The ecological term "population" means a fairly large group of individuals of the same species living in a certain area and interacting with each other. The life of its representatives is influenced not only by interspecies relations, but also by other animals or plants inhabiting the same territory, as well as climatic conditions and other external factors.
It is characterized by an ordered system of existence - the structure of a population of a spatial type. Let's take a closer look at all its features.
General information
Scientists have made a classification according to the types of spatial structure of the population. What it is, we will consider below. First, let's define structure. This is the distribution of individuals of a particular species in any territory, as well as the numerical ratio of their groups by sex, physiological, behavioral, morphological, genetic characteristics and age.
Based on the traits listed, the population structure is not stableindicator. It is changeable, depending on various factors.
Varieties of structure
There are several divisions:
- Genital.
- Mature.
- Environmental.
- Spatial.
- Genetic.
- Ethological.
Let's dwell in more detail on the consideration of the spatial type of the structure, as well as on the change in its indicators. In addition, consider its typical divisions.
Definition
The spatial structure of a population (briefly) is a way of placing specific individuals in a certain natural area. It will depend on the behavioral characteristics of the species, as well as on the environmental conditions of the territory.
Changes in the spatial structure of the population are also influenced by the way of life (sedentary or migratory).
A single area can feed only a certain number of individuals. Of great importance is not only the number of representatives of the species living in the range, but also their spatial distribution. Therefore, animals and plants, most often, inhabit their habitat unevenly.
A population occupies an area suitable for it and is distributed over it by individuals or united groups. This allows you to achieve an orderly use of food resources, natural shelters, etc.
Numerical changes
Fluctuations in animal and plant populations in nature are a common occurrence. Some types of insects can be up to severalmillion representatives, while others are only a few thousand.
In nature, there is undeniably the principle of the minimum population size. This means the following: absolutely any population in nature cannot consist of fewer representatives than is required to ensure the stable implementation of this environment.
This indicator is different for each type of organism. If it violates the boundaries of the minimum, then this will lead to the disappearance of the species.
Simultaneously with the population minimum, there is also a maximum indicator. It is also regulated in vivo. When more animals live on the territory than required, food and other necessary resources are rapidly reduced. This leads to the death of individuals, which leads to an adjustment of the indicator to the desired maximum. Simply put, nature will not feed more than its resources allow.
There are 3 types of population population dynamics:
- Stable. Fluctuations do not occur often and not by very significant values. It is typical for representatives of the animal world with high survival rates, low fertility, long life expectancy, and developed care for offspring.
- Cyclic type of oscillations, it is also periodic. Its duration is one season per year or for several years in a row. An increase in the number on average after 4 years was noted in animals inhabiting the tundra zone (lemmings, snowy owls, arctic fox). Seasonal population fluctuations are characteristic of many insects, mouse-like rodents, birds, small waterorganisms.
- Jumping. Depends on many biotic and abiotic factors. A change in certain conditions of the existence of a population leads to a decrease or increase in its number.
Types of spatial distribution
There are 3 types of spatial structure of animal and plant populations in the territory:
- Uniform (regular) distribution. It is characteristic that the individuals of the population are separated from each other separately and approximately at the same distance. Such placement is characteristic of those animals whose individuals are in a competitive relationship with each other.
- Uneven (aggregated) distribution. It is characterized by the fact that groups of several animals are formed in a population that inhabit a certain area of \u200b\u200bthe general habitat. The groups are separated by uninhabited territory.
- Diffuse (random) distribution. It is determined by the fact that the distance between individuals or groups of individuals is not the same. This distribution depends on environmental conditions (food supplies, for example), as well as on the relationships that develop within the population species.
Determination methods
Controlling the distribution of a population within a given area by traditional sampling methods often presents certain difficulties. For example, if one judges the way individuals are distributed among samples, one can easily confuse an aggregated species with a random one. This is relevant for caseswhen the area over which the sample is distributed is so large that several clusters of the studied organisms are placed on it at once.
When selecting samples, the type of distribution is usually determined based on methods for determining the spatial structure of the population:
- They differ in the relationship between the measure of dispersion or dispersion (σ2) - and the average value for density or biomass (N). More precisely, the result of calculating σ2/N tends to zero with a uniform distribution, is close to N with a random distribution, and exceeds N with an aggregate one.
- The occurrence of organisms in the population under consideration is almost 100% with a uniform distribution, less than 100% with a random distribution, and much less than 100% with an aggregate one.
- From the method of spatial distribution, the ratio of density in all samples (N) and in those in which representatives of the considered population appeared (N+). The value of N+will be close to N with a uniform distribution, more than N with a random distribution, and significantly more than N with an aggregate one.
Type of space usage
The spatial structure is also subdivided according to the way of using a certain habitat. There are 2 varieties: sedentary and nomadic. Each of them is subdivided into several types of accommodation.
Settled:
- Diffuse, in which animals are dispersed over the area, that is, in small groups or separately and practically nointeract with each other. Such placement can be observed in the conditions of steppes and deserts in small rodents.
- Cyclic, in which animals leading a sedentary life, due to some factors (weather, invasion of enemies) can change their location in one territory.
- Mosaic type. It is formed when a certain habitat is inhabited by one species of animal unevenly. For example, moles densely inhabit meadows and forest edges, but are absent in the forest belt.
- Pulsing. It is peculiar exclusively to sedentary animals. It manifests itself in the fact that a certain species during the year changes its habitat within the same territory.
Sedentary animals are instinctively attached to their home range. If for a number of reasons (for example, weather conditions) they have to leave the house, they will soon return back. This is especially true for birds. Here is a short list of migratory birds:
- Storks.
- Rooks.
- Swallows.
- Larks.
- Orioles.
- Thrushes.
- Srizhi.
- Starlings.
- Cranes.
- Wild geese, ducks, other waterfowl.
- Nightingales, flycatchers, other insectivores.
Roaming way of placement implies only one type - cyclic. The nomadic way of life is typical for large animals living in groups and requiring large areas. After a time when food resources are restored, nomadic animals and migratory birds, the list of which is indicated above, may return toformer habitats.
Some migratory species have the potential to develop isolated sedentary populations or to transition briefly to this way of life. For example, reindeer winter on the islands of the Arctic Ocean and do not migrate to more convenient lands on the mainland, while herds on the Taimyr Peninsula migrate more than 1000 km. However, there are also separate small groups of animals that do not leave their inhabited places (in the northern part of Taimyr).
Sedentary populations have two advantages:
- They know their way well. In case of danger, they can reliably hide from enemies.
- Can stock food at their chosen locations.
But the sedentary type of existence has a significant drawback, which is the depletion of food resources.
Types of coexistence
The territorial behavior of animals depends on the ways in which individuals co-exist in the same territory. They are divided into the following:
- Separated. It manifests itself in the fact that representatives of one species live separately from each other and are completely independent of the rest. This is observed only at a certain stage of their life: in childhood, animals are under the protection of their parents, therefore they live in groups. Having matured, they separate and begin an independent existence. During the breeding season, they create pairs or form groups. A completely solitary lifestyle is not found in any species of multicellular organisms. Otherwise, the breeding process was notpossible.
- Family. An example of such coexistence are lions, hyenas. It manifests itself in long-term relationships, cohabitation of parents and offspring.
- Colonial. This type of life is inherent in sedentary animals. It is formed both for a long time, and exclusively for the breeding season. It differs from the isolated one in that the couple does not break up immediately after mating, but raises the cubs together.
- Existence in packs. This type of residence is also temporary and unites the individuals of the population only for the period of need: searching for food, protection from enemies, migration over long distances. The flock has a small number of individuals. Wolves are an example.
- Existence in herds. It differs from the flock in that it exists for a longer time or constantly. In a herd, as a rule, there is a hierarchy based on dominance-submission. Individuals perform the same functions: protection from attack, food production, relocation, rearing of young animals. Herds of animals can number several dozen representatives. Example: antelopes, zebras.
- Harem existence. Represents a small (usually up to 10 individuals) group of animals breeding polygamously (seals, fur seals).
Types of populations depending on the size of the territory they occupy according to N. P. Naumov
Depending on the size of the area occupied by a population species, N. P. Naumov (a Soviet zoologist) identified 3 varieties of them:
- Elementary (local). Characterized by the fact thatseveral individuals of the same species inhabit a small area, homogeneous in terms of habitat conditions. The number of populations will depend on how heterogeneous the area is. The more diverse the conditions, the more simple groups will inhabit a particular area. An example of the spatial structure of an elementary type population is the rattle plant. In central Russia, on mowing meadows, 3 varieties of it have formed, differing in flowering time.
- Geographic. This is a group of several individuals of the same species inhabiting an area with similar conditions. Its parameters depend on the scale of the territory, as well as on the biological characteristics of the species itself. Geographical populations can differ in several ways: timing of breeding, number of eggs per clutch, nest characteristics, interaction with neighbors, migration distance, etc.
- Environmental (behavioral). This is an indicator of the coexistence of individuals of various forms. The single existence of an individual in nature is quite rare, it manifests itself, as a rule, only at certain periods of ontogeny.
Conclusion
The spatial structure of populations is very variable under the influence of certain factors. It is prone to seasonal and other adaptive changes, but is observed according to place and time.
It is worth noting that the parameters of possible changes and the general variant of the use of a particular area depend on the biological characteristics of the population species and on the nature of the relationships within it. significant role instabilization of the spatial structure is played by the behavior of individuals within the same habitat zone.
