According to the evolutionary doctrine of Darwin, the following forms of struggle for existence can be distinguished: intraspecific, interspecific, and the struggle with unfavorable environmental conditions.
Intraspecific struggle is a struggle for the same vital resources that arises between individuals of the same species.
- struggle for territory;
- prey competition;
- intraspecific cannibalism;
- struggle for primacy in the pack.
Intraspecific struggle is the most severe type of struggle, since individuals compete with each other for the same conditions of existence, the same food sources, and the same reproductive opportunities. The result of this struggle is the preferential right for reproduction of more adapted individuals and the death of less adapted ones.
Interspecies struggle is a struggle that occurs between individuals of different species living in a common area.
- displacement of one species by another;
- competition between plants in the forest for light;
This type of relationship may involve the use of one kind of another. Such relationships are built on the “predator – prey”, “herbivore – plant”, “host – parasite” types. But the struggle for existence can also be a mutually beneficial relationship between individuals of different species. For example, mammals and birds carry seeds and fruits, and insects carry pollen from flowering plants. As a result, the struggle contributes to the evolution of two types, causes the emergence of mutual adaptations.
The fight against unfavorable conditions of inanimate nature is the survival of the most adapted individuals, populations and species in the changed conditions of inanimate nature.
It is observed in those cases when the external environmental conditions worsen (daily and seasonal fluctuations in temperature and humidity), as well as wherever individuals find themselves in conditions of excessive heat or cold, dryness or humidity.
- seasonal change of fur (molt) in mammals;
- summer and winter hibernation in animals;
- seasonal flights of birds;
- adaptation to moisture retention in desert plants.
The fight against abiotic factors takes place constantly, since there are no absolutely stable conditions in nature. Environmental conditions are constantly changing, and the body is forced to either adapt to them, or die.
In STE, direct and indirect struggle for existence is distinguished.
Direct struggle is any relationship in which physical contact is observed between individuals of the same or different species.
- rivalry between males for a female;
- the relationship between predator and prey;
- the relationship between nodule bacteria and legumes;
- feeding the cubs with milk.
Direct struggle can be intraspecific and interspecific.
With direct interspecific struggle, the adaptation of individuals of both species (for example, predator and prey, parasite and host) is improved.
Indirect struggle – any relationship between individuals of different populations without direct contact with each other.
competition for light, water and minerals between young pines in dense plantings;
- the relationship between light-loving and shade-tolerant plants.