competition is a inharmonious or negative ecological relationship, in which interaction occurs between individuals looking for the same resource, usually when there is a shortage of that resource.
Interspecific Competition
Interspecific competition is an interaction between two species that harms one or both of them. In general, the competition can be for resources such as: space, food or nutrients, light, organic waste, between others.
Hyena competes with vultures and a jackal for food
Two species compete when resources are not enough for both, this can lead to a state of equilibrium, or if it is too intense it can make the stronger species make the other look for a new living space or other food.
Often two related species or morphologically similar and with similar niches live in different habitats. This means that the tendency is for ecological separation among them, what is called competitive exclusion principle.
An example of this was tested by Gause (hence the principle is also called Gause's Law) who compared species of protozoa Paramecium caudatum and Paramecium aurelia.
Competitive exclusion happens among some species of paramecium
When they were in separate cultures the growth was normal, when they were in the same culture only P. aurelia survived. There were no attacks from one species to another, no segregation of harmful substances, simply P.aurelia it grew faster because it won the competition for scarce food.
When they live in the same habitat, the species have different ecological niches, that is, they can look for food at different times or even look for different foods. Thus, the tendency is for there to be coexistence from them.
Competitive exclusion usually happens on islands or in laboratory cultures where it is more difficult to move. In nature, where organisms can migrate in resource-scarce situations, they are more likely to coexist.
The knowledge about the way species adapt to competition is essential even for evolution studies, as it is a mechanism of natural selection.
Intraspecific Competition
When individuals of a given species in a population have few available resources, intraspecific competition occurs.
two zebras in a fight
In the search for food, some individuals obtain the necessary resources, while others cannot and end up dying or being expelled from the group. It is usually the youngest who suffer this pressure, or even the sickest and most debilitated.