The application of species criteria in avian taxonomy and its implications for the debate over species concepts

Abstract

The debate over species concepts has produced a huge body of literature on how species can, may or should be delimited. By contrast, very few studies have documented how species taxa are delimited in practice. The aims of the present study were to (i) quantify the use of species criteria in taxonomy, (ii) discuss its implications for the debate over species concepts and (iii) assess recent claims about the impact of different species concepts on taxonomic stability and the 'nature' of species. The application of six species criteria was examined in taxonomic studies of birds published between 1950 and 2009. Three types of taxonomic studies were included: descriptions of new species (N = 329), proposals to change the taxonomic rank of species and subspecies (N = 808) and the taxonomic recommendations of the American Ornithologists' Union Committee on Classification and Nomenclature (N = 176). In all three datasets, diagnosability was the most frequently applied criterion, followed by reproductive isolation and degree of difference. This result is inconsistent with the popular notion that the Biological Species Concept is the dominant species concept in avian taxonomy. Since the 1950s, avian species-level taxonomy has become increasingly pluralistic and eclectic. This suggests that taxonomists consider different criteria as complementary rather than as rival approaches to species delimitation. Application of diagnosability more frequently led to the elevation of subspecies to species rank than application of reproductive isolation, although the difference was small. Hypotheses based on diagnosability and reproductive isolation were equally likely to be accepted in a mainstream checklist. These findings contradict recent claims that application of the Phylogenetic Species Concept causes instability and that broader application of the Biological Species Concept can stabilise taxonomy. The criteria diagnosability and monophyly, which are commonly associated with Phylogenetic Species Concepts, were used throughout the study period. Finally, no support was found for the idea that Phylogenetic Species Concepts have caused a change in the 'nature' of species taxa. This study demonstrates that there is a discrepancy between widely held perceptions of how species are delimited and the way species are actually delimited by taxonomists. Theoretically oriented debates over species concepts thus may benefit from empirical data on taxonomic practice.

Why is Pseudosphromenus cupanus (Teleostei: Osphronemidae) reported from Bangladesh, Indonesia, Malaysia, Myanmar, and Pakistan?

“…Out of 33032 valid fish species recognized in FishBase (Froese & Pauly, 2015), only 59 species include 2-6 subspecies, many of them obsolete. The use of subspecies is contentious in taxonomy as a whole and has been contested as being inconsistently applied and/or incongruent with genetic variation and/or lacking evolutionary context (e.g., Gippoliti & Amori, 2007;Kodandaramaiah et al, 2012;Kullander, 1999;Sangster, 2014;Wilson & Brown, 1953;Zink, 2004). The case of P. cupanus is further testimony to the confusing nature of trinomina.…”

Names are not good enough: Reasoning over taxonomic change in the Andropogon complex1

“…Weakley's (2015) classification recognizes seven species-level concepts -more than any other taxonomy. The taxonomic history is evidently complex, but no more complicated than that of many other continuously revised groups [1,20,32,35,43,68,77,90]. The poor performance of names as identifiers of divergent taxonomic meanings is not exceptional for the field (herein broadly defined to include phylogenetics).…”

“…Such cases are frequent in taxonomy, and they cannot be reduced to the differences in degree of resolution [26,65,68,77]. As an example, the 1950/1948 classifications of the Andro-UC concur that there are three identically named species-level concepts entailed in the complex (Fig.…”

When taxonomy meets genomics: lessons from a common songbird

“…The increase results from more taxonomic splits than lumps, while new species discoveries are rather few. A recent review of taxonomic revisions concluded that taxonomy has improved as a scientific discipline with a more integrative conceptual framework and better empirical evidence underlying species delimitation (Sangster 2014). Despite the debate over species concepts, where proponents of the phylogenetic species concept have been accused of causing taxonomic inflation (Isaac et al 2004), there is a growing consensus that species are cohesive lineages with a distinct evolutionary history and intrinsic barriers to gene flow across their borders.…”