Taxonomy, Speciation and Extinction

• Taxonomy: names organisms, assigns hierarchical relationships
  
• Populations: the individuals of a species in a (contiguous) area
  
• Cladogenesis: evolution and differentiation of species lineages
  
  • Gradualistic (FIG)
    
  • Punctuated (FIG)
    
  • Reticulate (FIG)
    

Species Concepts

Morphological Species: distinguishable from other species by its morphology
Biological Species: potentially isolated from interbreeding with other species (Mayr, 1963)

Biological Species Concept:

• Does not apply to fossil species
  
• Does not apply to asexual species
  
• Does not apply to many plants (hybridization)
  

Other Species Concepts

• Evolutionary Species: actually isolated from interbreeding
  A separate evolutionary lineage
  
• Phylogenetic Species: shared apomorphic (derived) characters that neither their ancestors nor other species have
  
• Polytypic "Species": distinct forms (color, behavior) that might interbreed snakes [r]
  
• Subspecies: populations within a species that are morphologically or genetically distinct Cassowary
• Ecotypes: morphologically distinct (plants) characteristic of a habitat Aradopsis

Macroevolution

• Species Selection: differential survival of species
• Punctuated Equilibrium: lineages undergo long periods of little morphological change (stasis) interspersed with brief intervals of rapid change (punctuation, speciation) (FIG) (text)
  
• Micro- vs. Macroevolution
  Microevolution: Natural Selection - differential survival due to inherited traits (individual selection)
  Macroevolution: differential survival of branches within lineages
  
  

  SCALE:
  Microevolution	individuals and populations	generations
  Macroevolution	species	evolutionary time scale

Speciation

Genetic Drift: random changes in the genetic composition of a population, important in small populations (< 100)
Founder effect: individuals colonizing an area are a subsample of the genetic diversity of the population (FIG) [+ r]

• Selection Pressure: over generations, gene frequency for traits favoring survival increase (FIG)
  
• Gene Flow: movement of genes in populations due to mating
  May act to homogenize genetic composition of species, preventing speciation
  Geographic variation barriers to gene flow determine pattern
  Cline: geographical variation of a trait along an environmental gradient [+ r]

• Vicariant Isolation: environmental change creates barrier to genetic exchange (FIG)
  
• Founder Events: [FIG] dispersal creates new population
• Results of Re-contact
  1. No Interbreeding (speciation complete)
     
  2. Interbreeding successful (populations merge) reticulate evolution (FIG)
     
  3. Interbreeding partially successful Reinforcement mechanisms continue speciation

• Disruptive Selection: strong, divergent selective pressures operating on population (FIG)
  
  Mate selection
  Primates: some in trees, some on ground
  Fish: some benthic others pelagic
  Doebeli & Dieckmann, Nature 421: 259-264 (2003)
  

Sympatric Speciation:

• Single mutation effecting reproduction
  Flower morphology, color influences pollinator
• Chromosomal Changes: greatly reduces production of fertile offspring when mated with parent population
  
  • inversion, translocation
    Disrupts meiosis and leads to Aneuploidy
  • Aneuploidy: change in chromosome number +/- one
    
  • Polyploidy: tetraploid hexaploid (Larrea)
    • Autopolyploidy: within a population
      
    • Allopolyploidy: hybridization of different species

• Ecological Diversification
  
  • Competitive Exclusion: similar species cannot coexist
    
  • Sibling (cryptic) species: reproductively isolated but ecologically equivalent
    
  • Character displacement: sibling species in contact have different morphologies (FIG)
    
  
  
• Adaptive Radiation: differentiation into multiple species in sympatric habitats or niches (FIG) [.] (Hawaiian Silversword

Extinction threshold

"The Evil Twin of Speciation"
Red Queen Hypothesis: "running as fast as we can to stay in place"


• Ecological Processes: habitat and population factors effecting likelihood of extinction
  
  • Competition: arrival of superior competitors (Pliocene Interchange)
    
  • Predators (parasites): may cause extinction if an alternate host supports population
    
    
• High Risk Groups: large carnivorous (more than small herbivorous mammals)
  

Extinction

Population Size K	Birth Rate b	Death Rate d	Time to Extinction yr E
1	0.35	0.00	2.9
2	0.35	1.63	6.9
3	0.35	2.44	46.2
4	0.35	2.84	405.1
5	0.35	3.15	3751.5

Recent Extinctions

• Over harvesting: passenger pigeon, Great auk, Carolina parakeet, Steller's sea cow
  
  
• Introduced pathogens: American chestnut, American Elm fig
  
  
• Destruction of Habitat
  Amazon Figs

Extinctions in the Fossil Record

• Background Extinction [FIG]
  
• Mass Extinction [FIG]
  • Cretaceous-Tertiary
    
  • Permo-Triassic
    
  Endangered Species
  • US Fish and Wildlife
  • Arizona
  • Recently Extinct Birds

• Process of Species Selection:
  strong selection pressure
  rapid environmental change
  
  
• Examples of Species Selection
  
  • Mesozoic diversification of Angiosperms
    
  • Cenozoic diversification of Mammals (FIG)
    
  • Mollusk larval distribution planktotrophic vs. nonplanktotrophic (FIG)
    
  • Bivalves vs. brachiopods (FIG)
    Other Families

Glossary of Phylogenetic Systematics

Grassland Types

Macroevolution: Speciation and Phylogenesis Illustrated Class Notes

Speciation of Ensatina eschscholtzi a lungless salamander

Southwest Biogeographic History

alien species