Competition is an interaction between two or more individuals, which exploit the same resources, accessible in a limited amount. These interactions are negative since they diminish the amount of resources available to others or prevent others from obtaining them or both. Competition among animals has an important behavioral component; nevertheless, there are also some morphological and physiological adaptations to competition. Behavior is regarded as a phenomenon restricted to animals or free-moving microorganisms; it does not occur in terrestrial plants. However, in competitive interactions, the form of plant growth may function like behavior in animals. While plant competitive properties are usually not classified as behavioral ones, they may help to understand better the competitive behavior of animals. Competition is defined as negative interaction; however, a reservation should be made, since a certain degree of competition at an early stage of an organism's life can be of advantage in its later life.
Competition is the basic concept for both the Darwinian theory of natural selection and the ecological theory of population dynamics. This is because under favorable conditions without competition, populations of organisms increase exponentially and this growth is usually arrested by competition. Competition for limited resources implies that only some of the newly born individuals survive and reproduce. They do not represent a random sample but usually those better adapted to their current environment. This process underlies natural selection. Competition adjusts population size to available resources by arresting the population growth but there are several open questions concerning this adjustment. What is the mechanism of this adjustment? Can competition lead to the depletion of available resources and population extinction or can population increase be stopped earlier, before resources are depleted?
Increasing interests in behavioral aspects of competition is due to the progress in evolutionary biology in the second half of twentieth century, the development of the kin selection theory, application of the game theory to biology, and clarification of the concept of group selection. This progress has inspired field studies of the behavioral mechanisms of population dynamics. There are two distinctions related to behavioral aspects of competition: exploitative versus interference competition, and scramble versus contest competition. For understanding the mechanism of the latter distinction, the differences between individuals and their mutual interrelations must be taken into account. Other two ideas concerning behavioral adaptations to competition are the ideal free distribution and the concept of population sources and sinks. These concepts and distinctions are presented below.
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