Number and density of the population. Population density growth
A population is a group of organisms of the same species,which for a long time occupy the same territory, that is, the range of habitats. This term is used in biology, ecology, medicine and other sciences.
This term means the number of organisms, be they animals, fish or plants, counting on any taken unit of volume or area of the territory where the population lives.
By "volume" can be meant the volume of water,air or soil, under the "area of territory" - the area of the reservoir or the surface of the earth. The density of the population depends on many factors: whether the climate is favorable, whether the distribution area is wide, and whether there are representatives of other populations in the given territory and how close contacts occur between species of two or more communities.
The most banal example: The density of the hare population depends on the size of the forest zone, where it is convenient to obtain food. If a pack of wolves appears in this area, the hares, trying to escape from them, try to expand their habitat - to go to where contact with the hostile population can be avoided. Hence, the wider the range of habitats, that is - the populated territory, the less the density of the community. Again, this does not work if the population increases with the habitat.
Not for nothing as an example was taken exactly the densityanimal populations. They, perhaps, are the most mobile individuals. Due to the constant search for prey, convenient places for feeding, or vice versa, flight from predators, animals are considered the most migratory on Earth. Of course, each population needs its own suitable climate and habitat, which is why elephants do not come to Siberia, and penguins do not visit Asia. But within their habitat, animals are in constant motion.
This concept denotes the total number of individualsa species, a population on earth, in water and in the air. That is, in this case, for an area of habitat is taken not limited area, for example, land or water body, but the whole Earth, the entire World Ocean as a whole.
The size of the population depends on the difference betweenmortality and fertility of one or another individuals of one species. If for a certain period of time the birth rate is higher than the mortality rate, the number of the particular population under consideration is growing, if the birth rate is lower - it falls. Perhaps, this is the main difference between population size and population density. If the former depends on many external factors, be it climate, emergencies and natural disasters, or even human intervention, then the density depends largely on the number, and then on everything else.
View - this is the main and the very first structuralunit in the system of living organisms. Here, individuals are capable of cross-breeding, which gives fertile offspring. The species is distributed in a certain habitat and is subject to the influence of the external environment. Now the number of described various living organisms that live on land, in water and in the air, amounts to almost two million. The total number of living species is about nine million. The number of extinct for the entire existence of the planet, according to scientists, is almost half a million.
The species population is made up of individuals. They are capable of interrelations, interbreeding, co-habitation in a certain area. Viability of species depends on many factors, among which one can distinguish such as the climate and the presence of competitors, that is, at least one species living in the same territory and able to fight for food with its neighbors. The density of species populations on the Earth's territory is very heterogeneous, especially for animals. If the migration is very common in birds, for example, during the cold season, and it is easier for fish to change their habitat, drifting around the oceans, the animals are very dependent on the climate and terrain of the territory where they live. "Convenient" areas of the earth's surface are very densely populated, but only certain species of animals can survive in the permafrost zone.
An individual is an organism or individual who hasproperties that distinguish it from inanimate matter: metabolism, the ability to reproduce, preserve heredity and transfer it to descendants. From individuals, the species, respectively, and the species population are formed.
Sometimes individuals of different species can interbreedbetween themselves. For example, tigresses can mate with both male tigers and male lions, while producing offspring. Another example, but even with human intervention, is the crossing of different types of plants, fruits, even animals to get something new, for example, as an attempt to adapt some kind of life to other conditions. The density of the population of individuals of this type, that is, the mixture, is small, since this is more an exception than the rule.
Natural and "unnatural" selections
If earlier there was only natural selection,Now, in connection with the development of such sciences as genetics and breeding, scientists are engaged in the breeding of various species on a very large scale. This contributes to the fact that there is an increase in the number, density of the population, for example, some animals or rare plants that are placed in a different habitat to facilitate living and breeding conditions.
Unfortunately, this does not happen everywhere and not always,an example is the "Red Book", the volume of which does not decrease, as one might expect, but it increases. Another disadvantage of such human intervention in the life of nature is that individuals raised in unnatural conditions can live only under guardianship - in zoosadhes, laboratories.
Before talking about a particular populationanimals, it is necessary to clarify the way of life of its representatives. Some species are grouped into groups only accidentally or for reproduction, others lead a herd, group way of life, moving around the whole range only together.
First of all, the way of life depends on twofactors. The first is the climatic conditions. In the deserts, where there is little water and a hot climate, one can live one easily, there is no need to divide water with representatives of its kind. In cold climatic zones, for example, at the pole, it is better to be in a group. Remember the penguins that survive in a cold climate, not only due to the "warm coat", but also through interaction, heating each other.
The second factor is the presence of predatory neighbors of othersspecies that can encroach on territory, food and water and even on the very life of the individual. Of course, the group in such conditions is easier to live - it's easier to fight back, learn about the danger in advance. There are even species that lead a "friendly neighborhood" in order to protect themselves from more predatory neighbors. For example, the neighborhood of antelopes, zebras and giraffes. The latter at the expense of growth, seeing lurking lions, raise the alarm, warning of the danger of everyone else. The density of the animal population depends on these two factors - climate and the presence of "neighbors."
Change in density and population size
Above we found out that the population is an individualone species that are not related to one flock, flock, pride, and so on, but common features that distinguish this species from all others. They, in one way or another, affect the fluctuations in the number and density of residence.
Usually, three types of population density depend on its density.
First: the growth of numbers sometimes begins to decrease with increasing density. However, the habitat of this community should remain unchanged. This is a process of "self-regulation." In order not to overpopulate a certain area, the species itself keeps track of the number of individuals that it needs. "Surplus" is sometimes destroyed in a very cruel way, for example, adult perch feed on their offspring, if it is born too much.
The second type is usually observed in species living in groups. With an average population density of its range, the population reaches a peak in population growth. Not surprisingly, everyone has enough space, water and food.
But the third type "follows" from the first. This is a sharper form of it. When the peak of the population size is reached, overpopulation of the habitat, the change of the range begins. In other words, migration, and therefore, an attempt to adapt to new conditions of life, the irreversible death of many representatives of this species and, accordingly, a sharp decline in the population size.
Influence "from the outside"
All that was mentioned above is a naturalinfluence on the number and density of the population. Now we will talk about an unnatural influence that can not be predicted or stopped. This impact on a certain kind of any external factors. Remember from the school course, from which the dinosaurs died? Correctly, the fall of the meteorite and the coming Ice Age. Or, for example, the strongest flood in the beginning of the XXI century of the Indian Ocean, not only people and cities, but also animals suffered. Here we will include viruses and diseases, human intervention in nature and the like. This is the unnatural effect on population dynamics and population density.
Strange as it may sound, but the problem ishumanity and any species on Earth is one - overpopulation. Of course, first of all, the question of overpopulation of the Earth concerns people. With a bad scenario, mankind will be able to "crowd out" the animals from the planet, but they do not force us to move. Resources, whether water, wood or minerals, are almost exhausted. With each year, the rate of consumption of their growing, and therefore less remains for those who do not have the capabilities of mankind, that is, animals, fish and birds.
Track and regulate the population densitya human population is possible, but I would like to see it happen not by force, but by a natural way. But how? To answer this question for scientists.