The struggle for existence is one of the driving factors of evolution, along with natural selection and hereditary variability, the totality of the diverse and complex relationships that exist between organisms and environmental conditions. Also, the third chapter of Charles Darwin’s book “The Origin of Species by Natural Selection” is entitled “The Struggle for Existence.
Intraspecific struggle is a struggle that proceeds most acutely, since all individuals of the species have an ecological niche. In the course of intraspecific struggle, organisms compete for limited resources – food, territorial, males of some animals compete with each other for fertilization of the female, as well as other resources. To reduce the severity of the intraspecific struggle, organisms develop various devices – the delimitation of individual sites, complex hierarchical relationships. In many species, organisms at different stages of development occupy different ecological niches, for example, coleoptera larvae live in soil, and dragonflies live in water, while adults inhabit the ground-air environment. Intraspecific struggle leads to the death of less fit individuals, thus contributing to natural selection.
Interspecific struggle – the struggle for existence between different species. As a rule, interspecific struggle is particularly acute if ecological niches overlap in species (often in representatives of the same genus or family). In the course of interspecific struggle, organisms also compete for the same resources – food, territorial. Interspecific struggle for existence includes relations such as predator – prey, parasite – host, herbivore – plant. The interspecific struggle for existence in many cases stimulates evolutionary changes in species. Another example of the struggle for existence is the mutually beneficial influence of one species on another or others (for example, mutualistic relations, commensalism), in this way animals pollinate plants and transfer seeds, eating nectar, pollen and fruits. Often the interspecific struggle for existence leads to the appearance of adaptations, as, for example, in the case of co-evolution of flowering plants and pollinating insects. Usually, the interspecific struggle for existence strengthens and aggravates the intraspecific struggle.