytes, succulents, lianas, etc., where perennating buds occurs at 10 cm or more height above ground level.
G .Ecosystem.
The word ecosystem was coined by A.G. Tansley in 1935.This term is derived from two words, namely eco and system. Eco refers to environment and system refers to a complex coordinated unit. An ecosystem is a basic functional ecological unit. It consists of living organisms (biotic factors) and non–living substances (abiotic factors). It is an interacting system where the biotic and abiotic factors interact to produce an exchange of materials between the living and non–living factors. An ecosystem is a sum total of living organisms, the environment and the process of interaction between and within all parts of the system (Mathavan, 1974). According to Odum an ecosystem is the basic fundamental unit of ecology which includes both the organisms and the non–living environment each influencing the properties of the other and each is necessary for the maintenance of life. Pond is a suitable example for ecosystem. Lake is another ecosystem. Other examples of ecosystem are river, estuary, ocean, forest, grassland, town etc.
(1)Structure : The structure of any ecosystem is formed of two components, namely :
(i) Abiotic factors (ii) Biotic factors
(i) Abiotic factors : The abiotic factors of an ecosystem include the non–living substances of the environment. eg. Water, soil, air, light, temperature, minerals, climate, pressure etc. The biotic factors of the ecosystem depend on the abiotic factors for their survival.
(ii) Biotic factors : The biotic factor include the living organisms of the environment. e.g. Plants, animals, bacteria, viruses etc. The biotic factors of an ecosystem are classified into three main groups, namely :
(a) Producers (b) Consumers (c) Reducers or Decomposers.
(a) Producers : The organisms which carry out photosynthesis constitute the producers of an ecosystem. eg. Plants algae and bacteria. The producers depend on the abiotic factors of the ecosystem for producing energy. They are provided with chlorophyll. Chloropyll is used in the synthesis of energy rich compounds with the utilization of abiotic factors like light, CO2, water and minerals. A portion of the energy synthesized, is used by the producers for their growth and survival and the remaining energy is stored for future use.
(b) Consumers : Consumers are organisms which eat or devour other organisms. The consumers are further divided into three or more types. They are primary consumers, secondary consumers and tertiary consumers.
❒ Primary consumers : They eat the products like plants, algae and bacteria. The primary consumers are also called herbivores. Elton referred the herbivores as key industry animals. Rabbit, deer, etc., are primary consumers in a terrestrial ecosystem.
❒ Secondary consumers : They kill and eat the herbivores. They are also called carnivores. As these carnivores directly depend on herbivores, they are specifically called primary carnivores. Fox, wolf, etc. are the secondary consumers in a terrestrial ecosystem.
❒ Tertiary consumers : They kill and eat the secondary consumers. They are also called secondary carnivores. e.g., Lion, tiger, etc.
(c) Reducers or Decomposers : The decomposers are heterotrophs organisms that break up the dead bodies of plants and their waste products. They include fungi and certain bacteria. They secrete enzymes. The enzymes digest the dead organisms and the debris into smaller bits or molecules. These molecules are absorbed by the reducers. After taking energy, the reducers release molecules to the environment as chemical to be used again by the producers.
(2)Typical ecosystem (Pond ecosystem) : A pond is a suitable example for ecosystem. It is a lentic fresh–water ecosystem. It contains shallow standing water. The pond ecosystem is formed of abiotic factors and biotic factors.
(i) Abiotic factors : The abiotic factors of the pond ecosystem are water, CO2, O2inorganic compounds, organic compounds, light, temperature, pressure, pHetc.
(ii) Biotic factors : The biotic factors of the pond ecosystem are producers, consumers and reducers.
(a) Producers : The producers synthesize the energy from abiotic substances. The producers of a pond include phytoplankton like diatoms, blue green algae (Oscillatoria), green algae, green flagellates (Volvox, Euglena, Chlamydomonas), rooted plants, submerged plants and floating plants.
(b) Consumers : Consumers eat other organisms. The organisms which depend on producers are called primary consumers or herbivores. e.g., Zooplankton (Cyclops, Daphnia, larvae of Chironomus etc), Dysticus (insect), Lymnaea(snail) etc. The primary consumers are eaten by the secondary consumers of carnivores. These carnivores are called primary carnivores because they are the first carnivores in the food chain. e.g., Small fishes, frogs etc. The secondary consumers are eaten by the tertiary consumers or secondary carnivores. e.g., large fish.
(c) Reducers or Decomposers : The decomposers are organisms that break up the dead bodies of organisms and their waste products. They include microbes like bacteria. They secrete enzymes. The enzymes digest the dead organisms and the debris into smaller bits or molecules. These molecules are absorbed by the reducers. After taking energy, the reducers release molecules to the environment as chemical to be used again by the producers.
(3)Types of ecosystem : The ecosystem may be large, as large as the world or small, as small as a cow dung ecosystem. The biosphere of (The total life content of the world) is the major ecosystem. It comprises all other ecosystems.
(i) Mega ecosystem : The biosphere is formed of four mega ecosystems. They are as follows :
(a) Marine ecosystem:It is the largest ecosystem of earth. Fresh water ecosystem are two types :
❒ Lotic :Runing water ecosystem as river.
❒ Lentic :Still water ecosystem such as pond or lake. It includes saline-water ecosystems like oceans, seas, estuaries, brackish waters, etc.
(b) Limnic ecosystem : It includes all fresh water ecosystems like ponds, pools, lakes, rivers, streams, etc.
(c) Terresrial ecosystem : It includes the ecosystems of air, forests, grasslands, deserts, etc.
(d) Industrial or Artificial ecosystems : These are man made ecosystems. e.g., Crop land, city, town, etc.
(e) Macro ecosystems : The four mega ecosystem is further divided into sub units called macro ecosystems. e.g., Forests. The terrestrial macro ecosystem is formed of many forest ecosystems.
(f) Meso ecosystem:The macro ecosystem is further divided into meso ecosystem. For example, the forest ecosystem if formed of many meso ecosystems like deciduous forest, coniferous forests, etc.
(g) Micro ecosystem : The meso ecosystem is further divided into micro ecosystems, e.g., A low land in a forest, a mountain in a forest, etc. All ecosystems in the world are further divided into natural and artificial ecosystems.
(h) Natural ecosystems : These are self–regulating systems without much direct human interference and manipulations. e.g., Ponds, lakes, rivers, seas, oceans, grasslands, deserts, etc.
(4)Dynamics of ecosystem : The various components of the ecosystem constitute an interacting system. They are connected by energy, nutrients and minerals. The nutrients and minerals circulate and recirculate between the abiotic and biotic factors of the ecosystem several times. The flow of energy, on the other hand, is one way, once used by the ecosystem, it is lost. The continuous survival of the ecosystem depends on the flow of energy and the circulation of nutrients and minerals in the ecosystem. Thus the dynamics (functions) of the ecosystem includes the following :
(i) Energy (ii) Primary production (iii) Secondary production (iv) Food chain
(v) Food web (vi) Trophic levels (vii) Energy flow (viii) Ecological pyramids.
(i) Energy :Energy is the ability of do work. The flow of energy is unidirectional in the ecosystem. The main source of energy for an ecosystem is the radiant energy or light energy derived from the sun. The amount of solar radiation reaching the surface of the earth is 2 Cals/sq.cm/min. It is more or less constant and is called solar constant or solar flux. About 95 to 99% of the energy is lost by reflection. Plants utilize only 0.02% of the energy reaching earth. The light energy is converted into chemical energy in the form of sugar by photosynthesis.
6H2O+ 6CO2+ Light → 6C6H12O6+ 6O2
The sugar synthesized is utilized for many purposes :
❒ It can be converted into starch and stored.
❒ It combines with other sugars to form cellulose.
❒ It combines with inorganic substances (N2, P, S) to form amino acids, protein, nucleic acids, pigments, hormones.
❒ Some amount of sugar is oxidised during respiration and the energy is released to do various functions.
C6H12O6+ 6O2→ 6CO2+ 6H2O+ Energy.
(ii) Primary production : Plants convert light energy into chemical energy in the form of sugar by photosynthesis. The total amount of sugar and other organic materials produced in plants per unit area per unit time is called gross primary production. During photosynthesis respiration is also going on side by side. During respiration some amount of sugar is oxidised. Hence it is not easy to measure gross primary production. The total organic material actually present (biomass) in plants is called net primary production.
Net primary production = Gross primary production – Respiration. i.e.
Pn= Pg– R
Where, Pg= Gross primary production
∴ Pg = Pn+ R Pn= Net primary production
R = Respiration
Thus the amount of organic material produced during a given period of time per unit area is called primary production. The productivity is generally expressed in terms of grams or kilocalories per square meter per day or per year. If Pg equals R no storage of energy occurs. When Pgis less than R, productivity decreases. When Pgis greater then R, productivity increases.
Measurement of primary production :Primary production refers to the amount and the rate of energy produced by autotrophs. There are many methods to measure the primary production.
