species concepts species concept: an idea of what kind of entity is represented by the word species....
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Species Concepts• Species Concept: An idea of what kind of entity is
represented by the word SPECIES.
• There are several concepts recognizing the special reality of species (entities that exist independent of definition).
• To be avoided: concepts considering species as classes of objects (entities that exist by definition).
• Species criteria = standards used for species recognition = operationalism.
• Most non-biologists recognize non-dimensional species.
Species defined by a species conceptSpecies diagnosed by unique differences
Holbrookia maculataCophosaurus texanusCallisaurus draconoides
Species levellineages
Biparental organismsOrganisms are unitedto form species-levellineages by sexualreproduction
Uniparental organismsConstant divergencebecause lineages arenot linked togetherby reproduction
Group held together byecological adaptations
• 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.
• Most widely used concept
• Used to make decisions re the Endangered Species Act, in anthropology, and many other biodiversity issues.
• Why don’t species interbreed?
BSC: isolating mechanisms (barriers)• Premating mechanisms (barriers): favored by selection
• A. Potential mates do not meet– Ecological mechanisms
– Temporal; habitat; for plants--species specific pollinators
• B. Potential mates meet but do not mate– Behavioral isolation
• Postmating mechanisms
• C. Potential mates meet and mate– Prezygotic isolation
• Gametic incompatibility
– Postzygotic isolation
– Developmental problems
– Reduced hybrid fitness (sterility, lower viability, etc.)
Aspidoscelis burti stictogramma A. burti burti
Problems with allopatry
• Problems with morphological characters• Morphological differences 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
Problem 1: Ontological variation Aspidoscelis stictogramma
A. tigris punctilinealis and A. tigris marmorata ORA. tigris and A. marmorata?
Problem 2. Geographic variation
Fertilehybrids
The hybridization zone: SW New Mexico
Problem 3: hybridization or intergradationHow much is permitted under the BSC?
Three concordantstep-clines
• 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
Aspidoscelis velox (3n, parthenogenetic)
1. A. gularis stictogramma ♀ x A. inornata ♂ 2. F1 diploid parthenogenetric ♀ x A. inornata ♂
Aspidoscelis uniparens (3n, parthenogenetic)
1. A. inornata ♀ x A. gularis stictogramma ♂ 2. F1 diploid parthenogenetic ♀ x A. inornata ♂
Problem 4: Cryptic species
velox
uniparens
• Phylogenetic Species Concept(s)
• Phylogenetic species: the smallest aggregation of individuals diagnosable by a unique combination of character states.
• Characters and character states• Organisms are grouped into species because of shared
derived character states (SDC).• SDC states inherited from a common ancestor• Ancestors and derived species form a branching pattern of
divergence• Ancestral populations typically do not (by definition)
persist past a speciation event.
• 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