Why is Environment Important

Published on May 2016 | Categories: Documents | Downloads: 58 | Comments: 0 | Views: 1505
of 53
Download PDF   Embed   Report

Comments

Content

UNIT 1
Structure

WHY IS ENVIRONMENT IMPORTANT?
,

1.1 1.2 1.3

Introduction
Objectives

What is Environment?
Concept of Environnlent

Biosphere
Divisions of Biosphere Atmosphere Hydrosphere Lithosphere

1.4

Biomes and Aquatic Life Zones
Different Types of Biomes Terrestrial Biollles Aquatic Zones

1.5 1.6

Ecosystem Components of Ecosystem
Abiotic Components Biotic Components Trophic Levels Food Chain Food Web Bioaccumulation and Biomagnification Pyramids

1.7 Energy in Ecosystem
Flow of Energy in an Ecosystem Laws of Thermodynamics

1.8

Matter in Ecosystem or Geochemical Cycles
Types of Nutrient Cycles Gaseous Cycles Sedimentary Cycle

1.9

Biotic Relations
Intraspecific Relations Interspecific Relations

-

1.10 Homeostasis
System Feedback Mechanism Ecosystem Homeostasis

1.1 1 Community and Ecological Succession
Succession in Terrestrial Community Succession in Aquatic Habitat General Characteristics of Succession Ecosystem and Human Intervention

1.12 Overview of Human Population
Population Characteristics Population Histograms Types of Histogram Populations of India Future of Human Populations: Where Are We Today?

1.13 Constitutional Obligations of a Citizen
Obligation to the Future Responsibilities and Duties of a Citizen

1.14 Let Us SumUp 1.15 Further Reading

Environmental Concerns

"This Planet has been delivered wholly assembled and in perfect working condition, and is intended for -fully automatic and troublefree operation-in orbit around its star, the &n. However, to ensure proper functioning all passenger are requested to familiarize themselves fully with the following instructions. Loss or even temporary misplacement of these instruction may result in calamity. Passenger who must proceed without the benefit of these rule are likely to cause considerable damage before they cnn learn the proper operating procedure to themselves. David R. Brower

1 .

INTRODUCTION

Earth is the only planet, among the nine around the sun which supports life. Despite the vastness of earth, life exists only in a very thin layer enveloping the earth called biosphere. Sun is the only source of energy which enables conlinuous interaction among various life forms. This unit being the first in the course brings out the holistic meaning of the word 'environment' which in broad terms, includes everything external to an organism that affect it, including physical as well as living factors. Their action and interaction make a systeim of relationship called ecosystem. This unit also deals with structure and properties of ecosystem, basic concepts of ecosystem functioning and the factors controlling it. It also deals with the development of ecosystem. The unit kill familiarise you with interactions like competition, parasitism and mutualism that exist between living beings. This unit will focus also on how we as living beings interact with other living aid non living conlponents of the ecosystem. You will also become aware that ecosystems are able to maintain homeostasis by active effort, resisting the tendencies toward disorder.

For centuries (liumans have considered the earth and environment as virtually u~~lirnited subtle and gradual changes have altered our environment in may but different ways.
Special mention has been made of human population within the changing scenario over the years, particularly since the industrial revolution. We hope that this unit will give you a better understanding of the environment and its various components. We wish that this unit enables you to use your intelligence and skills to the best of your advantage for managing our environment and keeping it healthy for future generations.

Objectives
After reading this unit you will be able to: explain the term environment biosphere, specie? and population, define and explain the basic concept of ecosystem, its structure, properties, hnction, development, control and stability in order to act positively towards the environment,

discuss that the flow of energy and cycling of material are central to the ecosystem functioning and indiscriminate intervention would lead to damage and disruption of the environment, discuss the environmental consequences of the current growth pattern of human population, and be aware of your duties and obligations towards environment.

Why is Environment Important?

I

1.2

WHAT IS ENVIRONMENT?

Each and every living organism has a specific surrounding or medium with which it continuously interacts, from which it derives its susteilance and to which it is fully adapted. This surrounding is the 'natural en'VironmentY The . word 'natural environment' brings to mind broad aspects of landscape, such as soil, water, desert or mountains wllich can be more exactly described ill terms of physical influences such as differences in moisture, temperature, texture of soil, and biological influences. Tlius, environment is defined as, "the sum total of living and non-living components; influences and events surrounding an organism". Broadly the environinent comprises of abiotic (non-living) and biotic (living) components. (Table 1.1) Table 1.1: Components of Enviro~ltnent I Biotic components Abiotic Components Light Precipitation Humidity & Water Temperature Substrate Atmospheric gases Altitude Latitude . Seasonal changes Topography Plants Animals iilcluding humans, parasites and microorganisms Decomposers

1.2.1
.

Concept of Environment

No organism can live alone without interacting with other organisms so each organism has other organisms as a part of its environment. You must know that all animals are directly or indirectly dependent upon green plants. Plants also depend on animals for a few things such as pollination of flowers and dispersal of fruits and seeds. Each and everything with which you interact or which you need Tor your sustenance fonns your environment. Let us try to understand the concept of environment with an example, Consider (Fig.1.1). Can you identify the environment of a single carp Gs'h in the pond? abiotic components such as light, temperature, Its environment ca~~.si'sts'.;of including the water & !h % 'c rinutrients, oxygen, other gases and organic matter are dissolved. The biqtic P m e n t consists of microscopic organisms called plankton as well as dquatic plai~tlts animals and decomposers. The and plants are of different kinds such as phytoplanktons, partly submerged plants and trees growing around the edge of the pond. The animals consist of
9

Environmental Concerns

zooplanktons, insects, worms, molluscs, tadpoles, frogs, birds and various kinds of fishes. The decomposers are the saprotrophs like bacteria and fungi.

Fig. 1 .l: Environment of a carp in a pond.

The environnlent of the fish described above is its external environment; living organisms also possess an internal environment, enclosed by the outer body surface. The internal environment is relatively stable as compared to the external environment. However, it is not absolutely constant. Injury, illness or excessive stress upsets the internal environment. For example, if a marine fish is transferred to a fresh water environment, it will not be able to survive. You should realise that the environment is not static. The biotic and abiotic factors are in a flux and keep changing continuously. The organisms can tolerate changes in en$konment within a certain range called 'range of tolerance'.

1.3

BIOSPHERE

You now know the constituents of the environment. You and I live in a defined area of earth where plants and animals, including ourselves, develop kinship with one another for life, food, water, shelter, mates etc. This descrete unit has living and non-living components, which are interdependent and interrelated in terms of their structure, components and functioning. Such a unit is called ecosystem. Ecosystems may vary in size froin the smallesl puddle of water to large forest, to a biome, to a habitat or to the entire global biosphere or ecosphere. (Fig 1.2)
'

Fig. 1.2: Biological systems represent a hierarchy of progressively increiesing level of complexity. Ecosystem represents a highly_complexlevel of organization.

-

Before we explain the functioning of the components of the ecosystem let us first discuss the larger unit of natural landscape the biosphere.

Why is Environment Important?

1.3:l

Divisions of Biosphere
Biosphere is that part of the ealth where life can exist. It is a narrow layer around the surface of the earth. I f you visualise the earth to be the size of an apple the biosphere would b~ as thick as its skin.

Biosphere is that part, of the earth, water and atmosphere in which many smaller ecosystems exist and operate. Three main subdivisions of the biosphere are: 1) lithosphere, (land) 2) hydrosphere (water), and 3) atmosphere (air) or the gaseous envelope of the earth which extends upto a height of 22.5 km. Fig. 1.3, shows the idealised scheme of biosphere in relation to hydrosphere, atmosphere and lithosphere. The area of contact and interaction between these three components is really important for life, as it is here that the entire life is confined and the basic processes of life, like photosynthesis and respiration occur.

.

.

Fig. 1.3: Idealised scheme of the biosphere.

Living organisms are, mostly, confined to the parts of biosphere that receive solar radiation during the day. As you can see in (Fig. 1.4) the biosphere extends from the floor of the ocean some 11,000 inetres below the surface of the earth to the top of the highest mountnins, or about 9,000 metres above the sea level. Its most d e n ~ e l ~ , ~ o ~ u region is just above and below the sea lated level.
$+

'Life in the biosphere is abundant between 200 metres (660 feet) below the sutface of the ocean and about 6,000 mctres (20,000 feet) above sea level as shohn in (Fig. 1.4). The energy required for the life within the biosphere comes from the sun without which the biosphere will collapse, The nutrients necessary for living organisms come from air, water and soil and not from outside and the same" nutrients are recycled over and over again for life to continue. Living

Biosphere is absent at extremes of the North and South poles, the highest mountains and the deepest oceans, since existing conditions there do not support life. Occasionally spores of fungi and bacteria do occur at great height beyond 9,000 metres, but they are not metabolically active, and hence represent only dormant life. ,

Environmental Concerns

organisms are not uniformly distributed throughout the biosphere.'Only a few organisms live in the polar regions, while the tropical rain forests possess an exceedingly rich diversity of plants and animals.

Fig.l.4: Vertical dimensions of the biosphere. Life exists from the highest mountain peaks to the depths of the ocean. Life at the extremes is however, rare. Most organisms are limited to a narrow region depicted here between 6000 metres above sea level and 200 metres below sea level.

1.3.2 Atmosphere

' i

Atmosphere is of vital significan&40 life as all components of air (except inert ones) serve as key metabolites for living organisms. Table 1.2. shows the composition of the atmosphere. In this section we will discuss about the metabolic role of a few .important gases, namely carbon dioxide6 oxygen and nitrogen, which highligG the importance of atniosphere.
Table 1.2: T h e relative proportions of gases in the lower atmosphere ' (below 80 kilometres), excluding water vapour.

Nitrous oxide

Xenon
Ozone

0.00005 0.000009 0.000007

Carbon Dioxide
You must be aware that chlorophyll bearing organisms namely green plants, green and purple bacteria and blue green algae are the only biological or biotic members in nature which manufacture their own food. They do so by the process of photosynthesis. In this process they use atmospheric carbon dioxide along with water and some minerals such as calcium, potassium, magnesium etc. in the presence of sunlight to produce organic substances or food such as glucose (a vital molecule in living things) and oxygen, which is essential for respiration. The carbon and oxygen supplied by carbon dioxide remain in living matter until death and the C 0 2 returns to the atmosphere, only after decomposition of the living matter, to complete the cycle as you can see in Fig.1.5. (Refer further to carbon cycle in subsection 1.8.2 as well)

Why is Environment ~rnportant? Carbon dioxide enters the living world as the. basic constituent of all organic compounds. Chemosynthetic bacteria are also producers. However, unlike plants these bacteria which occur in deep ocean trenches where sun energy is absent, derive energy by the process of 'chemosysthesis'. They use hydrogen sulphide, instead of sun, as the energy source.

i

Fig. 1.5: The linkage between carbon dioxide and oxygeli cycle. Plants use carbon dioxide during photosynthesis and give off oxygen. This oxygen is available to animals for process of the cellular respiration. Animals breathe out carbon dioxide; some carbon dioxide is released from decomposition of dead organisms.

Oxygen
Oxygen, an important constituent of the atmosphere, enters the living world through respiration, which is a familiar process in both plants and animals including humans. Oxygen is used by living organisms to oxidize food material mainly glucose molecules in order to release energy which is needed for various activities by organism. Food or nutrient is not only a source of energy but is also used to build up the organisms' bodies. Respiration atid photosynthesis, together form a cycle called photosynthesis - respiration cycle, as you can see in Fig.1.5. This cycle can be depicted as follows: 6C02 + 6 H z 0+ minerals
(carbon dioxide) -I- (water)

Energy is defined as the capacity to do work

LXXL+>
photosynthes~s

Sunlight

c ~ H+ ~ ~ o ~ 602t
glucose (food)

+ minerals

+ oxygen

respiration

C6H1206 602

> 6 C O ~ + +6H20 + energy to do work

4 heat energy

Environmental Concerns

Thus nutrients and energy are combined into one entity i.e. biomass by plants. This food manufactured by green plants is consumed by other organisms. Nitrogen Nitrogen is also an essential component of living systems. It is required by organisms for the synthesis of proteins, nucleic acids, and other nitrogellous compounds. While looking at table 1.2 you may have noticed that nitrogen fonns the main constituent of air and it appears that we seem to be living in an envelope of nitrogen. However, the paradox is that this large amount of nitrogen is uilavailable to living organisms in the gaseous state (N2). Nitrogen has to be 'fixed' into 'active' nitrogen largely as nitrates and ammonia by certain bacteria in order to become available to living organisms. In subsection 1.7.2 you will see how nitrogen becomes available to the living organisms when you study the nitrogen cycle. ,
1.3.3 Hydrosphere

You may know that water is the most important component of protoplasm; hence it is essential for life in all living organisms. In metabolic processes, it is the only source of hydrogen and one of the several sources of oxygen. Earth is sometimes called the watery planet as this is the only planet in the solar system which has an abundant supply of water. Water is used by organism as raw material for various metabolic processes and they draw it . mainly from the hydrosphere. During the process of metabolism, water consumed by organisins is partly excreted back into the environment and a portion used for building the organisms is returned to the environment after their death and decay. You will learn about the water movement in the biosphere when you study the hydrologic cycle in subsection 1.8.2. 1.3.4 Lithosphere The lithosphere helps in the metabolic process of organisms in two ways: i) it is the only source of most of the minerals for organisms belonging to either terrestrial or aquatic conditions, and ii) it forms the soil, which is required mainly by terrestrial plants. Many other nutrients, in addition to carbon, oxygen, hydrogen and nitrogen occur in the lithosphere and the organism requires them as well. All organisms also need phosphorus, sulphur, sodium, potassium, calcium, magnesium, iron, manganese, cobalt, copper, zinc and probably chlorine. In addition some organisms may also require for special functions for their survival, nutrients like aluminium, boron, bromine, iodine, selenium, molybdenum, vanadium, silicon, strontium, barium and possibly nickel, Movement of these nutrients or materials through the living orgallisms occur as well. (Refer to table 1.5 in section 1.8 as well)

.

1.4

BIOMES AND AQUATIC LIFE ZONES

The terrestrial part of the biosphere is divisible into enormous regions called biomes, which are characterized, by climate, vegetation, animal life and general soil ,type. The dozen or more biomes of the earth are spread over millions o f square kilometres and span entire continents. No two biomes are

alike. The climate determines the boundaries of a biome and abundance o f plants and animals found in each one of them. The most important climatic factors are temperature and precipitation. Aquatic systems are also divided into distinct life zones, which however are not called biomes but are very similar, in that they are regions o f relatively distinct plant and animal life. The major differences between the various aquatic zones is due to salinity, levels of dissolved nutrients, water temperature, depth of sunlight penetration.
1.4.1 Different Types of Biomes

Wliy is Environment Important?

We will lean1 about different types of vast ecosystems namely biomes and aquatic zones on our earth. We call get an idea about both of these ecosystems by looking at tables 1.3 and 1.4.
1.4.2 Terrestrial Biomes

Let us first study in brief the main features of the various types of terrestrial ecosystems wit11 the help of Table 1.3 and Fig.1.6. Table 1.3: Terrestrial biomes.
,

/

Nameof Biome 1. Tundra

1

Region

I

Flora and Fauna

I

Northein most region adjoining the ice bound poles

Devoid of trees except stunted ski-ubs in the southern part, ground flora includes lichen, mosses and sedges. The typical animal; arc reindeer, arctic fox, polar bear, snowy owl, lemming, arctic hare, patarmigan. Reptiles and amphibians are alnlost absent. The dominating vegetation is coniferous evergreens mostly spruce, with some pine and firs.
The fauna consist of small seed eating birds, hawks, fur bearing carnivores, little mink, elks, puma, Siberian tiger, wolverine, wolves etc. he flora includes trees like beech, oak, maple and cherry.

Northern Europe, Asia and North America but in areas of more moderate temperature than tundra. Also known as boreal forest.

3. Temperate Deciduous Forest

Extends over Central and So~theiil Europe, Eastern North America; Western China, Japan, New Zealand etc, Temperature on an average is moderate and rainfall is abundant. These are generally the most productive agricultural areas of the earth

Most aniinals are the familiar vertebrates and invertebrates.

Environmental Concerns

Nameof

1

Region
Tropical areas of high rainfall in the equatorial regions, which abound with life. Temperature is high.

Flora and Fauna
Tropical rainforest covers only about 7% of the earth's surface and houses. 40% of the world's plant and animal species. Multiple storey of broad-leafed evergreen tree species are in abundance. Most animals and epiphytic plants are concentrated in the canopy or tree top zones. Grasses with scattered trees and fire resisting thorny shrubs. The fauna include a great diversity of grazers and browsers such as antelopes, buffaloes, zebras, elephants and rhinoceros; the carnivores include lion, cheetah, hyena;,and mongoose, and many rodents. Grasses dominate the vegetation.. The fauna include large herbivores like bison, antelope, cattle, rodents, prairie dog, wolves, and a rich and diverse array of ground nesting bird. The flora is drought resistance vegetation such as cacti, euphorbias, sagebrush. Many species of reptiles mammals and birds occur.

Biome 4. Tropical ~ain Forest

'

6. Grasslands

North America Midwest and Ukraine: dominated by grasses. Temperate conditions with rather low rainfall. Continental interiors with very low and sporadic rainfall with low humidity. The days are very hot but nights are cold

7. Dessert .

Savanna
0"

Thornwood
-----b

-----+ Increasing Aridity

Fig.l.6: Simplified scheme of the major terrestrial biomes, arranged along ecoclines of increasing aridity at different latitudes, showing the predominant influence of moisture and temperature an the structure of plant communities. '

,

1.4.3 Aquatic Zones
Aquatic ecosystem covers more than 70% of the earth's surface and are as diverse in species as the biomes. Aquatic ecosysteps are distinguished into fresh water, marine and estuarine ecosystems on the basis of salt content. Their main charactehstics are given in table 1.4. Table 1.4: Aquatic Ecosystems. Characteristics Fresh Water Ecosystem (having flowing water) or lentic (still or stagnant water). Lotic water systems include freshwater streams, springs, rivulets, creeks, brooks, and rivers. Lentic water bodies include pools, ponds, some swamps, b ~ g and lakes. They vary considerably in s physical, chemical and biological characteristics. Marine Ecosystem Nearly three -quarters of earth's surface is covered by ocean wit11 an average depth of 3,750 m and with salinity 35 ppt, (parts per thousand), about 90 per cent of which is sodium chloride. Coastal bays, rivers mouths and tidal marshes form the gstuaries. In estuaries, fresh water from rivers meets ocean water, and the two are mixed by action are of tides. ~stuaries highly productive as compared to the adjacent river or sea.

Why is Environment Important?

Estuaries

1.5

ECOSYSTEM

Each biome can be subdivided into smaller units. For example the desert bionle of Rajasthan is characterised by arid conditions, sandy, terrain, cacti and succulent plants. Animals found there are lizards, snakes. A subdivision of biome such as a pond is called an ecological system or ecosystem. The various kinds of organisms that inhabit an ecosystem forms its populations. The term, 'population' has many uses and meanings in other fields of study. In ecology, 'a population is a group of potentially interbreeding individuals that occur together in space and time'. The individual comprising a population are members of the same species. Populations of plants and animals in the ecosystem do not function independently of each other. They are always influencing each other and organising themselves into communities and have functional relationship with their external environment.
'

'

was The word ecosysten~; coined by Prof. Arthur Tansley in 1935. The prefix 'eco' means environment.

An ecosystem is defined as, any unit (a biosystem) that includes all the organisms that function together (the biotic community) i n a given area, interacting with the physical environment (abiotic component) so t h a t flow of energy leads to clearly defined biotic structures and cycling of materials between living and nonliving parts and which is self regulatory based on feed-back information about the population, and the limiting factors which control the living and non-living components.

Environmental Concerns

The def nition of ecosystem as you can see involves the interaction between living and non-living components of an ecosystem and input, transfer, storage and output of energy as well as cycling of essential materials through the system. Each of these processes is energy dependent. As a result of these complex interactions, the ecosystem has to adjust to these changes to attain a state of equilibrium. Fig. 1.7, illustrates this beautifully. Ecosystems differ greatly in composition, in the number and kinds of species, in the kinds and relative proportions of non-biological constituents and in the degree of variations in time and space.

Fig. 1.7: Schematic representation of an ecosystem. The dotted lines represent the boundary of the system. The three major components are the producers, the consumers, and the abiotic elements: inactive or dead organic matter, the soil matrix, nutrients in solution in aquatic ecosystems, sediments, and so on. Tlie arrows indicate interactions within the system and with the environment.

1.6

COMPONENTS OF ECOSYSTEM

Recall the definition of an ecosystem from Section 1.3.1. Any complete definition of an ecosystem includes the biotic as well as the abiotic components and the interaction between the two.
1.6.1 Abiotic Components

One of the important components of the ecosystem are abiotic or nonliving components about which you have already read in section 1.2 (Refer to table 1.1 as well). The physical or abiotic components are the inorganic and nonliving parts of the world. The abiotic part consists of soil, water, air, and light energy etc. It also involves a large number of chemicals like oxygen, nitrogen etc. and chemical as well as physical processes including volcanoes, earthquakes, floods, forest fires, climates, and weather conditions. There are numerous chemical processes, but the most important include the carbon, nitrogen and phosphorous cycles. These physical and chemical processes are the result of the physical characteristics of the earth: air, moisture, light and heat, and the various chemical reactions. While each of these abiotic factors may be studied by itself, however, each of these factor is influenced by and in turn influences all the other factors.

Abiotic factors are usually the most important determinants of where and how well an organism exists in its environment. Although these factors interact with each other, usually there is one single factor which serves t o limits the range of an organism. That single factor is called the limiting factor. Let us now discuss some of the important abiotic factors: i) Light: Light energy is necessary for green plants to carry on photosynthesis. All animals are directly or indirectly dependent on the food substance produced by green plants. The intensity, duration and wavelength (color) of light are important factors that regulate the life activities of many living things. Light from the sun (solar energy) is the ultimate source of energy for all living things. The availability of light energy differs greatly on different parts of the earth. Precipitation: Precipitation in the form of fog, rain, sleet, snow, and hail is one of the most important abiotic factors. Most organisms depend on some form of precipitation, either directly or indirectly, from underground. The amount of precipitation differs, depending where on earth you are. Humidity & Water: Moisture in the air is very necessary for many plants and animals to function properly. Some animals are, active only at night when the humidity is higher. Aquatic habitats are subject to changes in chemical and gas content and to fluctuations of depth. Water holes in the Everglades of Florida and the Savannah of Africa are essential for the existence of native wildlife. Temperature: Many living things carry on their life activities at temperatures between 30 lo F and 185' F. Some organisms are able to exist at much lower temperatures. The daily and seasonal temperature changes of-ten act as limiting factors and determine the number and kind of organisms present in a region. Temperature patterns vary with latitudes and altitudes of the earth. Substrate: This is defined as the base of material on which an organism lives. The type of soil, for example, is a limiting factor for the vegetation, which in turn, may be a determinant for the animal life capable of living in the habitat. The type of soil will determine such factors as pH amount and type of minerals present. vi) Atmospheric gases: Oxygen and carbon dioxide are generally not limiting factors for terrestrial organisms. These two gases are abundant in our atmosphere. The atmospheric gases can be limiting factors for aquatic organisms.

Why is Environment Important?

ii)

iii)

iv)

-

vii) Altitude: Precipitation and temperature both vary with elevation. Usually precipitation increases with elevation although at extreme elevations it may decrease. Temperature usually decreases 2-3 degrees per thousand feet. viii) Latitude: As one moves north or south of the equator, the angle of the . sun' generally decreases, which results in a decrease in the average temperature. Topography: Landforms like mountains, valleys, basins, cliffs, etc. may encourage, restrict or isolate organisms. Seasonal changes: Because of the tilt of the earth on its axis, the angle of solar radiation varies during the year as one travels fi-om the equator,

ix)

Ehvironmental Concerns

It produces pronounced changes in the weather during the year, giving rise to seasons like winter, spring, summer, and autumn. xi) Weather: is the combination of temperature, humidity, preciptation, wind, cloudiness and other atmospheric conditions at a specific place and time and has profound affect on organism.

xii) Climate: is the long-term average pattern of weather and influences the vegetation and organisms of a place. It is in this abiotic background that biotic organisms i.e. plants, animals and microbes interact. (See Fig.1.7 again) ..

1.6.2
Food refers to complex organic compounds such as carbohydrates, proteins and fats. Greenglants first produce simple carbohydrates like glucose and later various complex carbohydrates, fats and proteins.

Biotic Components

The biological or biotic components (Fig.1.8) of an ecosystem interact in an abiotic background and include: i) Organisms, basically green plants, certain bacteria and algae, that in the presence of sunlight can synthesise their own food from simple inorganic substances. Organisms that are able to manufacture their own food are called autotrophs or primary producers, All other organisms that are unable to make their own food but depend on other organisms for food to meet their energy needs for survival are called heterotrophs or phagotrophs or consumers.

ii)

Among consumers, animals such as goat, cow, deer, rabbit and insects which eat green plants are called primary consumers or herbivores. Organisms which eat a herbivore, like a bird that eats grasshoppers are called secondary consumers. Organisms which eat secondary consumers are called tertiary consumers. While the primary consumers are herbivores, the secondary and tertiary consumers are carnivores. Animals like lions and vultures which are not killed or eaten by other animals are top carnivores.
Fragments of decomposing organic matter is called detritus

Secondary and tertiary consumers may be i) predators which hunt, capture and. kill their prey, ii) carrion feeders which feed on corpses, iii) parasites which are smaller than the host, and live on or inside the host on which they feed while the host is alive. The parasites depend on the metabolism of their host for their food supply. iv) there are some animals which have flexible food habits, as they eat both plants (therefore are herbivores) and animals (so are carnivores), They are called omnivores. We (humans) are good examples of an omnivore.

Both the consumers'and producers complete their life cycles and new generation of population develop while the old ones die. You must be wondering what happens to the dead. There is a continuous breaking up or decomposition of the ' dead organic matter everywhere in the ecosystem and there is a continuous cycling of materials. Certain fungi and bacteria, which are responsible for the decomposition are called decomposers or saprotrophs or reducers. Most of the saprotrophs are microscopic and they are all heterotrophic in nature. The role ' of decomposers is very special and important. Certain decomposers are also called scavengers. Some animals such as earthworms, soil inhabiting nematodes and arthropods are also detritus feeders and are called detrivores. They also contribute to the breaking down of organic matter. Water, carbon dioxide, phosphates and a number of organic compounds are largely the by-products of organism activity on dead organisms.
I

\ -2'
/?I,

, \ t i

1 1 4,

Why is Environment Important?

-

Sun

Green plants

Primary producers

-

Herbivores

Primary consumers

Carnivores

Tertiary consumers

Rg.1.8: Biotic members of the ecosystem and their position In the trophic level.

1.6.3 Trophic Levels

\

You are sow aware that an ecosystem is considered as a basic unit, where complex natural community obtain their food from plants through one, two, three or four steps and accordingly these steps are known as the first, second, third and fourth trophic (Trophe = nourishment) levels or food levels. (Fig. 1.8), Let us see the trophic levels to which autotrophs and different types of heterotrophs belong to: Green plants (producers); trophic level I - Autotrophs Herbivores (primary consumers); trophic level 11.- Heteiotrophs Carnivores (secondary consumers); trophic level I11 - Heterotrophs Carnivores (tertiary consumers); trophic level IV - Heterotrophs Top carnivores (quarternary consumers); trophic level V - Heterotrophs Thus energy also flows through the trophic levels: from producers to subsequent trophic levels (Fig.1.9). This energy always flows from lower (producer) to higher (herbivore, carnivore etc.) trophic level. It never flows in the reverse direction that is from carnivores to herbivores to producers. Furthermore there is a loss of some energy in the form of unusable heat at each trophic level so that energy level decreases from the first trophic level
'

Humans, being omnivores, may belong to more than one'trophic level;

,

Environmental Concerns

upwards. As a result there are usually four or five trophic levels and seldom more than six as beyond that very little energy is left to support any organism. The study of trophic level gives us-an idea about the energy transformation in an ecosystem. Furthermore it provides a usekl conceptual basis to include all organisms that share the same general mode of feeding into one group which together are said to belong to the same trophic level. This indicates that organisms belonging to the same trophic level obtain food through the same number of steps from the producer. Trophic levels are numbered according to the steps an organism is away from the source of food or energy, that is the producer. (see also Fig. 1.12)
Energy lost as heat

rnoveniedt

Ingestion consumers

1.9: Energy use by consumers - Energy ingested in food is either digested and dssimilated or passed through and eliminated In faeces. The assimilated energy is used for various functions of the body like respiration and movement, reproduction or stored and used for the growth of new tissues or excreted. When the organism dies the energy stored in tissues is used by the decomposers. Only the stored materials are available to organisms at the next trophic level,

1.6.4 Food Chain
Each link in the food chain can also be be calIed trophic level

You now know from the previous section that organisms in the ecosystem are related through feeding or trophic levels, that is one organism becomes food for the other. A sequence of organisms that feed on one another, form a food chain as depicted in Fig. 1.10. The arrows in the figure denote the direction and movement of nutrients and energy from producer to consumer. Similar to the trophic levels and for the same reasons the links or steps in a food chain are usually to four or five.

I

I I

I

Decomposer
I

22

Fig.1.10: A pond food chain

Some animals eat only one kind of food and therefore, are members of a single food chain. Other animals eat different kinds of food, so they are not only members of different food chains but may also occupy different positions in different food chains and trophic levels, thus ensuring the survival of their species. An animal may be a primary consumer in one'chain, eating plants but a secondary or tertiary consumer in other chains, eating herbivorous animals or other carnivores. (See also Fig.1.8) Since man can do nothing about increasing the amount of light energy and vely little about the efficiency of energy transfer, he can only shorten the food chain, to get energy i.e., by eating the primary producers - plants, rather than animals. In highly populated countries, people tend to be vegetarians because then the food chain is the shortest and a given area of land can in this way support larger number of people. Suppose that a fanner has a crop of wheat and vegetables. He can eat it directly or feed it to his goats and then eat the goats, Figure 1.11 shows that a large number of people can be supported on a vegetarian diet as compared to a non vegetarian diet on a given piece of land. Thus the sun's energy is used most efficiently if people are vegetarians.

Why is Environment Important? Humans are at the end of a numbxr of food chain.

a

b

Fig. 1.11: Tlie relative efficiency ofvegetarian and non-vegetarian diets. a) In a vegetarian diet 25,000 calories support 10 people. b) In the same time 25,000 calories of plant matter support only one person who eats meat,

TYPES OF FOOD CHAINS
In nature, two main types of food chains have been distinguished:

i)

Grazing Food Chain: The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain. This food chain begins from green plants at the base and the primary consumer is herbivore, for example: grass -+ grasshopper

-+ birds -+ hawks or falcon.

ii) Detritus Food Chain: The food chain starts from dead organic matter of ,decaying animals and plant bodies to the micro-organisms and then to detritus feeding organism called detrivores or decomposer then to herbivore and to other predators. Litter -+ springtail (insect) -+ sniall spiders (carnivore)
The distinction between these two food chains is the source of energy for the first level consumers. In the grazing food chain the primary source of energy is living plant biomass while in the detritus food chain the source

In a community of organisms in a shallow sea, about 30% of the total energy flows via detritus chains. In a forest with a large biomass of plants and a relatively small biomass of , animals even larger portion . of energy flow may be via detritus pathways.
All food webs begid with autotrophs and end with decomposers

.

Environmental Concerns

of energy is dead organic matter or detritus. The two food chains are linked, The initial energy source for detritus fobd chain is the waste materials and dead organic matter from the grazing food chain.

1 6 5 Food Web ..
A food chain represents only one part of,the food or energy flow through an ecosystem and implies a simple, isolated relationship, which seldom occurs in ecosystems. An ecosystem may consist of several interrelated food chains. More typically, the same food resource is part of more than one chain, especially when that resource is at one of the lower trophic levels. For instance a plant may serve as food source for. many herbivores at a time. For example, grasses can suppoh rabbit or grasshopper or goat or cow. Similarly a herbivore may be food source for many different carnivorous species. Also food availability and preferences of herbivores as well as carnivores may shiA seasonally e.g. we eat watermelon in summer and peaches in the winter. Thus there are interconnected networks of feeding relationships that take the form of food webs (Fig. 1.12). A food web illustrates, all possible transfers of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces only one pathway of the food.

Fig.l.12: A complex network or web of primary prodl,?cers,consumers and decomposers illustrated in a typical terrestrial food web in which trophic levels are depicted by Roman numerals,

1.6.6 Bioaccumulation and Biomagnification In this subsection, we will examine how pollutants specially nondegradable ones m~ve~through various trophic levels in an ecosystem (Fig. 1.13). By the nondegradabale pollutants we mean those materials, which cannot be metabolised by the living organisms. For example chlorinated hydrocarbons. Movement of these pollutants involve two main processes: i) bioaccumulation and ii) biomagnification.
Bi'oaccumulation: refers to how pollutants enter a food chain. In bioaccumulation there is an increase in concentration of a pollutant from the environment to the first organism in a food chain. ii) Biomagnification: biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next. Thus in biomagnification there is an increase in concentration of a pollutant from one link in a food chain to another.
i)

Why is Environment Important?

We are concerned about these phenomena because togetl~er they enable cven small concentrations of chemicals in the environment to find their way into orgallisms in high enough dosages to cause problen~s. order for In biomagnification to occur, the pollutant must be:

1. 2. 3. 4.

long-lived mobile soluble in fats biologically active

Fig.l.13: The figure shows how DDT becomes concentrated in the tissries of organisms through four successive trophic levels in a food chain. The DDT concentration occurs because it is metabolised and excreted much more slowly than the nutrients that are passed from one trophic level to the next. So DDT accumulates in the bodies (especially in fat). The numbers in the figure represent the concentration values of DDT and its derivatives (in parts per million or ppm) in the tissues.

*

If a pollutant is short-lived, it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms. If the polhdant is soluble in water, it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for

Environmental Concerns

a long time. It is traditional to measure the amount of pollutants in fatty tissues of organisms such as fish. In mammals, we often test the milk produced by females, since the milk has a lot of fat in it and because the very young are often more susceptible to damage from toxins (poisons). If a pollutant is not active biologically, it may biomagnify, but we really don't worry about it much, since it probably won't cause any problems. 1.6.7

i

I

Pyramids

You have studied trophic Ievels in subsection 1.6.3.These steps of trophic levels can be expressed'in a diagrammatic way; and are referred to as ecological pyramids. The food producer forms the base of the pyramid and the top carnivore forms the tip. Other consumer trophic levels are in between. The ecological pyramids are of three categories.
a

a
a

Pyramid of numbers, Pyramid of biomass, and Pyramid of energy or productivity.

I .

Pyramid of Numbers
This deals with the relationship between the numbers of primary producers and consumers of different levels (Fig.l.14) It is a graphic representation of the total number of individuals of different species, belonging to each trophic level in an ecosystem. For example, we might have the following pyramid for a grass field as depicted in Fig. l.l4(a) where the base of the pyramid represents the food production base for other higher trophic levels. The pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producer level through herbivore, carnivore onwards. The length of each bar represents the total number of individuals at each trophic level in an ecosystem. The number of individuals drastically decreases with each steps towards higher trophic levels and the diagrammatic representation assumes apyramid shape and is called pyramid of numbers.
econdary consumers(1)

Primary consumers (11)

FIg.1.14: Pjrrarnid nl' numbers shows the number of organisms at each troplnic IcveB in the ecosystem (a) An llpright pyramid of numbers (la) l n invwteal pye.:rslitl of r n:ipn:k . :.s

I

However, it is very difficult to count all the organisms, in a pyramid o f numbers and so the pyramid of number does not completely define the trophic structure for an ecosystem. A pyramid of numbers does not take into account the fact that the size of organisms being couilted in each trophic level can vary. A count in a forest would have a small number of large producers, the big trees, which support a large number of herbivores. As a result the pyramid will assume an inverted shape as you can see in Fig. 1.14 (b). This is because the tree is a primary producer and would represent the base of the pyramid and the dependent herbivores and carnivore will represent the second and third trophic level respectively. Thus, depending upon the size and biomass, the pyramid of numbers may not always be upright, and inay even be completely inverted.

Why is Environment Important?

Pyramid of Biomass
In order to overcome the shortcomi&s of pyramid of numbers, the pyramid of biomass is used. (Fig. 1.15). In this approach individuals in each trophic level are weighed instead of being counted. This wo~lld give us a pyramid of biomass, i.e., the total dry weight of all organisms at a each trophic level at a particular time. Pyramid of biomass is usually determined by collecting all organisms occupying each trophic level separately and measuring h e i r dry weight. This overcomes the size difference problem because all kinds of organisms at a trophic level are weighed. Biomass is measured in g/m2. A t the time of sampling, the amount of biomass is known as standing crop or standing biomass. For most ecosystems on land, the pyramid of bioil~ass has-. a large base of primary producers with a smaller tz-ophic level perched on top. ertiary consumers (1.5 grams) econdary consumers (11 grams) rimary consumers (37 grams)

Producer (807 grams)

Pyramid of biomass ~ i ~ ~ l .The : 1 4 pyramid of biomass depicts total weight of organisms supportedlat each level.

-

,.

In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form. This is because the producers are tiny phytoplanktons that grow and reproduce rapidly. Here, the pyramid of biomass can have a small base, with the consumer biomass at any instant actually exceeding the producer' biomass. The phytoplanktons are consumed about as fast as they reproduce, it is just that the survivors (they may be few) are reproducing at a phellomenal rate.

Environmental Concerns

Pyramid of Energy
When we wish to compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is probably the most informative, for the pyramid shape is not distorted by over emphasis on variations in the size and weight ofthe individuals. An energy pyramid more accurately, reflects the with conversion of solar energy to chemical energy laws of themodynan~ics, and heat energy at each trophic level and with loss of energy being depicted at each transfer to another trophic level (See section 1.7). Hence the pyramid is always right side up (Fig. 1.16), with a large energy base at the bottom. A pyramid of energy must be based on a determination of the actual amount of energy that individuals take in, how inuch they burn up during metabolism, how much remains in their waste products, and how much they store in body tissue.
Secondary consumers (48 kilocalories)

XVX
Pyramid of energy

Priinarv consumers (596 kilocalories)

One calorie (cal) is the amount of heat needed to raise the temperature of one cubic centimetre of water through one degree centigrade. On5 kilo calorie (k cal = 1000 cal)

Fig. 1.16: The pyramid of energy depicts the amounts of energy available at each trophic level.

'A

Number or Calories

In energy pyraiii&> given trophic level, always has a smaller energy content than the trophic level immediately below it. This as you may recall from section 1.6.? is due to the fact that some energy is always lost as heat while going up from one trophic level to the next. Let us explain this with an se example. S ~ ~ p p oan ecosystem receives 1000 calories of light energy in a given day. Most of the energy is not absorbed; some is reilected back to space; of the energy absorbed only a sillall portioii is utilised by green plants, out of which the plant uses up some for respiration and of the 1000 calories, therefore only 100 calories are stored as energy rich materials. Now suppose an animal, say a deer, eats the plant containing 100 cal of food energy. The deer uses some of it for its own metabolisin and stores only 10 cal as food energy. A lion that cats the deer gets an even smaller amount of energy. Thus usabie energy decreases from sunlight to producer to herbivore to carnivore. Therefore, the energy pyramid will always be upright (see Figure 1.17). Each bar in the pyramid indicates the amount of energy utilistgl at each 'trophic level. The energy inputs and outputs are calculated so that energy flow can be expressed per unit area of land or volume of water per unit time. The unit of measupment is kcallm2iy, where k cal represents energy, rn2 represents unit area and y represents years. '

Green Plants

100 cal

Fig. 1.17: Pyramid of energy showing energy loss s, each higher level.

28

1.7

ENERGY IN ECOSYSTEM

Why is E~ivironrner~t Important?
Sun is the ultiinatc source of all our energy, which caters to the necd of our ecosystem. It has been observed that 30% of the total solar radiation entering our atmosphere is reflected by the earthatmosphere system. The remaining 70% of tile radiation' is absorbed by the earth's atinosphere. Of this 19% is absorbed directly by thc atmosphere and the rest by the earth surface.

-1s you know, by now energy used for all life processes is derived from solar cnergy. The flow of solar energy is unidirectional. Its immediate implication is that an ecosystem will collapse if the sun stops giving out energy. In the previous subsection you read that solar energy along with nutrients is converted by producers, into food materials and is stored within their bodies. All the food materials or nutrients that we or other animals consuine are obtained directly or indirectly from such producers. As a result there is continuous flow of energy from the sun through various organisins and then to outer spa(.:: Tliis process maintains the life on the earth. Trapping and flow of energy in, illvc.. cir.{-ul ,;onof nutrienis as well, which include the basic inorganic elements sucll as, carbon, hydrogen, oxygen and nir- ~l;cnas well as, occur in small am0~11~s. addition, 11 1 sodium, calcium, and potassium, wl~ich compounds such as; water, carbonates, phosphates and a few others also f o r ~ n part of living organisms. For an ecosystem to function, it is essential that there flow is a conti~~uous of energy and cycling of nutrients. 1.7.1 Flow of Energy in an Ecosystem With the help of the lollowing flow chart, we can interpret tlie f~~nctional aspect of an ecosysten~ the interactions between various components,wl~ich or involve the flow of energy and cycling of materials (Fig. 1.18).

Fig. 1.18: Natural balilnced ccosystcn~.

Inlplicit in the system, such as autotroph (producer) -+ heterotroph, (consumer), or producer + herbivore + carnivore relationship, is the direction of energy movement through the ecosystem. In the process, thc flow of solar energy is unidirectional and it is converted into chemical energy through photosynthesis by plants, which also incorporate in their protoplasm a number of inorganic elements and compounds. These green plants are grazed subsequently by heterotrophs. This means that chemical energy in the form of carbohydrates, fats, and proteins as well as a host of other liutrients are transferred into herbivores. This process continues upto the decomposer level through the carnivores. Another feature of the process is that the energy trapped by green plants when transferred from one food level or tropbic level

Environmental Concerns

An ecological rule of thumb allows a magnitude of 10 reduction in energy as it passes from one trophic level to another. If herbivores eat 1000 k c 1 of plant energy, about 1 0 k cal will get converted into herbivore tissue,lO k cal will get into first level carnivore production, and 1 k cal into second level carnivore production. However, data suggest that a 90 % loss of energy from one trophic level to another may be too high. Transfer of energy from one trophic level to another tells the real story, but such data are hard to collect.

to another also undergoes losses at each transfer along the chain. This is because in an ecosystem, energy is transformed in an orderly sequence (Refer again to Fig.1.8) and is governed by the two laws of thermodynamics. The first and second law of thermodynamics are given below:

1.7.2 Laws of Thermodynamics
1) The first law of thermodynamics deals with the conservation of matter and energy and states that energy cannot be created or destroyed but can only change from one form to another. For example the energy of visible light is absorbed by green plants through photosynthesis and is changed into chemical energy, which.is stored in glucose molecules. (Refer subsection 1.5.6) So in biological context, this principle means that "Energy may be transferred or transformed, but it is not lost". This chemical energy is transformed and used by the cells of the orgallisms through the process of the metabolism for their various activities. Most of the energy is used to for metabolic activities, movement, and other activities of living organisms. 2) The second law of thermodynamics states that part of some useful energy is degraded into unusable waste as heat energy during every energy transformation. The waste heat energy escapes into the surrounding enviroilrnent. This law clearly operates in the trophic levels where at each succeeding level some chemical energy of food is transformed into unusable heat energy. This is because cells of organisms continuously need energy, which is provided to it mainly in form of ATP while some energy gets transformed into unusable heat (energy). Since heat energy cannot do usehl works, more 'energy must be supplied to a biological system from outside to compensate the inevitable energy loss. In order to continue to function - organisms and ecosystenls must receive energy supply on a continuing basis which is provided by the sun. If the energy supply is interrupted, the cell will be unable to function and becomes disordered. Such disorganization can be either a cause or a consequence of cell death. The following diagram (Fig.1.19) depicts the energy transfers and energy losses and nutrient movernent in an ecosystem.

t

.

-

Energy movement

Nutr~ent movement
4

-

Fig. 1.19: A diagram illustrating the manlier in which nutrients cycle through an ecosystem. Energy does not cycle because all that is derived from the sun eventually dissipates as heat.

30

From the above figure, we can conclude the following:
a

Why is Environment Important? Human intervention in natural ecosystem is growing significantly. Human impact on the pattern and quanhlm of energy flow has changed significantly because of the considerable amount of fossil fuel used by urban, industrial and nlral communities. The developing countries of the third world lilce India face perpetual energy shortage. In tl>epresent day world, energy and prosperity go hand in hand. The rich countries have a high rate of consumption. As compared to a citizen in India, a typical person in the U.S. uses: 50 - times more steel 56 - times more energy 1 70F times more synthetic rubber and newspriilt 250 - times more motor fuel 300 times more plastic as much grain as five Kenyans, and as much energy as 35 (a wliole, village!) or 500 Ethiopians.

energy movement is unidirectional (unlike the nutrients which cycle) in an ecosystem, so the initial energy trapped by an autotroph does not revert back to solar input, energy that passes from herbivore to carnivore does not pass back to herbivore from carnivore. As a consequence of this unidirectional and continuous energy flow, the ecosystem maintains its entity and prevents collapse of the system. nutrients cycle in the ecosystem and transfer of nutrients does not involve loss of nutrients like that of energy. This is because the faecal matter, excretory products and dead bodies of all plants and animals are broken down into inorganic materials by decomposers and are eventually returned to the ecosystem for reuse by the autotrophs. (Refer Sectionl.5)

I

Flow of energy through the ecosystem is a findanlental process which can be easily quantified if the energy input to theaecosystem and its subsequent level to another can be expressed in terms of transforination from one tropl~ic calories.

Activity - What would happen if all people in the world become vegetarians? Hints: Humans cannot digest most parts of plants, many kind of alga (which are the producer base of most aquatic food chain). So if people were to become herbivores they would be excluded from many food chains.

1.8

MATTER IN ECOSYSTEM OR GEOCHEMICAL CYCLES

I

By now you must be well aware that the living world depends upon the flow of energy and the circulation of nutrients through ecosystem. Both influence the abundance of organisms, the metabolic rate at which they live, and the complexity of the ecosystem, You have already read ill previous sections that energy flows through ecosystems enabling the organisms to perform various kinds of work and this energy is ultinlately lost as heat forever in terms o f the usefulness of the system. On the other way hand, nutrients of food matter never get used up. They can be recycled again and again indefinitely. This becomes clearer when we say that, when we breathe we inay be inhaling several million atoms of elements that may have been inhaled by the Emperor Akbar or any other person from history. Nutrients that are needed by organisms in large amounts are called macronutrients while those, which are needed in traces are called micronutrients (see Table 1.5). Among the more illan 100 chemicals that occw in nature about 40 are present in living organisms.
Table 1.5: Chemical elements or mineral nutrients that make up living things.
-

Groups
Group I Macronutrients which constitute more than I percent each of dry organic weight

Element

Main Reservoir
Atmosphere
Hydrosphere Atmosphere Atmosphere and Soil Lithosphere The reservoirs or pools of nutrients are the regions where the nutrients occur in bulk.

-

Carbon
Hydrogen Oxygen

Nitrogen
Phosphorus

(Cont.)

Environmental Concerns

* Group IT Macronutrients ( Calcium - which constitute 0.2 to 1 Chlorine Copper percent of dry organic Iron weight Magnesium Sulphur Sodium Potassium
Micronutrients which occur in very miniscule amounts and constitute less than 0.2 percent of diy organic weight, although not present in all species Aluminium Boron Bromine Zinc Cobalt Iodine Chromium

Groups

Element

Main Reservoir
Lithosphere ~ithosphere Lithosphere Lithosphere Lithosphere Lithosphere and Atmosphere Lithosphere Lithosphere Lithosphere Lithosphere Lithosphere Lithosphere Lithosphere Lithosphere ' Lithosphere

-

* Some of the second group of macronutrients may be n~icronutrients some for species and some of the micronutrients may be macronutrients for other species.
1.8.1 Types of Nutrient Cycles
A nutrient cycle may also be referred to as perfect or imperfect cycle. A perfect nutrient cycle is one in which nutrients are replaced as fast as they are utilised. Most gaseous cycles are generally considered as perfect cycles. In contrast sedimentary cycles are considered relatively imperfect, as some nutrients are lost from the cycle and get locked into sediments and so become unavailable for immediate cycling.

Carbon, hydrogen, oxygen, nitrogen and pl~osphorus elements and as compounds make up 97% of the mass of our bodies and are more thai195% of the mass of all living organisms. In addition to these about 15 to 25 other elements are needed in some form for the survival and good health of plants and animals. These elements or mineral nutrients are always in circulation moving from non-living to living and then back to the non-living coinponents of the ecosystem in a more or less circular fashion. This is k~lown as biogeochemieal cycling (bio for living; geo for atmosphere. There are of two basic types of cycles, depending on the nature of the reservoir: Gaseous Cycle - where the reservoir is the atmosphere or the hydrosphere and (ii) Sedimentary Cycle - where the reservoir is the earth's crust. (i)

1.8.2 Gaseous Cycles
a

Let us first study some of the most important gaseous cycles; namely water, carbon and nitrogen. Water Cycle (Hydrologic) -water is one of the most important substances for life. On an average water constitutes 70% of the body weight of an organism. It is one of the important ecological factor, which determines the structure and function of the ecosystem. Cycling of all other elements is also dependent upon water as it provides their transportation during the various steps and it also is a solvent medium for their uptake by organisms. Water covers about 75% of the eartll's sulface, occui-ring in lakes, rivers, seas and oceans. The oceans alone contain 97% of all the water dn earth. Mucli of the remainder is frozen in the polar ice and glaciers. Less than 1% water is present in the form of ice-free fresh water in rivers, lakes, and aquifers. Yet this relatively negligible portion of the planet's water is crucially

-

I

Protoplasm, the physical basis of life, is made up of 90 - 95% of water. Human blood contains 90% of water.

Why is Environment Important?

(

Oceans 97.6 percent

and ghciers 1.8699 percent

[J
(

Ground water 0.5 percent

Rivers, lakes, inland seas 0.02 percent Soil moisture 0.01 percent Atmosphere 0.0001 percent

Fig. 1.20: Global distribution of water. Majority of the world's supply of water is in the oceans. The readily available fresh water is found as ground water in porous rock beds. Although ice sheets and glaciers hold a large amount of fresh water, their turn over is too slow to be usable.

The hydrologic cycle (Fig. 1.21) is the movement of water fiom oceans to atmosphere by evaporation and from atmosphere to oceans and land by m precipitation in the fonn of rain or snow, from land to oceans by n off, rrom streams and rivers and subsurface ground water flow, and from land to atmosphere by evaporation again. This cycle is driven by solar energy in which about one third of all solar encrgy is dissipated on cycling about 10 x lo2' g of water, which is nearly 0.004% of the total; and this is all the cycle. The rest of the earth's water as you know already is time moving in t l ~ c in cold storage (in the form of glaciers and ice).

Figures in diagram based on; mean annual global precipitation of 100 units

,

Total water Oceans 97% Fresh water 3%

F h water m ice sheets and glaciers 75% ground water 25% lakes b.396 soil moisture 0.06% atmosphere 0.035% rivers 0.03%

Fig. 1.21: The water or hydrological cycle depicting most of the major pathways of water movement through the ecosystem - but it does not depict the more recent pathways that have been created due to human activities

Environmental Concerns

The Carbon Cycle
Carbon is present in the atmosphere, mainly in the form of carbon dioxide (C02). It is a minor constituent of the atmosphere as compared to oxygen and nitrogen (Refer again to table 1.5). However, as you are well aware without carbon dioxide life could not exist, for it is vital for the production of carbohydrates through photosynthesis by plants and is the building block of life. It is the element that anchors all organic substances from coal and oil to DNA (deoxyribonucleic acid: the compound that carries genetic information).

Fig. 1.22: (a) Generalized global carbon cycle. The carbon cycle The atmosphere contains about 740 x 1012kilogram (kg) of carbon, while the oceans hold approximately 43,000 x 1012kg. Deforestation and burning of fossil fuels contribute about 1 x 1012and 5 x 1012kg annually, respectively, of which about 3 x 1012accumulates in the atmosphere. Some of tile remaining 3 x 10" kg is dissolved into the oceans, but the fate of much of this carbon dioxide is yet to be traced.

Carbon is returned to the environment about as fast as it: is removed. Figure 1,22 illustrates the global carbon cycle. Carbon froin the atlliospheric pool moves to green plants, and then to animals. Finally, from them directly to the atmosphere by process of respiratian at various trophic levels in the food chain or to bacteria, fungi and other micro-organisms that return it to atmosphere through decomposition of dead organic matter. Somc carbon however enters a long term cycle. It may accumulate as undecomposed organic matter as in the peaty layers of bogs and moorlands or as insoluble carbonates (for exainple the insoluble calcium carbonate ((CaC03) of various sea shells) which accunlulate in bottom sediments in aquatic systems. This sedimentary carbon eventually turns into sedimentary rocks such as lime stone and dolomite and may take a long time to be released. In deep oceans such carbon can remained buried for millions of years till geological movement may lift these rocks above sea level.

These rocks may be exposed to erosion, releasing their carbon dioxide, carbonates and bicarbonates into steams and rivers: hard water has usually flowed throcgh lime stone at some point, picking up carbonates which they accumulate as 'fur' in kettles when .the water is boiled. Fossil fuels such as coals, oil and natural gas etc. are also part of the carbon cycle which may release their carbon compounds after several of years. These fossil h e l s are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When fossil fuels are burned the carbon stored in them is released back into the atmosphere as carbon-dioxide. Carbon cycle basically involves a continuous exchange of carbon dioxide between the atmosphere and organisms on one hand, and between the atmosphere and the sea, on the other. The immediate source of carbon dioxide for exchange in the oceans is restricted to surface layers of water. The carbon balance of the biosphere as a whole is moderated by exchange of COa between the atmosphere and oceans (which are the richest source of carbon today). The oceans contain about 50 times more COz than the atmosphere. This regulates atmosphere COz level to 0.032% despite photosynthetic uptake. Scientific concerns over the linked problems of increased atmospheric COz concentrations, massive deforestation and reduced productivity of the oceans due to pollution will be discussed in coming units. The Nitrogen Cycle Nitrogen is an essential constituent of protein which is a building block of all living tissue. It constitutes nearly 16% by weight of all the proteins. There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms. Nitrogen needs to be 'fixed', that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. Nitrogen fixation on earth is accomplished in three different ways: (i) by certain free-living and as well as bluegreen algae (e.g. Anabaena, Spirulina) symbiotic bacteria and blue green algae, (ii) by man using industrial processes (fertilizer factories) and (iii) to a limited extent by atmospheric phenomenon such as thunder and lighting. At present, the amount fixed by man industrially, far exceeds the amount fixed by biological and atmospheric actions. As you can see from Figure 1.23, ilitrogen at any time is tied up in different 'compartments' or 'pools' - the atmosphere, soil and water, and living organism. The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth's surface througl~ precipitation and then into the soil to be utilized by plants. More importantly, however, are certain microorganisms capable of fixing atmospheric nitrogen into ammonium ions ( N H ~ These include freeliving nitrifying ~. bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguininous plants and symbiotic bacteria living in nonleguminous root nodule plants (e.g. Rhizobium) as well as blue green algae (eg. Anabaelza, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria: Nitrosomonas bacteria promote

Why is Environment Important?

Volcanoes are also important sources of nitrogen. They have been emitting small quantities of nitrogen for centuries and contribute significantly to the nitrogen reservoir of the atmosphere.

The symbiotic bacteria capable of fixing atmospheric nitrogen live in the root nodules of leguminous plants like beans, peas, alfalfa etc. In agricultural ecosystem legumes of approximately 200 species are the pseeminent nitrogen fixers. In non-agricultural systems some 12,000 species ranging from cyanobacteria to nodulebearing plants, are responsible for nitrogen fixation.
/

35

Environmental Concerns

transformation of ammonia into nitrite. Nitrite is then further transfoimed into nitrate by the bacteria Nitrobacter. The nihates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem. During excretion and upon the death of all organisms nitrogen is returned to the soil in the fomm of ammonia. Certain quantity of soil'nitrates, being highly soluble in water, are lost to the system by being transported away by surface run-off or ground water. In the soil as well as oceans there are special denitrifyiilg bacteria (e.g. Fseudomonas), which convert the nitrateslnitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus completing the cycle. Nitrogen has become a pollutant because of human intrusion into the natural cycle and this can disrupt the balance of nitrogen in the air.

Fig.1.23: Generalized nitrogen cycle.

1.8.3 Sedimentary Cycle
Phosphorus, calcium and magnesium circulate by means of the sedimentary cycle. Sulphur is to some extent intaymediate, since two of its compounds hydrogen sulphide (H2S) and sulphur dioxide (SOz), add a gaseous coillponent to its normally sedimentary cycle. The element involved in the sedimentary cycle normally does not cycle through the ahnosphere but follows a basic pattern of flow through erosion, sedimentation, mountain building, volcanic activity and biological transport through the excreta of marine birds. The sulphur cycle is a good example for illustrating the linkage between air, water and the earth's crust, and hence, a brief account of this cycle is given. Sulphur Cycle

The sulphur cycle is mostly sedimentary except for a short gaseous phase. (Fig. 1.24) The large sulphur reservoir as mentioned before is in the soil and

sediments where it is locked in organic (coal, oil and peat) and inorganic rock) in the form of sulphates, sulphides and deposits (pyiite rock and sulphr~r organic sulphur. It is released by weathering of rocks, erosional runoff and decomposition by bacteria and fungi of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution. Sulphur is found in gaseous forms like hy& *nsulphide and sulphur dioxide in small quantities in the atmosphere, wtll. is thti:, a small reservoir. Sulphur enters the atmosphere fi-om several sources lilce volcanic eruptions, combustion of fossil fuels, from surface of ocean and from gases released by decomposition. Atnlospheric hydrogen sulphide also gets oxidised into sulphur dioxide (SO2). Atmospheric SO2 is carried back to the earth after being dissolved in rainwater as weak of sulphuric acid (H2S04). Whatcver the source, sulphur in the f o m ~ sulphates. ( ~ 0 ~is'take) up by plants and incorporated through a series of metabolic ~ processes into sulphur bearing amino acid which is incorporated in the proteins of autotroph tissues. It then passes through the grazing food chain. Sulphur bound in living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excrelion and deconlposition of dead organic material. Under aerobic conditions h n g i like Aspergillus and Neurospora and under anaerobic conditions the bacteria like Escherichia and Proteus are largely responsible for the decomposition of proteins.
{I

Why is Environment Important?

= oxidation

m = mobilization im = immobilizatiog

Fig.1.24: The sulphur cycle showing the two reservoirs namely, sedimentary and gaseous. Major sources from human activity arc the burning of fossil fuels and acid drainage from coalmincs.

In anaerobic soils and sediments hydrogen sulphide is formed by sulphate reducing bacteria like Desulfavibrio. Species of Beggiatoa oxidise hydrogen sulphide to elemental sulphur and species of Thiobacillus oxidise it to sulphate, There are also green and purple sulphur photosynthetic bacteria that oxidise hj;drogen sulphide to elemental sulphur. You should bear in mind that the nutrient cycles discussed here are only a few of the many cycles present in the ecosystem. You should also be aware that these cycles usually do not operate in independently but interact with each other at some point or the other. This can be been clearly in Fig.1.25.

Environmental Concerns

1.9

BIOTIC RELATIONS

Why is Environment

Important?

The biological community is a complex network of interactions. These interactions take place not only among different individuals of the population of the same species intraspecific relation but also among individuals of different species in a community - interspecific relations.

1.9.1 Intraspecific Relations
The interactions between members of the same species are known as intraspecific relations and these are frequently very strong varying from open conflict to gregariousness (social togetherness). Some species like inoose are quite solitary while some animal populations exhibit varying degrees of social organisation. Many species exhibit territoriality i.e., individuals compete for the 'rights' over some poriions of their habitat. The winner uses the territory and the losers have to leave. Territoriality serves to diminish destructive competition for resources such as food or habitat etc. by limiting the number of organisms of a species in a given area. Intraspecific relations are also expressed in pattern of hierarchy of species or dorninanl and subordinate relationship in the population, The dominant subordinate relationships are more prominent when the choices for inates arises. Extreme social organisation is found in the structure of colonies of insects like termites, ants and bees. Let us see how intraspecific relalionships affect the population.
Population growth, when resources are not limited

Population growth can be determined by looking at factors tl~at.tend increase to the number of individuals in thal population, like birth and im~nigration and chose factol-sthat tend to decrease the number like death and emnimgration. By looking at table 1.6 you can see [he factor that increase or decrease the populations. For example by looking at the table you can note that higher reproductive potential of a species increases its population while low reproductive potential decreases it.
Table 1.6: Population growth depends on the net effect of all the given factors. These factors in turn are the result of species characteristics and environmental conditions Factors
I . Reproductive

Increase in Population High

Decrease in Population Low

2.

3. 4. 1 5. 6.

7. 8.
9.
L

potential Number of individuals capable of reproduction Food I-labitat Clirnale Irumigration Emigration Disease Predation

Large nlentv Space available favourable
high low Low Low

small Scarce Space not available

Hi fill
high
---^.

_

r

Let us imagine [hat we select a single bacterium and allow all its descendents to grow hnd reprocluce without any restriction. In a month this bacterial colony

39

Environmental Concerns

would be larger than the visible universe and it would be expanding outwarc at the speed of light. All populations have the potential for explosive growtl under optimal growth conditions because nearly all mature individuals can produce offspring.

Population with a positive rate of natural increase grow large each year. Thc expected increase (I) for a year can be calculated by multiplying the rate of natural increase (r) by the current population size (N) I=rN b 2.d where r = N

N = Number of individuals
b = birth rate d = death rate

This formula indicates that population growth is exponential: which mea that population size increases by an ever larger amount each year under favourable coliditions. When a graph is plotted for the populatioil size, the resulting growth curve is J shaped as shown in Figure 1.26. This type of exponential growth occurs mly under conditions of unlimited resources. However, Except under laboratory conditions, no population can expect find resources unlimited for population growth. In unlimited resources a~ ideal environmental conditions, a species can produce offspring at the maximum rate. This is called biotic potential. We will discuss these conce in greater details in section 1.13 dealing with human population. Population growth when resources are limited

Fig.1.26: The J-shaped curve of population growth of a species.

.
I

Species like bacteria and mice which can produce a large number of offspring in a short time have high biotic potential while larger species like elephants and humans that produce only a few offspring have a low biotic potential.

If the chief resources such as food and space are limited, a habitat cannot support any populatibn beyond a certain size. If the population goes beyoiid i limit, resources limitation shows its adverse effects on population by increasing death rates and decreasing birth rates and population density declines to a limit set by available resources in the habitat. The maximum number of individuals of a population that its enviro~~ment support can and sustain is called the carrying capacity (K). The carrying capacity is a concept related to sustainability. It is usually defined as the maximum number of individuals of a species that can be sustained and supported b the environment in a given area.

Population size is believed to level off at the carrying capacity (K) of the environment (Fig. 1.27). When carrying capacity is reached the11N = K and r yalue will be zero. In other words, birth rate equal death rates and population . should maintain a steady state equilibrium. However, as the population increases in size, there will be more competition for the available space and food, which in turn will affect population growth.
I

I

All the limiting factors that reduce the growth rate of a population constitute environmental resistance. These factors include predation, competition for resources, food shortage, disease, adverse climatic conditions and unsuitable habitats. So what happens to the J-shaped curve that you have studied earlier due to limiting factors? You will see that it changes to S shape or to a sigmoid curve: (Fig. 1.27)

Exponential

Dynamic steady.state-phase

I I

Why is Environmeot Important?

Time

Fig.:1,27: The J-shaped curve is converted to an S-shaped curve when a population of encounters environmental resistance and tl~resl~old ally one of the limiting factors is exceeded.

1s 1

to ~d 1ts

When we are talking about carrying capacity it is'also important to talk about the carrying capacity of the earth. For the human population, the cai~ying capacity depends in part on our value for the environment. So we have to question ourselves as to whether we want our f~lture generation to live short lives in crowded surroundings without a chance to enjoy the Earth's scenery and diversity of life? Or do we hope that our descendants will have a life of high quality and good health? Once we choose a goal for the quality of life, we can use scientific information to understand what the carrying capacity might be and how we might achieve it. 1.9.2 Interspecific Relations Interspecific relations involve more complex iiiteraction since the set of environmental factors influencing each of the interacting species !re often so different. The relation may be direct and close as bet*een a tiger and deer, or indirect and remote as between an elephant and a beetle. There are several interspecific relationships between different species. W e will be dealing with three main types of relationships namely - symbiotic relations, competition and predation

L

I. SYMBIOTIC RELATIONS

Y

Some time two types of organisms have a permanent relationship in which at least one depends upon the other for survival. This is called a symbiotic relationship or.symbiosis. There are several types of symbiosis, out of which we will deal only a few namely Parasitism, Mutualism and Commensalism. Parasitism is an interaction in which one species, namely the parasite benefits and the other, the host, is harmed. For the parasite (which is much smaller in size) the host is a source of both food and shelter. A well adapted parasite does not kill its host, otherwise its source of nourishment would be lost. Parasites generally have.higher teproductive rate and exhibits a greater host specificity. They are often highly specialized in structure, physiology and life history patterns, Because of host specificity many parasites can live in only one or a few related host species, and such intimate host - parasite interaction could be potentially limiting to both the population. ii) Mutualism is a symbiotic relationship that is beneficial to both organisms. Lichens are a well known example of mutualism. Lichen consists of fungi and algae growing in close association with one i)
Tapeworm and malarial parasite have become adapted to a totally parasitic life.

i

Environmental Concerns

another. The fungi can hold water but cannot produce their own food due to lack of chlorophyll while the algae cannot hold water but can produce their food when supplied with water. Thus these two organisins combine their functions by living together and both get enough food and water. There are several cxamples of mutualism of plants and animals in nature. iii) Commensalism is a symbiotic relation in which one organism benefits z the other is unaffected. An example of coinmensalism is that of the rcm fish and shark. Remora, a small fish attaches itself to the under side of shark from where it feeds on leftovers from the shark's meals and gets f transport. The presence of the remora does not benefit the shark but neither does it harm the shark.
11. COMPETITION

Competition occurs in nature usually, but not necessarily, when resources liE food, space, mates etc. are limited. Resource limitation leading to competitil is implicit in Drawin's idea on struggle for existence and survival of the fitte What happens when two related species compete for the same resource? Thi outcome usually depends on how 'competitive' the species are. If one specic is competitively superior, it will eventually exclude the other species from tlhabitat, a phenomenon referred to as 'Gause's Principle of Competitive Exclusion', named after the Soviet biologist G.F. Gause (Fig. 1.28). If both ; equally strong competitors, the outco~ne depends on the initial conditions; ar , uncertain and unstable coexistence is possible. If however, both species are weak competitors, both could co-exist p.eacefully indefinitely in the same habitat.

c

time (days)

,

Fig. 1.28: Competition between two species of Paramecium. When grown separately, Pi caudatum (a) and P. aurella (b) established stable populations (c) When grow ' together,'P.aurelia (bold line) drove the other species (dotted lines) toward extinction.

Gause's competitive exclusion principle states that two species having identical requirements cannot occupy the same 'niche' indefinitely. So what is the niche of a species? A niche is the unique functional role or place of a species in an ecosystem (Fig. 1.29). It is a description of all the biological, physical and chemical factors that a species needs to survive, stay healthy and reproduce. A niche is unique for a species, that means no two species have exactly identical niches. Niche play an important role in conservation of organisms. If we have to conserve a species in its native habitat we should be knowledgeable about the niche requirements of the species and should ensure that all requirements of its niche are fulfilled.

Why is Environment Important?
1. Habitat niche - where it lives 2. Food niche - what is eats or decomposes & what species it competes with 3. ~eproductive'niche how and when it reproduces. 4. Physical & chemical niche - temperature, land shape, land slope, humidity & other requirement.

d

Fig.1.29; A niclie is unique for a species. No two species have exactly tlie same niches. If two species (lid have identical niclies then coinpetition for the sanie food and living space would mean that one species would either die out or be driven away.

111.

PREDATION

This is an interaction in which one organism, the predator kills another, nanlely the prey for food. This is a process of paramount importance not only i n natural ecosystems but to man as well, because he is either directly a predator himself or has to deal with natural predators which ace directly harmfill to him or kill prey that are beneficial to him. First let us consider the importance of predation in nature. Following are its important roles:

Environmental Concerns

1) Predation helps to channelise the energy fixed by photosynthetic pi through different trophic levels. , 2) Predators can bring down the intensity of interspecific competition community by selectively preying on the competitively superior spc and thus keeping their densities low. This permits the weaker speci persist in the habitat. 3) Predators also appear to be responsible for maintaining high specie: diversity in many biological communities. Experimental removal o predators from a community has been known to lead to the eliminat some species and a general decline in species diversity. 4) Predators in some cases can regulate the population densities of thei Predation is obviously not beneficial to the individual organism that killed and eaten as food, but could be very beneficial to the prey population as a whole.

In an ideal situation, the prey and predator populations show what are ca 6coupledoscillations' over a period of time. Let us see how these oscil
occur in a habitat with plenty resources, prey numbers start increasing. result predators get more food & produce more offspring. With increasin predator population in the habitat, more and more prey are killed, bringi~ down their populatiol~ eventually. Now due to low density of prey'ir size habitat the predators cannot obtain enough food and so their number star falling. These events lead to oscillation in densities of both prey and prec It is important to mention that the situation will turn out different if the predator is not prudent or is too efficient at killing prey. This could resuli killing of every prey individual, driving the prey species to extinction. TI. would subsequently lead to elimination of the predator as well, due to starvation.

I . HOMEOSTASIS
In order to find solutions for environmental problems the understanding c systems and rates of change occurring in the systems illcluding the ecosy! is essential.
1

110.1 System
A system, may be broadly defined as any part of the universe that car isolated for the purposes of observntipn and study. Some systems may physically isolated - for example bacteria culture in a petri dish - or may isolated in our minds or in a computer database. In another way you can visualise a system as a set of components or parts that function together tc as a whole. A single organism may be considered a system as may be a ri1 your office, a city or a thermal' power plant. On a much larger scale, you already know that biosphere is also a system.
"

44

At every level in environmental science we have to deal with a variety oP systems that may range from simple to complex and irrespective of how v approach environmental problems its is necessary that we have an understanding of the systems and of how various parts of the systems int with one another, Systems may be open or closed. A system, which is op with respect to some factor, exchanges that factor with other systems. Th Ocean is an open system in regard to water, which it exchanges with the, atmosphere. A system that is.closed in regard to some factor does not ex6

i

that factor with other systems. Earth is an open system in regard to energy and a closed system (For all practical purposes) in regard to material. All these systems in order to operate smoothly need to maintain their existing constant condition. This capacity of a system to self regulates or self maintain itself is called homeostatis. What keeps the system fairly constant is a feedback mechanism. The feed mechanism provides environmental information to which a system responds.

Why is Environment Important?

1.10.2 Feedback Mechanism
Systems respond to inputs and have outputs. Our body for instance is a complex system. If by chance you ellcounter a snake, whicll you think is poisonous, then the sight of the snake is an input. Our body reacts to the input. The adrenaline level in our blood rises; our heart rate increases and the hair on our body may rise. Our response - perhaps standing still or moving away from the snalte - is an output. Feedback, a special type of system response occurs when the output of the systemalso serves as input and leads to changes in the state of the system. A classic example of feedback is temperature regulations in human (Fig. 1.30). The normal temperature for humans is 37°C. We call such a norm - a set point: When the temperature of the environment rises the sensory mechanisms in the skin detect .the change (input) and the body responds physiologically.
Stilnulus (input)

:d Lions a

tor.

n

tern

act ~er ,
)

I
ract
e

Effectors

I

en

hange

Fig. 1.30: Negative and positive feedback mechanisms. In negative feedbadk the response inhibits or reverses any change from the normal. Positive feedback leads to further change in the same direction. Negative feedback brings the system back to the set point. Positive feedback leads away from the set point and can damage the system.

Concerns

A message is sent to brain, which automatically relays the message to the receptors which enhances increase in blood flow to skin, induce sweating anc stimulate behavioural responses. Water excreted through the skin evaporates cooling the body. The person may also respond behaviourally: as on feeling hot (input) he or she may move into the shade as a result of which the temperature would return to nolmal. This is an example of negative feedbac since the systems response is in the opposite direction from the input, and ha1 or reverses any deviation movement away from set point (an increase in temperature leads due to response a decrease in temperature).

In the case of positive feedback, an increase in input leads to a further increa in output. For example if the enviro~lmental temperature bccomes extreme ar the body temperature keeps on increasing correspondingly the hoineostatic system of the body breaks down, which is because when it gets too hot, the body is unable to lose heat fast enough to maintain normal temperature, as a result of which the metabolism speeds ups, raising body temperature until the person dies of heat stroke. Thus a situation in which feedback reinforces change, driving the system to higher and higher or lower and lower values is called positive feedback.
Negative feedback is generally desirable as it is stabilizing. 1t.usually leads t a system that remains in a constant condition. Positive feedback often called vicious circle is destabilizing.

1.10.3 Ecosystem Homeostasis

Let us see how the feedback in an ecosystem helps to maintain homeostasis or balance. The ecosystem as you must know by now is a dynamic system, wher

i

a lot of events occur, like plants eaten by animals, which in turn are eaten by other animals. Water and nutrients flow in and out of the system and the weather changes. However, despite all these events the ecosystem persists anc recovers from minor disturbances due to homeostatis. Consider a grassland which has suffered from drought due to which plants do not grow well and which have a mice population. The mice that feed on grass become malnourished due to lack of food, When this happens, their birth rates decreases. Furthermore, the hungy inice retreat to their burrows and sleep. B j doing so, they require less food and are exposed less to predators. As a result their death rates decreases. Their behaviour protects their own population , balance as well as that of the grasses, which are not being eaten, while the mick hibernate (sleep). Thus you can see that the ecosystem has maintained its balance or ecological homeostasis as a result of negative feedback mechanism, which is the prime regulatory mechanism for the ecosystem as a whole. You must be fully aware by now that in an ecosystem several kinds of organisms ar; present. Thus all the organisms in an ecosystem are part of several of different feedback loops. A feedback loop may be as a defined relationship in which a change in some original rate alters the rate of direction of further change. Now let us consider another important parameter of ecosystem balance, which is species diversity, Species diversity - the number of different species and their relative abundance - in a given ecosystem accord the stability or persistence to the ecosystem under small or moderate environmental stress. High species diversity tends to increase long-term persistence of the ecosystem. This resilience is due to the fact that risk is spread more widely with the presence of many different species and the linkages between them.

An ecosystem having several well-adjusted species has more ways available to
d
>

:k ts

se ld

respond to most environmental stresses. For example, in an ecosystem endowed with complex food web, the loss or drastic reduction of one species does not threaten the existence of others, as Most con*sumershave alternative food supplies. Ih contrast, the highly specialised ecosystem, planted with only one kind of crop (monoculturin'g) plant like wheat or rice is liigbly v'ulner'able to destruction from a single plant pathogen or pest. The essence of the above discussion is that most balanced ecosystems contain many different types of species and that the presence of many types of or high species diversity imparts stability to the ecosystem.

Why is Environment Important?

r

The ability of an ecosystem to cope with any disturbance or disruption is however limited and fails in cases of positive feedbacks like fires (destruction of landscape), over exploitation (widespread mining, deforestation), excessive simplification (monoculture, plantation, crop fields) or extreme and prolonged stresses (like drought, pollution). In extreme cases the homeostatic mechanism are overshadowed leading to ecosystem degradalion. It is essential that we sl~ould check and control our actions, so that we do not overload the ecosystem and disrupt its homeostasis.

Activity
Discuss how monoculturing can cause disaster in Indian farming,

1.11

COMMUNITY AND ECOLOGICAL SUCCESSION

You will recall fro111subsection 1.5.2 that a community is also called biotic community. It is a group of interacting populations living in a given area. It represents the living pait of an ecosystem and functions as a dynamic unit with trophic levels, an i ~ i eflow and a cycling of nutrients as described earlier. r ~ ~ Some of the species interactions such as predator-p ey relationships, mutualism and cornpetition have been described earlier. (see subsection 1.922). The organizational components of a biotic community seem to us for the most part to be static or suspended in time. However, biotic communities do exhibit their normal developmenl. Com~n~~rlities for progressive change as part%of example, change in response to climatic and geological forces as well as in response to the activities of their inhabitants. In some cases even within n parlicular climate, the inhabitants of a location are not h e same from one year .to the next. Organisms that live in a given location may change [he environment by their very presence or activities. An environrner~t favoured that an organism earlier may over time becomes progressively less favourable to them and may become more favourable to other life forms. Thus one type of organism may make way for another.

~he,orklerl~ process of change or replacement of.some inhabitants or species of the conhunity in an area, through time is known as community development or more traditionally as ecological succession.
E.coolgica1 succession, on lhe basis of the force responsible for.tlie chang'e.or succession are of two kinds: (1) autogenic succession - where ecolbgical succession is the product of the organisms-themselves and (2) Allogenic. succession - where succcssion occurs due to outside Iorces particul,arly physical forces such as fire or flood which regularly affect change. In most

Environmental Concerns

cases, succession is a result of both autogenic and allogenic factors although one or the other may have triggered the process. Allogenic succession is less predictable than autogenic succession. For example, the sudden bloom of unexpected opportunistic species such as weeds often interrupts an orderly progression of species during succession. The accidental introduction of congress weed (Parthenium sp.) along with wheat imported from the USA (PL480) into India is a good example of opportunitic species. Often one population does not give up its place for the next gracefully. On the contrary species are often quite persistent and seemingly resist their own displacement. Ecological succession includes both (1) primary and (2) secondary succession. Each succession stage or the series of sequential changes in its entirety is known as a sere and each sere is made LIP of a series of seral communities (seral stages).
1.11.1 Succession in Terrestrial community

I

-A

..,.

Seres of particular environments tend to follow similar successions and may therefore be classified according to environment for example, a hydrosere develops in an aauatic environment as a result of the colonisation of open water; and a halosere develops in a salt marsh.

1. Primary succession occurs where no community exists before, such as rocky outcropping, newly formed deltas, sand dunes, emerging volcanic islands and lava flows. An example, which can be used as a model s&winR development of primary successibn, is the invasioil and colonisation of bare rock as on a recently created volcanic island.

I

,

Trees and shrubs are unable to grow on barelrock due to insufficieilt soil. Primary succession sere thus begins with lichens. Lichens can invade and colonise such areas, coming in, by various methods of dispersal and gaining a foot hold by means of their tenacious, water-seeking fungal component anc thus forming the first community, very appropriately often called the p i o ~ ~ community. (Fig.1.31). Lichens are soil builders, producing weak acids that . very gradually erode the rock surface. As organic products and sand particle accumulate in tiny fissures, mosses, larger plants, such as grasses also get an opportunity to establish themselves and begin a new seral stage. In time lichens that made the penetration of plant roots possible are no longer able ti compete for light, water and minerals and will be succeeded by larger and , more nutrient demanding plants such as shrubs and trees.

Ultimately "the final stable and self perpetuating community which is in equilibrium with its environment", is formed and this is qalled climax , community. The climax community is the most productive commuility that' the environment can sustain. The animals of such a community also exhibit succession, which to a large extent is governed by the plant succession, but , ' is also influenced by the types of animals that are able to migrate from neighbouring communities. I
I,
1

I

A climax community is more complex and is dominated by a few species that came Iate in the succession. The community becomes self perpetuating and its appearance remains the same though there is constant replacement of individuals. The nature of the climax is determined by environmenta1 I conditions such as temperature, humidity, soil cl~aracteristics, topographic ! a features and so on. A climax community has much less tendency than earlier successional communities to alter its environment in a manner injurious to itself. Fig. 1.3 1 illustrates the primary ecological succession in a, terrestrial habitat.

I

1

The succession on bare rock out croppings is initially an extremely slow process with a sere often lasting hundreds of years or more. But once soil formation has begun, the process usually accd~erates: Succession in other types of habitat may be slow. It has been estimated that succession from sand dune to climax' forest community on the shores of Lake Michigan took about a thousand years.
Fir, birch and white spruce
community

..

A.

black spruce

Why is Environment Important? though succession ends with the establishment of a climax community, this does not mean that a climax community is static. It does change though slowly, even when the climate is constant. It will change rapidly however, if the community is disturbed in some way.

Fig. 1.31: The orderly series of species replacement during succession can be seen in this sequence of plants from a bare rock outcropping to a fir-birch-spruce community. Pioneering lichens and mosses begin the soil-building process, followed by the invasion of increasingly larger plants until a more stable longlived, climax forest community emerges.

2. Secondary succession occurs where a community has been disrupted, sucli as previously burned or neglected farms reverting to the wild, or a forest community that has been subjected to 'forest clearing' or a mining area that has been reclaimed (Fig. 1.32).

Fig.1.32: A community formed through secondary su&:'ession subsequent to the area being reclaimed after limestone mining.

Environmental Concerns
Secondary succession in grassland communities is much faster, taking 20 to 40 years while on the other hand, fragile disturbed tundra may require many hundreds of years to recover, if it ever does.

In secoi1dar-y succession, the basic features are similar to those of primar succession, but the seres occur at a more rapid pace. This is possible because the soil is already fonned and available. Secondary succession said to occur when the'surface is completely or largely denuded of vegetation but has already been influenced by living organisms and has i organic component: I11 such areas seeds, spores and plant propagates, su as rhizomes may be present in the ground and thus influence the successi As'secondary succession progresses, the initial invader species are eventually replaced by plants froin surrounding communities. Larger, fa, growing trees appear and may block the sunlight and so a new generatior shade -tolerant shiubs emerge below the canopy of trees. Finally there i general blending with the surrounding community. Such a transition ma7 take well over 100 years, depending on the cornn?unity. In both primary and secondary succession the flora and fauna, of suirounding areas are major factors influencing the types of plants and animal entering the succession through chance dispersal and migration.

1.1 1.2
Lakes and ponds rich in nutrients and high in productivity are called eutrophic (true foods), while those with limited nutrient supply and little productivity are termed oligotrophic.

Succession in Aquatic Habitat

Aquatic habitats also undergo community development or succession althou such changes may be held in check by shortages of nutrients. Succession in ponds and lakes take place as a result of eutrophication. Eutrophication means changes brought about by increase in nutrients carried by strean and runoff from the land. The general trend in fresh water bodies is towards increased eutrophication E thus increased community growtll, but the deficiency of any of the essential nutrient rnay reverse the trend.

Fig. 1.33: Succession in a pond.

As the commul~ity development in a fresh water body progresses, the sediments increase and the depth decreases, The shores are crowded by littort zone plants, which extend further and further into the water body, followed b; I increasing numbers of water tolerant shore plants (Fig.1.33). Unless this progress is interrupted, the water body will be transformed into a marsh and ;

Environmental Concerns

Natality - is an expression of the production of new individual in the population. In human population natality is equivalent to the birth rate, and is usually expressed as the number of births per year per thousand persons in the population. The growth rate of the population can be zero or positive but neve negative. The natality rate of the population is expressed by

L

where B = birth or natality rate Nn = number of newboi-ns, and t = time. Mortality refers to death rate of individuals. In a population, members die du to various causes, such as malnutrition, disease, accidents and old age. Mortality is also expressed as death per year per thousand persons in the population.

where d = mortality or death rate D = total number i f death and t = time Migration is the niovement of people to new hoines either within tlie boundaries of a countly (internal migration) or across the boundaries to anothe country (international migration). Only international inigration can affcct the growth of population within a countly. In some countries migration is large enough to have a significant effect on the growth rate.
-"

Emigration is the entry of people into a city or couiltry and this also affects the population. Thus in order to take account of the movement of people in calculatiilg population growth, we must add the ne$ migration (which is negative if emigration is greater than migration), to the population count.
1.12.2 Population Histograms

A population histogram (Fig. 1.34) is a bar graph, drawn for a particular y2ear, in which each horizqntal b a r represents a particular age group of thc population. The length of the bar on the left tells us the number of percentage of male (of the total population) in this age group, and tlie saille is shown for female on the right. A histogram can tell us a n~rmber things such as: of
1) The Age structure of the population i.e., the percentage of the population in a significant age group, such as those who are dependent on others for support, or those who can do productive work. 2) The sex composition i.e. the number (percentage) of males and females in each age group, from which we can also tell the number of females in the reproductive ages 15 - 44. 3) The impact of growth and changes in the population over several decades in the recent past, and 4) The likely growth of the population in'the next few decades, at the current growth rates.

1.12.3
j

Types of Histogram

Why is Environment Important?

:r

Expansive histogram - The population histograin with an expanding base is . called an expailsive histogram. It is typical for the developing countries, whose populations are growing very rapidly. (Fig. 1.34a) Constrictive histogram - In this type of histogram the base is smaller (constrictive). As you can see in Fig. 1.34 bywhich depicts a population constrictive histogram of USA, there are fewer children being born in each 5 year group than before. However, this does not mean that the population in the United States'is not growing. You can see a definite bulge during the year 5065 during which period there was a 'baby boon^'. As this bulge passes through, ' the reproductive years this will result in more children than the parents. Thus even if China's one child - per - couple policy was enforced during early 1980's, China did not achieve its goal of stabilizing population at 1.2 billion in the year 2000. Instead, it grew to 1.3 billion in 2000 and will inevitably increase to about 1.5 billion by 2025. Stationary histogram - In this type of histogram (Fig. 1.34 c) each bar is not very different till we come to the age groups (over 75 years) where death rates are significant. This means that for inany years the average family size has just been sulficient to replace itself. Such a population is not growing at all, hence the name stationary.

e

Expansive
Rapid growth : Kenya

Constructive
Slow growtlr : United States

Near stationary
Decline in growth : Austria

Year of birth.

Percentage of population

Percentage of population

Perdentage gf population

Pig.1.34: Population histograms for Kenya, the United States and Austria

.

53

Environmental Concerns

1.12.4 Population of India

India next only to China is one of the most populated countries in the wo Although India occupies only 2.4% of the total area of the world it suppc over 15.6% of the world population, as revealed by statistics.

On sunday August 15, 1999, India's population passed one billion mark. Ea year India is adding 18 million people (roughly another Australia). U.N. demographers project that by 2050 it will have added another 530 millioil people for a total of more than 1.5 billion. If India coiltinues on the demographic path as projected, it will overtake China by 2045, becoming tht world's most populated countiy, but there are doubts as to whether the natur resource base will support such growth.

Demographers estimate that even if India could reduce its average family s to 2.2 children (replacement level fertility) in the next 33 years its cun population would continue to grow until it reaches two billion by 2100.

-

1.12.5

Future of Human Population: Where Are We today?

Global population has quadrupled in 100 years, a rate of increase unlcnow~~ il previous history. Especially since 1960, several developments have dramatically reduced infant and child mortality throughout the world. (The u of DDT to eliminate the mosquito - borne malaria; childhood immunizations and antibiotics). During the same period, the "Green Revolution" has greatly boosted food output through the cultivation of new disease resistant, high yic hybrid varieties of wheat. These changes have been greatly responsible for a dramatic increase in human population.

The global earth population crossed 6 billion mark in September 1999. Duri! this decade it will increase by another billion, the fastest population growth i, history. It was only 2 billion in 1930. Every second about three people are added to the world; every day a quarter of a million are added. Evely year, about 87 million people are added to the world. A recent joint statenlent by t U.S. National Academy of Sciences and the British Royal Society finds that population is growing at a rate that will lead to doubling by 2050.

It seems clear that in the next century, the earth will have to support twice as many humans as it does today. Can our planet do this? Cleai.ly, the answer i We are maintaining our present population of 6 billion oilly by rapid depletio our resources: ground water, topsoil, tropical forests, biodiversity, fossil fuel: clean air, etc. Today, approxiniately 40 per cent of the earth's photosyntlietit productivity is used or influenced by human activities. Thus we will have to the consequences of over population and degradation o r our environment.

The question arises can we build a "sustainable society"? For an answer in th affirmative we have to make profound changes on a global level. We have to develop international policies to regulate critical resources such as fresh wate forests, fossil fuels, and the atmosphere and take steps to minimize the damah that has already taken place. Now is the time to tackle serious problems because to delay will have dire consequences.

Activity
years and t y to plot a graph. Make your inferences by observing the graph. r

,

Try to find out the population data of your city/village/State for at least past 3

.ld. lrts
2t l

What is the shape of curve and why it is so? Has the population gone up or down during these years? Identify the factors responsible for the population level. Discuss the factors you think are responsible for growth or downfall of population growth. Also suggest ways to reduce the population as we are seeing high population growth rate in India and we need sustainable development.
--

Why is Euvironment Important?

1
11
.

CONSTITUTIONAL OBLIGATIONS OF A CITIZEN

ize :nt

In the later part of this course you will learn about the laws or legislations pertaining to the environment. We have national and international laws on environment. However, the fact is that enviroilment knows no boundaries. If the snow melts from polar caps, all the cities lying in low areas of the world will get flooded. In case of a nuclear disaster, deadly radiations are bound to travel as much as the climate permits as radiations do not know boundaries of citylstate/countiy/continent or direction. Radiations are going to affect who ever comes on their route. So the environment is our's not his or her's. It is our constitutional obligation to care for the erlvironment and have sustainable development. This is more important because Nature does not have rights. This question can be debated long. It is time now to think about nature seriously and carefully and this can probably be done through Environmental Ethics,

1

se Id

1.13.1 Obligation to the Puture
The most important question that comes to our mind is what do we owe to our 'future generations'? These questions have beconle Inore relevant because we know that modem technology is affecting the environment in ways that will last hundred and thousand years. The particular coilcerns are: Long-term climatic change resulting from land-use changes, urbanisation and technological activities. * The destruction of forests and fertile agricultural soils. 0 Radioactive wastes from nuclear power plants. Worldwide spread of non-radioactive toxic chemicals. 0. 0 Environmental effects of thermonuclear war. 0 The direct effects of rapid increases in human population. The long term impacts of apparently short - term technological benefits, such as the iinpact on natural systenls caused by rapid advances in genetic engineering.

1g
1

I1e

s no.

n of
'7

face

1.13.2
I

Responsibilities and Duties of a Citizen

r,

,e

Before reading about responsibilities and duties you should know about the extent of major damage to the environnlent due to human activities. These details and data of damage to the environment have been provided by 'peter J. Bryant and are as follows:
e

We have already transfonned or degraded 39 - 50% of earth's land surface (agriculture as well as urban)
Biodiversity and conservation - A Hypertext Book by Peter J. Bryant.

3

I

Environmental Concerns

e

e
e

a

e

e

We use 8% of the primary pl.oductivity of the oceans (25% from upw areas and 35% from temperate continental shelf'areas). We have increased atmospheric COz concentration by 30%. We use more than half of the accessible fresh water sources. Over 50% of terrestrial nitrogen fixation is caused by huinan activit~ of nitrogen fertilizer, planting of nitrogen-fixing crops, release of re; nitrogen from fossil fuels into the atmosphere). On many islands, more than half of plant species have been introducl humans; on continental areas the fraction is 20% or more. About 20% of bird species have become extinct in the past 200 1 almost all of them because of human activity. About 22% of marine fisheries have been overexploited or depleted, more are at the limit of exploitation

c These problems seem to be too difficult to be solved but there should be s initiation. Individuals can become involved in improving the environmen which encoinpasses a wide range of approaches.

As we have explained, you will study in coming units that environineiltal problems are in part, the result of the growing number of hunlan beings or earth. This means individual actions, summed over, due to a large numbel people, can have great influence on the environment. There are a wide ran environmental issues so it becomes confusing as to: in which of the many environmental issues one should participate. We think one n~ust attend to i problem that has the most personal meaning and then try to find solutions. People should help themselves rather than lookii~g towards authority for answers and solutions. We hope that after reading this course you would participate in the efforts designed to address the environmental issues, whi challenge us today.

3.14

LET US SUM UP

-

*

Environment is the sum total of living and non-living components that suqound and influence an organism. Living components are called bio components while non-living coinponents are called abiotic coinponen The biosphere is that region of water, earth, atmosphere and where life systems exist. Within the biosphere there are several major regions containing specific types of ecosystems. The major terrestrial regions a called biomes, which are characterised by their dominant vegetation. T other portion of the biosphere is the aquatic zone. An ecosystem is the simplest entity that can sustain life. At its most bat an ecosystem is fonned of a variety of individual organisms both plant! and animals which interact with each other and with their physical environment. It sustains two processes, the cycling of chemical elemen and flow of energy. It is self-regulatory based on feedback infoiemation given by its living and non-living components. Ecosystems are conside functional units of nature having no specific size or limits. Ecosystems highly dynamic entities. They have evolved effective hoineostatic mechanism for self regulation through feedback. The abiotic components of the ecosystem consist of physical factors su as light, temperature, rainfall, water, nutrients etc. The biotic componei the ecosystem consists of autotrophs or producers and heterotrophs or
I

0

(use ctive

ears,

le

ic,

are

,

consumers and decomposers. These organisms belong to different trophic levels. Trophic levels tell us how far the organism is removed from the plant in its level of nourishment and which organisms share the same general source of nutrition. Sun is the main source of energy needed for functioning of an ecosystem. The flow of energy through the ecosystem is gt one-way process or is unidirectional. The sequence of organisms through which the energy flows is known as food chain. Two main types of food chain can be distinguished namely grazing and detritus food chain. The flow of energy is governed by the two laws of thermodynamics. First Law of thermodynamic states that energy cannot be created or destroyed while the second Law says that as energy is used to do wor;k, some energy is wasted as heat at each transformation. As a result of this all living systellls need a continuous supply of energy. The loss of energy at each trophic level limits the number of trophic levels in a food chain to four or five. Several intersecting food chains form a food'web, which depicts the pattern of food consumption in an ecosystem. Trophic relationships of an ecosystem can bc represented graphically in the form of ecological pyramids. The base of the pyramid represents the producers and the successive tiers represent the subsequent highcr trophic levels. Ecological pyramids are of three types: (i) pyranlid of number depicting the number of individual organisms at each trophic level; (ji) pyramid of biomass - representing total weight of living organisms at each trophic level and (iii) pyramid of energy - showing the amount of energy utilised at successive trophic levkls. , Nondegradable pollutants often accumulate (bioaccun~ulation) magnify <and (biomagnification) at each trophic level in the food chain and inay become lethal when compared to the amount initially introduced into the biosphere. The nutrients in an ecosystem are continuously cycled and recycled. Nutrients essential to organisms are distributed in various chemical forms in air (atmosphereJ, soil or rock (lithospherc), water (hydrospl~ere) and living beings. Over timd elements move from one sphere to another in biogeocllemical cycles. Key cycles described in the unit are water, carbon, oxygen, nitrogen and sulphur. Soil microorganisnls play a key role in cycling of elements, particularly nitrogen and sulphur. In general some chemical element may cycle quickly compared to others. Biogeocheinical cycles that include a gaseous phase in the atmosphere tend to have more rapid recycling than those that do not. Ecosystenl succession occurs when a series of commiinities replace one another. Each community changes the environment to make conditions favourable for a subsequent community and unfavourable for itself till the climax comnlunity is established. The first plants to colonise an area are called pioneer community. The final stage of succession, which is quite stable, is called the climax community. The stages leading to clifnax community are called successional stages or seres. When succession is brought about naturally by the living inhabitants, the process is called autogenic succession, while changes brought about by outside forces is called allogenic succession. The pattern of interaction between living things are at1important dimensioil in an ecosystem and include intraspecific relations - interactions between members of same species and inter specific relations -interactions between members of different species.

Why is Environment Important?

Environmental Concerns

e

e

i

k

e

Human population throughout history has been quite small but has been increasing since the onset of the industrial revolution. It has now back being growing is an explosive manner. Human populations have specific characteristics such as density, natalit and mortalily, age str-uctui-e,biotic polential dispersal or migration and growlh rate. Population histogra~ns helpful in showing tlie recent are history of a population as well as its sI101.t-termgrowth trends. We distinguish three types of histogram: expansive, constrictive and station; The future of human population with current trends is bleak, due to rap;, depletion of resources, over crowding and destruction of the ecosystem. The future lies in slowing down population growth rapidly enough to ensure a smooth demographic transition in the developing countries, fail which, large-scale disasters inay occur.
L
-

---

3.15
1.

FURTHER READING

.

Basic Ecology - Eugene P. Odum. 2. Biology Today Vo12 - Sandra S. Gottfr-ied 3. Biology the Science of Life - Robert A. 4. Biology an Exploration of Life - Carol H. Mc Fadden and WilIian~ T. Keeton. 5. Biological Science, NPO Green, G.W, Stout, D. J . Taylor. 6. Biology - Ruth Bernstein & Stephen Bernstein 7. Concepts of Ecology. Edward J. Kormondy. 8. Demography http:/lwww.trini ty.edulinkearIlcle~1iogr~i~~~1it1nl. 9. Environmental 'Science - A framework for decision making. Daniel D. Chiras. 10. Environmental Science - Earth is a living planet. Daniel Botkin and Edward Keller. 11. Elements of Ecology - Robert Leo Smith and Tliomas M. Smith. 12. Huinan Environnient - Block- 1 (AHE-01). 13. Human population Growth li'lt~~:/Idarwin.bio.uci.edu/-sus~ain/, 14. Heath Biology - James E. McLaren, Lissa Rolundo. 15. INDIA: Quantitative Fi-eedom, Democracy, Progress [email protected] 16. Population Council/Asia-India, ~ ~ ~ ~ : / / \ \ ~ w w . ~ ~ ~ .? L~'~oI ~ ~IsI~I:c ~~ ~ o c) I/ 17. Population and human developluent - the key connect~ons l1tlp://www.ueop~ea11~~1~~net~nell~I0~. 18. Slandwd Grade Biology - James Tol~aracc 19. Wallace Jack L. King Gerald P, Sanders.

UNIT 2
Structure

NATURAL RESOURCES

2.1 Introduction
Objectives

2.2 Resource Availability and Potential
Air Water Forest Resources Biological Resources (Biodiversity) Food Resources Land Mineral Resources Energy: Non-conventional Renewable Sources of Energy

ing

2.3 Resource Scarcity and Degradation 2.4 Optimum Resource Potential and Utilisation
Waste Recycling Land Use Utilisation of Forest Resources Conservation and Efficient Use of Water Resources Conservation of Mineral Resources

2.5 Activities 2.6 Let Us Sum Up 2.7 Further Reading

2.1

INTRODUCTION

In the previous unit you have studied what constitutes your environment and how ecosystem supports myriad living organisms including human beings. You have also understood the importance of environment. In the present unit we shall discuss the resourcks or the wealth, nature has given to us as these are essential for survival and future development. Therefore, it is our prime concern to use our natural treasures wisely and judiciously. Our demand on natural resources is rapidly increasing. However, it is believed that thd resources are being used increase in our indiscriminately. This is partly because of the tre~ncndous population and partly there is lack of realisation on our part that these resources are limited and will be exhausted one day. Our industrial and technological development has surpassed the rate at which thesc resources are being used. It is significant to lllentivll here thal, for centuries, the resources of some of thc countries have bcen exported as raw material to dominant 01.developed countries. The poor countries still have to cxpor( sonlc precious mineral.: co ti~c same coui.lti.ies which are now called dc\,eloped countries. For e,uamyle wrc arc now-a-days exporting cadmium, a silvury mctal, to Sol.cign ~:uuntrittsso as tcr earn foreign cwcncy to meet out other necessi~ies. iiletal I;s extrcmel, The usefill and is used for a variety of pilrposcs Jlkzmaking chdrni~lrn ~ b foi r s watches c:: ?LS nf ;!G~.Y nuclear reactors and cadmium-silver cell:, for electl-o~lic wz are not able to make much use of this precirpus metal due to low level of technological developlnent in our country. If tonlorrow ou: min!2ral resel-ires,of this metal are exhausted. c inay bc f ~ ~ r c e dimport it at m~iclx to higl~er cu::t Some countries which are im?ortilig this rneta; ma;,.--j:. , : i ~ x k :litlg it and t h y ; may sell it at an exorbitailt price when 111.~;.;L,:c~,:.at.< .:xha~stt:i:. There is another reason to conserve and safeguard our natural resources as their' supply is not unlimited and in fact some of the resources occur only in scant

59

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close