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Species

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• What is a Species?

  • "Proto-Cell," Cell, Organism, Population all easily defined.  But what is a species?

  • Biological Species Concepts--reproductive isolation pre-zygotic or post-zygotic

  • Taxonomic Species

  • Morphological Species

  • Genetic/Sequence Species

• How does speciation happen?

  • allopatric speciation--geographic separation

  • sympatric speciation--separation by time, behavior, chromosomes

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What is a Species?

SPECIES IN THE HIERARCHY OF LIFE

"Proto-Cell" was a self-organizing, replicating molecular system--will we ever see one?  Would we recognize it if we did?

Cells are easily understandable and prokaryotic/eukaryotic organization clearly distinct

An organism is an assemblage of cells that undergo a life cycle, with some cells forming "somatic" non-reproducing structures, and others forming the germline that does reproduce

Populations are groups of similar cells or organisms that live close by and share genes

But a species is harder to define, although easily recognizable as a distinct entity, at least usually (folk versus scientific taxonomies usually agree about species or distinct entities)

SPECIES CONCEPTS

The Biological Species Concept (BSC)---probably most commonly used:  "a population of organisms that can interbreed to produce viable and fertile offspring."

Ernst Mayr---famous evolutionist from "Modern Synthesis" era, created and promoted BSC--great article from him about species concepts 

OTHER SPECIES CONCEPTS

Morphological or Phenotypic--species are like other taxonomic groups--can be distinguished by appearance (almost always used for fossils)

Genetic--a certain genetic distance is considered a new species (often used for prokaryotes and micro-organisms)

From Nature Reviews on prokaryotic species                                       from article in Genetics

Evolutionary/Taxonomic--a species is a new interbreeding population that appears in time after isolation from a previously existing species

How does speciation occur (of course depends on your species concept!)

The most famous ring species of all--Ensatina eschscholtzii    Dave Wake article on Ensatina

GEOGRAPHIC ISOLATION--ALLOPATRIC SPECIATION

NO GEOGRAPHIC ISOLATION--SYMPATRIC SPECIATION--the great Cichlid example

Article on genetics of Lake Malawi cichlids 

Short report article on "ecological speciation" for color in cichlids

Reasons for reproductive isolation in allopatry:  ecological niche division, sexual selection, temporal division (cicadas as example) 

Web Resources

Larry M Frolich, Ph.D.  ∞   Miami Dade College  ∞   Wolfson Campus   ∞   Natural Sciences   ∞   Miami, FL  33132  ∞  Office 1504   ∞  (305) 237-7589  ∞  e-mail