2. The causes of ecological succession and their implications

For each biogeocoenose characteristic succession of some other groups of organisms - succession, thus forming new biocenosis to best meet the requirements of the environment. For example, at a depth of not flowing water bodies due to lack of oxygen of the organic matter is less than fully oxidized and used in further circulation of substances. Piled silt pond milli, it also enhanced deposition of clay and sand coming from the catchment area. Coastal aquatic vegetation extends farther toward the center of the reservoir, formed peaty sediments. The lake is gradually turning into a swamp. Disappearing fish and plankton exposed areas. Many plants and animals changes other species more adapted to the marsh. The surrounding terrestrial vegetation gradually comes to the place of the former reservoir. Depending on local conditions, there may be a bow, wood or other type biogeocoenose .

Some resistant biocenosis after the initiation able to heal itself, which is implemented through a series of sequential steps. An example is the regular change biomes in the recovery process fir forest. After cutting or fire conditions in place so spruce change that spruce can again occupy vacant space. In the open staircase spruce damaged by spring frosts, suffer from excessive heat and can not compete with high light plants. In the first two years of clearings and fires rapidly developing herbaceous plants: ivanchay, Calamagrostis and others. Soon there are numerous stairs birch, aspen, sometimes pine seed which is easily carried by the wind. They displace herbaceous vegetation, and gradually form a small-leaved and pine forest. Only now, the conditions conducive to the restoration of spruce. Tine-hardy spruce shoots successfully compete with adolescents sun-hardwood. When spruce up the upper tier, it completely replaces the deciduous trees. So through a series of temporary biocenosis biocenosis restored original fir forest. This process continued for over 100 years, with each successive biocenose more durable than the last.

Accordingly, changes and fauna.

2.1 Changes in primary and secondary succession

There are primary and secondary succession. Primary occur at the site area (cliffs, sandy beaches, etc.), where there is no vegetation. (Fig.4) Secondary believe those that occur in the recovery of natural vegetation after fires, cuttings and so on. (Fig.5) Succession always occur in the same direction, ie biocenose some time in the development process can not return to their previous state. During a succession of increasing species diversity of organisms, trophic network of branches. This reinforces the regulatory mechanisms biogeocoenose reduces the probability mass reproduction of individual species. The process of succession continues to achieve significant biogeocoenosis diversity, which ensures the stability of circulation of substances and energy. In this biogeocenose (with stable diversity of species developed mechanisms for self-regulation and the ability to reproduce) the emergence of new species or the disappearance of existing sprychynyuvatyme no significant changes in its structure.

Fig 4. Scheme of primary succession.

In the nature of primary succession are relatively rare and continue much longer secondary - up to several centuries. Primary succession - is overgrown space previously occupied by vegetation, bare rocks or frozen lava. To live in such a soil capable of only a few plants are called pioneers succession. Typical pioneers - mosses and lichens. They change the soil, highlighting acid loosens and destroys the stone. Mosses and dying, and lichens under the influence of bacteria decomposers decompose, and their remains mixed with loose rocky substrate (sand). Thus is formed the first ground on which already can grow other plants. The need for the destruction of the parent rock - the main reason for the slow progress of primary succession; note an increase in the thickness of the soil layer as succession. The soils poor in nutrients, herbs settle, more specifically capable and displace lichens and mosses. Grassroots penetrate the cracks stony rock, pushing these cracks and destroy the stone more and more. Instead herbs come perennials and shrubs, such as alder and willow. At the roots of alder are nodule - special bodies that contain symbiotic bacteria that fix atmospheric nitrogen and contribute to the accumulation in the soil its large reserves, due to which the soil becomes more fertile. Now in it already can grow trees, such as pine, birch and spruce. Thus, the driving force of succession is that plants alter soil under them, affecting its physical properties and chemical composition, so that it is suitable for competing views, displacing the original inhabitants, causing a change in the community - succession.

Fig.5. Scheme of secondary succession.

In places where the economic activity of people does not interfere with the relationship of organisms consists klymaks community that could be vaguely long time - until some external influence (plowing land, chopping wood, fire, volcanic eruption, flood) will not violate its natural structure. In the case of the destruction of the community it begins succession - the slow process of restoring the original state. Examples of secondary succession: abandoned overgrown field, meadow, hary or logging. Secondary succession takes several decades. It starts from the fact that the liberated area of ground appear Annual herbaceous plants. This is - typical weeds: dandelion, thistle, mother-and-stepmother and others. Their advantage is that they quickly grow and make seeds adapted to spread over long distances by wind or animals. However, even after two or three years, replacing their competitors - grasses, and then - shrubs and trees, especially aspen. These rocks shade the ground, and their large root systems take all the moisture from the soil, so that the seedling species, first hitting the field, it is difficult to grow. However, the succession does not stop there; by aspen pine appears; and last - slow-growing shade-tolerant species, such as spruce or oak. One hundred years in this region is restored community that was in place before the erection polyuchy forest and arable land.

The importance of assessing the status and regulation of populations. In order to establish the causes of fluctuations in population abundance of any kind is necessary to know the biology of this species, its enemies, the impact of environmental factors on reproduction and survival of organisms of this type, as well as the causes that affect the change in intensity of these factors. Since environmental factors are the most important restrictive.

Human activities significantly affect the species composition of biomes. Unrestricted hunting and gathering herbs can not only reduce the number of game animals and plants, but also bring them to the brink of extinction. Cultivation of crops causing mass outbreaks of pests. The use of chemical means of pest control reduces not only the number of pests and other insects, including enemies of pests. As a result of the grouping of populations of different species loses its originality and sustainability. Each type of organisms biogeocoenose (no matter how small it was not) has multiple relationships with a large number of other species. The disappearance of some animal species, especially plants may cause unintended consequences and destruction of all biogeocoenose.

Productivity natural biogeocoenose much higher than biomes exposed to human activities. For example, one could argue that a hectare of forest emit oxygen four times more than the same area of the park. Attribute this to the fact that the species composition of biomes urban parks is much poorer than the forest. Diversity and stability of species composition of vegetation in forest ecosystems is closely associated not only with higher plants that grow there, but also fungi and animals, from the inhabitants of the soil - round and annelid worms and mammals, excavation and finishing insects and birds that living in the treetops.

From these examples it is clear how important and necessary to study the dynamics of processes in Biogeocenoses to control the populations of useful and harmful to humans plants and animals. Invaluable assistance in this computer. Due to the high speed of work and the ability to accumulate and store huge amounts of information enable computers to simulate the possible changes in ecosystems that occur in response to natural changes in the environment and human activity. Simulation in general terms - a method of knowledge or study of a process, phenomenon or body by playing his own material or its properties in a material or theoretical model. The latter category includes and models.

An example of a classical model that describes the interaction of two species, is a model Trays - Walter, known as a model predator - prey. The model consists of two systems of differential equations, which describe respectively the rate of change of populations of predator and victim. The disadvantage of this model is that it is based on many assumptions that simplify the flow of biological phenomena. However, this model gives a more or less clear idea of the life of certain components of ecosystems.

Virtually use so-called a priori model. They are based on a considerable amount of experimental data on the structure of populations, their dynamics, ecology and biology of the species, as well as empirical relations between various parameters of the model organism - environment.

The need for such models often occurs during when a certain probability must determine how to behave or that the population of animals or plants in the case of, for example, construction of dams, drying of wetlands, ie, to forecast the development of the ecosystem