A population is a collection of organisms of one species, capable of self-reproduction, more or less isolated in space and time from other populations of the same species.
The population includes individuals of the same species. They live together in a certain area and constantly interact with each other.
Example: the population is formed by all spruce trees in a coniferous forest or all individuals of the common perch living in a small lake.
Populations are the main elements of ecological systems, representing a set of co-living organisms of different species and conditions of their existence.
The organisms that make up the population are related to each other by various relationships: they jointly participate in reproduction; compete for food, territory, or sexual partner; they can defend themselves against enemies together, but they can also eat each other.
The relationships between individuals in populations are complex and contradictory. Changes in some environmental factors can lead to different, often opposite, reactions of individual organisms and the population as a whole. So, if in a population some individuals become victims of predators, then this can increase the survival rate of the population and improve its quality indicators. Weakened or sick individuals most often become the prey of predators. Removing them prevents the spread of diseases that can be fatal to the entire population.
Here we are faced with one very important rule applicable to complex biological objects, consisting of many elements related to each other by various relationships: the state of a biological system (be it a population, a community or an ecosystem) cannot always be judged by the state of its individual elements.
Populations of different species constantly interact between and form integral systems of a higher level of organization – biotic communities.
In these communities, populations of different species form a single whole. Each biotic community exists and develops according to its own laws.
It is thanks to the functioning of populations that conditions are created that contribute to the maintenance of life on our planet. Occupying this or that space, building shelters, moving, using certain types of food, populations of each species in a certain way affect the surrounding nature. The circulation of substances, energy exchange between living and inanimate nature depends on populations. The joint activity of populations determines many important properties of biotic communities and ecological systems.