There are many different concepts of what constitutes a species. These concepts include biological, ecological, evolutionary, and phylogenetic species concepts. There is no universal agreement on how to define species. Determining whether species are real, and delineating species boundaries accurately is challenging given the various concepts and lack of consensus on an approach. Higher taxa concepts are also debated in terms of their philosophical reality.

1. Species Concepts

2. Species concepts do matter Endangered Species estimating biodiversity Using different species concepts __comparing apples with oranges; higher taxa are generally not comparable; species should be as they are generally considerd as the units of conservation.

3. Species concepts do matter the specific status of diagnosable populations; estimates of species diversity; the historical analysis of these units an understanding of patterns of gene flow within and among these units; delineation of areas of endemism;

4. There is a need to universally: identify real species understand real species

5. Key questions to be answered How to define species? How to decide between species concepts? Do species really exist?

6. Present day species concepts The pre-Darwinian species concept (cf. Linnaeus) was essentialistic Number of species concepts in use today 24 species concepts Agamospecies Concept; Biological Species Concept Cladistic Species Concept Cohesion Species Concept Composite Species Concept Ecological Species Concept Evolutionary Significant Unit Evolutionary Species Concept Genealogical Concordance Concept Genetic Species Concept Genotypic Cluster Concept Hennigian Species Concept Internodal Species Concept Morphological Species Concept Non-dimensional Species Concept Phenetic Species Concept Phylogenetic Species Concept (Diagnosable version) Phylogenetic species concept (Monophyly version) Phylogenetic Species Concept (Diagnosable and monophyly version) Polythetic Species Concept Recognition Species Concept Reproductive Competion Concept Succesional Species Concept Taxonomic Species Concept

7. Similarity Concepts Overall similarity and/or gaps in character distributions (<MorphSC, PhenotSC, TaxSC,...) Evolutionary Concepts Theoretical commitment to evolutionary theory (BioSC, EcolSC, EvolSC, RecogSC, CohSC,...) Phylogenetic Concepts Commitment to phylogenetics (<CladSC,PhyloSC, HennigSC,...) Three main breeds of species concepts

8. Some Definitions Biological species A group of interbreeding natural populations that do successfully mate or reproduce with other such groups The smallest group of cohesive individuals that share intrinsic cohesive mechanisms (e.g. interbreeding ability, niche) A lineage which occupies an adaptive zone. Ecological species concept defines a species as a group of organisms that share a distinct ecological niche. A single lineage of ancestor-descendant populations which is distinct from other such lineages and which has its own evolutionary tendencies and historical fate Cohesion species Ecological species Evolutionary species

10. Some Definitions Morphological species The smallest natural populations permanently seperated from each other by a distinct discontinuity in heritable characteristics (e.g. morphology, behavior, biochemistry) The smallest group of organisms that is diagnostically distinct from other such clusters and within which there is parental pattern of ancestry and descent A group of organisms that recognize each other for the purpose of mating and fertilization Phylogenetic species Recognition species Species definitions are made ad hoc and thus adopting a pluralistic attitude is key Species concepts have theoretical and/or practical strengths and weaknesses

11. Biological species Cohesion species Ecological species Evolutionary species Cohesion is difficult to recognize, prezygotic and postzygotic isolating mechanisms are mostly unknown Species concept Practical application Strengths / weaknesses Difficult Difficult Difficult Difficult Popular, explains why the members of a species resemble one another and differ from other species (shared gene pool + reproductive isolation). Irrelevant to fossils, asexual organisms, complicated by natural hybridization, polyploidy, etc. Adaptive zones/ Niches, difficult to define, assumes two species cannot occupy the same niche for even a short period (but what to do with life stages…) Criteria vague and difficult to observe (see also PSC)

12. Morphological species Phylogenetic species Recognition species Morphological criteria may not reflect actual links that hold organisms together into a natural unit; only possibility for paleontologists; but what with cryptic species? Will give rise to recognition of many more species than more traditional concepts; but from what point onwards do we conceive différences to be ‘statistically significant’? Determining if a feature is used to recognize potential mates is difficult or impossible in many populations (note that this concept has been succesfully demonstarted with amphibians, crickets,…) Species concept Practical application Strengths / weaknesses Common Increasing Difficult

13. The phylogenetic species concept Speciation and phylogenetic relationships Dispersal + subsequent character change Vicariance Sympatric

15. 1.7 to 1.9 million species described ___ At least 8 million species are yet to be discovered Most of our species knowledge comes from a single point in space and time__ ___ variability of Littel Concern J. Ray (1653): “Species are merely what competent naturalists says they are” ... We need more competent naturalists, and hence taxonomists!

16. The Species Category is Real? Suppose we go with the biological species concept , Then the species category is real insofar as organisms are actually divided up into sexually reproducing groups. If we looked into the world and saw only clonal, asexual lineages, we would conclude that the species category (so defined) is not real.

17. Higher taxon reality Are genera, families, etc., real? At the species level there are a number of competing concepualizations. At higher levels we have the opposite problem. We lack criteria to use in evaluating the question.

18. Higher taxon reality If a genus is just a mono- phyletic group larger than a species and smaller than a family, we can determine if such groups exist.

19. Cited works: R. Descartes, 1641. Meditationes de prima philosophia. Published by someone a really long time ago. M.T. Ghiselin, 1974. A radical solution to the species problem. Systematic Zoology, 23(4): 536-544. M. Pigliucci, 2003. Species as family resemblance concepts: the (dis-)solution of the species problem? BioEssays, 25(6): 596-602. F. Pleijel & M. Harlin, 2004. Phylogenetic nomenclature is compatible with diverse philosophical perspectives. Zoologica Scripta, 33(4): 587-591. L. Wittgenstein, 1921. Tractatus Logico-Philosophicus, trans. by D. Pears and B. McGuinness. London: Routledge & Kegan Paul.

20. “ Damn your principles, stick to your party” Benjam Disraeli (1804-1881)