Species Concepts

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Species Concepts

• Species Concept an idea about the kind of
  entity represented by the term SPECIES.
• Some concepts recognize the special reality of
  species (entities that exist independent of the
  investigator).
• Other concepts consider species to be classes of
  objects that exist because of the way that they
  are defined by an investigator.
• Species criteria standards for deciding whether
  or not a particular entity is a species.
• range of operationalism

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Morphological Species Concept

• Operationalism morphological discontinuities
  among assemblages of similar organisms.

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Species defined by a species concept Species
diagnosed by unique differences
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Species level lineages
Biparental organisms Organisms are united to form
species-level lineages by the process of
reproduction
Uniparental organisms Constant divergence because
lineages are not linked together by reproduction
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• The Biological Species Concept
• Ernst Mayr 1942, 1963. Animal Species and
  Evolution.
• Species are groups of actually or potentially
  interbreeding natural populations that are
  reproductively isolated from other such groups.
• Species ranking criterion absence of
  interbreeding
• Ancestral population may persist after
  speciation.
• This concept used to make decisions re the
  Endangered Species Act and many other important
  issues.
• Two obvious problems
• 1. Similar but divergent allopatric populations.
• 2. Asexuals and uniparental groups.

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• Morphological differences and similarities may
  not be effective in distinguishing species under
  this concept.
• 1. Individual variation (e.g., ontological
  variation)
• 2. Geographic variation
• 3. How much hybridization is permitted?
• 4. Cryptic species

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Problem 1 Ontological variation
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Problem 2 Geographic variation
Aspidoscelis tigris Clinal variation in
southern Arizona
South-central AZ
Southwest AZ
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Problem 3 How much hybridization is permitted?
Discordant hybridization
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Is there presently such a thing as a Red wolf?
Readily hybridizes How much should be allocated
to its survival?
The red wolf problem
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A. tigris punctilinealis and A. tigris marmorata
OR A. tigris and A. marmorata?
3. One species or two?
Fertile hybrids
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The hybridization zone SW New Mexico
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Three concordant step-clines
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uniparens
velox
Aspidoscelis velox (3n, parthenogenetic) 1. A.
gularis stictogramma ? x A. inornata ? 2. F1
diploid parthenogenetric ? x A. inornata ?
Problem 4 Cryptic species
Aspidoscelis uniparens (3n, parthenogenetic) 1.
A. inornata ? x A. gularis stictogramma ? 2. F1
diploid parthenogenetic ? x A. inornata ?
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• Barriers to interspecific hybridization
• Reproductive isolating mechanisms
• A. Prereproductive (favored by natural selection)
• 1. Ecological
• Temporal (phenological)
• Habitat segregation
• 2. Behavioral
• 3. Mechanical
• B. Postreproductive
• Gametic wastage
• Other species concepts

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• Phylogenetic Species Concept(s)
• The smallest aggregation of individuals
  diagnosable by a unique combination of character
  states.
• Characters and character states
• Organisms are grouped into species because of
  evidence of monophyly.
• Monophyletic group a group that contains all
  known descendants of a common ancestor

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• Monophyletic relationships
• 1. a branching pattern of divergence
• 2. ancestral and derived character states of
  characters determined
• 3. pattern of shared derived character states
  used to construct the tree
• 4. ancestral populations do not persist past a
  speciation event.

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• The Evolutionary Species Concept
• E. O. Wiley. 1978,1981, 2001.
• A species is an entity composed of organisms
• maintaining its identity from other such entities
  through time and space
• and having its own independent evolutionary fate
  and historical tendencies.
• Operationalism absent
• Use fixed diagnostic differences