The Species Debate
This page is a work in progress....
"Notwithstanding the continuing differences in opinion, there are certain conceptual elements that most workers would now acknowledge as fundamental properties of species in general.....at any particular moment in the history of an established species, such entities are best viewed as ‘‘packages of information’’ more or less isolated and protected from other such entities. Viewed over time, many theorists acknowledge that species are separate lineages that (1) have beginnings (speciation), (2) unique evolutionary and ecological histories (reflected in the extended internal structure of demes, unique biogeographic histories, and different kinds of ecological ‘‘involvements’’), and (3) an eventual termination (lineage extinction); they are simultaneously wholes and parts.....Species are thus the smallest twigs in the tree of life resolvable over geologically significant periods of time. Each has a different history and status; reproductive isolation and strong phenotypic differentiation are characteristics of many but not all lineages, and so are best treated as secondary properties of species. Furthermore, ecology is no longer considered as merely a backdrop, but rather as an essential component of the emergence, life history and extinction of species of all kinds (Miller, 2005).
Further, many operational concepts seem to be homing in on essentially the same ontological target—something like G. G. Simpson’s Evolutionary Species Concept (1961: 153), or at least an ultimate picture of species that encapsulates both the genetic autonomy criterion and the fact that species are historical, hierarchical entities..." (Lieberman, Miller and Eldredge. 2007. Paleontological patterns, macroecological dynamics and the evolutionary process. Evol. Biol. 34: 34 PDF)
Discoveries of cryptic species of African mammals, especially bats, and the routine challenges of trying to identify bats in the hand (doing ecological and life history research) impressed upon me the critical importance of articulating what species concept one employs in doing science. Unfortunately, too few scientists even mention their stance of how they classify biodiversity (even though this stance can usually be inferred from the nature of their decisions, subjective and other). This is the appropriate place to dispose of a subspecies concept in taxonomy. Equally, the notions of the ESU, and any other phylogeographical concept of species' substructures, offer no improvement over the time-honoured, albeit obsolescent, concept of the subspecies category (Cotterill 2001a-f, 2002, 2003a). The majority of fish taxonomists and herpetologists appear to have moved on from the subspecies concept, with healthy consequnces for their science. Major challenges remain to be overcome if we are to define an ontological explanation for the subspecies category that bears even a modicum of application to biotic reality (Cotterill 2003a,b, 2005).
Ornithology and mammalogy persist in applying the Biological Species Concept (BSC) or Morphospecies concept (MSC) with unfortunate repercussions on the veracity of a great deal of published knowledge (Cotterill 2004, 2006). So much the worse for the credibility of any publications that report data about species diversity that has been parsed through biologically unrealistic filters. These unfortunate consequences of applying the BSC or MSC manifest when we try and reconstruct biogeographical narratives, such as how vertebrates have evolved in relation to formative events in landscapes (Cotterill 2003a-c, 2005). These deficiencies of the BSC (and also undisciplined application of the PSC) highlights the foibles of Operationalism (Hull 1968), which emphasizes the criticality of distinguishing the ontology of the species category from the discovery operations in which we engage to discern species boundaries.
An intimate exposure to the challenges of cryptic speciation in African bats has aided and abetted publications on Natural History and Natural Science Collections. It has especially reinforced an appreciation for the critical role of the tentelic properties of voucher specimens in the epistemology of the life sciences. These factors become really critical when faced by subtle differences between cryptic species, whose evolution has profound impacts on how one resolves not only biogeographical processes and patterns (exemplified in some Large Mammals), but more especially deciphers the palaeo-environmental context of speciation. Aetiological aspects of these facets of a species' history have a great deal to do with Landscape Evolution.
Most recent contributions are in response to criticisms of Ungulate Taxonomy by Groves and Grubb. See these papers that responded to others in debates in Hystrix and Mammalian Biology and Systematic Biology:
- Gippoliti S. Cotterill F.P.D. Zinner D. & Groves C.P. 2018. Impacts of taxonomic inertia for the conservation of African ungulate diversity: an overview. Biological Reviews 93: 115–130. doi: 10.1111/brv.12335 PDF
- Cotterill F.P.D., C.P. Groves & P.J. Taylor 2017. Taxonomy: refine rather than stabilize. Nature 547: 13. PDF
- Groves C.P. Cotterill F.P.D. Gippoliti S. Jan Robovský J. Roos C. Taylor P.J. & Zinner D. 2017. Species definitions and conservation: a review and case studies from African mammals. Conservation Genetics 18:1247–1256. DOI 10.1007/s10592-017-0976-0 PDF
- Cotterill, F.P.D., P.J. Taylor, S. Gippoliti, J.M. Bishop, C. P. Groves. 2014. Why One Century of Phenetics is enough: response to ‘are there really twice as many bovid species as we thought?’ Systematic Biology 63(5): 819–832. doi: 10.1093/sysbio/syu003 PDF
- Gippoliti, S., F.P.D. Cotterill & C. Groves. 2013. Mammal taxonomy without taxonomists: a reply to Zachos and Lovari. Hystrix, Italian Journal of Mammalogy 24: 3-5. doi:10.4404/hystrix-24.1-8881 PDF
The Solution to the Species Problem
ʺOnly the ESC is acceptable as a guide to discovering diversity referable to biological species as Individuals; all other concepts require a predetermined type of divergence or process.ʺ R. D. Mayden (2002: 181)
The benefits of studying incidents of cryptic speciation has lent valuable support to the only realistic solution to the species problem, in research that faces complex challenges in characterising biodiversity (pertinently when evaluating the status of allopatric populations). In these cases, one applies empirical evidence (whatever is available: morphological, behavioural, genetic) to test whether or not a vicariant population represents a lineage that has persisted as an isolate through evolutionary time. This research strategy employs a consilient solution under the framework of the ESC, applying operational species concepts (e.g a PSC or the RSC) as species criteria. The ingredients of this approach have been eloquently articulated by Adams, de Quieroz, Mayden, Miller and several other evolutionary biologists (Cotterill 2002, 2003a,b). see References below
ʺ...the operational point of view depends for what success it does have on the very element of science which it is designed to eliminate. Operationism was intended as a cathartic to purge physics of all non-empirical wastes, but it proved to be so strong that the viscera were eliminated as well.ʺ D. L. Hull (1968: 440, italics his)
Publications and Pertinent References
Adams, B. J. (2001) The species delimitation uncertainty principle. J. Nematol. 33: 153-160.
Adams, B. J. (1998) Species concepts and the evolutionary paradigm in modern nematology. J. Nematol. 30:1-21.
Brooks, D. R. & D. A. McLennan (1999) Species: turning a conundrum into a research program. J. Nematol. 31:117-133.
Cotterill, F.P.D., P.J. Taylor, S. Gippoliti, J.M. Bishop, C. P. Groves. 2013. Why One Century of Phenetics is enough: response to ‘are there really twice as many bovid species as we thought?’Systematic Biology doi: 10.1093/sysbio/syu003 PDF
Cotterill, F. P. D. 2006. Taxonomy and conservation importance of particular birds occurring in Katanga (southern Congo basin) and its environs. The Ostrich 77: 1-21. PDF
Cotterill, F. P. D. 2005. The Upemba lechwe: an antelope new to science emphasizes the conservation importance of Katanga, Democratic Republic of Congo. Journal of Zoology, London 265: 113-132 PDF
Cotterill, F. P. D. 2004. Drainage evolution in south-central Africa and vicariant speciation in swamp-dwelling weaver birds and swamp flycatchers. The Honeyguide. 50: 7-25. [in Silver Anniversary Issue] PDF
Broadley, D. G. & Cotterill, F. P. D. 2004. The reptiles of southeast Katanga, an overlooked 'hot spot'. African Journal of Herpetology 53: 35-61. PDF
Cotterill, F. P. D. 2003a. Species concepts and the real diversity of antelopes. In: A. Plowman. (Ed.) Proceedings of the Ecology and Conservation of Mini-antelope: An International Symposium on Duiker and Dwarf Antelope in Africa. Filander Verlag: Füürth. pp. 59-118. PDF
Cotterill, F. P. D. 2003b. Insights into the taxonomy of tsessebe antelopes, Damaliscus lunatus (Bovidae: Alcelaphini) in south-central Africa: with the description of a new evolutionary species. Durban Museum Novitates 29: 11-30. PDF
Cotterill, F. P. D. 2003b. Geomorphological influences on vicariant evolution in some African mammals in the Zambezi basin: some lessons for conservation. In: A. Plowman. (Ed.) Ecology and Conservation of Small Antelope. Proceedings of an International Symposium on Duiker and Dwarf Antelope in Africa. Filander Verlag, Fürth. pp 11-58. PDF
Cotterill, F. P. D. 2002a. A new species of horseshoe bat (Microchiroptera: Rhinolophidae) from south-central Africa: with comments on its affinities and evolution, and the characterization of rhinolophid species. Journal of Zoology, London 256: 165-179. PDF
Cotterill, F. P. D. 2002b. Notes on mammal collections and biodiversity conservation in the Ikelenge Pedicle, Mwinilunga District, northwest Zambia. Occasional Publications in Biodiversity No. 10: 1-18. Bulawayo: Biodiversity Foundation for Africa. PDF
Cotterill, F. P. D. 2001a. New specimens of lesser house bats (Vespertilionidae: Scotoecus) from Mozambique and Zambia. Arnoldia Zimbabwe 10(20):219-224. PDF
Cotterill, F. P. D. 2001b. The first specimen of Thomas's flat-headed bat, Mimetillus moloneyi thomasi (Microchiroptera: Mammalia) in southern Africa from Mozambique. Arnoldia Zimbabwe 10(19):211-218. PDF
Cotterill, F. P. D. 2001c. Further notes on large Afrotropical free-tailed bats of the genus Tadarida (Molossidae: Mammalia). Arnoldia Zimbabwe 10(18):199-210. PDF
Cotterill, F. P. D. 2001d. New distribution records of leaf-nosed bats (Microchiroptera: Hipposideridae) in Zimbabwe. Arnoldia Zimbabwe 10(17):189-198. PDF
Cotterill, F. P. D. 2001e. New records for two species of fruit bats (Megachiroptera: Mammalia) in southeast Africa, with taxonomic comments. Durban Museum Novitates 26:53-56. PDF
Ghiselin, M. T. 2002. Species concepts: the basis for controversy and reconciliation. Fish and Fisheries 3: 151-160. PDF
Gippoliti, S., F.P.D. Cotterill & C. Groves. 2013. Mammal taxonomy without taxonomists: a reply to Zachos and Lovari. Hystrix, Italian Journal of Mammalogy 24: 3-5. doi:10.4404/hystrix-24.1-8881 PDF
Hull, D. L. 1968 The operational imperative: sense and nonsense in operationism. Syst. Zool. 17: 438-457.
Lieberman, D., W. Miller and N. Eldredge. 2007. Paleontological patterns, macroecological dynamics and the evolutionary process. Evol. Biol. 34: 28-48. PDF)
Mayden, R. J. 1999. Consilience and a hierarchy of species concepts: advances towards closure on the species puzzle. J. Nematol. 31:95-116.
Mayden, R. L. 1997. A hierarchy of species concepts: the denouement in the saga of the species problem. In: M. F. Claridge, H. A Dawah & M. R. Wilson (eds). Species: the Units of Biodiversity. Chapman & Hall, London. pp 381-424.
Mayden, R. L. 2002. On biological species, species concepts and individuation in the natural world. Fish and Fisheries 3: 171-196.
Miller, W. 2001. The structure of species, outcomes of speciation and the 'species problem': ideas for paleobiology. Palaeogeography Palaeoclimatology Palaeoecology 176: 1-10.
Miller, W. 2006. What every paleontologist should know about species: new concepts and questions. N. Jb. Geol. Palaont. Mh. 2006 (9): 557-576.