聆听与学习科学/环境
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Ecology is an inter disciplinary science. Many branches of science, have to come together to understand ecology. It seeks to explain The processes of Life, and adaptation. The movement of materials and energy, through living communities. The development of ecosystems Bio diversity in the context of the environment
Life exists in a relatively narrow zone, in planet earth. This zone is called, the biosphere. It can also be called, the zone of life. Life exists on land, which is called the lithosphere. Life exists in water, which is called the hydrosphere. Life exists in air, which is called the atmosphere. Lithosphere, Hydrosphere, and atmosphere of the Earth, together constitute, the biosphere.
Biosphere, is the sum total of all the organisms, and their habitat or the outermost part of the planet's shell including air land, surface rocks, and water - within which life occurs. Life exists, only in a few kilo meters above and below, the surface of the earth. If we go too deep, below the surface, the temperature and pressure, is too high, for life. If we go too high, in the atmosphere, there is no air, to support life. At high altitudes, we have ultraviolet radiation, which is harmful for life. This makes high altitudes, unsuitable for life. So, Planet earth has a limited zone, in which life exists. In this zone, living organisms interact with atmosphere, hydrosphere and the lithosphere.
The biosphere can also be considered, as a globally inter related ecological system. This ecological system, integrates life, with the lithosphere, hydrosphere and the atmosphere. Ecology can also be considered, as the total relationship of life, and its environment. It is also known as, environmental science.
Life in the biosphere is influenced, by its surroundings. In turn, life influences the surroundings. There is a natural, dynamic balance in this process. Human beings have made tremendous progress, in science and technology. This is commendable. Unfortunately, we are also disturbing, the natural dynamic processes in the biosphere. This is a distressing trend. Many things can go wrong, if we disturb the natural dynamic balance in the Biosphere. True development needs to ecologically friendly, or eco friendly.
All around us we can observe, the intricate relationship, between life and the environment. For example, plants absorb mineral nutrients, and water from the soil. Plants take in C O 2 from the atmosphere, and give out oxygen, to the atmosphere. The fruits and leaves, of plants are eaten, by animals. These animals can itself, become food for other animals. When animals die, their bodies decompose. Other living organisms like trees, plants and insects, also die and decay. Micro organisms feed on, and breakdown, the decayed matter. Ultimately, this goes back into the soil, as nutrients. These nutrients help plants, to grow again. We can see that, there is a natural cycle, in this. We can also perceive that many things, are closely interrelated. There are a vast number, of such interrelationships, in the biosphere.
These links or interrelationships, explain the two basic laws, of ecology. In nature, any one component cannot exist, by itself. In nature every component, is related to every other components, in some way. We have not fully understood all the intricate inter relationships in Ecology. This makes it all the more, a fascinating subject.
The Planet Earth was formed, about 4.8 billion years ago. The other planets in the solar system, Mercury, Venus, Mars, Saturn, Uranus, Neptune and pluto, were formed, at around the same time. Earth is a unique planet, in the solar system. But Earth is the only planet, that is known to support life. In our solar system, it exists in what is known as the Goldilock zone. Most of planet Earth has a climate, which is neither too hot, or too cold, Which makes it conducive for life. It has a protective atmosphere. The atmosphere protects life, from harmful radiation. The atmosphere also moderates the day and night temperature. Planet earth has plenty of oxygen and water, so essential for life. The first sign of life appeared, about 3.8 billion years ago. The first multi cellular organisms appeared, about 1.4 billion years ago. Other forms of life, plants, animals and human beings evolved, from these organisms. Compared to other forms of life, human beings are recent entrants, to our planet. If life on the planet is scaled to one day, We Human beings appeared only a few seconds back. In many ways we are guests, in planet earth. Scientists are searching the universe, for other planets, of other stars, in the Goldilock zone. This is with the hope of finding life, some where else in the Universe.
About 71 percent of Earth's surface, is covered by water. This part of the earth, is called hydrosphere. Earth is the only planet, in the solar system, with abundant liquid water. Water makes life possible, on Earth. Water has some unique, physical and chemical properties, which is essential for, supporting life.
The water cycle plays a crucial role, in creating a climate, to support life. The water cycle involves the exchange, of energy. This exchange of energy influences, temperature and climate. The suns energy heats up the oceans, which comprises most of the Earth. Some of the water evaporates, and takes up energy from the surroundings. This cools the environment. When water condenses, it releases energy. This released energy, warms the environment. This process takes place, in a cyclical and seasonal form. When water from the sea evaporates, it becomes fresh water vapour, in gaseous form. This condenses and comes back to Earth, as fresh water, in rain and snow. This fresh water, flows through rivers, and aquifers, and flows back to the sea. This forms the basis, of the water cycle.
Water offers an excellent habitat, for living organisms. A large proportion of life on Earth, live in the oceans. In fact, primitive life emerged, from water. All other forms of life emerged from it. Water has got an interesting property, of expanding, when it freezes into ice. This is why ice floats on water, though it is a solid. Usually a substance in solid form is heavier, than the same substance, in liquid form. It is the opposite, for water. Ice is lighter, than water. Imagine what would happen, if solid ice was heavier, than water. When oceans freeze, the whole ocean will become solid ice. All the life, in the ocean, will freeze to death. Fortunately, this does not happen. Because, the frozen layer of ice, floats on the water, and protects the water underneath, from freezing. This allows all marine life, to live.
Planet Earth has got, a unique atmosphere. The atmosphere is gaseous. Gases, like oxygen and nitrogen, are in the atmosphere. The atmosphere also has water vapour, and other gases like, C O 2. 78%, of the atmosphere is nitrogen. 21%, of the atmosphere is oxygen. The rest is a mixture, of other gases. In the early stages of the Earths formation, the atmosphere mostly had C O 2. One of the first forms of life, is a sea weed, called algae. Algae, is a photo synthetic organism. Photosynthetic organisms absorb sun's energy. They breathe in C O 2. They use sunlight, C O 2, and nutrients, to form, other organic molecules. In the process, they release oxygen. Most living organisms, including ourselves, require oxygen for survival. Over millions of years, organisms like algae, converted most of the C O 2 in the atmosphere, to oxygen. Thanks to them, Oxygen breathing organisms, like animals and human beings, are able to live today.
If we go deep into the earth, we will reach the mantle. If we go deeper, we reach the core of the earth. As we go deeper, the temperatures rises to more than 4000 degrees centigrade. At these high temperatures, most solid materials become viscous. Near the core of the earth, the materials are in molten form. The mantle of the earth, literally floats, on the liquid molten materials. Only the crust, of the earth, is fully solid.
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This is called, the lithosphere. In the litho sphere, we have the familiar land, we live on, and the mountains, and the hills. It is on this solid ground that all of land life exists The ocean floor, which is solid, is also part of the lithosphere. The depth, of the lithosphere, ranges from, 40 to 200 kilometres. Man has travelled to the moon. But the deepest point that man has been able to drill down to, on earth, is about 12 km.
One way to look at the organisation of natural systems, is from a hierarchical view point. It provides a simplified, but convenient framework, for understanding complex interrelationships. The hierarchy levels of natural systems are organisms, species, populations, communities and, eco systems.
Any form of life, is an organism. A vast variety of organisms, are found on the planet Earth. Bacteria, insects, fish, animals, plants, Trees are all organisms.
An organism is an individual member, of the next level, called species. A species is a group of similar organisms, having a similar genetic structure. Organisms within a species, breed among themselves, and reproduce.
Human beings belong, to the Homosapien species. Dogs belong, to the canidae species. Pea plants belong, to the Pisum sativum species.
A collection of individuals, belonging to the same species, occupying a given area, at a given time is called,a population.
The same area can have populations, of different species of plants, animals and other organisms. A forest for example, has may species, of plants, Trees, Insects and Animals. These different populations together, constitute a biotic community. Members of a community interact, with each other.
The community interacts, with the environment, of non living components, like air, water and soil. Such a system of living organisms, and non living components, is called an eco system. Eco systems are the basis of study, of environmental science. We have a number of eco systems, in planet Earth.
The Biosphere, is the global sum of all eco systems, in earth. The Biosphere can be called, as the zone of life, on planet Earth.
The eco system forms, the basic unit of study, in Ecology. It is a the functional unit, in the biosphere. An eco system comprises a number of communities, interacting with the environment. We can see a variety of eco systems, around us. A lake, grassland, a forest, a sea are examples, of eco systems. Even a desert, is an eco system. An aquarium is an example of manmade, eco system. Natural eco systems can be broadly classified, into aquatic eco systems, and terrestrial eco systems. Aquatic eco systems are water based, like in ponds, lakes, rivers and oceans. Terrestrial eco systems are land based, like gangetic plain, Himalayas and western ghats.
An eco system has two basic components, the non living components, and the living components. These interact with each other. Non living components are the physical, chemical, and climatic conditions, in the environment. Physical factors include light, air, soil and water. Chemical factors are various chemical substances. Some climatic factors are temperature, humidity and rainfall. The non living components are called, as abiotic components. Physical, Chemical, and climatic conditions, are abiotic components. The living components are called, as biotic components. Biotic components can be Bacteria, plants, Trees, Insects, animals, Birds etc. The Biotic and Abiotic components are inter related.
All organisms need energy to live. Organisms derive their energy from food. Production and consumption of food, is an important feature of Ecosystems. The principal components of the food web are, Solar Energy. Nutrients. Autotrophs. Heterotrophs. Decomposers.
The food web is a cycle. It is also called as a food cycle. Autotrophs use sunlight and nutrients to produce food. Heterotrophs consume food produced by autotrophs. When Autotrophs and heterotrophs die, they decompose. Decomposers feed on decaying life, and return the nutrients to the soil. These nutrients are reused by autotrophs, to produce more food.
Sunlight provides the energy for photosynthesis. Earth receives more solar energy in 1 hour, Than the energy, the whole world consumes in 1 year. Autotrophs use photosynthesis to produce food. Food provides the energy to live. All the energy required by living organisms, indirectly, comes from the sun.
Natural nutrients are present in the soil. They are replenished by decaying organic matter, with the help of decomposers. Nutrients are absorbed by Autotrophs to produce food.
Autotrophs produce their own food. Plants are autotrophs. Plants are capable of producing their own food. They produce organic compounds, such as carbohydrates. Plants use the nutrients present in the soil. For example, Nitrogen compounds. Decaying organic matter in soil, is a natural nutrient for plants. Plants use the C O 2 gas, present in the atmosphere. They get their energy, from sunlight. Plants produce food, by series of organic chemical reactions. The process of producing food from nutrients, using sunlight, is called photosynthesis.
Plants belong to the first trophic level, in the food chain All autotrophs like plants, belong to the first trophic level. Organisms in the first trophic level, are producers of food.
The food produced by plants is consumed by other organisms. Insects,Animals, Birds and human beings, consume the food, produced by plants.
Heterotrophs cannot produce their own food. Heterotrophs depend on autotrophs, for their food. Insects,Animals, Birds, and human beings are examples of heterotrophs. They cannot produce their own food. They depend on plants, or other animals, for their food. Such type of organisms are called heterotrophs. There are basically two types of heterotrophs. They are herbivores, and carnivores.
Animals which feed, only on plants, are called herbivores. Cows, goats and sheep, deer and elephants are examples of herbivores. They are consumers of plant food. Herbivores are primary consumers of food. Herbivores belong to the second trophic level, in the food chain. In Herbivorous food chains, the primary consumers, are plant eating animals. Most of the food chains in our eco system, are herbivorous food chains
There are animals, which obtain their food, by eating herbivores. Such animals which eat other animals are called carnivores. Lions which consume deer, and other animals is a carnivore. Carnivorous animals like lions are secondary consumers of food. Carnivores belong to the third trophic level, in the food chain. Many carnivores also eat plants. Organisms which eat both plant and animals are called omnivores.
Decomposers feed on decaying organic matter. They help in recycling the nutrients, from the organic matter, back to the soil. Bacteria is an important decomposer. Bacteria can decompose just about any organic matter. One gram of soil contains about 40 million bacterial cells. The bio mass of bacteria that is present on earth, exceeds the bio mass of all plants and animals. Sometimes we do not give importance, to what we cannot see. We cannot see bacteria, but they play a crucial role in the food web. There are other organisms also, which help in the decomposition of decaying organic matter. They are called detritivores.
Decomposing dead plants, trees and animals, are called detritus. Insects and organisms which consume detritus, are called detritivores. Ants, termites, earthworms, and millipedes consume detritus. These are some examples of detritivores.
Detritivores are not glamorous creatures, like lion and tigers. You will not find them in any zoo. But they play a crucial role as nutrient recyclers, in eco systems. They return the nutrients, in dead organisms, back to the soil. Plants, consume these nutrients, and produce more food. If nutrients are not recycled, food production, will come to a halt. The bio waste that human beings produce, can be recycled. We currently do not give much importance to this. Recycling is a great eco friendly habit, which we need to cultivate.
Some organisms are parasites. Parasite species live, at the expenses of another species, called the host. Some parasites are plants, or insects. Some parasites are bacteria, or viruses.
A food chain has different levels. Each level is called as a trophic level. The first trophic level is the food producer. Example plants. The second trophic level is the Primary consumer. Example Cows. The third trophic level is the secondary consumer. Example Lions. Some times there is a fourth trophic level, which is, the Tertiary consumer. The producer, the primary consumer, the secondary and tertiary consumers, are interrelated. Every organism in our eco system, is at one of the trophic levels. A Eco system has many food chains. These food chains are inter related. The complex network, of inter connected food chains, forms the food web. Food is a form of energy. Food stores the energy, that is required for living organisms. Energy in the form of food, is transferred from one trophic level, to another. The food chain essentially transfers energy from a lower trophic level, to a higher trophic level.
Organisms are constantly growing, reproducing, dying and decaying. All Organisms, need energy for living. When organisms consume food, the food is converted into energy. The stored energy, in food becomes available, for doing work. The main source of energy, for all eco systems, is solar energy. The sun is the source of energy of life. Without the sun, there wont be any life.
Plants harvest the sun’s energy, by photosynthesis. They store the energy, in the form of carbohydrates, fats and proteins. When primary consumers, eat the producers of food, energy moves up the trophic level. Only 10% of the energy transferred is usable energy. 90% of the energy gets converted to other forms. From a practical perspective, we say that 90% of the energy, is lost. Usually the lost energy is released as heat. As we move up the trophic levels, the amount of usable energy, at each level keeps decreasing. That is, only about 10% of the energy available, in one trophic level, is usable in the next higher trophic level. If the producer has 10,000 units of energy, the primary consumer receives only about, 1000 units. The secondary consumer gets, only about 100 units. In a simplified example, If a plant produces 1000 units of energy A deer, by eating the plants, gets about 100 units of energy. A lion by eating the deer, gets about 10 units of energy. This is why, there not too many lions in the forest.
Organisms at different trophic levels, have a nutritional relationship, between them. That is, each trophic level supplies food, or nutrition to the next high level. Each trophic level, has a number of individual members. These individuals together have, an associated biomass. It is possible to graphically represent, the relationship between trophic levels, like a pyramid. A pyramid in one dimension, is like a triangle. It has a wide base, and tapers to a point, at the top. In two dimensions, it is a rectangle at the bottom, and a point at the top. The top of the pyramid, is also called, the apex of the pyramid. This is called as, an upright pyramid. That is, the apex is at the top. Such a graphical representation, of eco systems is called, an ecological pyramid. In an ecological pyramid, producers are at the lower level, and consumers are at higher levels.
When we represent the number of individuals, at each trophic level, it is called, a number pyramid. The number of consumers, is usually less than the number of food producers, at the level below. For example, the number of lions, will be less than the number of deers, and other animals. The number of deers and other animals, will be less than the number of plants, they eat. Most of the food chains in our eco system, are upright pyramids. That is, the consumers at the higher level, are less than the producers, at the lower level.
The weight of all the organisms, is called the biomass. A pyramid constructed with the biomass, at different trophic levels, is called a biomass pyramid. The biomass reduces at every higher trophic level. In a forest the biomass of all the animals, will be less than the biomass of the plants and trees.
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A pyramid constructed with the amount of energy, at different trophic levels, is called an energy pyramid. Usable energy is lost, in each higher trophic level, of an energy pyramid. Energy available at a higher level, is lower than energy available, at a lower level. This concept of decreasing energy, is in accordance with, laws of thermo dynamics.
Human population has been growing at an accelerating rate.
Human population in 1804 was 1 billion.
In 1927 it was 2 billion.
In 1960 it was 3 billion.
In 1974 it was 4 billion.
In 1987 it was 5 billion.
In 1999 it was 6 billion.
In 2011 it was 7 billion.
More human beings have been added to the our planet in the last 12 years
Compared to the entire population of the planet, in 1804.
We can imagine the increasing amount of food that has to be produced, to feed this increasing population.
We said that there is a dynamic balance in the food web.
It is obvious that, unmanaged increase in human population, will disturb this balance.
Population management, is of crucial importance, for ecological balance.
There is one more simple but powerful truth, we can learn from ecology. In the food energy pyramid only 10% of the energy is transferred, to a higher level. 90 % is lost. Simple arithmetic tells us that vegetarian food is much more eco friendly. Having a larger proportion of vegetarian food, in our diet, makes ecological sense.
Thermo dynamics, is the study of energy relationship. It involves the use of energy, and the release of energy. For example, when we consume a fruit, which is mostly carbohydrate, we use the energy. The carbohydrate in the fruit, releases the energy. The basic principles, of thermo dynamics is stated, as the laws of thermo dynamics. The laws of thermo dynamics, apply to eco systems also.
Energy can neither, be created nor be destroyed, but can be transformed, from one type to another.
Energy transformations are never, hundred percent efficient. When energy is transformed, only part of that energy is transferred as useful energy. Total energy content of a system, always remains constant.
In food chains, food and energy gets transferred, from one trophic level to another. Food can sometimes have Toxic substances. Toxic substances, are also transferred, from one trophic level to another. When this happens, the concentration of the toxic substance, increases. That is, the concentration of toxic substance in the consumer, is more than that, in the producer. Toxic substances in soil and water, is absorbed by plants. Animals and human beings, eat the plants, with toxic substances. The concentration of toxic substances in animals, compared to plants, is more. Such an increase in the concentration of pollutants, in the food chain, is called bio magnification.
Pollutants are substances which are harmful, to living beings, including human beings. To take an example, D D T was used as an insecticide. D D T is a toxic substance, and a pollutant. It is harmful to human beings. Bio magnification increased the amount of D D T, in many food chains. Now D D T is present in plants, animals, fish, and birds. It has also been detected, in mother's milk. We can imagine the amount of harm, it can cause to babies.
Modern life produces a lot of waste substances. Human population is growing at at an accelerating rate. The waste we produce is also growing at an accelerating rate. Much of the waste we produce, contain toxic substances, or pollutants. Vehicle exhausts produce pollutants, which is released into the air. Thermal power plants, burn coal and release pollutants into the air. Factories produce chemical waste, which is released into lakes and rivers. Agriculture uses insecticides and pesticides. These toxic substances enter the soil, and our food. Household waste contain many toxic substances. Waste is dumped in garbage yards. The toxic substances in this waste, enter the soil. Unfortunately industrial development, has also increased pollution. Our air, water and soil is getting increasingly polluted. Ultimately all these toxic substances come back to us. Many modern illnesses can be attributed to pollution. Only recently we are waking up, to realise the dangers of pollution. We said earlier that planet earth is uniquely suited for sustaining life. Pollution caused by humans, is now making it less suitable. In the future, we need to dramatically reduce our pollution levels. All individuals have to actively participate in this.