Population dynamics - features, significance and types

The first law of ecology says - everything is interconnected, not only among themselves, but absolutely with everything. You can not step a step so as not to hurt something. Man constantly breaks the balance in the environment. Every human step destroys dozens of microorganisms, even in an ordinary puddle, not to mention frightened insects, forced to change their migration routes, to reduce their productivity. The environment is polluted, natural resources are depleted, communications in ecosystems are violated. All this has developed into global problems. Many populations are on the brink of survival. If a person does not change, then his population runs the risk of disappearing in a couple of generations. What is a population and how its number can be traced will be discussed in this article.

Definition of a population

Organisms belonging to the same species, capable of exchanging genetic information within this group, occupying a specific space that are part of the biotic community and function within it - is a population. It has a number of characteristics, the only carrier of which is the group, and not individual individuals belonging to this group.

How does dynamics depend on density?

Such a factor as population dynamics depends on its density. There are three types of such dependence:

• The rate of population growth decreases with increasing density. This phenomenon is widespread and shows the reason for the resistance of some populations. With increasing density, fertility declines. For example, if the density of a large tit is less than 1 pair per 1 ha of land , then in one nest you can count about fourteen hatching chicks, at a density of up to 18 pairs - in one nest hatch up to 8 chicks. It is interesting that the dynamics of population size depends on the fact that density affects the sexual maturity of individuals. This is clearly seen on elephants, the ability to reproduce in which can occur at the age of 12 to 18 years. If the density is small, then we can talk about the birth of one elephant every four years, at high - one elephant in seven years.
• The growth rate of the population reaches a maximum at an average density. This is especially true for species that have a group effect.
• In the third type, on which the dynamics of the population size depends, the growth rates remain unchanged until the high density is reached, after which it begins to decrease sharply. This dependence is clearly visible in the lemming population. It begins to migrate at the peak of density.

Biotic factors

In equilibrium populations, population regulation is determined mainly by biotic factors. The main one in this case is competition within the species. A vivid example: the struggle for nesting (its place). Such competition can cause a shock effect (physiological effect). Such dynamics of the population size is well traced in rodents. If the density is too high, the physiological effect leads to a decrease in fertility and an increase in mortality. This is how the population returns to the natural normal level.

Factors affecting the number

There are some species of animals in which adult individuals eat their own offspring. Such a functioning population and the dynamics of its population is called cannibalism. It regulates the population size downwards. An example of this phenomenon can serve as perches in the lakes of Western Siberia. The food of adults is 80% of young animals of the same species. Young plants eat plankton.

Interactions between species are also important for controlling population density. Predators and victims, parasites and their masters are weighty factors of population dynamics in many species of living organisms. The density of the population often depends on such facts.

Other factors include diseases. Different kinds of viruses can reduce the population of certain individuals to those indicators that are most likely at that time relevant. This applies to all living organisms, including humans. The fastest infections are spread in populations with increased density.

Types of dynamics

Since population dynamics are changes in the number of individuals in this very population, although it is difficult to find two similar populations (the same in dynamics), it is still possible to reduce them approximately, with small errors, to three types of population dynamics:

1. Stable.
2. Fluctuating.
3. Explosive.

Description of stable and fluctuating type

Stable type - typical for most large birds and mammals. Effective regulatory mechanisms in combination with the biotic potential within the population and in external relations between other populations can give some fluctuations in numbers, but insignificant, several times, but not orders. The main role in the regulation system is assigned to the relationship between populations of predators and victims and to internal population behavior mechanisms, such as hierarchy, territoriality and the like.

Fluctuating type - typical for populations, the number and density of which varies from two to three orders of magnitude. Weakly inertial mechanisms and intrapopulation competition in the system of population regulation in such organisms is very important. This type is characteristic, for example, for many xylophagous insects.

More bark beetles are oblong - these are fluctuating types of population dynamics, which gnaw through the uterine passages and lay their eggs in the Siberian larch wood.

With this type of dynamics there are three stages:

1. Insects attack trees that have a weak resin compartment. They excrete pheromones, attracting other individuals. They mark the territory, and the tree is further weakened. With increasing density, migration to neighboring trees begins.
2. The density of insects continues to increase and the number of eggs laid by them decreases in females. Larvae begin to die in larger numbers.
3. The density of the population decreases, and the population stabilizes to the optimal level.

The population of bark beetles has a huge impact beetles predators. But it is paradoxical: when the number of beetles is kept at low and medium levels, the growth of the bark beetle population is restrained. Only the number of beetles becomes large - they reduce intraspecies competition, which contributes to maintaining a high level of numbers.

Explosive type and its distinctive features

Explosive type - typical for populations with outbreaks of mass reproduction, when the number increases by many orders of magnitude. These individuals have a fairly high level of biotic potential. Density for a short time may exceed the capacity of the habitat. Then mass migration begins. This primarily applies to locusts, mouse-like rodents and similar populations.

It is difficult to overestimate the importance of studying the dynamics of population numbers for the future of the entire planet.

If there is a mass reproduction, it means that they speak about the lack of control over interspecies relations. Then the return to a stable state, the regulation of the population is mainly due to intrapopulation mechanisms. An exception are mass diseases, when the population is overcrowded.

A dynamic characteristic of the population is homeostasis. This is a collection of facts and factors that are dependent on density and causing modifications. Homeostasis provides fluctuations in the number of individuals in the population within the norm (does not allow depletion of environmental resources). Thus, the ecological balance, biotic and abiotic environment is ensured.

The practical importance of population dynamics

In each population, the number is constantly changing. When the deviation from standard numbers (middle level) occurs under the influence of the environment, one speaks of the process of modification. Return to the average level of population is called regulation. Density always changes its meaning when it comes to changing the population size.

It can be said that the dynamics of population size is a concept determined by the magnitude of the biotic potential.

The impact of environmental factors on organisms that allow to regulate the population size depends on its density. These include biotic relationships and factors-resources of the abiotic environment. Under the influence of such factors, population homeostasis is established.

Regularities of homeostasis

• The basis of homeostasis is the system of modification-regulation, i.e., the error correction system.
• Most factors have a regulatory one-way effect, aimed at actively limiting the growth of the population.
• The number increases due to the decrease in the pressure of regulatory factors.
• For different density values, the role of different regulatory factors varies in the population.

The type of population dynamics in each population depends on how effective homeostatic mechanisms are. Theoretically, any population is capable of unlimited growth of population, if it is not limited by factors of the external environment. Then the rate of population growth is determined by the size of the biotic potential.