Introduction

One would have thought that the question, ‘What is competition?' should have been satisfactorily answered long before the year 2000. After all, the term has been a major topic for ecological theory for nearly a century, since the work of Alfred Lotka and Vito Volterra, which was described in Chapter 1.

Every modern ecology textbook gives competition extensive coverage. Current articles about competition seldom if ever define the term, which should indicate that the definition is almost universally agreed upon. In addition, one would think that research usually proceeds by agreeing on exactly what defines a process before developing theory to understand that process. Nonetheless, competition theory has been around almost as long as the interaction has been recognized, and it became one of the most popular topics for ecological research in the 1970s. Nevertheless, Paul Keddy felt compelled to open his book on competition (Keddy 2000, p. 4) with the statement, ‘The right definition is like a sword that will clearly cleave nature into pieces that we can understand; the wrong definition is like a blunt instrument that only mashes the object of our inquiry into more confusion.'

A range of definitions were used before Keddy made this statement, and a similar range have continued to be used since. In fact, there was considerable disagreement on that definitional question among ecologists when I began my formal training in the field in the early 1970s. This surprised me, as a large number of ecologists at that time seemed convinced that competition was the most important interaction in natural communities. A variety of textbooks and articles from that era identified competition as one of the two basic types of interspecific interaction, the other one being predation. (A few added mutualism as a third category.) Predation was accepted to be an interaction in which individuals of one species consumed all or part of individuals of another species.

There was an active debate about whether competition or predation had a greater effect on the abundances of species (e.g. Connell 1975). Resolving the debate was difficult, in part because the literature at that time contained several quite different definitions of competition. How could competition not have had a universally accepted definition in 1970? Even more surprising than the lack of a clear definition of competition at that time is the fact that the vast majority of ecologists have avoided an active debate on the definitional issue over the intervening half century. In spite of Keddy's admonition, there is no single widely accepted definition of

Competition Theory in Ecology. Peter A. Abrams, Oxford University Press. © Peter A. Abrams (2022).

DOI: 10.1093∕oso∕9780192895523.003.0002 competition. This chapter will document the definitions used by various authors over the years. It will also present reasons why the definitional issue needs to be settled, and will suggest a resolution.

The above paragraph has used the term ‘competition’ to refer to a process that involves two or more species; this is ‘interspecific’ competition. The same basic mechanism that results in interspecific competition also operates within species, resulting in ‘intraspecific’ competition. This within-species form is commonly referred to as ‘density dependence’ by ecologists. For evolutionary biologists, intraspecific competition is fundamental to understanding the outcome of natural selection on ecologically important traits. In addition to the definitional issue for interspecific competition, there is a strange lack of consistency in the theoretical and empirical work on the intra- and interspecific forms of competition. This inconsistency will be discussed in Chapter 5.

‘Competition’ is not the only problematic term in the classification of interspecific interactions that occur in ecological communities. Defining and classifying interactions of all sorts has been a long-standing problem for ecologists (Abrams 1987a). This chapter will therefore touch upon the more general problem of establishing a logical and self-consistent set of rules for categorizing interactions between species.

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Source: Abrams Peter A.. Competition Theory in Ecology. Oxford University Press,2022. — 336 p.. 2022

Introduction

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