The Debate over Species Concepts and Its Implications for Ornithology

Abstract

We review recent developments in the debate over species concepts, exploring differences between the species concept (BSC) and the phylogenetic species concept (PSC). Three principal flaws in the BSC are reviewed: (1) the occurrence of paraphyletic or nonhistorical groups; (2) the misrepresention of the significance of hybridization among differentiated taxa; and (3) the logical difficulty in handling allopatric populations. Simple cline theory shows that likely times to fusion for hybridizing taxa exceed the average duration of most species in the fossil record. We address criticisms of PSCs (of which there are several), including the application of phylogenetic methods to populations, and whether species can be monophyletic. We suggest that the evolutionary species concept and the PSC might be more similar than generally appreciated. Empirical studies of variation in the Brown Towhee (Pipilo fuscus) complex and Fox Sparrow (Passerella iliaca) reveal that the BSC and PSC can lead to different species limits. Reasons are given for why the PSC is the preferred concept for comparative biology, phylogenetic inference, historical biogeography, estimation of bio- diversity, hybrid-zone analysis, conservation biology, and speciation analysis. Despite prob- lems associated with all species concepts, we think that a concept consistent with the PSC should replace biological species concepts. Received 12 April 1994, accepted 4 November 1994.