The ecological term "population" means a fairly large group of individuals of one species living in a certain territory and interacting with each other. The life of its representatives is influenced not only by interspecific 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 spatial type population. Let us consider in more detail all its features.
General information
Scientists compiled a classification according to the types of spatial structure of the population. What is it, we will consider below. First, let us define the structure. This is the distribution of individuals of a particular species over any territory, as well as the numerical ratio of their groups by sex, physiological, behavioral, morphological, genetic characteristics and age.
Based on these characteristics, the population structure is not a stable indicator. It is volatile, depending on various factors.
Varieties of structure
There are several of its units:
- Sexual
- Age.
- Ecological.
- Spatial.
- Genetic.
- Ethological.
Let us dwell in more detail on the consideration of the spatial type of structure, as well as on the change in its indicators. In addition, we consider its typical divisions.
Definition
The spatial structure of the population (briefly) is a way of placing specific individuals on a specific natural territory. It will depend on the behavioral characteristics of the species, as well as on the environmental conditions of the territory.
The changes in the spatial structure of the population are also influenced by the way of life (settled or migratory).
A single territory can feed only a certain number of individuals. Of great importance is not only the number of species living in the range, but also their spatial distribution. Therefore, animals and plants most often inhabit their habitat unevenly.
A population occupies a locality suitable for it and is distributed among it by individuals or combined groups. This allows you to achieve an orderly spending of food resources, natural shelters, etc.
Numerical changes
Fluctuations in the population of animals and plant organisms in nature is a common occurrence. Some species of insects can be up to several million representatives, while others - only a few thousand.
In nature, there is an undeniable principle of minimum population size. This means the following: absolutely any population in nature cannot consist of fewer representatives than is required to ensure stable implementation of this environment.
This indicator is different for each type of organism. If he violates the boundaries of the minimum, then this will lead to the disappearance of the species.
Along with the population minimum, there is also a maximum indicator. It is also regulated in vivo. When a greater number of animals live on the territory than required, food and other necessary resources are quickly reduced. This leads to the death of individuals, which leads to the 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 dynamics:
- Stable. Oscillations occur not often and not by very significant values. It is characteristic of representatives of the animal world, which have high survival rates, poor fecundity, long life expectancy, and developed care for offspring.
- The cyclical type of oscillation, it is periodic. Its duration is one season for a year or for several years in a row. An average increase after 4 years was observed in animals inhabiting the tundra zone (lemmings, polar owls, arctic fox). Seasonal fluctuations in numbers are characteristic of many insects, mouse-like rodents, birds, and small aquatic organisms.
- Spasmodic. Depends on many biotic and abiotic factors. A change in certain conditions of a populationβs existence leads to a decrease or increase in its number.
Spatial Distribution Types
There are 3 types of spatial structure of animal and plant populations in the territory:
- Uniform (regular) distribution. It is characteristic that individuals of the population are separately from each other and at approximately 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 the population that inhabit a certain area of ββthe general habitat. Groups are divided 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. Such a distribution depends on environmental conditions (food stocks, for example), as well as on the relationships that develop within a population species.
Determination methods
By controlling the distribution of a population within a specific area using traditional selective methods, certain difficulties often appear. For example, judging by the method of distribution of individuals by samples, you can easily confuse the aggregated view with a random one. This is relevant for cases when 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 determining samples, the type of distribution is usually determined based on methods for determining the spatial structure of the population:
- They differ in the ratio between the measure of dispersion or dispersion (Ο 2 ) - and the average value for density or biomass (N). More precisely, the calculation result of Ο 2 / N tends to zero for a uniform distribution, is close to N for a random distribution and exceeds N for an aggregated one.
- The occurrence of the organisms of the population in question is almost 100% with a uniform distribution, has an indicator of less than 100% for random and much less than 100% for aggregated.
- From the method of spatial distribution, the density ratio in all samples (N) and in those in which the representatives of the population in question appeared (N + ). The value of N + will be close to N with a uniform distribution, greater than N with a random distribution and substantially greater than N with an aggregated distribution.
Space usage type
The spatial structure is also subdivided according to the method of using a specific habitat. There are 2 varieties: sedentary and nomadic. Each of them is divided into several types of accommodation.
Settled:
- Diffuse, in which animals are dispersively distributed over the area, that is, in small groups or separately and practically do not interact 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 populated unevenly by one species of animal. For example, moles densely inhabit meadows and forest edges, but are absent in the forest belt.
- Throbbing. It is peculiar exclusively to settled animals. It manifests itself in the fact that a certain species during the year changes its habitat within the same territory.
Settled animals are instinctively attached to their home range. If for some reason (for example, weather conditions) they have to leave the house, they will soon come back. This is especially true for birds. Here is a short list of migratory birds:
- Storks
- Rooks.
- Swallows
- Larks.
- Orioles.
- Blackbirds.
- Swrig.
- Starlings.
- Cranes.
- Wild geese, ducks, other waterfowl.
- Nightingales, flycatchers, other insectivores.
The nomadic way of placement implies only one type - cyclic. A nomadic way of life is characteristic of large animals living in groups and requiring large areas. After the time when food resources are restored, nomad animals and migratory birds, the list of which is indicated above, can return to their previous habitats.
Some migratory species have the potential for the emergence of isolated settled populations or a short-term transition to such a way of life. For example, reindeer winter on the islands of the Arctic Ocean and do not migrate to the more convenient lands of the mainland, and herds on the Taimyr Peninsula migrate for more than 1000 km. However, there are some small groups of animals that do not leave their habitable places (in the northern part of Taimyr).
Settled populations have two advantages:
- They are well oriented in their area. In case of danger, they can safely hide from enemies.
- They can stockpile food in their chosen places.
But the settled type of existence has a significant drawback consisting in the depletion of food resources.
Types of coexistence
The territorial behavior of animals depends on the methods of coexistence of individuals in one territory. They are divided into the following:
- Isolated. 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 auspices of their parents, therefore they live in groups. Having matured, they separate and begin 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 reproduction process would not be possible.
- Family. An example of such coexistence are lions, hyenas. It manifests itself in a long relationship, cohabitation of parents and offspring.
- Colonial. This kind of life is inherent in settled animals. It is formed both for a long time and exclusively for the period of reproduction. It differs from the isolated one in that the couple does not break up immediately after mating, but together grows cubs.
- Existence in packs. This type of residence is also temporary and unites individuals only for the period of need: food search, protection from enemies, long-distance migration. The flock has a small number of individuals. An example is wolves.
- The existence of herds. It differs from the pack in that it exists for a longer time or constantly. In the herd, as a rule, there is a hierarchy based on dominance-submission. Individuals perform common functions: protection against attack, food production, relocation, rearing of young animals. Herds of animals can include several dozen representatives. Example: antelopes, zebras.
- Harem existence. It is a small (usually up to 10 individuals) group of animals that breed 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 the population, N.P. Naumov (Soviet zoologist) identified 3 of their varieties:
- Elementary (local). It is characterized by the fact that several individuals of the same species inhabit a small area, homogeneous in terms of habitat. The number of populations will depend on how heterogeneous this area will be. The more diverse the conditions, the more simple groups will inhabit a specific area. An example of the spatial structure of an elementary type population is the rattle plant. In central Russia, on the mowing meadows, 3 of its varieties were formed, which differ in flowering time.
- Geographical. 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: breeding periods, number of eggs in a clutch, characteristics of a nest, interaction with neighbors, distance of a nomad, etc.
- Ecological (behavioral). This is an indicator of the coexistence of individuals of various forms. The single existence of an individual in nature is quite rare, and usually manifests itself only in certain periods of ontogenesis.
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 in accordance with the place and time.
It is worth noting that the parameters of possible changes and the general use of a specific area depend on the biological characteristics of the population species and on the nature of the relationship within it. A significant role in stabilizing the spatial structure is played by the behavior of individual individuals within the same habitat zone.