Introduction
The previous chapters suggested that a consumer-resource approach should always be taken in modelling competition, because competition is an indirect interaction that always involves resources.
Nevertheless, resources have often been omitted, even in the most influential recent research. This probably reflects the undue influence of past literature based on Lotka-Volterra (LV) models. As Getz (1998, p. 541) pointed out, ‘reason can be dominated by historical precedent in the development and elaboration of models in population ecology’. The original models by Lotka and Volterra did not contain resources, so many have simply followed this historical precedent.Resources represent distinct dynamic entities that transmit the interaction, and all other indirect interactions of this sort (trophic cascades in 3-level systems, apparent competition, or mutualism via shared predators) are modelled with explicit dynamics of the transmitting entity. Thus, the first step in addressing the adequacy of recent theory on competition is to examine whether and how it accounts for resources. However, even in those models that incorporate resources, the range of cases examined in recent theoretical work has been limited; theory has retained its LV-era focus on systems with only two competing species, and models having equal numbers of consumers and resources. While reliable complete counts of the number of competing consumer species in natural guilds of competitors are rare, having only two is uncommon, even in species-poor groups (e.g., hermit crabs; Abrams, Nyblade, and Sheldon 1986; see discussion in Chapter 7). The number of resources consumed is almost always much greater than the number of consumers, if resources are distinguished properly (Haigh and Maynard Smith 1972; Abrams 1988b; see Chapter 3). Finally, the majority of influential studies that use a consumer-resource approach have used linear forms for the three basic components discussed in the previous chapter.
Linearity is very unlikely and produces many unusual properties for the models. Thus, many of the findings maybe misleading with respect to competition in natural communities.Another metric for judging recent studies of competition is the extent to which they provide a description of the interaction that would allow prediction of the effects
Competition Theory in Ecology. Peter A. Abrams, Oxford University Press. © Peter A. Abrams (2022).
DOI: 10.1093∕oso∕9780192895523.003.0004 of various environmental changes on the abundances of the species. Environmental change is known to affect the several parameters of the simplest consumer-resource systems differently, and the same must be true of multi-consumer systems (Ama- rasekare 2015). Manystudies in the past have either focused exclusively on the issue of when species can coexist, or have observed the consequences of addition or removal of one species on a small spatial scale. These experiments generally do not provide a basis for estimating responses to climate change, harvesting, or several other common types of environmental alterations.
4.2