Succession is an irreversible change in one biocenosis, the appearance of another. It can be caused by any natural phenomena or occur under the influence of man. Ecological succession was initially investigated by representatives of such a science as geobotany. In the future, this phenomenon became the subject of interest of other ecologists. The pioneers who revealed the importance of succession were F. Clements, V. N. Sukachev, S. M. Razumovsky. Next, we analyze the concept in more detail, we give a classification. In addition, the article will describe the process with examples.
Terminology
Who introduced the definition? The concept of “succession” was directly proposed by F. Clements to determine the specific biological communities replacing each other in time. They are characterized by the formation of a series or series so that the preceding creates the conditions for the development of the next. In the case when no factors arise that can provoke another succession, the series ends with a relatively stable community, which is characterized by constant exchange. The education described above was defined by Clements using the special term “menopause”. According to the scientist, this is a sustainable community, within which there are no factors contributing to any changes in its development. In this case, the duration of menopause is not important.
Classification
Successions can be ordered for various reasons. With the help of classification according to various characteristics, various types of successions can be distinguished. Among these signs: the rate of formation / attenuation, duration of existence, reversibility, constancy, origin, development trend (progress or degradation), changes in the number and diversity of species.
Successions can be classified for many reasons. The process of grouping in the first place depends on what purpose the scientist sets himself. At the same time, there are types of successions grouped by the nature of the processes occurring in this stable community. On this basis, scientists distinguish two main categories: endogenous and exogenous. What is the difference? Endogenous succession is a change due to the activities of the communities themselves. The root cause of the process is usually an imbalance in the exchange. In other words, the change is due to the activity of internal factors. Exogenous succession is a change provoked by
external factors.Microbiology
In forest litter, for example, successions can be investigated in several stages simultaneously. This possibility is due to a change in the direction from top to bottom when moving. In addition, the phenomenon can cause changes in humidity, the content of any special compounds or gases, temperature, etc. The process of soil formation is accompanied by a rather long change in both the plant and microbial communities.
Succession primary and secondary
What do these concepts mean? We will analyze further. Primary succession is characterized by what takes place on a lifeless area. It can be bare rock without vegetation, sandy areas, frozen lava and the like. When organisms begin to populate such territories, their metabolism affects the environment and changes it. Then begins a more complex development. And then the species begin to succeed. An example of succession is the formation of the initial soil cover, the settlement of the initially lifeless sandy territory, primarily microorganisms, plants, and then fungi and animals. A special role is played by the remains of plants and substances resulting from the decomposition of organics. Thus, the soil begins to form and change; under the influence of microorganisms, plants, and fungi, the microclimate changes. As a result, the community of organisms is expanding. This succession is an ecogenetic change. It is called so because it changes the very territory on which it exists. And the initial occurrence of soil in a lifeless area is called a syngenetic shift.
Substrate moisture
This indicator affects the type of succession. So, the following groups are distinguished:
- Hierarchical, on an anhydrous substrate.
- Psammoxeroseries, in the sand.
- Lithoxeroseries, on a rocky terrain.
- Geoxeroseries, on dry clay or loam.
- Mesarchic, if the substrate has a fairly significant humidity.
- Hydrarch, if the substrate is extremely wet.
Primary successions take place in several stages. Interesting examples of succession can be given. For example, in a forest zone, a lifeless and dry substrate is replaced first by lichens, then by moss, then forbs (annual plants) grow, after which perennial shrubs, trees, grasses begin to develop the territory. There are other examples of succession. So, the settlement of the territory of frozen lava after eruptions or a slope after an avalanche is often mentioned.
Process flow
The development of primary succession occurs simultaneously with soil formation. The influence on the process is exerted by seeds from outside, the death of seedlings that are unstable to extreme conditions and (from a certain time) interspecific competition. A particular community develops or is replaced mainly due to the difference in the nitrogen content in the soil and the degree of destruction of its mineral part. In soil and other natural microbial communities, succession is a phenomenon usually caused by the receipt of a certain portion of the organic compound in one form or another. Since microorganisms adapt either to the destruction of various complex polymers, or to the absorption of any monomers at high concentrations, or to existence under severe conditions of hunger, structural changes in the community are observed during the destruction and during the use of organics.
Secondary succession
These processes lead to the settlement of species after some damage. For example, a forest partially destroyed by a fire. The territory on which it was previously located preserved soil and seeds. A community of herbs will form literally next year. And then deciduous trees appear . Under the cover of an aspen or birch forest, spruce trees begin to grow, subsequently displacing hardwood. The restoration of dark coniferous trees takes place over approximately 100 years. But the forest in some areas is again being felled. In this regard, in such areas recovery does not occur.
Continualism and structuralism in the study of biological communities
Despite the fact that the definitions that Clements postulated are applied everywhere in science, there are two paradigms that are significantly different from each other. Let's consider them in more detail. Within each of these paradigms, the meaning of Clements' definitions is different. What is the difference between these approaches? The followers of the paradigm of structuralism strongly support Clements' conclusions and continue the development of his theory. Continualists, on the contrary, do not agree with the actual existence of such phenomena as biological communities, successions, menopause, post-menopause, menopause-continuum. In the latter paradigm, ecosystem processes are reduced to the interaction of various categories among themselves. These species, according to continualism, randomly begin to interact with each other and with inanimate nature. How did continuum come about? The fact is that there is no one author of this theory: this paradigm was born almost simultaneously in two countries, in two independent scientific communities: L. G. Ramensky in the USSR and G. Gleason in the USA.
The role of successions in the formation and change of the biosphere
Thanks to successions, the study of which continues in geobotany to this day, the formation of the soil cover takes place, its composition changes, the once lifeless areas are populated, first by microorganisms, and then by plants, fungi and animals. A study of the schemes and mechanisms by which both primary and secondary community changes occur clearly shows that it is impossible to predict in advance unambiguously which species will replace each other in the chain. However, the replacement of biological communities more often occurs in such a way that the biological diversity in the study area increases.