Ecosystem Components and Cycles

An ecosystem is a complex of many variables, all functioning independently yet are interdependent, with complicated flows of energy and matter. As stated above, an ecosystem includes both biotic (living) and abiotic (non-living) components. Nearly all are dependent upon an input of solar energy. The few limited ecosystems that exist in dark caves or on ocean or depend upon chemical reactions. Ecosystems are divided into subsystems, with the biotic portion composed of producers, consumers, and decomposers. The abiotic flows in an ecosystem include gaseous and sedimentary nutrient cycles.

A brief description of some of the abiotic cycles is given below:

Gaseous and Sedimentary Cycle

The most abundant natural elements in living matter are hydrogen (H), oxygen (O), and carbon (C). Together these elements make up more than 99 per cent of Earth's biomass. In fact, all life (organic molecules) contain hydrogen and carbon. In addition, nitrogen (N), calcium (Ca), potassium (K), magnesium (Mg), sulphur (S), and phosphate (P) are significant nutrients, elements necessary for the growth and development of a living organism.

Several key chemical cycles function in nature. Oxygen, carbon, and nitrogen each have gaseous cycles, part of which are in the atmosphere. Other elements have sedimentary cycles which principally involve the mineral and solid phases (major ones include phosphorous, calcium, and sulphur). Some elements combine gaseous and sedimentary cycles. These recycling processes are called biochemical cycles, because they involve chemical reactions in both living and non-living systems.

Carbon and Oxygen Cycles

These two cycles have been considered together as they are closely interlinked through photosynthesis and respiration. The atmosphere is the principal reserve of available oxygen. Large reserves of oxygen exist in Earth's crust, but they are unavailable as it is chemically bound to other elements.

As for carbon, the greatest pool is in the ocean 'about 39,000 billion tons, or about 93 per cent of Earth's total carbon. However, all of this carbon is bound chemically in carbon dioxide. The ocean absorbs carbon dioxide through photosynthesis by small phytoplankton. Carbon is stored in certain carbonate minerals, such as limestone.

The atmosphere, which is the integrating link in the cycle, contains only about 700 billion tons of carbon (as carbon dioxide) at any moment. This is far less than in fossil fuels and oil-shales (12,000 billion tons as hydrocarbon molecules) or living and dead organic matter (2275 billion tons, as carbohydrate molecules). Carbon dioxide in the atmosphere is produced by the volcanic activity, respiration of plants and animals, and fossil fuel combustion by industries and transportations.

The Nitrogen Cycle

The nitrogen cycle involves the major constituent of the atmosphere, 78.084 per cent of each breath we take. Nitrogen is also an important in the formation of organic molecules, especially proteins, and therefore essential to living processes. However, this vast atmospheric reservoir is inaccessible directly to most organisms. The key link to life is provided by nitrogen-g bacteria, which live principally in the soil and are associated with the roots of certain plants. For example, the legumes such as clover, alfafa, pulses, peas, soybeans, beans, green-manufacturing crops and peanuts. Bacteria colonies reside in nodules on the legume roots and chemically combine the nitrogen from the air in the form of nitrates (NO3) and ammonia (NH3). Plants use these chemically bound organic matter. Anyone or anything feeding on the plants thus ingest the nitrogen. Finally, the nitrogen in the organic wastes of the consuming organisms is freed by denitrifying bacteria, which recycle it back to the atmosphere.

Hydrological Cycle

A simplified model of the w of water and water vapour from place to place as energy powers system operations. Water flows through the atmosphere, across the land water, it is also stored as ice, and within groundwater.


That physical location in which an organism is biologically suited to live. Most species have specific habitat parameters, or limits.

Niche (French word 'niche', to nest)

The basic function, or occupation, of a life-form within a given community. The way an organism obtains and sustains the physical, chemical and biological factors it needs to survive. It is the basic function or occupation of a life-form within a given community; the way an organism obtains its food, air and water. In other words, it is the description of an organism's functional role in habitat ' its 'job'. Among the functions, a niche includes: (i) a habitat niche, (ii) a trophic (food) niche, and (iii) a reproductive niche.

Food Web (Food-Chain)

A complex network of interconnected food chains. It is the way an organism obtains and sustains, the physical, chemical and biological factors it needs to survive. Basically, all animals depend on plants for their food. Foxes may eat rabbits, but rabbits feed on grass. A hawk eats a lizard, the lizard had just eaten a grasshopper and the grasshopper was feeding on grass-blade. is relationship is called food-chain. In a food-chain, for example, a caterpillar eats the leaf; the blue-tit eats the caterpillar but may fall prey to the kestrel.

The food-web can be illustrated with the help of a salt marsh ecosystem. In a salt'marsh ecosystem, a variety of organisms are present- algae, and aquatic plants, microorganisms, insects, snails, and crabfish, as well as other larger organisms such as fishes, birds, shrew, mice, and rats. Inorganic component will be found as well'water, air, clay particles and organic sediment, nitrogen nutrients, trace elements, and light energy. Energy transformations in the ecosystem occur by means of a series of steps or levels, referred to as food chain or food web. The plant and algae in the food web are the primary producers. They use light energy to convert carbon dioxide and water into carbohydrates (long chain of sugar molecules) and eventually into their biochemical molecules needed for the support of life. This process of energy conversion is called photosynthesis. Organisms engaged in photosynthesis form the base of the food web.

The primary producers support the consumers ' organ isms that ingest other organisms as their food source. At the lowest level of consumers are the primary consumers (the snail, insects, and fishes). At the next level are the secondary consumers (the mammals, birds and larger fishes), which feed on the primary consumers. Still higher levels of feeding occur in the salt-marsh ecosystem as marsh- hawks and owls consume the smaller animals below them on the food web. The decomposers feed on detritus, or decaying organic matter, derived from all levels. They are largely microscopic organisms (microorganisms) and bacteria. In brief, decomposers (bacteria, fungi, insects, worms and others) are the internal links in the food-chain. Waste products, dead plants and animals, and other organic remains are their principal food source. Material is released by the decomposers and enters the food chain'and the cycle continues.

The food web is really an energy w system, tracing the path of solar energy through the ecosystem. Solar energy is absorbed by the primary producers and stored in the chemical products of photosynthesis. As these organisms are eaten and digested by consumers, chemical energy is released. This chemical energy is used to power new biochemical reactions, which again produce stored chemical energy in the bodies of the consumers.

At each level of energy w in the food web, energy is lost to respiration. Respiration can be thought of as the burning of fuel to keep the organism operating. Energy expanded in respiration is ultimately lost as waste heat and cannot be stored for use by other organisms higher up in the food chain. This means that, generally, both the numbers of organisms and their total amount of living tissue must decrease greatly up the food chain. In general, only 10 to 50 per cent of the energy stored in organic matter at one level can be passed up the chain to the next level. Normally, there are about four levels of consumers.

Food chain concepts are becoming politicized as world food issues grow more critical. Today, approximately 'half of the cultivated acreage in the United States and Canada is planted for animal consumption. This includes more than 80 per cent of the annual corn (maize) and non-exported soybean harvest. In addition some rain forests cleared of in Central and South America have been converted to pasture to produce beef for export to some restaurants, stores, and fast-food outlets in developed countries. This influences lifestyle decisions and dietary patterns in North America and Europe and is perpetuating certain food chains, not to mention the destruction of valuable resources, both in America and overseas.

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