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Ecology 

Introduction 
Ecology, study of the relationship between the organisms and their physical and biological environment. The physical environment includes the light and the heat or solar radiation, the humidity, the wind, the oxygen, the dioxide of carbon and the nutrients of the floor, the water and the atmosphere. The biological environment is formed by the alive organisms, mainly plants and animals. 
Due to the different necessary focuses to study to the organisms in their natural environment, the ecology is served as disciplines as the climatology, the hydrology, the physics, the chemistry, the geology and the analysis of floors. To study the relationships among organisms, the ecology appeals to sciences so disparate as the animal behavior, the taxonomía, the physiology and the mathematics. 
The growing interest of the public opinion regarding the problems of the environment has often transformed the word ecology into a term not well used. She/he made a mistakes with the environmental programs and the environmental science (to see environment). Although it is a different scientific discipline, the ecology contributes to the study and the understanding of the problems of the environment. 
The term ecology was coined by the German biologist Ernst Heinrich Haeckel in 1869; it derives of the Greek oikos (home) and it shares their root with economy. That is to say, ecology means the study of the economy of the nature. In certain way, the modern ecology began with you Talk Darwin. When developing the theory of the evolution, Darwin made stress in the adaptation from the organisms to its environment by means of the natural selection. They also made big naturalistic taxes as Alexander von Humboldt, deeply interested in the how and the why of the distribution of the vegetables in the world. 

THE BIOSPHERE 
The thin mantel of life that covers the Earth receives the biosphere name. To classify their regions different focuses they are used. 

Biomas 
The big units of vegetation are called vegetable formations by the European ecologists and biomas for those of America of the North. The main difference between both terms are that the biomas includes the associated animal life. The big biomas, nevertheless, receives the name in the dominant ways of vegetable life. 
Under the influence of the latitude, the elevation and the regímenes associated of humidity and temperature, the terrestrial biomas varies geographically from the tropics to the Ártico, and they include diverse types of forests, prairies, low mount and deserts. These biomas also includes the associated communities of water candy: currents, lakes, ponds and humedales. The marine ambient means that some ecologists also consider biomas, understand the open ocean, the coast regions (you dilute not very deep), the regions bentónicas (of the oceanic bottom), the rocky costs, the beaches, the estuaries and the plains get dizzy them associate. 
See you also Chaparral; Coral reef; Estuary; Marine communities; Pantanal; Peat-bog; Savanna; Communities of the area intermareal; Tundra. 

Ecosystems 
It is more useful to consider to the terrestrial and aquatic environments, ecosystems, term coined in 1935 by the ecologist vegetable sir Arthur George Tansley to enhance the concept that each ecosystem is an everything integrated. A system is a group of interdependent parts that you/they work like an unit and it requires entrances and exits. The fundamental parts of an ecosystem are the producers (you plant green), the consumers (herbivores and carnivorous), the organisms responsible for the decomposition (mushrooms and bacterias), and the non alive component or abiótico, formed by dead organic matter and present nutrients in the floor and the water. The entrances to the ecosystem are solar energy, it dilutes, oxygen, dioxide of carbon, nitrogen and other elements and compound. The exits of the ecosystem include the heat taken place by the breathing, it dilutes, oxygen, dioxide of carbon and nutritious. The force fundamental instigator is the solar energy. Lastly, in a level of superior organization they are the relationships between the different elements or parts of the ecosystem. 

Energy and nutritious 
The ecosystems work with energy coming from the Sun that flows in an address, and with nutritious that are recycled continually. The plants use the light energy transforming it, by means of a process called photosynthesis, in chemical energy under the form of hydrates of carbon and other compounds. This energy is transferred to the whole ecosystem through a series of steps based on eating or to be eaten, the call net trófica. In the transfer of the energy, each step is composed of several levels tróficos or of feeding: you plant, herbivores (that eat vegetables), two or three levels of carnivorous (that eat meat), and organisms responsible for the decomposition. Part of the energy fixed by the plants only follows this road, called alimentary net of production. The vegetable matter and animal not used in this net, as fallen leaves, branches, roots, tree trunks and dead bodies of animals, give sustenance to the alimentary net of the decomposition. The bacterias, mushrooms and small animals (generally spineless) that feed of dead matter they become energy source for levels superior tróficos linked to the alimentary net of production. This way the nature takes advantage of to the maximum the energy initially fixed by the plants. 
In both alimentary nets the number of levels tróficos is limited because in each transfer she/he gets lost great quantity of energy (as breathing heat) that leaves of being usable or transferable to the following level trófico. Therefore, each level trófico contains less energy than the one that sustains him. Due to this, for example, the deer or the elks (herbivores) they are more abundant than the wolves (carnivorous). 
The energy flow feeds the cycle biogeoquímico or of the nutrients. The cycle of the nutrients begins with its liberation with waste and decomposition of the organic matter in a form that can be an employee for the plants. These incorporate the available nutrients in the floor and the water and they store them in their fabrics. The nutrients pass from a level trófico to the following one along the net trófica. Since many plants and animals don't arrive to be eaten, ultimately the nutrients that contain their fabrics, after traveling the alimentary net of the decomposition, they are liberated by the bacterial decomposition and fúngica, process that reduces the complex organic compounds to compound inorganic simple that are to disposition of the plants. 

Imbalances 
The nutrients circulate inside the ecosystems. Nevertheless, losses or exits exist, and these should be balanced by means of new entrances or the ecosystem will stop to work. The entrances of nutritious to the system come from the erosion and waste of the rocks, of the powder transported by the air, and of the precipitations that can transport materials at big distances. The terrestrial ecosystems lose variable quantities of nutritious, crawled by the waters and deposited in aquatic ecosystems and in the associate low lands. The erosion, the pruning of forests and the crops extract of the floor a considerable quantity of nutrients that you/they should be replaced. Of not being this way, the ecosystem becomes poor. It is for this reason for what the cultivation lands must be fertilized. 
If the entrance of a nutrient exceeds in a lot to its exit, the cycle of nutritious of the affected ecosystem is overloaded, and contamination takes place. The contamination can be considered an entrance of nutrients that overcomes the capacity of the ecosystem to process them. The nutrients lost by erosion and lixiviación in the cultivation lands, together with the urban residual waters and the industrial residuals, they will stop to the rivers, lakes and estuaries. These pollutants destroy the plants and the animals that can not tolerate their presence or the environmental change that take place; at the same time they favor to some organisms with more tolerance to the change. This way, in the clouds full with dioxide of sulfur and nitrogen oxides coming from the industrial areas, these become diluted sulfuric and nitric acids and they fall to earth, in form of sour rain, have more than enough big extensions of terrestrial and aquatic ecosystems. This alters the relationships acid-base in some of them, the fish and the spineless ones die aquatic and the acidity of the floor is increased, what reduces the forest growth in the northern ecosystems and in others that lack limestones to neutralize the acid. 
To see Cycle of the carbon; Cycle of the nitrogen. 

POPULATIONS AND COMMUNITIES 
The functional units of an ecosystem are the populations of organisms through which the energy and the nutrients circulate. A population is a group of organisms of the same species that you/they share the same space and time (to see Species and especiación). The groups of populations of an ecosystem interactúan in several ways. These interdependent populations form a community that embraces the portion biótica of the ecosystem. 

Diversity 
The community has certain attributes, among them the dominancia and the diversity of species. The dominancia takes place when an or several species control the environmental conditions that influence in the associate species. In a forest, for example, they can be dominant an or more species of trees, as the oak or the fir; in a marine community the dominant organisms are usually animal, as the mussels or the oysters. The dominancia can influence in the diversity of species of a community because the diversity doesn't only refer to the number of species that you/they compose it, but also to the proportion that each one of them represents. 
The physical nature of a community is in evidence for the layers in those that is structured, or its stratification. In the terrestrial communities, the stratification is influenced by the form that you/they adopt the plants when growing. The simple communities, as the grasses, with scarce vertical stratification, they are usually formed by two layers: I am accustomed to and herbaceous layer. A forest can have several layers: I am accustomed to, herbaceous, bushes, trees of behavior under, trees of high behavior with inferior or superior glass, among others. These strata influence in the physical environment and in the hábitats diversity for the fauna. The vertical stratification of the aquatic communities, for contrast, receives the influence of the physical conditions mainly: depth, illumination, temperature, pressure, salinity, content in oxygen and dioxide of carbon. 

Hábitat and niche 
The community contributes the hábitat, the place in the one that the different plants or animals live. Inside each hábitat, the organisms occupy different niches. A niche is that is to say the functional paper that carries out a species in a community, its occupation or way of being earned a living. For example, the olive candelo lives in a hábitat of leaf forest it expires. Their niche, partly, is to feed of insects of the foliage. The more stratified a community is, in more additional niches their hábitat will be divided. 

Rates of the population's growth 
The populations have a rate from birth (number of breedings taken place by population's unit and time) a rate of mortality (number of deaths for unit of time) and a rate of growth. The main agent of the population's growth is the births, and the main agent of the population's descent is the death. When the number of births is superior to the number of deaths the population grows and when you/he/she happens the opposite, you/he/she falls. When the number of births is similar to that of deaths in a given population its size it doesn't vary, and it is said that its rate of growth is zero. 
When being introduced in a favorable environment with abundant resources, a small population can experience a geometric or exponential growth. Many populations experience an exponential growth in the first stages of the colonization of a hábitat, since they take possession of a niche infraexplotado or they expel other populations of one profitable. The populations that continue growing exponentially, nevertheless, finish taking to the limit the resources, and they enter quickly in decline due to some catastrophic event as a famine, an epidemic or the competition with other species. In general terms, the populations of plants and animals that are characterized to experience cycles of exponential growth they are species with abundant descendant and they are in charge of little of their breedings or they produce abundant seeds with few nutritious reservations. These species that accustom to have a short life, are dispersed quickly and they are able to colonize hostile or altered ambient means. They are known as species generalistas or strategists of the R, although often they also receive the name of species opportunists, and they are characterized to present discharges reproduction rates, few ecological demands and to not explode with effectiveness the resources. 
Other populations spread to grow from an exponential way to the beginning and logistically their growth goes next, that is to say, diminishing when going increasing the population, and it is stabilized when reaching the limits of the capacity of sustentation of its environment. Through diverse mechanisms regulators, such populations maintain a certain balance between their size and the available resources. The animals that show this type of populational growth spread to have less breedings, but they provide them family attention; the plants produce big seeds with considerable nutritious reservations. These organisms have a long life, low dispersion rates and they are bad settlers of altered hábitats. They usually respond to the changes in population's density (number of organisms for surface unit) with changes in the rates of natality and of mortality instead of with the dispersion. When the population approaches to the limit of the available resources, the rates of natality diminish and those of mortality among young and adults increase. They are known as specialist species or strategists of the K and they are characterized to present smaller fecundity, bigger demands ecological and better use of the resources. 

Interactions in the community 
The main influences about the growth of the populations are related with diverse interactions that are those that maintain together to the community. These include the competition, so much in the breast of the species like among different species, the pillaging, including the parasitism, and the coevolución or adaptation. 

Competition 
When a shared resource is scare, the organisms compete for him, and those that make it with more success survive. In some vegetable and animal populations, the individuals can share the resources in such a way that none of them obtains the enough quantity to survive as adult or to reproduce. Among other populations, vegetables and animals, the dominant individuals take possession of the entirety of the resources and the other ones are excluded. Individually, the plants spread to cling to the place where they root until they lose vigor or they die, and they prevent other individuals to survive controlling the light, the humidity and the nutrients of the environment. 
Many animals have a social organization very developed through which resources like the space, the foods and the couple are distributed among the population's dominant members. These competitive interactions can show in form of social dominancia, in which the dominant individuals exclude to the subdominantes of a certain resource, or in territorialidad form, in which the dominant individuals divide the space in excluding areas that themselves takes charge of defending. The individuals subdominantes or excluded they are forced to live in poorer hábitats, to survive without the resource in question or to abandon the area. Many of these animals die from hunger, for exhibition to the elements and victims of the depredadores. 
The competition among the members of different species causes the allotment of the resources of the community. The plants, for example, have roots that penetrate in the floor until different depths. Some have superficial roots that allow them to use the humidity and the next nutrients to the surface. Others that grow in the same place have deep roots that allow them to exploit a humidity and some non available nutrients for the first ones. 

Pillaging 
One of the fundamental interactions is the pillaging, or I consummate of an alive organism, vegetable or animal, for another. Although it is good to make circulate the energy and the nutrients for the ecosystem, the pillaging the population can also control and to favor the natural selection eliminating to the less capable ones. Therefore, a rabbit is a depredador of the grass, in the same way that the fox is a depredador of rabbits. The pillaging of the plants includes the defoliation and the consumption of seeds and fruits. The abundance of the depredadores of plants, or herbivores, it influences directly about the growth and the survival of the carnivores. That is to say, the interactions depredador-prey to a certain level trófico influences on the relationships depredador-prey in the following one. In certain communities, the depredadores ends up reducing the populations of their preys that in the same area several species can coexist in competition to such an extent because none of them is plentiful enough like to control a resource. Nevertheless, when it diminishes the depredadores number, or these they disappear, the dominant species spreads to exclude the competitors, reducing this way the diversity of species. 

Parasitism 
The parasitism is closely related with the pillaging. In him, two organisms live united, and one of them obtains their sustenance to expense of the other one. The parasites that are smaller than their guests, include virus multitude and bacterias. Due to this dependence relationship, the parasites don't usually put an end to their guests, like they make the depredadores. As a result, guests and parasites are accustomed to coevolucionar until a certain degree of mutual tolerance, although the parasites can regulate the population of some species guests, to reduce their reproductive success, to modify their behavior and even to produce their death. To see Parasite. 

Coevolución 
The coevolución is that is to say the combined evolution of two non related species that you/they have a narrow ecological relationship, that the evolution of one of the species depends partly of the evolution of the other one. The coevolución also plays a part in the relationships depredador-prey. With the step of the time, when going developing the depredador more effective forms of capturing their prey, this develops mechanisms to avoid their capture. The plants have developed defensive mechanisms as thorns, spikes, hard sheaths for the seeds and poisonous sap or of bad flavor to discourage their potential consumers. Some herbivores are able to overcome these defenses and to attack to the plant. Certain insects, as the monarch butterfly, they can incorporate to their own fabrics taken poisonous substances of the plants of those that feed, and they use them as defense against their depredadores. Other similar organisms related with her (to see Butterfly viceroy) they can acquire, through the natural selection, a pattern of colors or a form that she/he imitates that of the non eatable species. Since they resemble each other to the unpleasant pattern, the imitators are able to avoid the pillaging. Other animals appeal to assume an appearance that makes that they made a mistake with their environment or that they seem to be part of him. The chameleon is a very well-known example of this interaction. Some animals that use unpleasant scents or poisons by way of defense usually exhibit also warning colorations, usually brilliant colors or attractive drawings that act like additional warning for their potential depredadores. To see Adaptation; Mimetismo. 
Another relationship coevolutiva is the mutualismo, in the one that two or more species depend the one of the other one and they can not live more than associate. A mutualismo example is that of the micorrizas, mandatory relationship between certain mushrooms and the roots of certain plants. In one of the groups, that of the ectomicorrizas, the mushrooms form a layer or mantel around the radicelas. The hifas of the mushrooms invades the radicela and they grow among the cellular walls, besides extending I am accustomed to inside starting from her. The mushrooms that include several mushrooms common of the forests, depend on the tree to obtain energy. To change, they help to the tree to obtain nutritious of the floor and they protect their raicillas of certain illnesses. Without the micorrizas, some groups taxonómicos, as the gimnospermas and some angiospermas (I plane, tree of the paradise), they can not survive and to be developed. On the other hand, the mushrooms can not exist without the trees. The most conclusive example in mutual symbiosis constitutes it the líquenes: an association between a mushroom and a simbionte fotosintético, an alga of whose interaction originates a stable talo with structure and specific physiology. To see Symbiosis. 

Succession and communities climax 
The ecosystems are dynamic in the sense that the species that compose them are not always the same ones. This is reflected in the gradual changes of the vegetable community with the step of the time, well-known phenomenon as succession. It begins with the colonization of an altered area, as a field of abandoned cultivation or a recently exposed river of lava, on the part of species able to tolerate their environmental conditions. In their bigger one she/he leaves it is about species opportunists that cling to the land during a period of variable time. Since they live little time and that they are bad competitors, they end up being replaced by more competitive species and of longer life, like it happens with certain bushes that later are replaced by trees. In the aquatic hábitats, the changes of this type are in great measure result of changes in the physical environment, as the accumulation of silts in the bottom of a pond. When going being made this less deep, the invasion of floating plants is favored as the irises of water and of emergent plants as the reed-maces. The speed of the succession depends on the competitiveness of the implied species; of the tolerance to the environmental conditions taken place by the change in the vegetation; of the interaction with the animals, mainly with the ruminant herbivores, and of the fire. With the time, the ecosystem arrives to a state called climax (good state of a biological, given community the conditions of the means), in which all ulterior change takes place very slowly, and the location is dominated by species of long life and very competitive. When going advancing the succession, nevertheless, the community becomes more stratified, allowing that they occupy the area more species of animals. With the time, the characteristic animals of more advanced phases of the succession replace to those characteristic of the first phases.

 


 

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