Surely you have some idea of what a population is. Examples and definition of it we all went through biology classes. In school textbooks, this topic is disclosed in sufficient detail. But if you are preparing for the exam or want to know more about what a population is (examples, characteristics, numbers), this article will be useful to you.
The distribution of the species on the example of a frog
The population of any kind is distributed in space extremely unevenly, in full accordance with the well-known proverb: in one place it is dense, in another it is empty. This is quite natural. Where to start consideration of the topic "Population"? Examples will probably help you to visualize what are the features of the distribution of species on our planet.
Pond frog is often found throughout Europe. But it is unlikely that anyone would think of looking for frogs in a dry pine forest or on stony placers. They live in swamps, near ponds and in other wet places. Although such habitats are found in all countries, they do not completely cover the whole of Europe. This means that the frogs are not evenly distributed in groups. These groups of individuals can be large and small, existing a couple of years or for centuries. In a particularly wet year, when each lowland is filled with water, frogs from the swamp spread relatively far and can even lay eggs in some temporary large puddle. But in the dry summer, the puddle will dry out, and all the frogs that came into the world will die. That is where the short story of such a small group ends.
Much more important for evolution is the fate of a group of frogs, constantly living in a large swamp. Now decreasing, then increasing in number - depending on living conditions - the population of frogs of a large swamp can exist for many hundreds and thousands of generations. The life of such a group will proceed relatively isolated from the rest of the groups, because another nearest big swamp with suitable conditions for a long existence can be located tens of kilometers from the first. And although the frog in its entire life, of course, will go a total of tens of kilometers, not one of them in nature will skip ten kilometers in a straight line.
The degree of isolation of species
Of course, our swamp is not completely isolated from others. A stork flying over him, who loves to hunt not on this, but on a neighboring swamp, and who does not cost anything to overcome a dozen kilometers, can drop a frog above our pond intended for his chicks. Ducks or other waterfowl flying here in the spring can transfer several eggs to another body of water that is in their way; with luck, eggs can develop in another, completely alien place. Such events, of course, happen extremely rarely, but from time to time necessarily occur.
It is not necessary to think that life in such isolated groups is characteristic only for inhabitants of swamps and other water bodies. Mole colonies, clearly visible on the mounds of land that grow overnight, are also found only in places suitable for the life of this insectivorous mammal - in the fields, along the edges of the forest. Nettle thickets also exist only where there are favorable conditions for this plant: shady and the soil is rich in nitrogen. Butterflies easily flying from place to place, which, it would seem, can live anywhere, each meet strictly in their place: mourning in birch forests, whites where there are any cruciferous plants, and so on.
So we come to consider the concept of "population". Its definition and characteristics are presented below. We begin, of course, with the most important thing - with the definition.
The concept and characteristics of the population
The center of population density of a species that persists for a long time is called a population. Its most important feature is its genetic unity: individuals that belong to such a group and live close to each other can mate more often than individuals belonging to different populations. For evolution, of course, it is important that the genetic information is exchanged: after all, the descendants receive half of the chromosomes from one parent, and half from the other. Therefore, when mating for a number of generations, each isolated group of individuals turns out to be a single large system with a certain complex of hereditary traits — the genetic fund, or gene pool.
Exchange between neighboring populations
If the exchange of individuals between neighboring populations in nature turns out to be noticeably greater than a few percent in each generation, then very soon these two groups acquire common properties due to the complete mixing of genetic material. If the exchange is only not more than a few individuals for every thousand in each generation, then each population of animals or plants "retains its color." In other words, it remains at the same time part of a complex system of many populations called a species.
The distance that individuals move
Now it becomes clear why it is so important to know how far organisms actually travel in nature and, most importantly, how far they can transfer their genes and pass them on to the next generation. Finding out this is not at all so easy: you need to mark, release and again catch a lot of animals, establish how far the pollen of different plants really scatters, their seeds are carried. The results of such studies were largely surprising.
Range of distribution of animals and plants
What territory can a population occupy? The examples we give give a clear idea of this.
Only five of the hundred wild roe goats run away at a distance of 10 km from their habitat, and the vast majority stay their whole life in a territory with a diameter of 3 km. In North American white-tailed deer , only 5% of individuals also spend their entire life spanning up to 10 km in a straight line, and the vast majority of the population (95% of individuals) live in an area of about one and a half kilometers in diameter. Both wild rabbits and European hare-hares behave very much like deer. In general, field sparrows do not fly away for life beyond 400 m from the marking site. And the large American muskrat rodent, which has now populated suitable reservoirs almost throughout Northern Eurasia, does not go further than 1 km from the marking site, with most of the animals living all their lives in space with a radius of about 100 m.
And what is the population of plants in this regard? Examples of the distribution of pollen show that its range is not much different in some species. Oak pollen in the forest, for example, is carried by the wind only a few hundred meters.
The teal was the champion in range of distribution among animals. The teal-whistle-tagged in England were then found nesting thousands of kilometers from their native nest: on the Kola Peninsula and in the Arkhangelsk Region, in Iceland and Belarus.
Population area
All the above figures indicate what territory individual populations of different species can occupy, what distance is sufficient for neighboring groups to be isolated from each other. Individual roe deer populations can live on small mountain ranges at a distance of only tens of kilometers, groups of sparrows can be located two kilometers from each other, but duck populations, apparently, occupy an area equal to almost the whole of Europe. Incidentally, the enormous size of the duck population is well explained by the fact that scientists were surprised for a long time: all of them differ in surprisingly small variability, and among them, unlike most other birds, subspecies are rarely distinguished. It has now become clear that all ducks of the same species belong to one or very few populations. They constantly interbreed with each other, so no accumulation of new traits in any part of the range occurs.
Number of populations
So, it is characterized by a strong, but not absolute isolation from its neighbors. Thanks to this, the originality of the genetic fund of each of them is preserved and maintained.
Another important characteristic of a population is the number, that is, the number of individuals making up it. How many individuals are included in it? It is difficult to answer this question unequivocally, since in different species of animals and plants this number is different. In insects - for example, in mosquitoes - millions of individuals can enter one population. The population of one of the dragonfly species on the lake near the town of Orekhovo-Zuyevo in the Moscow Region is about 30 thousand individuals, and the number of several groups of lizards in Kazakhstan was from several hundred to several thousand individuals. But such data are still scarce, and scientists still do not know what exactly the number of populations of even the most ordinary species is.
The problem of determining the number
Today, this problem has ceased to be only purely theoretical. To preserve a species, it is important to know the minimum number of individuals at which it is able to exist for a long time and reliably. To understand the significance of this problem, it must be added that the number of individuals in a population always fluctuates: several times, sometimes several hundred, and sometimes thousands of times. A population of large animals, on average consisting of fewer than several hundred individuals, cannot exist long enough. Smaller groups, sooner or later - simply as a result of inevitable fluctuations in numbers, quite by accident - can be reduced to zero.
Due to the fact that the long-term existence of small populations is practically impossible, most scientists are skeptical of such, for example, sensational reports as the "discovery" of several prehistoric dinosaurs in the Scottish lake Loch Ness . All such few monsters should have disappeared a long time ago.
Population evolution
Real populations are potentially immortal: they can exist until the conditions suitable for them disappear. But at the same time, in any, even the most favorable conditions, these groups should change slightly from time to time. In other words, a population is evolving.
New mutations in nature appear continuously, although the speed of this process is relatively low. However, over time, the genetic composition of the population still changes. Of course, not a single mutation, not even a dozen, can still change it. However, they accumulate generation after generation until they appear in one or another combination of parental makings. If this combination is successful, then after one or two generations, individuals with it will be numerous in this group, because of which the genetic composition of the population will noticeably change. The exit of a particular mutation into the evolutionary arena is a very important event in the life of both a single group and a whole species. This is the smallest step of the evolutionary process, but from these steps the whole grandiose process of evolution is formed.
So, we briefly reviewed the topic "Population". Its definition, examples and characteristics were presented in the article. We hope you find this information useful.