Surely you have some idea of what a population is. We all went through examples and definitions of it in biology lessons. 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.
Spreading the species using the example of a frog
Population of any kind is extremely unevenly distributed in space, in full accordance with the well-known proverb: dense in one place, empty in another. This is quite natural. Where to begin consideration of the topic "Population"? Examples will probably help you visualize what are the features of the distribution of species on our planet.
The pond frog is often found throughout Europe. But it would hardly occur to anyone to look for frogs in a dry pine forest or on stony placers. They live in marshes, near bodies of water, and in other wetplaces. Although such habitats are found in all countries, they do not completely cover the whole of Europe. This means that the frogs are distributed unevenly, in groups. These groups of individuals can be large or small, existing for a couple of years or for centuries. In a particularly wet year, when every lowland is filled with water, the frogs from the marsh spread relatively far and may even spawn in some temporary large puddle. But in a dry summer, the puddle will dry up, and all the frogs born here will die. This is the end of the short history of such a small group.
The fate of a group of frogs permanently living in a large swamp is much more important for evolution. Either decreasing or increasing in number - depending on living conditions - the population of frogs in a large swamp can exist for many hundreds and thousands of generations. The life of such a group will proceed relatively isolated from other groups, because another nearest large swamp with suitable conditions for a long existence can be located tens of kilometers from the first. And although a frog will certainly travel tens of kilometers in its entire life, none of them in nature will run 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, which loves to hunt not in this, but in a neighboring swamp, and which does not cost anything to overcome ten kilometers, can drop a frog over our reservoir, intendedfor his chicks. Ducks or other waterfowl passing through here in the spring may carry a few eggs to another body of water that is in their path; if you're lucky, the eggs can develop in another, completely foreign place. Such events, of course, happen extremely rarely, but they do happen from time to time.
Don't think that life in such isolated groups is typical only for the inhabitants of swamps and other water bodies. Mole colonies, clearly visible on the mounds of the earth that grow during the night, 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 are also found only where there are favorable conditions for this plant: it is shady and the soil is rich in nitrogen. Easily flying from place to place butterflies, which, it would seem, can live anywhere, each meet strictly in its own place: mourning in birch forests, whites where there are some cruciferous, and so on.
So we come to the consideration of the concept of "population". Its definition and characteristics are presented below. Let's start, of course, with the most important thing - with the definition.
The concept and characteristics of a population
The center of population density of any species, which persists for a long time, is called a population. Its most important feature is its genetic unity: individuals that are part of 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,the fact that in this case there is an exchange of genetic information: after all, the descendants receive half of the chromosomes from one parent, and half from the other. Therefore, when mating over 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 - a 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 amounts to no 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.
Distance individuals travel
Now it becomes clear why it is so important to know how far organisms actually move in nature and, most importantly, how far they can transfer their genes and pass them on to the next generation. Finding this out is not so easy at all: you need to mark, release and catch again many individuals of animals, to establish how far the pollen of different plants really scatters, their seeds are carried. The results of such studies were surprising in many ways.
Distribution range of animals and plants
Whatthe territory can be occupied by a population? The examples that we will give give a visual representation of this.
Only five out of a hundred wild roe deer goats run away to a distance of 10 km from their permanent habitat, and the vast majority stay all their lives in an area with a diameter of 3 km. In the North American white-tailed deer, too, only 5% of individuals go for a distance of up to 10 km in a straight line in their entire life, and the vast majority of the population (95% of individuals) lives in an area with a diameter of about one and a half kilometers. Both wild rabbits and European hare hares behave very much like deer. Field sparrows in mass do not fly further than 400 m from the place of tagging in their entire life. And the large American water rodent muskrat, which has now settled in suitable water bodies almost throughout Northern Eurasia, does not go further than 1 km from the place of marking, and most of the animals live all their lives in a 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 a forest, for example, is only carried by the wind for a few hundred meters.
Champion in the range of distribution were among the animals of the teal. Teal-whistle chicks 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 Belarus.
Population area
All the above figures speak ofabout what territory individual populations of different species can occupy, what distance is enough for neighboring groups to be isolated from each other. Separate populations of roe deer 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 populations of ducks, apparently, occupy an area equal to almost the whole of Europe. By the way, the huge size of the territory of the duck population well explains the fact that has long surprised scientists: they all differ in surprisingly low variability, and among them, unlike most other birds, it is rarely possible to distinguish subspecies. 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 there is no accumulation of new characters in any part of the range.
Populations
So, it is characterized by 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 its abundance, that is, the number of its constituent individuals. How many individuals are included in it? It is difficult to answer this question unambiguously, since this number is different for different species of animals and plants. In insects, such as mosquitoes, one population can include millions of individuals. The population of one of the species of dragonflies on the lake near the city of Orekhovo-Zuevo in the Moscow region is about 30 thousand individuals, and the number of several groups of lizards in Kazakhstanranged from several hundred to several thousand individuals. But such data is still scarce, and scientists do not yet know what the exact population size of even the most common species is.
The problem of determining the number of numbers
Today this problem is no longer just a purely theoretical one. To preserve any species, it is important to know the minimum number of individuals at which it is able to exist for a long time and reliably. In order 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, averaging fewer than a few hundred individuals, cannot last 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 almost impossible, most scientists are skeptical of sensational reports such as the "discovery" of several prehistoric pangolins in Loch Ness, Scotland. All those 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, there is an evolutionpopulations.
New mutations in nature appear continuously, although the speed of this process is relatively low. However, over time, the genetic composition of the population does change. Of course, not a single mutation, not even a dozen, can still change it. However, they accumulate generation after generation until they manifest themselves in one or another combination of parental inclinations. If this combination turns out to be successful, then in one or two generations individuals with it will be numerous in this group, due to which the genetic composition of the population will noticeably change. The entry of one or another mutation into 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 in the evolutionary process, but the whole grandiose process of evolution is made up of such steps.
So, we briefly reviewed the topic "Population". The definition, examples and characteristics of it were presented in the article. We hope you find this information useful.
