A population is a group of organisms of the same species that occupy the same territory for a long time, that is, their habitat. This term is used in biology, ecology, medicine and other sciences.
Population density
This concept refers to the number of organisms, whether animals, fish or plants, based on any taken unit of volume or area of the territory where this population lives.
Under the "volume" can mean the volume of water, air or soil, under the "area" - the area of a reservoir or land surface. Population density 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 population density of hares depends on the size of the forest zone, where it is convenient to get food. If a pack of wolves appears in this area, then the hares, fleeing from them, try to expand their habitat - go there,where contact with a hostile population can be avoided. This means that the wider the habitat, that is, the inhabited territory, the lower the density of the community. Again, this does not work if population increases along with habitat.
It is not for nothing that the population density of animals was taken as an example. They are perhaps the most mobile individuals. Due to the constant search for prey, convenient feeding places, 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 inside their habitat, animals are in constant motion.
Population
This concept refers to the total number of individuals of a particular species, population on land, in water and in the air. That is, in this case, not a limited area, for example, land or a reservoir, is taken as a habitat, but the entire Earth, the entire World Ocean as a whole.
The population size depends on the difference between the mortality and the birth rate of certain individuals of the same species. If for a certain period of time the birth rate is higher than the death rate, the number of the particular population under consideration grows, 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 naturalcataclysms, or even human intervention, then the density depends largely on the number, and then on everything else.
Species population
View is the main and very first structural unit in the system of living organisms. Here, individuals are capable of interbreeding, which produces fertile offspring. The species is widespread 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, is almost two million. The total number of living species is about nine million. The number of extinct for the entire time of the existence of the planet, according to scientists, is almost half a million.
Species population is formed by separate individuals. They are capable of relationships, interbreeding, living together in a certain area. The viability of species depends on many factors, among which one can distinguish such as climate and the presence of competitors, that is, at least one more species living in the same territory and able to compete for food with neighbors. The density of species populations on the territory of the Earth is very heterogeneous, especially for animals. If birds have a very common migration, for example, for the cold season, and it is easier for fish to change their habitat, drifting across the oceans, then animals are very dependent on the climate and topography of the territory where they live. "Convenient" areas of the earth's surface are very densely populated, andonly certain species of animals can survive in the permafrost zone.
Special
An individual is an organism or an individual that has properties that distinguish it from inanimate matter: metabolism, the ability to reproduce, the preservation of heredity and its transmission to descendants. A species is formed from individuals, respectively, and a species population.
Sometimes individuals of different species can interbreed. For example, tigresses can mate with both male tigers and male lions and produce offspring. Another example, but already with human intervention, is the crossing of various types of plants, fruits, even animals to get something new, for example, as an attempt to adapt a species to life in other conditions. The population density of individuals of this species, that is, a mixture, is low, since this is the exception rather 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 selection, scientists are breeding various species on a very large scale. This contributes to the fact that there is an increase in the number, population density, for example, some animals or rare plants that are placed in a different habitat to facilitate living conditions and reproduction.
Unfortunately, this does not happen everywhere and not always, an example of this is the "Red Book", the volume of which does not decrease, as one might expect, but increases. Another minussuch human intervention in the life of nature is that individuals grown in unnatural conditions can only live under care - in zoos, laboratories.
Animal populations
Before talking about a particular population of animals, it is necessary to clarify what lifestyle its representatives lead. Some species form groups only by chance or for reproduction, others lead a herd, group lifestyle, moving around the entire habitat only together.
Lifestyle primarily depends on two factors. The first is climatic conditions. In deserts, where there is little water and a hot climate, it is easier to live alone, there is no need to share water with members of your own species. In cold climatic zones, for example, at the pole, it is better to be in a group. Think penguins, who survive in cold climates not only by "warm coats" but also by interacting to keep each other warm.
The second factor is the presence of predatory neighbors of other species that can encroach on territory, food and water, and even on the very life of an individual. Of course, it is easier to live in a group in such conditions - it is easier to fight back, to learn about the danger in advance. There are even species that keep "friendly neighborhood" in order to protect themselves from more predatory neighbors. For example, the neighborhood of antelopes, zebras and giraffes. The latter, due to their growth, seeing the lurking lions, raise the alarm, warning everyone else of the danger. The density of the animal population depends precisely on these two factors - the climate and the presence of "neighbors".
Change in population density and size
Above, we found out that a population is individuals of the same species, which are interconnected not by belonging to the same flock, herd, pride, and so on, but by common features that distinguish this species from all the others. It is they who, one way or another, affect fluctuations in the number and density of residence.
Typically, there are three types of dependence of population size on its density.
First, population growth sometimes begins to decline as density increases. At the same time, the habitat of this community should remain unchanged. This is a process of "self-regulation". To prevent overpopulation of a certain area, the species itself tracks the number of individuals it needs. "Surplus" is sometimes destroyed in a very cruel way, for example, adult perches feed on their offspring if too much is born.
The second type is usually seen in species that live in groups. With an average population density of its range, the population reaches a peak in population growth. No wonder there is enough space, water and food for everyone.
But the third type "follows" from the first. This is its sharper form. When the peak of the population is reached, the overpopulation of the habitat, the change of the habitat itself begins. In other words, migration, which means an attempt to adapt to new living conditions, the irreversible death of many representatives of this species and, accordingly, a sharp decline in the population.
Influence"outside"
All that was mentioned above is a natural influence on the number and density of the population. Now we will talk about unnatural influences that cannot be predicted or stopped. This is the impact on a certain type of any external factors. Do you remember from the school course what dinosaurs died from? That's right, the fall of the meteorite and the onset of the Ice Age. Or, for example, the strongest flood at the beginning of the 21st century of the Indian Ocean, not only people and cities, but also animals suffered. Here we include viruses and diseases, human intervention in nature, and the like. This is the unnatural influence on the dynamics of the number and density of the population.
Population issues
Strange as it may sound, but the problem of humanity and any species on Earth is one - overpopulation. Of course, first of all, the issue of overpopulation of the Earth concerns people. In a bad scenario, humanity will be able to "force out" animals from the planet, but they will not force us to move. Resources, be it water, wood or minerals, are nearly exhausted. Every year the rate of their consumption is growing, which means that less remains for those who do not have the capabilities of humanity, that is, animals, fish and birds.
It is possible to monitor and regulate the population density of a human population, but I would like it to happen not by force, but in a completely natural way. But how? To this question, look for an answer by scientists.
