The Meaning and Measurement of Frequency‐Dependent Competition

This paper criticises use of the concept of frequency—dependent competition. The usual definition of frequency—dependent competition, based on deWit's Replacement Series Analysis is trivial in the sense that it admits no interesting alternative hypotheses. A more general definition is proposed: competition is frequency—dependent whenever per individual competitive effects vary with species frequency. Frequency—dependent competition may be distinguished from density—dependent competition. Replacement Series Analysis, although a useful indicator of possible competitive interactions, is incapable of discriminating between frequency—dependent and frequency—independent competition as defined herein. Data reported by previous investigators are reanalyzed and found generally to support the claim that Drosophila competition is frequency—dependent. However, these data do not eliminate the possibility that changes in competitive abilities are simply density—dependent. Little other evidence of the phenomenon exists.