Interspecific competition is central to the equilibrium versus nonequilibrium debate. It is intuitively likely that under equilibrium conditions and in saturated niche space, competition will be more common and more intense than under nonequilibrium conditions and in nonsaturated niche space. In this chapter, I discuss evidence for and against the occurrence and significance of interspecific competition. The discussion begins with a definition of competition and its different types, and the main cause thought to be responsible for its occurrence, i.e., resource limitation. A discussion on the effects of competition on species in this chapter is followed by one on effects in communities in Chapter 4. The final section in Chapter 4 deals with general aspects and gives a conclusion.

Definition and types of competition, resource limitation as its main cause

Definition and types of competition

Interspecific competition results in the increase of the population density of one species at the expense of the reproductive rate and population density of another (Crawley 1986). However, it is not species but individuals within species that interact, and therefore, competition (at least as a starting point, but see p. 50) is better defined as an interaction between individuals that arises because of shared requirements for a limiting resource. It leads to reduced survival, growth and/or reproduction of at least some of the individuals (Begon et al. 1996).

Competition may be between individuals of the same species, i.e., it is intraspecific, or it may be between individuals of different species, i.e., interspecific.