Increasing numbers of bird species result from taxonomic progress, not taxonomic inflation

Abstract

The impact and significance of modern taxonomy on other fields in biology have been subjects of much debate. It has been proposed that increasing numbers of vertebrate species are largely owing to 'taxonomic inflation'. According to this hypothesis, newly recognized species result from reinterpretations of species limits based on phylogenetic species concepts (PSCs) rather than from new discoveries. Here, I examine 747 proposals to change the taxonomic rank of birds in the period 1950 -2007. The trend to recognize more species of birds started at least two decades before the introduction of PSCs. Most (84.6%) newly recognized species were supported by new taxonomic data. Proposals to recognize more species resulted from application of all six major taxonomic criteria. Many newly recognized species (63.4%) were not based exclusively on PSC-based criteria (diagnosability, monophyly and exclusive coalescence of gene trees). Therefore, this study finds no empirical support for the idea that the increase in species is primarily epistemological rather than data-driven. This study shows that previous claims about the causes and effects of taxonomic inflation lack empirical support. I argue that a more appropriate term for the increase in species is 'taxonomic progress'.

How Many Kinds of Birds Are There and Why Does It Matter?

“…In contrast, Sangster [47] suggested that taxonomic progress, not taxonomic inflation, led to increasing numbers of recognized species of birds. It is not clear that a more accurate understanding of evolutionary diversity is detrimental to conservation practices.…”

Deep genealogical lineages in the widely distributed African helmeted terrapin: Evidence from mitochondrial and nuclear DNA (Testudines: Pelomedusidae: Pelomedusa subrufa)

“…In several groups of organisms claims for possible taxonomic inflation, an exaggerated recognition of species-level taxa, have recently been voiced (Isaac et al, 2004; but see Padial and De la Riva, 2006;Sangster, 2009). This also extends to chelonians, where several species and subspecies turned out to be ecotypes or geographical variants not representing independent evolutionary lineages (e.g., Daniels et al, 2010;Fritz et al, 2005.…”

How does the discrepancies among taxonomists affect macroecological patterns? A case study of freshwater snails of Western Siberia

“…For example, the results obtained by Jones et al (2012) imply that the large-scale patterns of diversity and other macroecological conclusions may be qualitatively unaffected by taxonomic overdescription. Sangster (2009) has shown that the recent increase in bird species number may be explained by progress in taxonomical methodology rather than by increased ''splitting effort''. Thus, the form and strength of dependence of such patterns on the quality of taxonomic work need to be further studied by using data from a broader set of plant and animal taxa.…”