Ecosystem is a complex system formed by organisms that live in a specific environment. Animals and plants are the biotic components of the ecosystem, while the subsoil, the air and the water, the light,the temperature, the climate, the rains and so on are members of the abiotic component.

Biotic and biotic components establish a combination of connections that characterize the same ecosystem and they bring it to a situation of temporary "balance".

The fundamental functions within an ecosystem, the biotic components  (living organisms) can be subdivided into:

producers (plants, weeds and some bacteria) =  they are the "autotrophic water, carbon dioxide(CO2) and nitrates.

-consumers: they are "eterotrophic" organisms,because they can't produce their own nourishment,and so they eat producers (for example herbivorous consumers,like cows and sheeps,that they eat the grass of meadows )or other consumers (the carnivorous consumers like lion or the human).

-decomposers: they are mushrooms and bacteria that eat decomposing tissues of dead organisms.

Every ecosystem contain a defined amount of organic matter that comprises all her vegetable and animal organisms: with the term of biomass you identify the weight of this matter,calculated at the dry state and for unity of surface taken by the same ecosystem.

Transfer of energy into the ecosystem

Connections between different components of an ecosystem are so close that,if one of them is injured,the whole ecosystem results upset. The main connections are those consistuted by flows of energy and flows of nourishing. Ecosystem is a open system as regards the energy, that is energy continuosly enter and exit from the system. Energy mainly enters the ecosystem from the sun,crosses the biotic community and her food chain,and leaks like heat,organic matter and produced organisms. More in the detail,producer organisms can catch and utilize the sun energy to transform some inorganic compounds in organic compounds across the process of photosynthesis. These compounds are used by the same producers in two ways: to live and grow larger ( in that case organic compounds go and form new structular elements of plants like leaves or new stakes). The erbivorous,eating vegetable,assume from them organic substances and metabolize,that is they transform them in other organic substances adapted to be used for all the vital functions ( breathing,movement,the bodily heat and many other) and like structural material for their increase. Analogously, carnivorous animals behave,eating other animals.The process continues like this from a category of organisms to the other. The transfer of energy acroos the food chain is accompanied by losses disguised as heat dissipated in the environment like the second principle of thermodinamycs. It means that in the nourishment of the carnivorous will be available less energy than it is available of the erbivorous,that in their turn they receive less energy than it is used by plants in the process of metabolising of nourishing, (the organic matter formed thanks to process of photosynthesis ). Pecentage transfer of energy from a trophic level to the next is defined "ecoligical efficienty" or efficienty of the food chain.

The trophic chain

There are two kinds of food chains: The chain of the pasture and the chain of the debris. The first part of green plants,passes across pasturing erbivorous,then at the carnivorous of the first level that eat erbivorous,then at the carnivorous of the second level,that they eat other carnivorous. The second part of the dead organic matter,passes across microorganism,from these to detritivorous animals( consumers of debris),to finish at their predators,that are carnivorous animals. Food chains are close interconnected between them,and this is the reason for which it speaks about trophic bet(or food). In natural ecosystems, organisms that get their nourishment from the sun with the same number of passages,belong to the same trophic level. So,green plants( producers) occupy the first trophiv level,organisms that eat plants occupy the second level(primary consumers), the carnivorous belong to the third level and predator carnivorous to the fourth level(secondary and tertiary consumers). The source and the quality of the available energy establish,for all levels,the kind and the number of organisms,and their development processes.

The nourishing

Unlike energy,that enter and exit form the ecosystem following a linear route,the matter followes a circular route passing form the abiotic division to living organisms to finally return at the abiotic division. These routes are defined biogeochemical cycles. Carbon,hydrogen,nitrogen,phosphorus and calcium are necessary st living organisms in big amounts and that's why they are defined macronourishing. Other elements like iron,magnesium,manganese,zinc,exc.,are sought-after in smaller amount and that's why defined micronourishing. That division is purely academic,because organisms to grow larger and reproduce need all these sustances in different measure in function of the physiological time of the own development. Substances that can be defined essential vary from species to species. Both the numerical development of a population,and the individual growth of the organism depend on that element or compound that,compared to requirements of the organism,is in the environment in smaller amount: the limiting factor.

Primary productivity

Alteration of the food chain

Technological innovations applied to agriculture to combat the pest organisms that damage crops has led to the use of pesticides in large quantities and for a long time. These substances are toxic and their accumulation has changed the balance of the biosphere because they have harmful effects on many organisms including man. DDT is a substance which, introduced into the environment, has caused damage to ecosystems, creating a phenomenon of widespread pesticide contamination on a global scale. Studies have found that the amount of DDT present in organisms have confirmed its presence in fish from around the world, in the Inuit, in animals living in polar regions and in breast milk. This passage through the various levels of DDT in the food chain is possible because the molecule remains unchanged, it does not degrade easily. It follows that at each jump of level (from the plant the insect, insectivorous bird, the mammal predator), the concentration of DDT in organisms increases by about 10 times. That is, if the mass of bodies became the tenth part, the concentration of the pesticide becomes ten times higher.
The damage done to the bodies by DDT are alarming: when the molecule reaches the sea, it slows down the photosynthetic activity of algae, birds' eggs are fragile and break easily during the hatching because they are poor in calcium, decreases the number of individuals population, humans relate to damage organs and systems.


An example of altered ecosystem

In Borneo, the use of DDT has caused the deterioration of the ecosystem, indirectly affected the man. The widespread use of DDT to kill mosquitoes that transmit malaria has killed all insects, including useful to humans as cockroaches. These insects are the main food of lizards, whose population has fallen greatly as the number of cats that ate the lizards. The cats, however, kept under control the population of mice: reduction of cats has led to an increase in the number of rats in overcrowded conditions that transmit dangerous diseases to humans.
Borneo, after DDT spraying campaigns, was hit by infectious diseases that have caused more victims of malaria.

The ecosystem is important for human beings 

Terrestrial and aquatic ecosystems are "factories" natural complex and perfectly organized that produce all that is necessary to enable life on Earth and to cover basic human needs: food, fiber, water. Some of these functions of ecosystems are essential for humans, such as air and water purification, climate control, the cycle of nutrients, soil fertility. In addition, some ecosystems (beaches, forests, lakes, high mountains, isolated valleys) are the ideal places for recreation and tourism. In addition, it also recognized the importance in economic terms: 50% of the inhabitants of the world finds employment in agriculture, forestry and fishing. This percentage rises to 70% when considering only the sub Saharan countries, Asia and the Pacific. 25% of the countries of the world has an economy that still depends almost entirely from the areas mentioned above. Only agriculture produces 1.3 trillion dollars in food and fiber every year.

The biome

A forest, a lake, a river, a meadow, a beach, the sea, even the green spaces of the city are all ecosystems. In short, every inch of our planet is, or is part of an ecosystem. Ecosystems can have very different sizes. Ecosystems are considered to be the temperate forest, which occupies most of North America, Europe and northern Asia, and the cavity filled with water and life of a beech forest that is part of the same (in this case is called microecosystem).
The Earth itself can be considered one large ecosystem. The division into smaller ecosystems and defined is necessary in the case of targeted studies, but in fact the limits of an ecosystem normally blend into those of another, and most of the bodies may belong to different ecosystems at different times. For example, fresh water becomes brackish near the coast, and in this way the ecosystem of the sea and fresh water are linked by flows of energy and food. The boundaries of an ecosystem can also vary over time due to various factors that alter the balance, including the extinction of a species, human intervention, the introduction of exotic species in an ecosystem and others. Under ideal conditions, areas that have uniform physical and chemical characteristics should have ecosystems that are well defined and easily recognizable. In nature, however, is not possible to find conditions so uniform. Especially in the case of terrestrial ecosystems, it is easier to identify groups of ecosystems. In particular, neighbors that share ecosystems and biogeochemical cycles have similar abiotic components are called "biomes". Terrestrial ecosystems can thus be grouped in several biomes.

Earth's ecosystem

Based on the type of vegetation that characterizes them most, ecosystems are recognizable, and are divided into:

• Deserts
• savannah
• steppe
• temperate forests
• tropical
• boreal forest (taiga)
• tundra
• Mediterranean

Aquatic ecosystems are divided in hand:

• freshwater ecosystems: lakes and ponds, rivers and streams, swamps and marshes
• marine ecosystems: coral reefs, oceans, continental shelves, areas of slope of nutrients, estuaries.

On Earth, however, there are not only natural ecosystems, but also those created artificially by humans at the same time that development has led him to organize his social life and way of living and produce according to specific characteristics.
The artificial ecosystems are divided into:

• Urban-industrial ecosystems (metropolis)
• ecosystems rural (small towns)
• agroecosystems (cultivated field).

A changing world: the ecological succession

The story of an ecosystem, from birth to maturity, is called ecological succession. The ecological succession, in practice, is a continuous sequence of changes in biotic and abiotic components of an area, so we come to a stable ecosystem (what is called a "climax") characterized by a balance between its various components, namely no prevail decreed the extinction. The sequence of communities that gradually replace the ecosystem is known as "serious" and are called "serial stages" the different stages of transition. In some cases, the people themselves alter the environment in which they live and cause their own extinction for the benefit of other species of organisms. Examples of this evolutionary process can easily be found in nature, where the formation of any new environment (due to fire in a forest, diversion of a watercourse, to an abandoned agricultural field, etc..) Initially determines the spread of organisms as "pioneers," meaning they are able to grow despite the difficult conditions of the area (low presence of nutrients). The vital activity of these early organisms change the environment, creating new conditions that are favorable for other organisms more demanding. These are developed often causing the elimination of the entities pioneers.


To understand this better

For example, mosses, lichens and grasses are often pioneer species on or solidified lava bedrock. These bodies are able to shatter the bedrock to extract the minerals necessary for their survival. Furthermore, once dead, they provide that the organic material that decomposes, becomes "soil" used by plants and are setting up at a later time to feed and grow. An example of ecological succession is what happens on the sand dunes: the first plant species and are setting up are very adaptable and able to use the modest availability of nutrients. These first pioneer species establish, with their root system, making the sand dunes are more stable. Moreover, after death, remain on the ground and enrich organic matter resulting from their decomposition. This creates an environment richer and therefore more suitable for sustaining life of organizations demanding that gradually supplant those pioneers, and the species composition becomes increasingly diversified and is set in natural processes of power and competition becoming more complex.

An artificial ecosystem: agro-ecosystem

A typical example of artificial ecosystem is the cultivated field, or agro-ecosystem. This is a natural system modified by humans through agricultural activity. It differs from the ecosystem natural for four aspects:

• simplification: the farmer prefers a type of plant fighting all those animal and plant species that could damage
• the input of energy by humans in the form of machinery, fertilizers, pesticides, selected seeds, work
• biomass (harvest) is removed once mature. This makes an open ecosystem, ie dependence on nutrient re likely to fuel a new process of birth and development of organic material (plants). A natural ecosystem, however, the biomass remaining in the original manure alone.
• the release of pollutants which, in the case of intensive farming, chemical fertilizers, pesticides and other chemicals that accumulate in the ecosystem is not biodegradable or are lost in the underground, and in some cases to seriously pollute groundwater, rivers and seas .

The house is a small artificial ecosystem. Come from outside objects, food, solar energy, water, etc.. and are placed outside the solid and liquid waste generated by human activities. Similarly the city. It depends on outside supplies of water, food, construction materials and other resources necessary for its development and always outside discharge their waste (in landfills and incinerators), ie everything that does not contribute to the survival of the ecosystem city.