Ecosystem 

Introduction 
Ecosystem, relatively autonomous dynamic system formed by a natural community and their physical environment. The concept that began to be developed in the decades of 1920 and 1930, keeps in mind the complex interactions among the organisms -plants, animals, bacterias, algae, protozoos and mushrooms, among other - that form the community and the energy flows and materials that cross it. 
There are many forms of classifying ecosystems, and the own term has been used in different contexts. They can be described as ecosystems areas so reduced as the puddles of tide of the rocks and as extensive as a complete forest. But, in general, it is not possible to determine with accuracy where it finishes an ecosystem and another begins. The idea of clearly detachable ecosystems is, therefore, skillful. 

MAIN ECOSYSTEMS 
Nevertheless, the ecosystem concept has demonstrated its utility in ecology. It is applied, for example, to describe the main types of hábitats of the planet. Terrestrial ecosystems: arctic and alpine, characteristic of cold regions and without trees; forests that can be subdivided in a wide fan of types, as tropical rainy forest or pluvisilva, forest mediterranean perennifolio, temperate, northerly forests and forests temperate caducifolios; prairies and savannas; and deserts and semi-arid ecosystems. Ecosystems of sweet water: lakes, rivers and swamps. There are also hybrid, terrestrial ecosystems and of sweet water, as the seasonal flood plains. The range of marine ecosystems is amplísima: coral reefs, swamps, channels of algae and other ecosystems aquatic coasts and of shallow waters, ecosystems of open sea or the mysterious and not very well-known systems of the plains and graves abisales of the oceanic bottom. 
The term ecosystem can also be used to describe geographical areas that contain a wide spectrum of hábitats types mutually linked by ecological phenomenons. This way, the region of the Serengeti-Seronera, in oriental África, one of the most spectacular wild regions in the world, it usually considers as an only ecosystem formed by different hábitats: herbaceous plains, arboreal savanna, thickness, forest stains, rocky blooming (locally denominated koppies or kopjes), rivers, streams and seasonal charcas. Also, the most productive areas in the oceans have been divided in a series of big marine ecosystems that you/they contain very varied hábitats. They are examples of big marine ecosystems of characteristic very different: the Black sea, the system formed by the current of Benguela, in front of the coast África suroccidental, or the gulf of Mexico. 

NATURAL CHANGES OF THE ECOSYSTEMS 
The natural world is in perpetual transformation state. The change operates to all the scales of time, from the shortest to the longest. The short term changes, observables for people, they are usually recurrent and predictable: night and day, monthly cycle of the tides, annual change of the stations, growth, reproduction and the individuals' death. To this scale, many non exposed ecosystems to the human action seem stable and invariable, in a state of ' balance natural'. 
Every time is more evident than this it is not this way. But the long term changes, those that act during decades, centuries, millennia and until dozens of millions of years, they are more difficult of continuing. The own ecology is a science with less than a century of antiquity, a simple blink in the history of most of the natural ecosystems. Also, it is evident that almost all these long term changes are not neither regular neither predictable. 
On the whole, the climate is, without a doubt, the most influential factor to short and half term. In earth, the temperature, the precipitation and the estacionalidad are the three factors that more they affect to the distribution of ecosystems. The changes of anyone of them can have durable consequences. In recent geologic times, the most visible example of this is, without a doubt, the glaciaciones series that you/they have characterized to great part of the pleistoceno. These lingering periods of global cooling have affected deeply from all over the world to the ecosystems, they have caused the invasion for the polar caps of ice of temperate regions and the contraction of the humid forest hábitats in parts of the tropic. 
To shorter scales storms climatic alterations of wide geographical influence can also take place. One of the most spectacular examples is The Boy's current, a current of warm water that travels the Pacific periodically. It exercises an enormous influence on the marine ecosystems and it causes, for example, the death of coral reefs in many places of the Pacific or the loss of productivity of the fisheries of the ecosystem of the current of Humboldt, in front of the costs of Peru and Chile. The Boy's current follows an irregular cycle and it varies as for intensity and impact; they rarely spend more than twenty years without she/he takes place, but in occasions the phenomenon has repeated with an interval of only one or two years. It also affects to the terrestrial ecosystems, because it alters the precipitation rules, mainly in America. 
Certain local episodes also affect with force to the ecosystems: fires, floods and landslides of lands are natural phenomenons that can have catastrophic repercussions to local scale. This impact is not necessarily negative: in fact, many ecosystems need these periodic interferences to stay. Certain ecosystems, once reached the good state or climax, they are dependent of the fire, since the periodic fires are essential part of the cycle of growth; these ecosystems are very common in semi-arid areas, as great part of Australia. 
To more lingering scales of time, the geologic phenomenons and the evolution they carry out a crucial function in the change of operation of the ecosystems. The continental drift alters, literally, the face of the Earth, destroys landscapes and believe other new ones, while the evolution gives place to new forms of life that, in turn, they can create new ecosystems at the time that you/they induce the extinction of other species and the loss or transformation of the ecosystems of those that were part. 
But this doesn't mean that the natural ecosystems lack continuity. Many have demonstrated an elasticity and an enormous persistence during millions of years. They are examples of ecosystems that have stayed seemingly stable during a lot of time: the extensive plains of the oceanic bottom, the ecosystems of mediterranean type of the África south and the west of Australia and some areas of rainy tropical forest or pluvisilva, as those of the continental Asian Southeast or the mountains of the África east. 

It INFLUENCES HUMAN ON THE ECOSYSTEMS 
All the means and natural ecosystems face an unprecedented difficulty now: the humanity. The human being has compressed in some few centuries changes that has demanded thousands or millions of years in his absence. The consequences of these changes are still to see. Next the most important impacts in the activity of the human beings are described on the ecosystems (sees you environmental Impact). 


Destruction and hábitats fragmentation 
The man's more direct influence on the ecosystems is its destruction or transformation. The pruning to matarrasa (the cut of all the trees of a forest extension) it destroys, like it is logical, the forest ecosystem. The wooden selective exploitation also alters the ecosystem. The same thing happens with the humedales drying that has been carried out in a systematic way (to win cultivation lands or to eliminate the source of illnesses) and whose bigger exponent is the drying of the sea of Aral for the use of the waters of its tributary ones. The fragmentation or division in small stains of what was a continuous ecosystem can alter ecological phenomenons and to prevent that the surviving parcels continue working like before the fragmentation. 

Change climatic 
Now it is accepted in widespread way that the humanity's activities are contributing to the global heating of the planet, mainly for accumulation in the atmosphere of gases of effect hothouse. The repercussions of this phenomenon will probably be accentuated in the future. As it has already been pointed out, the climatic change is a natural characteristic of the Earth. But before their effects could be assimilated, because the ecosystems ' emigraban' moving in latitude or altitude as it changed the climate. As now the human being has appropriated of great part of the floor, in many cases the natural ecosystems or seminaturales don't have any place to the one that to emigrate. 

Contamination 
The contamination of the environment for herbicides, plaguicidas, fertilizers, poured industrial and residuals of the human activity are one of the most pernicious phenomenons for the environment. The pollutants are in many invisible cases, and the effects of the atmospheric contamination and of the water they can not be immediately evident, although they are devastating long term. The consequences of the sour rain for the sweet and forest ecosystems of water of great part of northern Europe and power station is a phenomenon that illustrates this section. 

Introduced species 
The man has been responsible deliberate or accidental of the alteration of the areas of distribution of an enormous number of animal species and vegetables. This doesn't only include the domestic animals and the cultivated plants, but also parasites like rats, mice and numerous insects and mushrooms. The naturalized species can exercise a devastating influence on the natural ecosystems by means of their pillaging activities and competition, mainly in islands in those that there are natural species that have evolved isolated. This way, the introduction of foxes, rabbits, toads, mountain cats and until buffalos they have desolated many ecosystems of Australia. You plant, as the South American bush of the gender Lantana, they have invaded the natural forest in many tropical and subtropical islands and they have caused serious alterations in these ecosystems; the African aquatic hyacinth, gender Eichhornia, it has also perturbed in a similar way the ecosystems of sweet water of many warm places of the world. In the mediterranean coast, the accidental introduction of the alga marine Caulerpa taxifolia is causing the disappearance of the rich and productive communities of marine fanerógamas, the prairies of Posidonia. 

Sobreexplotación 
The capture of an excessive number of animals or plants of an ecosystem can induce substantial ecological changes. The most important example at the present time is from all over the world the sobrepesca in the seas. The exhaustion of most of the populations of fish is, without a doubt, cause of important changes, although its long term repercussions are difficult to evaluate (sees it is Fished commercial). 

CONTROL OF THE HUMAN INFLUENCE ON THE ECOSYSTEMS 
To control the change of the ecosystems can be for the humanity the most important challenge during the present millennium. It will be necessary to find solutions to all the scales, from the local one until the world one, impacting in all the social strata, from the political class, until the children and students, promoting programs of environmental education in schools and educational centers. 
The protection of the natural ecosystems that you/they are in national parks and other protected areas is decisive. But this won't avoid the influence of factors like the climatic change or the contamination crawled by the air and the water. Also, the continuous land loss that you/they experience the natural areas means that they will probably demand a more active administration to maintain its ecological functions: control of exotic species, manipulation of the levels of water in the humedales, periodic fires controlled in forest hábitats, among others. This class of interventions is always dangerous, because we still ignore the operation of most of the ecosystems. 
The control of the contamination and of the emission of hothouse gases it will demand to adopt measures to world scale; it also requires coordinated measures of this type the interruption of the deterioration of the marine fisheries for sobrepesca. Ultimately, the solution rests in controlling the human population's growth and in adopting a much more restrictive posture as for the use of natural resources and energy.