Population: examples, characteristics, population growth

Surely you have some idea of what a population is. Examples and the definition of it we all went through the lessons of biology. In school textbooks this topic is revealed in sufficient detail. But if you are preparing for an exam or want to learn more about what a population is (examples, characteristics, numbers), this article will be useful to you.

Distribution of the species by the example of a frog

The population of any kind is distributed in the space extremely unevenly, in full accordance with the known proverb: in one place it is dense, in another it is empty. This is quite natural. Where do we start with the topic "Population"? The examples are likely to help you visualize the specific features of species distribution on our planet.

The pond frog is common throughout Europe. But hardly anyone would come up with the idea of looking for frogs in a dry pine forest or on stony placers. They live in swamps, near water bodies and in other humid places. Such habitats, although they are found in all countries, do not cover the whole of Europe at all. Means, and frogs are distributed unevenly, in groups. These groups of individuals can be large and small, existing for 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 may even lay eggs in some temporary large puddle. But in a dry summer, the puddle will dry up, and all the frogs born here will die. That's where the short story of such a small group ends.

Much more important for the evolution of the fate of a group of frogs, constantly living in a large swamp. Then shrinking, then increasing in numbers - depending on the conditions of life - the population of large marsh frogs 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 large swamp with suitable conditions for long-term existence can be located tens of kilometers from the first. And although the frog in its entire life, of course, will pass a total of tens of kilometers, none of them in nature will not skip ten kilometers in a straight line.

Degree of species isolation

Of course, our swamp is not completely isolated from others. A stork flying over it, who loves to hunt not on this, but on a neighboring swamp, and who does not need to cover a dozen kilometers, can drop a frog designed for its chicks over our reservoir. Ducks or other waterfowl flying here in the spring can carry several eggs to another pond that is on their way; If you're lucky, eggs can develop in another, completely alien place. Such events, of course, happen very rarely, but from time to time they always happen.

It is not necessary to think that life with such isolated groups is characteristic only of the inhabitants of swamps and other water bodies. Mole colonies, well-marked on the hills of the earth, growing overnight, are also found only in places suitable for the life of this insectivorous mammal, in the fields, along the edges of the forest. Nettles are also found only where there are favorable conditions for this plant: shady and the soil is rich in nitrogen. Easily flying from place to place, butterflies, who seem to be able to live anywhere, meet each in their own place: a mourning woman in birch forests, Belyanka where there are some crucifers, and so on.

So we came to the concept of "population". The definition and characteristics of it are presented below. Let's start, of course, with the most important thing - with the definition.

Concept and characteristics of the population

The center of population density of any 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, it is important, of course, that in this case there is an exchange of genetic information: after all, descendants receive half of the chromosomes from one parent, and half from another. Therefore, when mating for a number of generations, each isolated group of individuals turns out to be, as it were, a single large system with a certain set of hereditary traits, the genetic fund, or the gene pool.

Exchange between adjacent populations

If the exchange of individuals between neighboring populations in nature is significantly greater than several percent in each generation, then very soon these two groups acquire common properties due to complete mixing of the genetic material. If the exchange is not more than a few individuals per 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 to which individuals travel

Now it becomes clear why it is so important to know how far the organisms actually move in nature and, most importantly, how far they can transfer their genes and pass them on to the next generation. It is not so easy to find out: it is necessary to mark, release and again catch a lot of animals, determine how far the pollen of different plants really flies, their seeds are carried. The results of such studies were in many ways surprising.

Range of distribution of animals and plants

What territory can the population occupy? The examples that we give give a clear idea of this.

Only five out of a hundred wild goat-goats escape to a distance of up to 10 km from their permanent habitat, while the overwhelming majority keep their whole lives for a period of 3 km in diameter. In the North American white-tailed deer, too, only 5% of individuals leave for a lifetime at a distance of up to 10 km in a straight line, and the vast majority of the population (95% of individuals) live in a territory about one and a half kilometers in diameter. Both wild rabbits and European hare-hares behave very much like deer. Field sparrows in the mass do not fly away for life beyond 400 m from the place of tagging. A large American water rodent muskrat, now inhabiting suitable reservoirs almost throughout Northern Eurasia, does not go beyond 1 km from the place of tagging, and most of the animals live their entire lives on a space of about 100 m radius.

What is the population of plants in this respect? Examples of the distribution of pollen show that its range is not much different in some species. Pollen of oak in the forest, for example, is carried by the wind only a few hundred meters.

The champion in terms of range of distribution was among the animals teal. The chick-whistled chicks that were tagged in England were then met nesting thousands of kilometers from their native nest: on the Kola Peninsula and in the Arkhangelsk Region, in Iceland and in Byelorussia.

Territory of the population

All of the above figures indicate the territory that individual populations of different species can occupy, which distance is sufficient to ensure that neighboring groups are isolated from each other. Individual populations of roe deer can live on small mountain ridges at a distance of only tens of kilometers, groups of sparrows can be located two kilometers apart, while the populations of ducks seem to occupy territory that is equal to almost all of Europe. By the way, the huge size of the duck population explains the fact that they are surprisingly surprising for a long time: they all have surprisingly low variability, and among them, unlike most other birds, it is rare to distinguish subspecies. Now it became clear that all ducks of the same species belong to one or very few populations. They are constantly interbreeding with each other, so there is no accumulation of new signs in any part of the range.

Number of populations

So, it is characterized by a strong, but not absolute isolation from neighboring. Thanks to this, the originality of the genetic fund of each of them is preserved and maintained.

Another important characteristic of the population is the number, that is, the number of its constituent individuals. 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, mosquitoes - millions of individuals may be included in one population. The population of one of the dragonfly species on the lake near the town of Orekhovo-Zuevo 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 few, and scientists do not yet know what the exact number of populations is even in the most common species.

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 capable of lasting and reliable existence. In order to understand the significance of this problem, we must add that the number of individuals in the population always fluctuates: several times, sometimes several hundred, and sometimes thousands of times. The population of large animals, an average of less than a few hundred individuals, can not exist long enough. Groups of lesser numbers, sooner or later, simply as a result of inevitable fluctuations in numbers, quite accidentally, can be reduced to zero.

Due to the fact that the long existence of small populations is almost impossible, most scientists are skeptical of such, for example, sensational reports as the "discovery" of several prehistoric pangolins in the Scottish lake of Loch Ness . All such a few monsters must have disappeared long ago.

Evolution of populations

Real populations are potentially immortal: they can exist until the conditions that are 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, the evolution of the population occurs.

New mutations in nature appear continuously, although the speed of this process is relatively low. However, over time, the genetic composition of the population changes. Of course, not a single mutation, not even a dozen, can change it. However, they accumulate generation after generation, until they manifest themselves in this or that combination of parental grants. If this combination turns out to be successful, then in one or two generations the individuals with it will be numerous in this group, because of what the genetic composition of the population will change noticeably. The emergence of a mutation in the evolutionary arena is a very important event in the life of both a separate group and an entire species. This is the smallest step of the evolutionary process, but from these steps the whole grandiose process of evolution is being formed.

So, we have briefly considered the topic "Population". The definition, examples and characteristics of it were presented in the article. We hope that this information will be useful to you.