Organisms and Environment

Reiter first 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.Misra is known as �ther of ecology in India”. Other famous Indian ecologists include G.S.Puri, S.C.Pandeya. Dudgeon (1921) started ecological studies in India. Study of ecology is important to strike a balance between development and maintenance of natural environment and its biotic communities, use and conservation of resources, solve local regional and global environment problems.

Branches of ecology

(1) Autecology/Species ecology : The study of reciprocal relationships between every stage of development of a population/species and its environment is called autecology.

(2) Synecology : It is the study of reciprocal relationships between composition, organisation and development of communities and their environment.

(3) Applied ecology : It is the study of specialised fields of ecology which are concerned with conservation and economic exploitation of organisms, e.g., agronomy, agriculture, animal husbandry, forestry, wildlife management, conservation ecology and pollution ecology.

(4) Paleoecology : Study of relationship between organisms and environment in the past.

(5) Systems ecology : Branch of ecology dealing with interpretation of ecological concepts and processes in terms of mathematical models and formulae.

(6) Genecology : Study of genetic composition and changes in relation to the origin of ecads, ecotypes, new species, etc. 

Levels of ecological organisation : Organisation is the arrangement and coordination of small components into larger components in a hierarchy where each level is formed of components of lower level and itself becomes constituent of still higher level. The hierarchy in the levels of organisation connected with ecological grouping of organisms is called ecological hierarchy or ecological levels of organisation.

(1) Organism : An individual organism is a distinct living entity made up of one or more cells which carries out all the life processes in its body which are quite separate from life processes being performed in the body of others.

(i) Basic unit : Organism is the basic unit of ecological hierarchy.

(ii) Size : It may be microscopic (e.g., Amoeba, Chlorella, bacterium) or macroscopic (e.g., Rose, Mango, Crocodile, Dog, Human being).

(iii) Cellularity : An organism can be unicellular (e.g., Amoeba, Euglena, Chlamydomonas), colonial (e.g., Volvox) or multicellular (e.g., Fish, Lizard, Mango tree).

(iv) Subunits : An organism has a number of subunits in the form of organ systems, organ system with organs, organs with tissues, etc. The subunits coordinate to produce a functional whole. They themselves cannot survive independently.

(v) Life processes : It performs all the life processes independent of life processes being performed in the body of others.

(vi) Self regulation : Each organism is capable of growth, self repair, movement and self regulation of its activities.

(vii) Distinct identity : Organisms possess a distinct identity so that they can be easily identified, counted and measured e.g., Mango tree, Acacia, Sunflower, Mustard, Rat, Deer, Cow.

(viii) Interdependence : Organisms do not live in isolation. They show interactions with other organisms of the same species as well as organisms of other species.

(ix) Environment : Organisms obtain matter and energy from their environment and pass out wastes into it. They are also perfectly adapted to their environment. Environment is also changed to suit the organisms.

(x) Life span : An organism has a definite life span which involves definite series of stages like birth/hatching, growth, maturity, ageing and death.

(xi) Reproduction : New individuals develop from the pre-existing ones through the process of reproduction. Reproduction can be vegetative, asexual and sexual.

(xii) Resemblance : Organisms resemble their parents because they receive the genes for various traits from them.

(xiii) Continuity of race : Individuals die but the race continues due to regular formation of new individuals through reproduction.

(2) Population : It is a grouping of similar individuals in a particular geographical area or space. The different populations of the same organism present in particular geographical areas are called local populations/demes. A local population adapted genetically to its particular environment is called ecotype. There may be several ecotypes of the same organism which show variation amongst them. Various characteristics of a population are : population density, natality (birth) rate, mortality (death) rate, age distribution, biotic potential, dispersion and growth form.

Population density (D) = $\frac{\text{No}\text{.of individuals (N)}}{\text{Space (S)}}$

N= Total no. of individuals, S= No. of units of space m²/m³.

Factors affecting population

(i) Natality : Birth rate.

(ii) Mortality : Death rate.

(iii) Population growth : Shows two types of curve :

(a) S. shaped curve.

(b) J. shaped curve.

(iv) Emigration : Permanent outward movement. Decreases population.

(v) Immigration : Permanent inward movement. Increases population.

(vi) Migration : Two way movement of entire population. Does not change the size of population.

(vii) 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.

(viii) Carrying capacity : 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.

(ix) Biotic potential : Maximum capacity of a population to reproduce under ideal conditions (environmental).

Control of population : It is by three factors :

(i) Geographic factors

(ii) Demographic factors

(iii) Socioeconomic factors.

(3) Species : It is grouping of individuals of one or more populations which resemble one another in all important morphological, anatomical, biochemical and genetic characters besides ability to interbreed freely. The sum of all the populations of same kind of organisms all over the world is called species. It is basic unit of classification and the population is subordinate to species. Only the species has a real existence, other units of classification (e.g., Genus, Family, Order, Class, Phylum and Kingdom) are man made artificial groups.

Exceptions to species concept

(i) Difference in the morphology of developmental stages of an individual.

(ii) Sexual dimorphism : Occurrence of two forms among the organisms of the same species is known as dimorphism. Plants such as the date palm 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.

(iii) 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).

Speciation or Origin of species : May be

(i) Due to physical barrier (Allopatric)

(ii) Due to reproductive barrier (Sympatric)

(iii) Mutation

(iv) Polyploidy

(v) Genetic (Wright effect)

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.

Niche/Ecological Niche (Grinnel, 1917)

It is specific part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator and timing of activity.

A habitat has several ecological niches and supports a number of species. An ecological niche is used by a single species. Two or more species cannot use the same niche despite having a mutualistic association.

Where two different species happen to occupy the same niche, one is excluded, e.g., Paramecium aurelia eliminates Paramecium caudatum while Tribolium confusum exterminates T. castaneaum. This is known as Gause&aposs Principle or Principle of competitive exclusion.

(4) Biotic community : The assemblage of interdependent and interacting populations of different species present in an area. It has three components –

(i) Plant community or community of producer.

(ii) Animal community or community of consumers.

(iii) Microbial community or community of decomposers. Animal community may show diurnal and seasonal changes. Annual plants also show changes with change of season.

(5) Ecosystem : The sum of the biotic (living) and abiotic (non-living) components of a particular geographical area, collectively called ecosystem.

(6) Biome : It is a large ecosystem or a group of small ecosystems which is delimited by a specific climate or geographical area. A biome may also possess a patch of different ecosystem, e.g., lake in a forest.

(7) Biosphere : Biosphere, also called ecosphere or giant ecosystem is the largest and nearly self-sufficient biological system. It is formed of all the ecosystems of the world. It is also called "life-supporting zone" of the earth.

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. Any external force or influence, which surrounds and affects the life of a plant in any way, becomes a factor of its environment. These factors are called environmental factors and may be living (biotic) as well as non-living (abiotic). The abiotic factors affect the structure, life history, physiology and behaviour of organisms. The biotic factors mostly influence growth and reproduction. The environmental conditions which influence the life and development of plants, each part of the environment is called ecological factors. Ecological factors are grouped into four main classes (ecological factors) which are as follows :

Climatic factors : The study of climatic factor is known as climatology. The chief climatic factors are :

(1) 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.

(2) Light : Light (solar radiations) is a very important ecological factor as it is the source of energy to the whole biosphere. It enters the biosphere through the process of photosynthesis performed by green plants and other autotrophs. Here organic food is manufactured from inorganic raw materials. Solar energy is changed into chemical energy of food. 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 :

(i) Heliophytes are popularly called sun plants because they grow in open in full sunlight. They possess a number of characteristics like.

(ii) Sciophytes are shade plants which grow in areas having moderate to low intensity light, as below the shade of other plants. Optimum growth occurs with light of 10-30% of full sunlight.

The plants grow in total darkness are called etiolated (Long, thin, weak and yellow in colours).

(3) Temperature : Temperature influences every reaction and activity of organisms. Temperature shows daily as well as annual variations. The phenomenon of change of temperature between day and night and in different seasons of the year is called thermoperiodicity. It is of two types, diurnal (or daily) and seasonal (or annual). Thermoperiodicity determines periodical phenomena like seed germination, stem growth, flower formation, fruiting, dispersal, maturation of gonads, breeding, egg laying, etc. Low night temperature is suitable for seed germination in many plants, e.g., Rumex, Asclepias. Cooler nights also help in increasing size of tuber in Potato and fruit setting in Tomato. Organisms adapted to live at relatively constant temperature during the whole year are known as stenothermal, e.g., many palms, corals, snakes and some fishes. The organisms which can tolerate large changes of temperature are called eurythermal, e.g., Artemesia, Cyclops, Toad, Wall Lizard.

On the basis of temperature the plants are classified as below :

(i) Megatherms or Climate or Tropical : The vegetation growing in the condition in which high temperature prevails throughout the year (30-40ଌ). The dominant vegetation is tropical rain forest.

(ii) 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).

(iii) 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 (Taiga).

(iv) Hekistotherms : The vegetation growing in the very low temperature (0-10°C) conditions. The dominant vegetation is Alpine vegetation (Tundra).

The plants growing at very low temperature are called cryophytes or psychrophytes.

(4) 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.

(5) Atmospheric humidity : Moisture in form of invisible vapours in atmosphere is called humidity.

Atmospheric humidity is generally expressed in terms of relative humidity (R.H.) which is defined as, "amount of vapours in atmosphere as the percentage of total amount which the air or atmosphere can hold at the existing temperature." Rate of transpiration is inversely related to relative humidity. Area having high humidity have dense vegetation due to lower rate of transpiration. The areas with low relative humidity are dry. They produce sparse vegetation due to high rate of transpiration.

R.H. is influenced by environmental conditions like solar radiation, temperature, wind, etc. If temperature is high, R.H. is low and if temperature is low, R.H. is high.

(6) Atmosphere

Gaseous cover over the earth surface is called atmosphere. Earth&aposs atmosphere is about upto height of 300 km, out of which 95% of gases is upto height of 20 km and rest 5% in next 280km.

Earth&aposs atmosphere is having a mixture of gases out of which important ones are :

Earth&aposs atmosphere is divided into four different zones from below to above :

(i) Troposphere : First 20 km of earth&aposs atmosphere is called troposphere in which different physical phenomena, i.e., lightening, thundering and cloud formation occur.

(ii) Stratosphere : About 30 km zone over troposphere is called stratosphere.

Temperature increases in this zone (upto 90ଌ) due to ozone formation. In this zone under the influence of ultra-violet rays, this ozone layer is formed, which prevents entry of harmful UV-rays to reach the earth surface.

(iii) Mesosphere : Next 40 km zone above stratosphere is called mesosphere. Last limit of mesosphere is called mesopause.

(iv) Ionosphere : Uppermost zone of atmosphere is ionosphere and in this zone all the gases are in ionized form.

(7) Fire

Fire may be man caused or natural. It is basically of three types :

(i) Surface fire (ii) Ground fire (iii) Crown fire

Such plants which grow well in fire burnt condition are called pyrophytes or fire loving plants.

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.

(1) Altitude : Height of mountain chains. 300 feet rise in altitude decreases temperature by 1ଏ. There is also increase in humidity and wind velocity. Slope winds are local wind movements which are uphill during the daytime and downhill at night. Shade caused by mountains reduces the total sunlight falling on an areas. Sunlight has more of ultraviolet rays. In high mountains situated in tropical areas, all the vegetation zones are found – tropical, subtropical, temperate and alpine. With the increase in altitude climate changed as decrease in temperature, increase in humidity, increase in precipitation and increase in wind velocity.

Generally the vegetation that develops on base of mountain to top is Tropical $\to$ Temperate $\to$ Taiga $\to$ Tundra. Species diversity generally increase as one proceeds from high altitude to low altitude and from high latitude to low latitude.

(2) 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.

(3) 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.

(4) Direction of mountains chain : Mountains steer or deflect winds into different directions. Outer Himalayas show frequent rains with luxuriant 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.

Edaphic factor : The study of soil is called edaphology or 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 word solum.

(1) Soil formation : It is derived from rocks by weathering which is of three types :

(i) Chemical weathering : It is caused by oxidation, hydrolysis or carbonation.

(ii) Mechanical weathering : It is caused by living organisms, e.g., lichens, grazing animals or earthworm.

(iii) Physical weathering : It is caused by water, wind, gravity, glaciers, etc.

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 :

(a) Residual soil : If the soil remain at the same place where it is formed.

(b) Transported soil : This soil brought from their place of origin to other place by some agents. It may be :

Alluvial soil            :     ꃊrried by running water (rivers).

Colluvial soil          :      Carried by gravity.

Eolian soil              :      Carried by wind.

Glacial soil             :     ꃊrried by glacier.

The soils of planes of India is mainly alluvial. In India the principal residual soil types are :

(a) Reddish soil of Vindhyas and South.

(b) Black soils of South West India.

(c) Calcareous soil : With 20% CaCO₃.

(d) Laterite soil : Oxides of iron and aluminium.

(e) Peat soil : With high percentage of humus 90%.

(f) Black soil : Predominantly with clay and humus (very fertile because most of minerals are present in it).

(2) 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.

(i) 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 :

(a) O₁ region (Aoo) : It is uppermost layer which consists of freshy added organic matter such as dead leaves, branches, flowers and fruits.

(b) O₂ region (Ao) : It is present below O₁ region. It consists of organic matter which is in different stages of decomposition.

(ii) Horizon 𠆊’ : It is rich in mineral elements. A large amount of completely decomposed organic matter is present in this region.

(iii) Horizon 𠆋’ : 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.

(iv) Horizon 𠆌’ : It consists of partially weathered parental rock material. It is called as sub soil.

(v) Horizon ‘R’ : It is the lowermost layer of soil which consist of bed rocks (unweathered).

(3) Composition of soil : The garden soil is made up of :

(i) Mineral matter (40%) : They are derived from rocks (by disintegration). The soil, derived from lime stone, is called chalky soil.

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.

(ii) 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 humification which is caused by microbial activity.

The three distinct layers of humus in soil of forests are :

(a) Litter : All dead fresh organic matter fallen (undecomposed) recently to the ground is called litter.

(b) Duff : The layer, where decomposition is just started, is called as duff as duff layer. Partially decomposed litter is called duff.

(c) 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%).

(iii) 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. pH below 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 eutrophic and soil with less amount of minerals is called as oligotrophic.

(iv) Soil air : 20-25% air or O₂ is necessary for proper growth of plants. The well aerated soil support the plant growth well because :

(a) Root respiration increases.

(b) The capillary potential of the soil increases.

(c) The accumulation of CO₂ could not take place.

(d) The root growth increases.

(e) Poor soil aeration supresses root hair development and may reduce the rates of absorption of water and minerals.

(v) Soil micro-organims : Soil contains a number of organisms. They are classified into four groups – microflora, macroflora, microfauna and macrofauna.

(a) Microflora : It consists of microscopic nonphagotrophic organisms.

(b) Macroflora : It consists of those fungi which form fructifications, e.g., mushrooms, tubers, truffles. The fungi are otherwise saprohytic in nature.

(c) Microfauna : It consists of microscopic phagotrophic microorganisms like protozoans (e.g., Amoeba, Arcella), rotifers, nematodes (e.g., Rhabditis).

(d) Macrofauna : They are animals residing in the soil. The common ones are insects (ants, beetles, mites, termites), spiders, millipedes, earthworms, snails and burrowing vertebrates.

Biotic factor : Living organisms living together influence each other&aposs life and these living organisms constitute biotic factors. In these biotic interactions both the organisms may be benefitted or one is benefitted or one is benefitted while another is harmed or both are harmed. These biotic interactions are of two main types :

(1) Positive interactions : Where both the organisms or one organism is benefitted. The main types of positive interactions are :

Mutualism or Symbiosis : Here both the organisms in association are mutually benefitted and further this association is obligatory, i.e., necessary for existence of both organisms. The term symbiosis or mutualism was given by DeBary.

Important examples of symbiosis are :

(i) Dispersal of fruits and seeds by living organisms.

(ii) Pollination by insects, animals, etc.

(iii) Symbiotic nitrogen fixation : In the root nodules of legumes and some non-legumes, Rhizobium bacteria (symbiotic) are present which obtain food and shelter from parent plant and in turn fix atmospheric nitrogen.

(iv) Mycorrhiza or Mycorrhizal association : Association between roots of higher plants and fungal hyphae is called mycorrhiza. It is of two types :

(a) Ectotrophic or Ectophytic mycorrhiza : In this association fungal hyphae are on surface of roots, e.g., in Pinus.

(b) Endotrophic or Endophytic mycorrhiza : Here fungal hyphae are inside the root tissue, e.g., in orchids.

(v) Lichens : These are composite plants in which algal partner and fungal partner are mutually associated.

(vi) Myrmecophilly : Association between ants and higher plants is called myrmecophilly, e.g., jamun, litchi, mango, etc., where ants live. The ants get their food from the plants and in turn act as body-guards.

(vii) Zoochlorellae : Unicellular green alga Chlorella vulgaris lives in gastrodermal cavity of Hydra. The alga gives food and oxygen to Hydra and Hydra in turn gives shelter and nitrogenous substances to alga.

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, e.g. :

(i) Epiphytes or Aerophytes : These are vascular plants which are not rooted in soil and grow upon other plants for support (but not food), e.g., some orchids like Vanda, Dendrobium, etc., members of family Bromeliaceae (bromeliads), Dischidia (here a pitcher like structure is present for accumulation of water), Asplenium (bird&aposs nest epiphyte), etc.

Three types of roots are present in epiphytes :

(a) Clinging roots for attachment.

(b) Absorptive roots for absorption of nutrients and minerals from organic matter accumulated in crevices of bark.

(c) Aerial roots possess a special tissue having thickenings called velamen, which help in absorption of moisture from atmosphere.

(ii) Lianas : These are vascular plants rooted in soil and get support of other plants or objects for their erectness.

Most common lianas in Indian tropical forests is Bauhinia vauhilii.

(iii) Rhizosphere, Rhizoplane, Phyllosphere and Phylloplane : Soil zone around the roots in which a large number of microbes are present due to secretion of sugars, etc., by roots is called rhizosphere. The root proper surface is called rhizoplane. Similarly air zone around leaves having good population of microbes due to secretion of volatile substance by leaves is called phyllosphere and leaf proper surface is called phylloplane.

Some workers consider these as example of mutualism.

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.

(2) Negative interactions : Here one or both organism in association are harmed. Important examples of these interactions are :

Parasitism : A parasite is an organism which lives in constant association with host and gets its food directly or indirectly without killing the host. This phenomenon is called parasitism. In plants four major types of parasites are present.

(i) Total stem parasite, e.g., Cuscuta.

(ii) Total root parasite, e.g., Rafflesia and Orobanche.

(iii) Partial stem parasite, e.g., Viscum and Loranthus.

(iv) Partial root parasites, e.g., Santalum and Thesium.

Predation : A predator is an organism which gets its food from the host after killing it. It does not live in constant association with host. This phenomenon is called predation.

Important examples of predation are :

(i) Grazing and Browsing

(ii) Carnivorous or Insectivorous plants : These plants grow in marshy conditions where there is lack of nitrogen, so in order to fulfil their nitrogen requirement, they catch small insects by some special adaptations in them.

(iii) Predaceous fungi : In soil there are present some fungi like Dactylella, Dactylaria, Arthobotrys and Zoophagus, etc., which are called predaceous fungi.

Competition : It is a type of cold war in which both the organisms in association are harmed. Competition is for basic necessities of life. Competition may be interspecific or intraspecific but intraspecific competition is more severe because organisms of same species have similar basic requirements.

Amensalism : This is a type of association in which one organism in association is harmed and second is not affected.

Amensalism is of two types :

(i) Antibiosis : Some micro-organisms secrete certain chemical substance which kill or inhibit other micro-organisms. These substances are called antibiotics and phenomenon is called antibiosis.

(ii) Allelopathy : Some higher plants also secrete certain poisonous substances which inhibit the growth of other plants. This phenomenon is called allelopathy, e.g., roots of carrot grass or congress grass (Parthenium argentatum), which is most troublesome terrestrial weed in India secrete trans-cinnamic acid which checks the growth of other plants.

Man as biotic factor : Man is always most important biotic factor. He changes the environment by his activities regularly, e.g., by excessive cutting of trees, fire, domestication of plants and animals, by causing different types of pollution, etc.

Biome

Definition : Each of the major terrestrial ecosystems or distinctive terrestrial areas with their group of climax plants and associated animals constitutes biomes. A biome is the largest terrestrial community. Rainfall, temperature range, nature of soil, barriers, latitude and altitude determine the nature and extent of biomes.

Major biomes of world : Biomes are often classified in seven categories :

(1) Tropical rain forests : The tropical rain forest, a biome occurs in regions of high temperature (average 25ଌ) and high rainfall (200-450 cm per year). These tropical rain forests occur in Central America, around Amazon basin in South America, in Africa and in South-East Asia.

(i) This biome is characterized by multistoried vegetation (upto five distinct layers or storeys of vegetation). Further maximum biodiversity on land is shown by this biome and it is estimated that one half to two-thirds of all species of terrestrial plants and insects live in tropical forests.

(ii) Lianas (vascular plants rooted in soil and they only get support of trees for climbing to top) and epiphytes (air plants) are common in this biome due to excess of moisture. Further giant trees of the tropical forest support a rich and diverse community of animals on their branches.

(iii) No one species dominates in this biome.

(iv) The productivity of this biome is maximum.

(v) The trees of this biome possess buttressed trunks and phenomenon of cauliflory (presence of flowers and fruits on main trunk and main branches) is common in this biome.

(2) Savannahs : Like tropical forests, savannahs are found near the equator but in areas having less annual rainfall (90-150 cm/year). Some areas near the equator experience prolonged dry seasons. The heat, periodic dryness and poor soils cannot support a forest but have led to evolution of tropical open grasslands with scattered shrubs and trees.

(i) The vegetation of this biome support large grazing herbivores like buffalo, zebra, etc., which are food for carnivores like lions, tigers, etc. The savannah also supports a large number of plant eating invertebrates like mites, grasshoppers, ants, beetles and termites.

(ii) The termites are one of the most important soil organisms in savannahs.

(iii) Indian tropical grasslands are not true savannahs but these are the result of destruction and modification of tropical deciduous forests by cutting, grazing and fire.

(3) Deserts : These are the biomes that have 25 cm (10 inches) or less of precipitation annually.

(i) Sahara of North Africa, Thar of West Asia and Gobi of Asia are most important deserts.

(ii) Annual plants are abundant in deserts and tide over unfavourable dry season in the form of seeds. Succulent plants are characteristics of deserts. Trees and shrubs present in deserts have deep roots.

(iii) Desert animals have also fascinating adaptations that enable them to adjust with limited water supply.

(iv) Desert plants show phenomenon of Allelopathy, i.e., they secret some chemical substances which inhibit the growth of plants growing in their near vicinity.

(v) Deserts show poor biodiversity and their productivity is minimum.

(4) Temperate grasslands : Temperate grasslands experience a greater amount of rainfall than deserts but a lesser amount than savannahs. They occur at higher latitudes than savannahs but like savannahs are characterized by perennial grasses and herbs of grazing mammals.

Temperate grasslands have different names in different parts of the world, e.g., Prairies of North America, Steppes of Russia, Veldts of South Africa, Pampas of South America, Pusztas of Hungary and Tussocks of New Zealand.

(5) Temperate deciduous forests : Temperate deciduous forests occur in areas having warm summers, cold winters and moderate amount of precipitation (75 – 150 cm annually). The trees of this forest loose their leaves during autumn and remain dormant throughout winter (term �iduous’ derived from Latin word meaning ‘to fall’). These forests are present in Eastern United States, Canada and extensive region in Eurasia.

(i) In temperate forest biome, there is an upper canopy of dominant trees like beech, oak, birch, maple, etc. followed by lower tree canopy and then a layer of shrubs beneath.

(ii) Animal life in this biome is abundant on the ground as well as on the trees.

(6) Taiga : The taiga or northern coniferous forests or boreal forests consist of evergreen, cone bearing trees like spruce, hemlock and fir and extend across vast areas of Eurasia, and North America.

(i) The taiga is characterized by long, cold winters with little precipitation.

(ii) The harsh climate limits productivity of the taiga community. The cold temperatures, very wet soil during the growing season and acids produced by fallen conifers needles and Sphagnum inhibit full decay of organic matter, due to which thick layers of semidecayed organic material called peat is formed, which acts as energy source.

(7) Tundra : The tundra encircles the top of the world. This biome is characterised by desert like levels of precipitation (less than 25 cm annually), extremely long and cold winters and short warmer summers.

(i) Tundra is uniform in appearance and is dominated by scattered patches of grasses, sedges and lichens. Some small trees do grow but are confined to margins of streams and lakes (In general treeless).

(ii) Tundra is a biome of low diversity and low productivity.

(iii) The precipitation that falls remains unavailable to plants for most of the year because it freezes. During the brief arctic summer, some of the ice melts and permafrost (or permanent ice) found about a meter down from the surface, never melts and is impenetrable to both water and roots. However, the alpine tundra found at high elevation in temperate or tropical regions does not have this layer of permafrost.

Indian biomes : Indian forests are classified into three major types based on temperature are tropical, temperate, alpine.

(1) The marine environment : It is characterized by its high concentration of salt (about 3.5 percent in open sea) and mineral ions (mostly sodium and chloride followed by sulphur, magnesium and calcium).

(i) The vertical zones of the ocean are determined on the basis of availability of light for photosynthesis. The lighted upper 200 metres form the photic or euphotic zone. The next zone upto the depth 200� metres gets less light which is insufficient for photosynthesis form the aphotic zone. Below 2000 metre is the area of perpetual darkness, the abyssal zone.

(ii) Three major environments may be recognized in the ocean basin

(a)  The littoral zone : The sea floor from the shore to the edge or the continental shelf.

(b) The benthonic zone : The sea floor along the continental slope and the aphotic and abyssal zone.

 (c) The pelagic zone : Constituting the water of the ocean basin.

$\bullet$ Marine life : It can be grouped into three main categories :

(i)   Plankton : These are passively drifting or floating organisms. Most of these minute organisms, plankton includes photosynthesizing organisms like diatoms (phytoplankton) as well as heterotrophic organisms like small crustaceans (zooplanktons).

(ii)  Nektons : These consist of actively moving organisms with well developed locomotory organs.

(iii) Benthonic organisms : These are found along the floor of the sea bed and include creeping, crawling or sessile organisms.

(2) Other (Lakes and Ponds) : Lakes and ponds are stagnant fresh water bodies and are found practically in every biome. Many lakes are direct or indirect result of glaciation. Others are natural or man made depression filled with water. The relatively shallow lakes, called eutrophic lakes, have a rich accumulation of organic products e.g., Dal lake of Kashmir.

Generally deep lakes, often with the steep and rocky sides, are poor in circulating nutrients like phosphates. These are called oligotrophic lakes. Some of the lakes contain a saline or brackish water (Sambhar lake of Rajasthan).

Biosphere

All the thousands of ecosystems together constitute the biosphere, which exists as a thin envelope around the earth’s surface. The global environment consists of three main sub division :

(1) Hydrosphere : All the water (liquid) component of the oceans, seas, rivers and other island water bodies.

(2) Lithosphere : The solid components of the earth crust, rocks, soil and minerals.

(3) Atmosphere : The gaseous cover which envelops the hydrosphere and the lithosphere and the atmosphere. The entire inhabited part of the earth and its atmosphere (including the living and the non-living components) forms the biosphere.

As a result of manipulation by man, the biosphere has become transformed into a human dominated environment of noosphere $(noo=$mind).

Role of atmosphere in metabolism : Of much greater significance to metabolism, however, are the biogeochemical cycles of the atmosphere. The air consists mainly of oxygen (20.95 per cent), carbon dioxides (about 0.03 per cent), nitrogen (78.08 per cent), water vapour and minute traces of inert gases. Except the inert gases, all these components of air serve as metabolites each circulates through a cycle in which the organisms play an important role. As all gases are dissolved in natural waters, the hydrosphere maintains an equilibrium with the atmosphere.

Biogeochemical cycle

Organisms are built up on chemical substances. They require certain chemicals like N₂, O₂, H₂, P, C, etc. continuously for their survival. These chemicals enter the organisms from the environment and come out after undergoing changes or without changes. Thus these elements tend to circulate in a characteristic path from the environment to the organism and back to the environment. This cyclical path of the elements from the abiotic system to the biotic system and back is called biogeochemical cycles (Bio = living organism Geo = water, air, earth). As these chemicals form the components of food, these cycles are also called nutrient cycles.

Phases of biogeochemical cycles : Each biogeochemical cycle has two phases, namely the biotic phase (organic phase) and the abiotic phase.

(1) Biotic phase : It refers to the flow of chemicals in the living organisms through food chain.

(2) Abiotic phase : It refers to the distribution and flow of chemicals in the non-living environment.

Types of biogeochemical cycles : The biogeochemical cycles are classified into two types, namely gaseous cycles and sedimentary cycles.

(1) Gaseous cycles : In gaseous cycles the main reservoirs of chemicals are the atmosphere and ocean. e.g., Carbon cycle, N₂ cycle, O₂ cycle, etc.

(2) Sedimentary cycle : In sedimentary cycles the main reservoirs are soil and rocks. e.g., Sulphur cycle, phosphorus cycle, etc.

Important biogeochemical cycles

(1) Carbon Cycle : The cycling of carbon between biotic and abiotic systems is called carbon cycle. It is a gaseous cycle. The main source of carbon is the carbon dioxide (CO₂). CO₂ is present in the air and water. Air is the main reservoir. CO₂ content of air is 0.03%. Its amount remains constant.

(i) Flow of Carbon into the biotic system : Carbon flows into the biotic system in two ways :

(a)  Photosynthesis : Carbon enters the biotic system through photosynthesis. In photosynthesis green plants utilize CO₂ and incorporate the carbon of CO₂ in glucose. Glucose is used for the synthesis of other types of carbohydrates, proteins and lipids. These compounds, containing carbon, are stored up in the plant tissues. When plants are eaten up by herbivores, the carbon flows into the body of herbivorous animals through food chain. When herbivores are eaten by carnivores, the carbon enters the body of carnivorus animals.

6CO₂ + 6H₂O $\to$ C₆H₁₂O₆ + 6O₂.

(b) Formation of shell : The CO₂ dissolved in sea water is utillized by the marine animals like protozoans, corals, molluscs, algae, etc., for the construction of shell. In these animals CO₂ is converted into calcium carbonate (CaCO₃) which is used for the construction of shells.

CO₂ + H₂O $\to$ H₂CO₃ (Carbonic acid)

H₂CO₃ $\to$ H⁺ + HCO₃ (Bicarbonate)

HCO₃ + Ca⁺ $\to$ H⁺ + CaCO₃ (Calcium carbonate)

(ii) Flow of Carbon into the abiotic system : The carbon of the biotic system flows into the abiotic system in five ways :

(a) Respiration : Plants and animals release CO₂ by respiration (biological oxidation).

C₆H₁₂O₆ $\to$ CO₂ + H₂O + Energy

(b) Decomposition : When plants and animals die, the dead bodies are decomposed into CO₂ by decomposers like bacteria, algae, etc.

(c) Shells : After the death of marine animals, CaCO₃ stored in the shells is either deposited as sedimentary rocks or dissolved in water to release CO₂ by the reversion of the above said reactions.

(d) Coal : A certain proportion of carbon from plants is deposited as coal. Carbon from coal returns to air in the form of CO₂ through combustion and weathering.

(e) Forest fire : Combustion of wood in the forest, releases carbon from plants in the form of CO₂.

(2) Nitrogen cycle : The cycling of nitrogen between abiotic and biotic systems is called nitrogen cycle. It is a gaseous cycle. The main source of N₂ is air which contains 79% N₂.

(1) Flow of Nitrogen into the biotic system : Nitrogen is an important nutrient of plants. But plants cannot utilize free N₂ of air. They obtain N₂ from ammonium salts, nitrites and nitrates. These compounds are formed from atmospheric N₂ by a process called nitrogen fixation.

Nitrogen fixation is a process by which atmospheric free N₂ is converted into soluble salts like nitrites and nitrates. It occurs in two ways namely electrochemical fixation and biological fixation.

(a) Electrochemical fixation : A certain amount of free N₂ is fixed by the action of lightning. The amount of nitrate formed by this method is about 35 mg/m²/year.

(b) Biological fixation : It refers to the conversion of free N₂ into soluble salts by the activity of certain organisms. These organisms are called N₂ fixing organisms. The amount of nitrate formed by this method is about 140 to 700 mg/m²/year, and in a fertile area it exceeds 20000 mg/m. The N₂ fixing organisms are bacteria, blue green algae, fungi and other micro-organisms. e.g., Rhizobium, Azotobacter, Closteridium, Bacillus, Nitrosomonas, Nitrococcus, Nitrobacter, Anabena, Nostoc, etc.

The fixed N₂ is absorbed by plants through the root system and is incorporated into the proteins. When herbivores feed on these plants, the N₂ flows on the carnivores through food chain.

(2) Flow of Nitrogen into the abiotic system : The nitrogen of the biotic system flows into the abiotic system by four methods, namely decomposition, excretion, denitirfication and sedimentation.

(a) Decomposition : Plants and animals contain nitrogen in their body protein. After death, the proteins of dead bodies are decomposed by decomposers into amino acids and ammonia. The convertion of protein from dead bodies into ammonia by decomposition is called ammonification. This ammonia may be converted into nitrates or free nitrogen.

(b) Excretion : Animals excrete nitrogenous waste products in the form of ammonia, urea and uric acid. These compounds are decomposed to release N₂.

(c) Denitrification : The conversion of nitrate into ammonia or free nitrogen is called denitrification. This is done by denitrifying bacteria. e.g., Pseudomonas.These bacteria utilize the O₂ present in the nitrate for the oxidation of carbohydrate.

(d) Sedimentation : Some amount of nitrate is lost from the ecosystem by sedimentation.

(3) Oxygen cycle : The cycling of O₂ between biotic and abiotic systems is called O₂ cycle. It is a gaseous cycle. Air is the reservoir for O₂. O₂ enters the biosphere through respiration. The O₂ taken into the body is used for oxidation of carbohydrates, proteins and fats. Certain amount of O₂ in atmospheric air is converted into ozone (O₃) the ozone forms an umbrella-like layer in the outer atmosphere. This layer prevents the ultraviolet radiations from reaching the earth&aposs surface.

$C_6{H}_{12}{O}_6\to 6CO+6H_{2}O+$Energy

$O_2+O\to O_3$

Carbon monoxide is released from volcanoes. This CO is unstable. It combines with O₂ to form CO₂.

O₂ combines with a variety of elements to form compounds. For example, it forms CO₂ with carbon, water with hydrogen, nitrates with N₂ ferric oxide with iron etc. O₂ returns to air by two main methods, namely photosynthesis and photodissociation.

{O_2}\ + \C\ \to \C{O_2}

{O_2} + \2{H_2}\ \to \2{H_2}O

{O_2}\ + \{N_2}\ \to \N{O_3}

(i) Photosynthesis : Green plants synthesize carbohydrate by photosynthesis. During photosynthesis water molecules break up into hydrogen and oxygen. O₂ is released into the atmosphere and H₂ is trapped and turned into carbohydrates.

$12H_{2}O+6C{O}_2\to C_6{H}_{12}{O}_6+6H_{2}O+6O_2$

(ii) Photodissociation : Water vapour is dissociated to release H₂ and O₂, in presence of light.

(4) Phosphorus cycle : The cycling of phosphorus between biotic and abiotic system is called phosphorus cycle. It is a sedimentary cycle. Phosphorus is an important mineral nutrient. The main source of phosphorus is rocks. Through erosion and weathering phosphorus is made available in the soil. Plants absorb ionic phosphate through roots. In plants it is incorporated into the protoplasmic components like DNA, RNA, AMP, ADP, ATP, GDP, GTP, NADP, phospholipids etc. from plants, it passes into herbivores and animals, the organic molecules containing phosphate are decomposed and phosphate is liberated as inorganic ion phosphate. It is again used by plants.

The excess of phosphate in the bodies of animals is excreted out through faces. The bird guano (excreta) contains a large amount of phosphate. Phosphate is also released to the soil through the combustion of forest trees and grasses. A large amount of phosphate is lost in the sea by sedimentation. A certain amount of phosphorus gets locked in bones and teeth.

(5) Sulphur cycle : The cycling of sulphur between biotic and abiotic systems is called sulphur cycle. It is a sedimentary cycle. Sulphur is an important component of proteins and amino acids.

Sulphur exists in a number of states. Of these, three are important. They are elemental sulphur, sulphides and sulphates. Sulphur is present in rocks. It is made available for plants in the form of inorganic sulphate by weathering and erosion. Sulphur passes into the animals through food chain. By the death of plants and animals, the decomposers again bring the sulphur to the soil for the use of plants.

Some sulphur in dead bodies is released into the air as hydrogen sulphide (H₂S) by the bacteria called Escherichia coli under anaerobic combustion. Similarly incomplete combustion of fossil fuel releases sulphur dioxide (SO₂) into the air.

Certain bacteria (green and purple photosynthetic bacteria) oxidise H₂S of air to sulphate which can be used by plants.

H₂S + 2O₂ $\to$ SO^–₄  + 2H⁺

Certain amount of sulphur is lost in the sediments. If iron is present in the sediments, sulphur combines with it to form iron sulphide.