Are All Species Created Equal? A Critique of the "Equal Fitness Paradigm".

My article criticizes the view held by many ecologists that species have evolved essentially equivalent levels of fitness, thus permitting their coexistence. I show that a recently proposed version of this view called the "equal fitness paradigm" (EFP) has multiple problems, empirically and conceptually. Some of these problems are (1) an energetic fitness measure (OPG = lifetime production of surviving offspring per parental body mass) that ignores the critical effect of the timing of reproduction; (2) flawed methods and data used to calculate and interpret the body-size scaling invariance of OPG upon which the EFP is based; (3) omission of the profound effects of population size and geographical range size on species-level fitness; and (4) lack of recognition that if the EFP were true, species-level selection would not be able to operate. By contrast, the "variable fitness paradigm" (VFP), which is a mainstay of modern evolutionary biology, is supported by numerous lines of evidence at multiple levels of biological organization. Extensive fitness variation allows natural selection to operate at all these levels. Distinguishing fitness and adaptiveness as reproductive power and efficiency of resource acquisition, respectively, helps explain species coexistence within the conceptual framework of the VFP. No EFP is needed.