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ECOLOGY
Ecology Ecology is the branch of science that is concerned with the relationships of life forms with each other and with their surroundings. The basic unit in ecology is the ecosystem; a fairly self-contained system of plants and animals living in a particular kind of environment. A forest is an ecosystem; so is a lake. Ecosystem Ecosystem signifies organisms living in a particular environment, natural systems in constant interchange among their living and non-living parts. Ecosystem is the study of relationships between organisms and their physical environment. Components of Ecosystem At the top of the hierarchy is the planets entire living environment, known as the biosphere. Within this biosphere are several large categories of living communities known as biomes that are usually characterized by their dominant vegetation, such as grasslands, tropical forests, or deserts. The biomes are in turn made up of ecosystems. The living or biotic parts of an ecosystem, such as the plants, animals, and bacteria found in soil, are known as a community. The physical surroundings or abiotic components, such as the minerals found in the soil, are known as the environment or habitat. Any given place may have several different ecosystems that vary in size and complexity. A tropical island, for example, may have a rain forest ecosystem that covers hundreds of square miles, a mangrove swamp ecosystem along the coast, and an underwater coral reef ecosystem. No matter how the size or complexity of an ecosystem is characterized, all ecosystems exhibit a constant exchange of matter and energy between the biotic and abiotic community. Ecosystem components are so interconnected that a change in any one component of an ecosystem will cause subsequent changes throughout the system. The biosphere is the largest organizational grouping in ecology; it includes every place where life is found on Earth. A population is all of one species in one area at one time, a community is all of the species in one area at one time, and a biome is a specific climactic community established by the climate, which controls the plants living there, which in turn, control the animals living there. How Ecosystems Work The living portion of an ecosystem is best described in terms of feeding levels known as trophic levels. The trophic level of an organism is the position it occupies in the food web. The word trophic derives from the Greek troph referring to food or feeding. Green plants make up the first trophic level and are known as primary producers. Plants are able to convert energy from the sun into food through a process known as photosynthesis. In the second trophic level, the primary consumers known as herbivores are animals and insects that obtain their energy solely by eating the green plants. The third trophic level is composed of the secondary consumers, flesh-eating or carnivorous animals that feed on herbivores. At the fourth level are the tertiary consumers, carnivores that feed on other carnivores. Finally, the fifth trophic level consists of the decomposers, organisms such as fungi and bacteria that break down dead or dying matter into nutrients that can be used again.

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Food Chain Some or all of these trophic levels combine to form what is known as a food web/food chain, the ecosystems mechanism for circulating and recycling energy and materials. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism is from the start of the chain is a measure of its trophic level. For example, in an aquatic ecosystem algae and other aquatic plants use sunlight to produce energy in the form of carbohydrates. Primary consumers such as insects and small fish may feed on some of this plant matter, and are in turn eaten by secondary consumers, such as salmon. A brown bear may play the role of the tertiary consumer by catching and eating salmon. Bacteria and fungi may then feed upon and decompose the salmon carcass left behind by the bear, enabling the valuable non-living components of the ecosystem, such as chemical nutrients, to leach back into the soil and water, where they can be absorbed by the roots of plants. In this way nutrients and the energy that green plants derive from sunlight are efficiently transferred and recycled throughout the ecosystem. For example one food chain may be represented as follows:
(Energy )

Sun A lg ae
(Pr oducer ) ( Autotroph )

(First order consumer ) (Herbivore )

Fish

( Secondorder consumer ) ( Carnivore )

Salmon

Brown bear Bacteria and Fungi

The number of steps in the food chain is limited to four or five. At each step in a food chain, a large portion of energy is used for its own maintenance and lost as heat. As a result, organisms in each trophic level pass on less and less energy than they receive. The longer the chain the lesser is the energy available to the final member. In a simple food chain, out of say 1000 calories of energy reaching the plant, only 10 calories (1%) are stored by plant. The remaining are lost either to the environment or to the plant for its own maintenance. Of the 10 calories available to the herbivore, nine are lost at its level and one is passed up to the carnivores.
Food Web is complex of interrelated food chains in an ecological community. It is also known as Food Cycle.

The concept of food chains is part of the much larger idea of a food web. Whereas a food chain is a linear series of organisms dependent on each other for food, a food web is an interconnected set of food chains in the same ecosystem. Food webs make possible the transfer of energy from plants through herbivores to carnivores and omnivores, and ultimately to the detritivores and decomposers that enrich the soil with organic waste.

Food Web Made of Several Food Chains

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In addition to the exchange of energy, ecosystems are characterized by several other cycles. Elements such as carbon and nitrogen travel throughout the biotic and abiotic components of an ecosystem in processes known as nutrient cycles. For example, nitrogen travelling in the air may be snatched by tree-dwelling, or epiphytic, lichen that converts it to a form useful to plants. When rain drips through the lichen and falls to the ground, or the lichen itself falls to the forest floor, the nitrogen from the raindrops or the lichen is leached into the soil to be used by plants and trees. Another process important to ecosystems is the water cycle, the movement of water from ocean to atmosphere to land and eventually back to the ocean. An ecosystem such as a forest or wetland plays a significant role in this cycle by storing, releasing, or filtering the water as it passes through the system.
Ecosystem Management

Humans benefit from these smooth-functioning ecosystems in many ways. Healthy forests, streams, and wetlands contribute to clean air and clean water by trapping fast-moving air and water, enabling impurities to settle out or be converted to harmless compounds by plants or soil. The diversity of organisms, or biodiversity, in an ecosystem provides essential foods, medicines, and other materials. But as human populations increase and their encroachment on natural habitats expands, humans make detrimental effect on the very ecosystems on which they depend. The survival of natural ecosystems around the world is threatened by many human activities: bulldozing wetlands and clear-cutting forests the systematic cutting of all trees in a specific area to make room for new housing and agricultural land; damming rivers to harness the energy for electricity and water for irrigation; and polluting the air, soil, and water. Many organizations and government agencies have adopted a new approach to managing natural resources naturally occurring materials that have economic or cultural value, such as commercial fisheries, timber, and water in order to prevent their catastrophic depletion. This strategy, known as ecosystem management, treats resources as interdependent ecosystems rather than simply commodities to be extracted. Using advances in the study of ecology to protect the biodiversity of an ecosystem, ecosystem management encourages practices that enable humans to obtain necessary resources using methods that protect the whole ecosystem. Because regional economic prosperity may be linked to ecosystem health, the needs of the human community are also considered. Ecosystem management often requires special measures to protect threatened or endangered species that play key roles in the ecosystem.

THE EARTH AND ITS SURROUNDINGS

The biosphere is the biological component of earth systems, which also include the lithosphere, hydrosphere, atmosphere and other "spheres" (e.g. cryosphere, anthrosphere, etc.). The biosphere includes all living organisms on earth, together with the dead organic matter produced by them. The biosphere is dynamic, undergoing strong seasonal cycles in primary productivity and the many biological processes driven by the energy captured by photosynthesis.

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Atmosphere

Atmosphere is the mixture of gases surrounding any celestial object that has a gravitational field strong enough to prevent the gases from escaping. Specifically this is the gaseous envelope of Earth. The principal constituents of the atmosphere of Earth are: nitrogen (78 percent) and oxygen (21 percent). The atmospheric gases in the remaining 1 percent are argon (0.9 percent), carbon dioxide (0.03 percent), varying amounts of water vapour, and trace amounts of hydrogen, ozone, methane, carbon monoxide, helium, neon, krypton, and xenon.
Lithosphere The lithosphere is the rigid outermost shell of a rocky planet. In the Earth the lithosphere includes the crust

and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. The lithosphere is broken into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere. There are two types of lithosphere:

Oceanic lithosphere, which is associated with Oceanic crust and exists in the ocean basins Continental lithosphere, which is associated with Continental crust.

Hydrosphere

The hydrosphere is composed of all of the water on or near the earth. This includes the oceans, rivers, lakes, and even the moisture in the air. Ninety-seven percent of the earth's water is in the oceans. The remaining three percent is fresh water; three-quarters of the fresh water is solid and exists in ice sheets.

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The hydrosphere, like the atmosphere, is always in motion. The motion of rivers and streams can be easily seen, while the motion of the water within lakes and ponds is less obvious. Some of the motion of the oceans and seas can be easily seen while the large scale motions that move water great distances such as between the tropics and poles or between continents are more difficult to see. These types of motions are in the form of currents that move the warm waters in the tropics toward the poles, and colder water from the Polar Regions toward the tropics. These currents exist on the surface of the ocean and at great depths in the ocean (up to about 4 km).

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