Understanding intraspecific and apparent competition

Abstract

AbstractInterspecific competition shares the same dependence on consumer–resource interactions as intraspecific competition and apparent competition. These two related interactions are the subject of this chapter. Both interactions are present in most, if not all, systems in which interspecific competition occurs. Intraspecific competition is usually discussed in the context of models that lack resources, while models of apparent competition always involve explicit dynamics for consumers and resources. The chapter examines whether these differences are justified, and concludes that both interactions should be studied using a consumer–resource framework. The ‘theta-logistic’ is a popular model that extends the logistic by allowing for density dependence under which per capita growth rate decreases as abundance raised to a positive power other than unity. This, however, is shown not to correspond to popular consumer–resource models. In addition, it lacks the time lag in consumer response that follows from resource dynamics. Traditional measures of density dependence are complicated by the possibility that adverse changes in a neutral parameter can cause the equilibrium or mean abundance of a consumer to increase (i.e., a ‘hydra effect’). The forms of density dependence for several simple consumer–resource models are analysed and compared. Although apparent competition is always based on consumer–resource models, the vast majority of the literature only considers a single consumer, and usually assumes the systems are stable. The consequences of having instability and/or two or more consumer species are analysed.