Lecture 2-6 ENVIRONMENT ECOLOGY AND BIOSPHERE PDF

OUR ENVIRONMENT Environment : The term environment denotes all the physical, chemical and biotic conditions surrounding and influencing a living organism. Favourable environmental conditions are required to sustain life on earth. Ecosystem: The place where an org...

OUR ENVIRONMENT Environment : The term environment denotes all the physical, chemical and biotic conditions surrounding and influencing a living organism. Favourable environmental conditions are required to sustain life on earth. Ecosystem: The place where an organism lives is called its habitat. The different species living in a habitat form a community. The community with its natural surroundings is called an ecosystem. An ecosystem is the basic functional unit of biosphere. Biosphere A thin layer on and around the earth which sustains life is called biosphere. Life exists in the diverse forms of living organisms. All these living organisms of the biosphere are directly or indirectly dependent on one another as well as on the physical components of the earth. The three physical components of the earth are atmosphere, lithosphere and hydrosphere (air, land and water). The atmosphere is a gaseous envelope surrounding the earth’s surface, It is made up of nitrogen, oxygen, carbon dioxide and many other gases in very small amounts. Hydrosphere is all the water supply to the earth which exists as liquid, vapour or frozen form of fresh and salt water. Lithosphere comprises the soil and rock of the earth’s crust. Types of Ecosystems Our planet earth itself is considered as a unique, giant ecosystem. This is also called the biosphere or the ecosphere. It is divided into two major kinds: Natural ecosystem, and Artificial ecosystem  i. Natural Ecosystem: The ecosystem which operates by itself under natural conditions is known as natural ecosystem. Natural ecosystem is either totally dependent on solar radiation e.g. forests, grasslands, oceans, lakes, rivers and deserts (they provide food, fuel, fodder and medicines), or dependent on solar radiation and energy subsidies (alternative sources) such as wind, rain and tides. e.g tropical rain forests, tidal estuaries and coral reefs. Based upon the particular kind of habitat, these are divided into two groups : Terrestrial Ecosystem, and Aquatic Ecosystem Terrestrial Ecosystem: Forests, deserts and grasslands are examples of terrestrial ecosystem. Aquatic Ecosystem : It is classified into two types i.e. 1. Fresh water or limnetic ecosystem; This ecosystem is further divided into i)Lentic: Here the water is stationary as in a pond or lake. ii)Lotic: In this type, the fresh water flows as in a river or stream. 1. Salt water or marine ecosystem: this includes seas, oceans, coral reeves and the estuaries. i. Artificial ecosystem : This is operated by man. Artificial ecosystem is either dependent on solar energy-e.g. Agricultural fields and aquaculture ponds, or dependent on fossil fuel e.g. urban and industrial ecosystems. It is of two types, 1.Cropland - (e.g.) Rice field 2.An Aquarium COMPONENTS OF THE ECOSYSTEM The ecosystem has two basic components (A) Abiotic (B) Biotic (A) Abiotic Components (Nonliving): They can be classified into following two categories 1. Physical components They are the various climatic characteristics such as light, temperature, humidity precipitation, pressure and soil profile. These factors sustain and control the growth of organisms in an ecosystem. Deficiency or excess of any one of these is harmful for their growth. 2. Chemical components  a. Inorganic components: Substances such as carbon, carbon dioxide, nitrogen, oxygen, phosphorus sulphur, zinc, water and many other minerals are the inorganic nutrients required by all living beings. They may be classified into the micronutrients and macronutrients. Macronutrients are the essential inorganic elements such as carbon, hydrogen, nitrogen, phosphorus, calcium, potassium which are required in large quantities Micronutrients are the essential elements required in small amounts e.g. zinc, boron and magnesium. Sources of all nutrients for plants are air, water and soil. All these nutrients are converted into the living biomass by the plants. a. Organic components: The complex molecules such as carbohydrates, proteins and lipids are the organic substances in an ecosystem. These substances when out side the organism make the abiotic component but in the living organism they make an important component of the biomass. They make a link between the biotic and abiotic components. (B) Biotic Components (living) The living organisms form the biotic component of the environment. All the living things require energy for their life processes and material for formation and maintenance of their body structure. Food meets both these requirements. The biotic components can be classified as producers, consumers and decomposers. 1. Producers: The plants are capable of capturing solar energy and transforming it into food energy for all the other living organisms. Therefore, they are called as producers. These  Green plants are called autotrophs, as they absorb water and nutrients from the soil, carbon dioxide from the air, and capture solar energy to make their own food. 1. Consumers: They are called heterotrophs and they consume food synthesized by the autotrophs. Based on food preferences they can be grouped into three broad categories. i. Primary consumers or the Herbivores (e.g. cow, deer and rabbit etc.) feed directly on plants. ii. Secondary consumers or the carnivores are animals which eat other animals (eg. lion, cat, dog etc.). iii. Tertiary consumers or the omnivores organisms feeding upon both plants and animals e.g. human, pigs and sparrow. 1. Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed and the dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in recycling of nutrients. They are also called detrivores or detritus feeders. POND ECOSYSTEM A pond ecosystem is a fresh water ecosystem with a non-flowing body of water. There is an abundance of all the biotic and abiotic components in a continuous state of interaction in a pond.  Fig. 1 Pond Ecosystem Structure of Pond Ecosystem (A) Abiotic components i. Light: Solar radiation provides energy that controls the entire system. Penetration of light depends on transparency of water, amount of dissolved or suspended particles in water and the number of plankton. On the basis of extent of penetration of light a pond can be divided into limnetic or euphotic (eu=true, photic=light), Littoral or mesophotic and Profoundal or aphotic zones. Plenty of light is available to plants and animals in euphotic zone. No light is available in the aphotic zone (Fig. 2).  Fig. 2 Zonation in a pond ecosystem i. Inorganic substances: These are water, carbon, nitrogen, phosphorus, calcium and a few other elements like sulphur depending on the location of the pond. The inorganic substances like O2 and CO2 are in dissolved state in water. All plants and animals depend on water for their food and exchange of gases- nitrogen, phosphorus, sulphur and other inorganic salts are held in reserve in bottom sediment and inside the living organisms. A very small fraction may be in the dissolved state. i. Organic compounds: The commonly found organic matter in the pond are amino acids and humic acids and the breakdown products of dead animals and plants. They are partly dissolved in water and partly suspended in water. (B) Biotic components i. Producers or autotrophs: synthesize food for all the heterotrophs of the pond. They can be categorized into two groups: b. Floating micro-organisms and plants  c. Rooted plants a. Floating microorganisms (green) and plants are called phytoplankton (“phyto”- plants, “plankton” –floating). They are microscopic organisms. Sometimes they are so abundant in pond that they make it look green in colour e.g. Spirogyra, Ulothrix, Cladophora, Diatoms, Volvox. b. Rooted plants: These are arranged in concentric zones from periphery to the deeper layers. Three distinct zones of aquatic plants can be seen with increasing depth of water in the following order: i. Zone of emergent vegetation:. eg. Typha, Bulrushes and Sagittaria ii. Zone of rooted vegetation with floating leaves. eg. Nymphaea iii. Zone of submergent vegetation: eg. All pond weeds like Hydrilla , Rupia, musk grass etc. i. Consumers/Heterotrophs are animals which feed directly or indirectly on autotrophs e.g. Tadpole, snails, sunfish, bass etc. Pond animals can be classified into the following groups a. Zooplanktons are floating animals. Cyclops, Cypris b. Nektons are the animals that can swim and navigate at will. e.g. Fishes c. Benthic animals are the bottom dwellers: beetle, mites, mollusks and some crustaceans. i. Decomposers: They are distributed through out the entire in the whole pond but in the sediment most abundant. There are bacteria and fungi. (Rhizopus, Penicillium, Curvularia ,Cladosporium) found at the bottom of the pond. GRASSLAND ECOSYSTEM (TERRESTRIAL ECOSYSTEM) Grasslands (also called Greenswards) are areas where the vegetation is dominated by grasses and other herbaceous (non-woody) plants. Structure and functions of Grassland Ecosystems I. Biotic components 1) Producer Organisms In grassland, producers are mainly grasses; though, a few herbs & shrubs also contribute to primary production of biomass. Some of the most common species of grasses are: Brachiaria sp., Cynodon sp., Desmodium sp., Digitaria sp. 2) Consumers In a grassland, consumers are of three main types; a) Primary Consumers The primary consumers are herbivores feeding directly on grasses. These are grazing animals such as Cows, Buffaloes, Sheep, Goats, Deer, Rabbits etc. Besides them, numerous species of insects, termites, etc are also present. b) Secondary Consumers These are carnivores that feed on primary consumers (Herbivores) These include;-Frogs, Snakes, Lizards, Birds, Foxes, Jackals etc. c) Tertiary Consumers These include hawks etc. which feed on secondary consumers. 3) Decomposers These include wide variety of saprotrophic micro- organism like:Bacteria; Fungi; Actinomycetes They attract the dead or decayed bodies of organisms & thus decomposition takes place. Therefore, nutrients are released for reuse by producers. II. Abiotic components These include basic inorganic & organic compounds present in the soil & aerial environment. The essential elements like C, H, N, O, P, S etc. are supplied by water, nitrogen, nitrates, sulphates, phosphates present in soil & atmosphere. FOREST ECOSYSTEM The forest has the same structural organization as of a pond. Abiotic components: The most important non-living component is sunlight which is the principal source of energy. The other abiotic components arc soil water, various soil salts and different atmospheric gases like O2, CO2, and N2. Biotic components: These include producers, macro-consumers and micro-consumers. 1. Producers: (e.g.) bryophytes, pleridophytes, dicot and monocot plants. There is a four tiered stratification of vegetation in a forest namely tree layer, shrub layer, herb layer and ground layer. 1. Macro-consumers: There are three categories. a. Primary Consumers: These are the herbivores animals like rats, ants, grasshoppers, millipedes, fruit eating birds, deer, monkeys and elephants. a. Secondary consumers: These include wild dogs, jackals, tigers, snakes and frogs which feed on primary consumers. Hence they are the primary carnivores. a. Tertiary consumers: These are referred to as secondary carnivores (e.g.) eagles and hawks. 1. Micro-consumers: These are micro-organisms such as bacteria and fungi. They are also called as decomposers. FOOD CHAIN Transfer of food from the plants (producers) through a series of organisms with repeated eating and being eaten is called a food chain. Three important features in food chains are : 1. Weaker organisms are attacked by the stronger organisms 2. Number of organisms is reduced at each higher level but the size of organisms is increases. 3. The number of steps in a food chain is limited to 4-5. 4. Each step in the food chain is called trophic level. A food chain consists of the following trophic levels: i. (Producers) Autotrophs: They produce food for all other organisms of the ecosystem. Autotrophs represent the first trophic level. They are largely green plants they convert inorganic substances by the process of photosynthesis into food (organic molecules) in the presence of sun light. The total rate at which the radiant energy is stored by the process of photosynthesis in the green plants is called Gross Primary Productivity (GPP). This is also known as total photosynthesis. A part of the gross primary productivity is utilized by the plants for their own metabolism, maintenance and reproduction. Energy required for all these functions is produced by the process of respiration. The remaining is stored by them as Net Primary, Productivity (NPP) and is available to the heterotrophs or consumers, (The next trophic level). GPP = NPP + R or GPP – R = NPP Productivity in the biological system is a continuous process but it is different in different ecosystems. i. Primary consumers Herbivores: These are animals which feed directly on the plants. They are first level consumers and therefore they are also known as primary consumers and make the second trophic level in the food chain e.g. grasshopper in the above example. Other examples are insects, birds, rodents and ruminants. Herbivores are  capable of converting energy stored in the plant tissue into animal tissue and therefore they are also known as key industry. They can digest high cellulose diet. i. Secondary consumer Carnivores: Carnivores are the animals that feed on other animals or its tissues. Therefore they are secondary, tertiary or quaternary level consumers. Frog is secondary level consumers as it feeds on herbivorous grasshopper. Snake is tertiary level consumer since it consumes other carnivore that is frog. Frog, snake, dog, cat and tiger are all carnivores. Generally the size of the carnivore/ increases at each trophic level. i. Decomposers: They make up the final trophic level in a food chain. Decomposers are the organisms that feed on dead organic matter called detritus of all the trophic levels and help in recycling the nutrients. They can be grouped into two classes: micro-decomposers and macro-decomposers. Micro-decomposers are very small microscopic organisms like bacteria, fungi, and protozoans. Macro-decomposers are large but less in number. They are visible to the naked eye e.g. springtails, mites, millipedes, earthworms, nematodes, slugs, crabs and molluscs. Special feeding groups (Consumers) a. Scavengers : These are the animals that feed on the dead plants and animals. e.g. termites and beetles feed on the decaying wood, and many marine invertebrates. Vultures, gulls and hyena are other examples of scavengers. a. Omnivores : Omnivores consume both plants and animals as source of their food e.g. human beings. Some of the omnivores like the red fox feeds on berries small rodents as well as on dead animals. Thus it is a herbivore, carnivore and also a scavenger. a. Parasites : They live and feed on/in other living organisms called host. Parasites not only feed on their host but they also cause lethal or nonlethal disease in it. Position of human beings in the food chain Human beings are consumers and may occupy primary, secondary or tertiary levels. Vegetarian people are ‘primary consumers; when they consume small fish chicken or goat meat they are ‘secondary’ consumers and when they consume big fishes they are ‘tertiary’ consumers. TYPES OF FOOD CHAIN There are two types of food chains in nature i.e. Grazing food chain, and Detritus food chain. A. Grazing food chain: This type starts from green plants proceeds to herbivores and ends in carnivores. Examples of grazing food chain. 1. Grass cattle man 2.Grass rabbitfoxwolf tiger 3. Plants mouse snakehawk Food chain in an aquatic ecosystem. Phytoplanktonzooplanktonfishsnake Detritus food Chain: The dead organisms and the debris are termed as detritus. They are decomposed and taken as food by detrivores. Thus they release the essential elements into the environment. Producers use these elements for their life process. Termites, beetles and worms are some of the detrivores in the terrestrial ecosystem. Insect larvae are aquatic decomposers. The saprophytic fungi and bacteria come under this category. The detrivores are eaten up by some protozoans. They are in turn preyed upon by small fishes. Larger carnivorous fishes feed on these small fishes. Organic wastedetrivores protozoasmall fishlarge fish  Fig. 3 Some examples of food chain. FOOD WEB In nature the food chains are not isolated sequences but they are interconnected with one another. A net work of food chains which are interconnected at various trophic levels of the food chain to form a number of feeding connections is called a food web. In a food web one trophic level may be connected to more than one food chain. ENERGY FLOW IN ECOSYSTEM The flow of energy in an ecosystem is always linear or one way. The quantity of energy flowing through the successive trophic levels decreases as shown by the reduced sizes of boxes in Fig. 4. At every step in a food chain or web the energy received by the organism is used to sustain itself and the left over is passed on to the next trophic level.  Fig. 4 Model of energy flow through an ecosystem ECOLOGICAL PYRAMID Ecological pyramid is a graphic representation of various trophic levels of a food chain in an ecosystem These pyramids clearly reveal the trophic structure and function of the ecosystem. In this representation, producer level is represented at the base of the pyramid, herbivores lie above the base, followed by first order carnivores and so on with tertiary carnivores at the top. These pyramids are of three types. i. Pyramids of Numbers ii. Pyramids of Biomass iii. Pyramids of Energy iv. Pyramid of number: This represents the number of organisms at each trophic level. For example in a grassland (Fig. 5) the number of grasses is more than the number of herbivores that feed on them and the number of herbivores is more than the number of carnivores. In certain other cases, the reverse is true. For example, in a tree ecosystem, the number of the primary producers is the least and that of the ultimate consumers is the maximum. A single fruit tree supports a large number of fruit eating herbivorous birds. These in turn support a still higher number of parasitic insects which are further consumed by microbial parasites such as bacteria and fungi. In this case, there is an increase in numbers from producers to consumers of different orders, constituting an inverted pyramid (Fig. 6.)   Fig 5. Pyramid of numbers : grassland Fig 6. Pyramid of numbers : Tree i. Pyramid of biomass: Biomass is the total amount of organic matter present in the organism at a given time per unit area. Pyramid of biomass is a graphical representation of biomass present per unit area in different trophic levels. In grassland and forest ecosystem, the biomass of producers is the highest of all the trophic levels. The biomass goes on decreasing from primary producers to the top carnivores. Thus it forms an upright pyramid (Fig. 7). Fig. 7 Pyramid of biomass – Forest Fig. 8 Pyramid of biomass – Pond In an aquatic ecosystem like that of a pond, the situation is entirely reverse. The biomass of diatom and phytoplankton (Primary producers) is very little compared to small herbivorous fishes (primary consumers) that feed on them. The biomass of large carnivorous fishes (secondary consumers) which feed on the smaller fishes is the highest of all trophic levels. Thus the relationship of biomass among organisms in such a food chain results in an inverted pyramid (Fig.8).Pyramid of biomass follows 10 per cent law. Thus, 1000 Kg of grass would form only 100 Kg of biomass in mice while the later would produce only 10 kg of biomass in snakes. The snakes would produce only 1 Kg of biomass in hawks.  i. Pyramids of Energy: It is a graphic representation of amount of energy trapped in different trophic levels in a food chain. The primary producers of an ecosystem trap the radiant energy of the sun and convert it into potential chemical energy. This trapped energy lows in the food chain from the producers to the top carnivore which decreases at successive tropic levels. Thus an upright pyramid is always formed (Fig. 9). Fig. 9 Pyramid of energy BIOGEOCHEMICAL CYCLES The cycling of the nutrients in the biosphere is called biogeochemical or nutrient cycle. It involves movement of nutrient elements through the various components of an ecosystem. These elements are continuously cycling in the ecosystem through the biogeochemical cycles and the planet earth has no input of these nutrients. The nutrients (matter) from the dead remains of organisms are recovered and made available to the producers by decomposers. Thus the nutrients are never lost from the ecosystems.  Carbon cycle Atmospheric carbon dioxide is the source of all carbon in both living organisms as well as in the fossils (used as fossil fuel). It is highly soluble in water. Oceans also contain large quantities of dissolved carbon dioxide and bicarbonates. The carbon cycle comprises the following processes: Photosynthesis : Terrestrial and aquatic plants utilize CO2 for photosynthesis. Through this process the inorganic form of carbon is converted into organic matter in the presence of sunlight and chlorophyll. The carbon dioxide is thus fixed and assimilated by plants. It is partly used by them for their own life processes and the rest is stored as their biomass which is available to the heterotrophs as food. Respiration : Respiration is a metabolic process reverse of photosynthesis in which food is oxidized to liberate energy (to perform the various life processes) and carbon dioxide and water. Thus the carbon dioxide of the atmosphere is recovered through this process. Decomposition : After the death of the organisms the decomposers break down the remaining dead organic matter and release the left over carbon back into the atmosphere. Combustion : Fossil fuel such as crude oil, coal, natural gas or heavy oils on burning releases carbon dioxide and carbon monoxide into the atmosphere. Forests make a large amount of fossil fuel. Fossil fuel is product of complete or partial decomposition of plants and animals as a result of exposure to heat and pressure in the earth’s crust over millions of years. Forests also act like carbon reservoirs as carbon fixed by them cycles very slowly due to their long life. They release CO2 by forest fires. Impact of human activities : Carbon dioxide is continuously increasing in the atmosphere due to human activities such as industrialization, urbanization and increased use of automobiles. This increase in atmospheric CO2 is bading to green house effect and global warming.  Fig. 10 The Carbon Cycle Nitrogen cycle Nitrogen is an essential component of protein and required by all living organisms including human beings. Our atmosphere contains nearly 79% of nitrogen but it can not be used directly by the majority of living organisms. Broadly like corbondioxide, nitrogen also cycles from gaseous phase to solid phase then back to gaseous phase through the activity of a wide variety of organisms. Cycling of nitrogen is vitally important for all living organisms. There are five main processes which essential for nitrogen cycle are elaborated below. a. Nitrogen fixation: This process involves conversion of gaseous nitrogen into Ammonia, a form in which it can be used by plants. Atmospheric nitrogen can be fixed by the following three methods: i. Atmospheric fixation: Lightening, combustion and volcanic activity help in the fixation of nitrogen. ii. Industrial fixation: At high temperature (400oC) and high pressure (200 atm.), molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen to form ammonia. iii. Bacterial fixation: There are two types of bacteria- a. Symbiotic bacteria e.g. Rhizobium in the root nodules of leguminous plants. b. Free living or symbiotic e.g. 1. Nostoc 2. Azobacter 3. Cyanobacteria can combine atmospheric or dissolved nitrogen with hydrogen to form ammonia. a. Nitrification: It is a process by which ammonia is converted into nitrates or nitrites by Nitrosomonas and Nitrococcus bacteria respectively. Another soil bacteria Nitrobacter can covert nitrate into nitrite. b. Assimilation: In this process nitrogen fixed by plants is converted into organic molecules such as proteins, DNA, RNA etc. These molecules make the plant and animal tissue. c. Ammonification : Living organisms produce nitrogenous waste products such as urea and uric acid. These waste products as well as dead remains of organisms are converted back into inorganic ammonia by the bacteria This process is called ammonification. Ammonifying bacteria help in this process. d. Denitrification: Conversion of nitrates back into gaseous nitrogen is called denitrification. Denitrifying bacteria live deep in soil near the water table as they like to live in oxygen free medium. Denitrification is reverse of nitrogen fixation.  Fig. 11 The Nitrogen Cycle Phosphorus Cycle Phosphorous cycle is another important nutrient cycle-which is shown in Fig. 12. The reservoir of phosphorus lies in the rocks, fossils etc. which is excavated by man for using it as a fertilizer. Farmers use the phosphate fertilizers indiscriminately and as a result excess phosphates are lost as run-off, which causes the problem of eutrophication or over nourishment of lakes leading to algal blooms. A good proportion of phosphates moving with surface runoff reaches the oceans and lost into the deep sediments. The limited supply of phosphorus lying in the phosphate rocks of this earth is thus over-exploited and a large part is taken out of the normal cycle due to loss into oceans. Sea birds, on the other hand, are playing an important role in phosphorus cycling. They eat sea-fishes which are phosphorus rich and the droppings or excreta of the birds return the phosphorus on the land. Fig. 12 The phosphorus cycle