Taxonomic Inflation and the Stability of Species Lists: The Perils of Ostrich's Behavior

Abstract

Finding a new species is amongst the most impor tant discoveries a biologist can make (Wilson, 1998). The discovery of new species opens up countless research possibilities, because species are the primary objects of study in many research fields of biology, and the species is the unit most commonly used for conserva tion planning and management (Margules and Pressey, 2000). The formal description of species is one of sev eral major research themes of taxonomy (e.g., Cracraft, 2002) and, hence, a fundamental part of the science of bio diversity (Wilson, 1988,1992, 2003, 2004; Wheeler, 1995, 2004; Butler, et al., 1998; Disney, 1998; Causey et al., 2004). Thousands of new species are described each year and many still await description (e.g., May, 1988; Purvis and Hector, 2000; Meier and Dikow, 2004). However, despite the increasing rate of discovery, we are in the course of a major biodiversity crisis (Wilson, 1988). This has caused taxonomy to undergo a revival (Wheeler et al., 2004). Nevertheless, funds for taxonomy remain scarce and it is not strongly encouraged or promoted by academics (Dubois, 2003). But taxonomy has evolved, acquiring a better understanding of what species are and finding new tools to infer their boundaries (Mayr, 1942; Wiley, 1978; Cracraft, 1983; De Queiroz, 2005a). But there is still some confusion about the results of science (Will et al., 2005). Isaac et al. (2004) and Mace (2004) (hereafter, IEA and MAC, respectively) have recently explored the consequences of progress on macroecology and conservation biology For example, they argue that the elevation of subspecies to species caused by the increasing use of phylogenetic species concepts (PSCs) is responsible for most growth in the number of species. IEA term this phenomenon taxonomic (hereafter inflation s. s.). They suggest that as a consequence of inflation, taxonomy suffers from great uncertainty and species lists change too often, compromising current pre dictions in macroecology and conservation biology, two disciplines that heavily rely on species lists. They also argue that an increase in number of species would re quire a larger budget for conservation. Moreover, they accused instability of being a potential cause of unfounded shifts in conservation priorities (i.e., the relocation of hotspots). As a partial solution to this prob lem, IEA and MAC advocate a broader application of the biological species concept (BSC). Further, they sug gest that new additions to species lists should be con trolled, standardized, and stabilized due to the necessity for macroecology and conservation of working with sta ble units. A number of brief responses to IEA's arguments fol lowed shortly after. Harris and Froufe (2005) identify geopolitical bias in the study of interspecific genetic di vergences as the major cause of inflation. Agapow and Sluys (2005) argue that infla tion reflects the nature of species. They suggest that sta ble species lists and an ideal species concept are both unattainable solutions. Knapp et al. (2005) assert that most new plant species are described following classi cal methods. These responses lead to the recognition that inflation is a major cause of increase in species numbers only in charismatic vertebrates; that global lists with full information on synonymies and other details will be more useful than stable species lists; and that it is necessary to correctly identify the causes of inflation (Isaac et al., 2005; Mallet et al., 2005). The most detailed response was that of K?hler et al. (2005), who show evidence against in flation in amphibians in general and demonstrate it to be unrelated to the steady increase in the discovery of am phibian diversity in Madagascar. Nevertheless, they did not intend to explain the causes and consequences of tax onomic inflation and did not explore the causes of other changes involved in modifications of species lists. In summary, inflation has been consid ered an indirect result of procedures by most authors, but the origin and implications of in flation as a result of development of taxonomy have not been explored. Moreover, apart from the point of view of IEA and MAC, the causes of instability have still not been properly discussed. In our view, IEA and MAC have highlighted a relevant scientific issue with both theoretical and practical impli cations. However, such a debate should be free of pos sible misconceptions about species concept, taxonomy, and progress. Our discussion is based on five main arguments that need to be treated in detail and that in the best case have been only partially addressed: (1) inflation is just the logical result of recent con ceptual and methodological developments in research; (2) inflation, although widespread among taxa, is responsible for only a small fraction of the whole increase in species numbers; (3) changes in species lists are necessary to reflect the current state of biodiversity knowledge; (4) species lists divorced from progress would have serious negative conse