Ecosystem: a complex system.

Ecosystem is a complex system composed of organisms who live in a specific area. Animals and plants are biotic components of the ecosystem, while subsoil, the air and the water, the light, the temperature, the climate, the rains, ex... are abiotic components. Biotic and abiotic components found among their a group of relation that characterize the same ecosystem and take him in situation of temporary balance. On their function within the ecosystem, components biotic (living organisms), can be organized in:

•~                 Producers (plants and weeds and bacteria): are the organisms "autotrofi"(autotrophy) that produced themselves the organics substance to live and to increase, using simple inorganic molecule like the waters, carbons dioxide (CO2) and the nitrates.

•~                 Consumers: are organisms "eterotrofi" (heterotrophy), because they can't produce their food, and they eat producers (for example the consumers herbivores, like cows and sheep that eat the grass of meadow) or other consumers (consumers carnivore like lion or the men too).

•~                 Decomposers: are mushrooms and bacteria that eat decomposing "tessuti" of die's organisms.

Every ecosystems involve to determined quantity of organic matter that comprise all his vegetal and animal organisms; with the term of "biomassa" (biomass) we identify the weight of this matter.

Transfer of energy in the ecosystem.

Relations among different components of an ecosystem are so tight that if one of this is injured, the entire ecosystem will result upset. The principal relation are those with energy flow and of nutrient flow. The ecosystem is an open system respect the energy, that is the energy continually go in and out from the system. The energy go into the ecosystem principally from the sun, go through the biotic community and his food chain and go out like warmth, organic matter and produced organisms. A more precise definition the organisms producer can catch and use energy of the sun to translate some inorganic composts in organic composts thanks to photosynthesis. The same producers use these composts in two line: to live and to increase (in this situation the organic composts create new structural element of plants like leaves and new stake).

The herbivores, eating vegetal , employ organic substance and  "metabolizzano", that is they change them in other organic substances suitable to be utilize for all the vital function (respiration, movement, body warmth and other more...) and like structural material for their increasing. Carnivore animals behave analogously eating other animals. The process continue from one class to an other. The transfer of energy across food chain is however accompany to lass as warmth disperse in the environment for the second principle of thermodynamics. This means that in the diet of carnivores will be available less energy than is available to herbivores, which in turn receive from their food less energy than is used by plants in the metabolism of the food itself, (the organic matter formed through the process of photosynthesis). The transfer percentage of energy from one trophic level to the next is known as "eco-efficiency" or efficiency of the food chain.

Trophic chain

There are two types of food chains: the chain of grazing and the chain of debris. The first part of green plants, passes through herbivores grazing, then the top-level carnivores that eat herbivores, then to the second level carnivores that eat other carnivores. The second part instead of dead organic matter, passes through the micro-organisms from these animals detritivores (consumers of detritus), and ending their predators or carnivores. Food chains are densely interconnected among them, and that is why we talk about food web (or food). In natural ecosystems, organisms that obtain food from the sun with the same number of passes in the same trophic level. Then, the green plants (producers) occupy the first trophic level, organisms that feed on plants occupy the second level (primary consumers), carnivores belong to the third level and predators carnivores to the fourth level (secondary and tertiary consumers). The source and quality of energy available indicate, for all levels, the type and number of organisms, and their development processes.

Nutrients

Unlike energy, which enters and exits from the ecosystem along a linear path, the matter follows a circular route going from abiotic compartment to living organisms and back to the abiotic compartment. These paths are defined biogeochemical cycles. Carbon, hydrogen, nitrogen, phosphorus and calcium are needed by living organisms in large quantities and this is called macronutrients. Other elements like iron, magnesium, manganese, zinc, etc.. are required in lesser quantities and are defined for this micronutrient. This division is purely academic, as the organizations,  for grow and reproduce, they need all these substances in varying degrees depending on the time of their physiological development. Substances that can be defined as essential will vary from species to species. Both the numerical development of a population, both the individual growth of the organism depend on that element or compound that, given the needs of the organism, is found in lesser quantities in the environment: the limiting factor.

Primary productivity

The primary productivity of an ecosystem is defined as the rate at which solar energy is converted by photosynthesis into organic substance. We define:

• Gross primary productivity (PPL), the total rate of photosynthesis (called so even total photosynthesis)

• net primary productivity (PPN), the rate of storage of organic matter produced, excluding the one used by the plant to live (so that even apparent photosynthesis)

• net productivity of the community (PNC) is the rate of storage of organic matter not used by herbivores and carnivores

• productivity secondary (PS) is the rate of storage of organic matter for energy purposes by consumers ( heterotrophic organisms, unable to carry out photosynthesis). A high rate of primary productivity in ecosystems is achieved when physical factors (ex: the water, the nutrients and the climate) are favorable. The presence of secondary forms of energy can help to raise the rate of primary productivity. An example is that of estuaries, one of the most productive ecosystems in the world. In estuaries, fresh water mixes with the seawater. The plants here are extensive photosynthetic carpet. Stems and roots trap large amounts of food particles, and completed their life cycle, providing additional share decompose organic matter to the ecosystem. The secondary energy is represented here by the action of tides, which helps on the one hand, the rapid movement of nutrients and, helps remove waste products, so the organisms that live here (larvae of sea bass, sea bream, mullet and clams) did not spend energy to get food or to eliminate waste and can grow more quickly.

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 of DDT through the various levels of 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 organisms 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, in human the damages relate to organs and systems.

An example of an altered ecosystem

In Borneo use of DDT has caused the alteration 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 man

Land ecosystems 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, Asian 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 centimetre 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  that is part of the same forest(in this case is called "microecosistema "). 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 ecosystem 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, surrounding ecosystem that share biogeochemical cycles and have similar abiotic components are called "biomes". Terrestrial ecosystems can thus be grouped in several biomes.

Ecosystems of Earth

On the type of vegetation that characterizes them most, ecosystems are recognized, and are divided into:

•~   desert

•~   steppe

•~   savannahs

•~   tropical forest

•~   temperate forests boreal forest (taiga)

•~   tundra

•~   Mediterranean

Aquatic ecosystems instead divided into:

•~   freshwater ecosystems: lakes and ponds, rivers and streams, marshes and swamps

•~   marine ecosystems: coral reefs, oceans, continental shelf, slope areas 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 precise characteristics.

The artificial ecosystems are divided into:

eco-industrial urban (city)

ecosystems rural (small towns)

agro-ecosystems (cultivated field).

A changing world: the ecological succession

The history 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 modify 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 that 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 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 naturally for four aspects:

simplification: the farmer prefers one 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, machining biomass (harvest) is removed once mature. This makes it an open ecosystem, ie dependence  from outside to reintroduce fertilize substances adapt to feed a new process of birth and development of organic material (plants). A natural ecosystem, however, the biomass remaining in the original environment manure itself alone.

the release of pollutants which, in the case of intensive farming, chemical fertilizers, pesticides and other chemicals not biodegradable that accumulate theirselves in the ecosystem or they lose in the underground, and in some cases  they pollute seriously groundwater, sea and rivers. Also the house is a small artificial ecosystem. Come from outside objects, food, solar energy, water, etc.. and from outside are placed 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.