Today we will examine that evidence and the development of our understanding of the subject. We will begin with a definition of competition, because this provides a frame of reference against which to examine evidence. Competition occurs when two species each require a resource that is in short supply, so that the availability of the resource to one species is negatively influenced by the presence of the other species. Competition does not occur if the resource is too plentiful to limit the growth, distribution or abundance of at least one of the populations. We expect only one or a few resources to be limiting and therefore to be competed for.
Competition can occur between individuals that are members of the same species.
This is called intraspecific competition. Intuitively, intraspecific competition seems likely to be intense because two members of the same species are likely to have very similar resource needs. We will examine the limiting influence of intraspecific competition more fully under the subject of population growth in the second semester of this course . Today we focus on interspecific competition, which occurs between members of different species. The intensity of interspecific competition should be related to the similarity between the two species.