The first law of ecology says that everything is interconnected, and not only among themselves, but with absolutely everything. You can't take a step without hitting something. Man is constantly disturbing the balance in the environment. Each human step destroys dozens of microorganisms even in an ordinary puddle, not to mention frightened insects that are forced to change their migration paths and reduce their productivity. The environment is polluted, natural resources are depleted, links in ecosystems are broken. All this has grown into global problems. Many populations are on the verge 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 is traced, will be discussed in this article.
Population definition
Organisms belonging to the same species capable of exchangegenetic information within this group, occupying a specific space, being part of the biotic community and functioning within it - this 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 population growth rate decreases with increasing density. This phenomenon is widespread and shows the reason for the persistence of some populations. With an increase in density, the birth rate decreases. For example, if the density of the great tit is less than 1 pair per 1 ha of land, then about fourteen hatched chicks can be counted in one nest, with a density of up to 18 pairs, up to 8 chicks hatch in one nest. Interestingly, population dynamics depend on the fact that density affects the sexual maturity of individuals. This is clearly seen in elephants, the ability to reproduce in which can occur at the age of 12 to 18 years. If the density is low, then we can talk about the birth of one baby elephant every four years, with high density - one baby elephant in seven years.
- Population growth rates peak at medium density. This is especially true for species that show a group effect.
- In the third type, on which population dynamics depends, the growth rate remains unchanged untilhigh density, after which it begins to decline sharply. This dependence is clearly seen in the population of lemmings. She begins to migrate at the peak of density.
Biotic factors
In equilibrium populations, the regulation of numbers 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 the effect of shock disease (physiological effect). Such dynamics of the population size is perfectly 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 natural normal levels.
Factors affecting numbers
There are some species of animals in which adults eat their own offspring. This functioning of the population and the dynamics of its numbers is called cannibalism. It regulates the population size in the direction of decreasing. Perch in the lakes of Western Siberia can serve as an example of such a phenomenon. The food of adults consists of 80% of the young of their own species. The juveniles themselves eat plankton.
Interactions between species are also important in controlling population density. Predators and prey, parasites and their hosts are significant factors in population dynamics in many species of living organisms. From such factsoften affected by population density.
Other factors include illness. Various kinds of viruses are able to reduce the population of certain individuals to those indicators that are most likely relevant at that time. This applies to all living organisms, including humans. Infections spread fastest in dense populations.
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 (identical in dynamics) populations, it is still possible to reduce them approximately, with small errors, to three types of population dynamics:
- Stable.
- fluctuating.
- Explosive.
Description of stable and fluctuating type
Stable type - typical for most large birds and mammals. Effective regulatory mechanisms, combined 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 of magnitude. The main role in the regulation system is assigned to the relationship between populations of predators and prey and internal population mechanisms of behavior, such as hierarchy, territoriality, and the like.
Fluctuating type - typical for populations, the number and density of which ranges from two tothree orders. Weak inertial mechanisms and intrapopulation competition in the system of population regulation in such organisms are of great importance. This type is typical, for example, for many xylophagous insects.
Elongated bark beetles are also fluctuating types of population dynamics that gnaw through uterine passages and lay their eggs in Siberian larch wood.
This type of speaker goes through three stages:
- Insect individuals attack trees that have a weak resin compartment. They secrete pheromones, attracting other individuals. They mark the territory, and the tree further weakens. As the density increases, migration to neighboring trees begins.
- Insect densities continue to increase and the number of eggs they lay decreases in females. The larvae begin to die in greater numbers.
- The population density is decreasing, and the population is stabilizing to the optimal level.
Predatory beetles have a tremendous impact on the population of bark beetles. 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 intraspecific competition, which helps to maintain a high level of abundance.
Explosive type and its distinctive features
Explosive type - characteristic of 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 permay exceed the capacity of the habitat for a short time. Then the mass migration begins. This primarily applies to locusts, mouse-like rodents and similar populations.
It is difficult to overestimate the importance of studying population dynamics for the future of the entire planet.
If mass reproduction is observed, it means that interspecies relations are out of control. Then the return to a stable state, the regulation of the number mainly occurs due to intrapopulation mechanisms. The exception is mass diseases, when there is an overpopulation of the population.
The dynamic characteristic of a population is homeostasis. This is a set of facts and factors that depend on density and cause modifications. Homeostasis provides fluctuations in the number of individuals in the population within the normal range (does not allow the depletion of environmental resources). This ensures an ecological balance, a biotic and abiotic environment.
Practical significance of population dynamics
In each population, the number is constantly changing. When there is a deviation from the standard indicators of abundance (average level) under the influence of the environment, one speaks of a modification process. The return to the average level of population is called regulation. Density always changes its value when it comes to population changes.
It can be said that population dynamics is a concept determined by the magnitude of biotic potential.
The impact of environmental factors on organisms that allow you to regulate the size of the population depends on its density. These include biotic relationships and resource factors of the abiotic environment. Under the influence of such factors, population homeostasis is established.
Patterns of homeostasis
- The basis of homeostasis is the modification-regulation system, i.e. the error correction system.
- Most of the factors have a regulatory unilateral effect aimed at actively limiting population growth.
- The number is increasing due to a decrease in the pressure of regulatory factors.
- The role of various regulatory factors changes with different density values 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 in numbers, if it is not limited by environmental factors. Then the rate of population increase is determined by the size of the biotic potential.
