Biocoenosis

A biocenosis (also called a biotic community, biological community, ecological community or simply community) is a set of biological populations that coexist in space and time. These species occur in a defined space called a biotope, which offers the necessary environmental conditions for their survival. It can be divided into phytocenosis (which is the set of plant species), zoocenosis (set of animals) and microbiocenosis (set of microorganisms). An ecosystem, according to the original definition Tansley (1935), is formed by the biocenosis together with its physical environment or biotope. The cultivated field is the agrobiocenosis which, together with its physical-chemical environment (biotope) form an agroecosystem.

The term biocenosis was coined in 1877 by Karl Möbius, who thus underlined the need to focus attention not on the individual but on the group of individuals.

In other words, it is a community or set of populations of different species that inhabit a certain geographical area and is influenced by physical factors such as light, temperature, humidity, etc.

Biological community

It is the biological term that refers to the living beings present in an ecosystem. It could be defined as the set of biological populations that share a given area and differ over time. A community can be defined at any taxonomic or functional level and geographic scale. In the same way, we can speak of the community of microorganisms in the intestine of a herbivore, of marine mammals in the Atlantic Ocean, or of predators in the savannahs of East Africa. For extinct communities, which we know from their fossils, the terms paleobiocenosis or paleocommunity are used.

On a large geographical scale, the main factor that determines the type of communities is climate, while on a smaller scale it is more difficult to find which are the factors that would explain the groupings of species. One of the first objectives pursued by an ecologist is to know the composition of a community and its structure, understanding this as the set of relationships that exist between the different species among themselves and with the environment in which they live. There are several ways to characterize a community, the most appropriate would be one that considers both the composition of species and the number of individuals of each one of them. However, not all species have the same importance within a community; Key or dominant species are known as those that, if they disappeared, would cause a profound change in the community, since the entire community is based on them.

Communities can undergo changes over time called successions; these transformations are usually slow and lead to changes in the composition or populations of the species.

Sometimes it is difficult to define, in nature, a border that separates different communities and in many cases what is observed is a progressive gradation from one community to another. The transition areas that appear between two totally differentiated communities are called ecotones and are especially rich in species.

Ecological succession in communities

No community is permanent; some change abruptly, others persist for years or centuries. Typically anywhere, there is a sequence or succession of communities: first there is an exploratory phase, then they gradually change, mature (these changes are not reversible), and finally comes a relatively stable phase, the climax.

In the succession of communities, first there are small changes called microsuccessions that progressively come to form the main succession. The successions occur due to changes in abiotic factors (humidity, temperature, orogenic movements, thaws, etc.) or by the arrival or introduction of foreign or opportunistic organisms that originate a series of competitions with native species and in which the the most adapted, for this reason the successions are related to the evolution of the species. When a natural community is destroyed by natural causes or by human intervention and the area where they previously were is occupied by another; we say that secondary succession has occurred.

A clear example is the succession lake - pond - swamp - meadow that are observed in many areas occupied by ancient glaciations.

The principle of ecological succession is of practical importance to man. Any field that is plowed and then abandoned presents a sequence of successive vegetations and with them different animal species for each sequence of plants. Any change in the physical or biological characteristics of the environment will obviously affect all species, populations and communities to varying degrees.

Distribution

No animal species is evenly distributed across the Earth, but instead occupies a range. The entire extent on land or in water in which a species occurs is called its geographic range; and the kind of environment in which it lives, its ecological distribution. The geological distribution of a species depends on its existence in the past. The study of the distribution of animals and plants and the factors that influence them is the object of study of zoogeography and phytogeography. The dominant plant communities in their climax state have a physiognomy different from that of other plant communities, which in turn determine the type of animal communities. The special edaphic, atmospheric or hydric conditions are those that determine a "life zone" (Holdridge's classification that is valid only for the continents) and each life zone has a different type of community, therefore we can deduce that the communities are They are distributed in these life zones (deserts, steppes, forests, tundras and moors with their respective variants) and are adapted to the abiotic conditions that prevail in them (this classification does not include microclimates or other exceptional cases).

Factors that regulate it

External factors that limit distribution are called barriers. Among these are:

• Physical barriers, such as land for aquatic animals, and water for most land animals or the variation of soil and water characteristics.
• Climate barriers, such as temperature (media, seasonal or extreme), humidity (relative, mean, annual or monthly), etc.
• Biological barriers, such as the absence of appropriate food or the presence of effective competitors, enemies, diseases, etc.

These transition barriers between two or more diverse communities are called ecotones, this limit is a union zone that can be scarce or of a considerable linear extension, but in any case it is narrower than the areas of the adjacent communities. An ecotone usually contains the organisms of each of the communities and also organisms that are characteristic of the ecotonal community, which is why it is said that these communities are very rich in diversity and that characterize a certain place. The trend toward increased diversity and density at community junctions is called the edge effect.

Each species of plant or animal has a tolerance limit —maximum or minimum— to each factor in its environment. In plants, the tolerance to poisons from the soil or food can be narrow, while to the different wavelengths of the spectrum used for photosynthesis it is wide. Changes in a factor beyond tolerance limits result in migration or death, or the survival of only the best-adapted individuals; tolerant of altered conditions. The distribution of communities is limited by the sum total of external influences, many of which are interdependent. However, the distribution and equilibrium of a population are ultimately subject to Liebig's Law of Minimum, since it is limited by the essential factor that occurs in the least amount or by some critical phase or condition for which the species has. little latitude of adaptation. Oysters, for example, can live in waters of different salinities, but they only reproduce if the temperature exceeds a certain minimum.

There can be a contradiction between the attachment of animals to their territories and their movements. But the unity can also be seen: migration is a very important means of maintaining the organism's correlations with the environment. These migrations sometimes alter a community when the migrating species decides to settle in the migration area, originating another form of distribution and succession.