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Species

 

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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)

Re-evaluating prokaryotic species    

From Nature Reviews on prokaryotic specues                                       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

 

 Ranges of the Ensatina subspecies      

 

 

 

 

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  Creative Commons License