Facteurs biotiques (interactions entre les espèces)

Biotic factors are the set of actions (coaction) that living organisms exert directly on each other. And we have two types of coaction: Homotypic or intraspecific reactions: these are actions that occur between individuals of the same species. Heterotypic or interspecific reactions, on the other hand, occur between individuals of different species. But what exactly are homotypic and heterotypic reactions? We'll start with homotypic, or also called intraspecific, reactions. As we said, these are interactions that occur between individuals of the same species, and we find three types: group or mass effects and intraspecific competition. Intraspecific competition is a competition that occurs between individuals of the same species, which have the same resource requirements such as food, light, water, territory (habitat, shelter), and breeding grounds (spawning grounds). This means that the more similar the ecological requirements are, the more individuals will compete. It is important to know that this type of competition can occur at high densities but also at very low population densities, and manifests itself in very diverse ways: For example, in plants: Competition is linked to high densities and occurs mainly for limiting factors: water, light, and nutrients. And the consequences of this competition are manifested by: A decrease in the number of seeds formed An increase in mortality On the other hand, in animals: this competition occurs for territory, food, or the maintenance of dominance. And this will also have a consequence where there will be a decrease in the population growth rate. So, briefly, the group effect is: Beneficial (Positive) for animals Acceleration of their growth rate Occurs when they are grouped in pairs or more. On the other hand, the mass effect is: Harmful (Negative) for animals Decrease in birth rate, increase in mortality, etc. Occurs when the environment is overpopulated We can distinguish 8 types of reactions: neutralism, competition, predation, parasitism, symbiosis, commensalism, mutualism or cooperation, and amensalism 1- Neutralism: This is neutral, meaning that the two species coexist without any influence on each other. This case is rare. 2- Interspecific competition (-/-): Where we have several different species that are said to be competitors and that seek the same environmental resource (food, shelter, spawning ground, etc.), so if a resource is lacking, competition is triggered (fighting between them). 3- Amensalism This is an interaction in which one species is eliminated or inhibited in its growth or reproduction by another inhibiting species called amensal, which secretes toxic chemicals (tannins, phenols, alkaloids, etc.) released into the air or water. In plants, this is called allelopathy. 4- Symbiosis (+/+): Obligatory and indispensable association between two species In this association, each species can only survive, grow, and develop in the presence of the other. And symbiosis can be said to be a form of mutualism, but... 5- Mutualism or cooperation (+/+): This is a beneficial but not obligatory association between two living species. Where both species benefit from each other. For example, protection against enemies, pollination, nutrient provision, etc. Here we have another form: comensialism. 6- Commensalism (+/0): This is an interaction in which a species, called a commensal, benefits from the other species, called the host, but without harming the host. 7- Predation (+/-): This is the bond between the prey (rabbit) and the predator (fox), where there will be a relationship that is beneficial for the predator (+) but negative for the prey (-) because its population will decrease. 8- Parasitism (+/-): This is cohabitation with nuisance. Where we find a parasite which takes advantage of its host (parasitized species or other term which hosts the parasite) to feed, to reproduce without fatally causing its death.