Species Concepts

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.

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Species concepts do matterSpecies concepts do matter

i. the specific status of diagnosable populations;

ii. estimates of species diversity;iii. the historical analysis of these

unitsiv. an understanding of patterns of

gene flow within and among these units;

v. delineation of areas of endemism;

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

Key questions to be answered

How to define species?

How to decide between species concepts?

Do species really exist?

Present day species concepts

The pre-Darwinian species concept (cf. Linnaeus) was essentialistic

Number of species concepts in use today

24 species concepts

i. Agamospecies Concept;ii. Biological Species Conceptiii. Cladistic Species Conceptiv. Cohesion Species Conceptv. Composite Species Conceptvi. Ecological Species Conceptvii. Evolutionary Significant Unitviii. Evolutionary Species Conceptix. Genealogical Concordance Conceptx. Genetic Species Conceptxi. Genotypic Cluster Conceptxii. Hennigian Species Conceptxiii. Internodal Species Conceptxiv. Morphological Species Concept

xv. Non-dimensional Species Conceptxvi. Phenetic Species Conceptxvii. Phylogenetic Species Concept

(Diagnosable version)xviii. Phylogenetic species concept

(Monophyly version)xix. Phylogenetic Species Concept

(Diagnosable and monophyly version)xx. Polythetic Species Conceptxxi. Recognition Species Conceptxxii. Reproductive Competion Conceptxxiii. Succesional Species Conceptxxiv. Taxonomic Species Concept

Similarity ConceptsOverall similarity and/or gaps in character distributions(<MorphSC, PhenotSC, TaxSC,...)

Evolutionary ConceptsTheoretical commitment to evolutionary theory(BioSC, EcolSC, EvolSC, RecogSC, CohSC,...)

Phylogenetic ConceptsCommitment to phylogenetics(<CladSC,PhyloSC, HennigSC,...)

Three main breeds of species concepts

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

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 keySpecies concepts have theoretical and/or practical strengths and weaknesses

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)

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

The The phylogenetic phylogenetic

species species conceptconcept

Speciation and phylogenetic relationships

Dispersal + subsequent character change Vicariance

Sympatric

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!

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.

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.

Higher taxon reality

If a genus is just a mono-phyletic group larger thana species and smaller thana family, we can determineif such groups exist.

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.

“Damn your principles, stick to your party”

Benjam Disraeli (1804-1881)