Abstract
The “competitive exclusion principle” (CEP) states that two species with identical niches cannot coexist indefinitely. Natural historians (i.e., Grinnell) and ecological theorists (i.e., Lotka and Volterra) had concluded this during the early part of the 20th century; however, this concept has been primarily attributed to Georgii Frantsevitch Gause. In Gause׳s landmark 1934 book, The Struggle of Existence, his experimental tests using protozoa supported the predictions of Lotka–Volterra equations, finding protozoa that use similar resources could not coexist, leading ecologists to identify him with CEP. Gause helped propel ecology by his approach of experimentally testing mathematical models, and his unifying the concept of the niche with resource competition. Gause׳s CEP has been one of the central research themes in ecology: trying to understand the mechanisms of species coexistence and patterns of biodiversity. Most of the explanations for coexistence are niche-based in origin, including resource partitioning, character displacement, and niche tradeoffs. Criticisms (e.g., neutral theory) of these explanations state that these deterministic processes cannot, by itself, explain very high levels of species diversity; however, the current consensus is that species coexistence and diversity patterns are a combination of stochastic and niche-based explanations. Historically, CEP has been tested using theoretical, observational, and experimental studies, but phylogenetic approaches have been increasingly used over the past decade.