The first law of ecology states that everything is interconnected, not only among themselves, but absolutely with everything. You can’t take a step so as not to hurt something. Man constantly upsets the balance in the environment. Each human step destroys dozens of microorganisms even in an ordinary puddle, not to mention frightened insects, forced to change their migration paths and reduce their productivity. The environment is polluted, natural resources are depleted, communications in ecosystems are broken. All this has grown 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 after 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 exchanging genetic information within this group, occupying a specific space, being part of the biotic community and functioning within it, are a population. It has a number of characteristics, the sole carrier of which is a group, and not individual individuals belonging to this group.
How does dynamics depend on density?
Such a factor as the dynamics of the population size depends on its density. There are three types of this dependency:
- The population growth rate decreases with increasing density. This phenomenon is widespread and shows the reason for the stability of some populations. With increasing density, fertility decreases. For example, if the density of a great tit on 1 ha of land is less than 1 pair, then in one nest you can count about fourteen hatching chicks, with a density of up to 18 pairs - up to 8 chicks hatch in one nest. Interestingly, the dynamics of the population size depends on the fact that the 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 baby elephant every four years, with a high one baby elephant every seven years.
- The population growth rate reaches its maximum at medium density. This is especially true for species with a group effect.
- In the third type, on which the dynamics of the population size depends, the growth rate remains unchanged until a high density is reached, after which it begins to decrease sharply. This dependence is clearly visible in the lemmings population. She at the peak of density begins to migrate.
Biotic factors
In equilibrium populations, the regulation of abundance 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 a shock disease (physiological effect). Such a population dynamics is excellently observed in rodents. If the density is too high, the physiological effect leads to a decrease in fertility and an increase in mortality. That is how the population returns to its natural normal level.
Factors Affecting Abundance
There are some types of animals in which adults eat their own offspring. Such a functioning of the population and the dynamics of its number is called cannibalism. It regulates the population size downward. An example of such a phenomenon is perch in the lakes of Western Siberia. The food of adults is 80% composed of young animals of their own species. The young growth itself eats plankton.
Interactions between species are also important for controlling population density. Predators and victims, parasites and their owners are significant factors in the dynamics of the population size in many species of living organisms. Population density often depends on such facts.
Other factors include illness. Viruses of various kinds can 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. The fastest infections are in populations with increased density.
Speaker types
Since the dynamics of the population size are changes in the number of individuals in this same population, although it is difficult to find two similar (identical in dynamics) populations, they can nevertheless be approximately, with small errors, reduced to three types of population dynamics:
- Stable.
- Fluctuating.
- Explosive.
Description of the stable and fluctuating type
Stable type - typical of most large birds and mammals. Effective regulatory mechanisms, combined with the biotic potential within the population and in the relationships external between other populations, can produce some fluctuations in numbers, but slight, several times, but not orders of magnitude. The main role in the regulatory system is assigned to the relationship between predator and prey populations and internal population behavior mechanisms, such as hierarchy, territoriality, and the like.
The fluctuating type is characteristic of populations whose numbers and densities range from two to three orders of magnitude. Weakly inertial mechanisms and intrapopulation competition in the system of regulation of numbers in such organisms is very important. This type is typical, for example, for many xylophagous insects.
Even oblong bark beetles are fluctuating types of population dynamics that gnaw through uterine passages and lay their eggs in Siberian larch wood.
With this type of dynamics, there are three stages:
- Insects attack trees that have weak resin separation. They secrete pheromones, attracting other individuals. They mark the territory, and the tree further weakens. With increasing density, migration to neighboring trees begins.
- The density of insects continues to increase and in females the number of eggs laid by them decreases. Larvae begin to die in greater numbers.
- The population density is reduced, and the number is stabilized to the optimal level.
Predatory beetles have a tremendous impact on the bark beetle population. 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 numbers.
Explosive type and its distinctive features
Explosive type - typical for populations with outbreaks of mass reproduction, when the number increases by a lot of orders. These individuals have a rather high level of biotic potential. Density for a short time may exceed habitat capacity. Then the mass migration begins. This primarily relates 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 mass reproduction is observed, then they speak of the uncontrolled interspecific relations. Then a return to a stable state, the regulation of numbers mainly occurs due to intrapopulation mechanisms. The exception is mass diseases when overconsolidation of the population is observed.
A dynamic characteristic of a population is homeostasis. This is a combination of facts and factors that depend on density and cause modifications. Homeostasis provides fluctuations in the number of individuals within the normal range (does not allow the depletion of environmental resources). This ensures the ecological balance, biotic and abiotic environment.
The practical significance of population dynamics
In each population, the number is constantly changing. When a deviation from standard abundance indicators (average level) occurs under the influence of the environment, they speak of the modification process. A return to the average abundance is called regulation. Density always changes its meaning when it comes to changes in population size.
We can say 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 you to control the population size 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.
