UNIT 3

• Biological Species Concept

  Reproductive isolation (species don't interact with species outside their area)
• Biological Species Concept

  • No gene flow or hybridization
• Prezygotic Isolation

  • Temporal
  • Habitat
  • Behavioral
  • Gametic barrier
  • Mechanical
• Postzygotic Isolation

  Hybrid offspring of parents from different species is not able to reproduce
• Postzygotic Isolation

  • Hybrid viability: offspring don't develop and die as offspring
  • Hybrid sterility: offspring mature but are sterile as adults
• Phylogenetic Species Concept

  Monophyly (groups of taxa that contain all known descendants of a common ancestor)
• Phylogenetic Species Concept

  Species is defined by statistically significant differences in diagnostic traits (genetic or physical) among populations
• Morphological Species Concept

  Morphology (shape)
• Speciation

  • Isolation of populations
  • Dispersal and colonization
  • Vicariance: splitting of a population into isolated ranges
  • Genetic isolation: changes in chromosomes
  • Sympatric speciation: populations occupy the same location but there can be local differences
• Divergence between populations

  • Allopatry: populations occupy different locations
  • Sympatry: populations occupy the same location
• Reproductive isolation of populations

  • Selection against gene flow
  • Hybridization reduces fitness - selection for assortative mating
  • Reinforcement: selection that reduces the likelihood of hybridization
• Extirpation

  A local loss of species (populations may exist in other locations)
• Extinction

  A complete loss of species (leads to biodiversity, speciation, extinction)
• Background extinction

  The average rate of species loss over time
• Mass extinction

  The loss of a large number of species in a short amount of time
• Characteristics of mass extinctions: Defined by particular characters, Global in extent, Involved a broad range of organisms, Rapid effect relative to the expected lifespan of taxa
• 1. P Mass Extinction

  65 million years ago, Caused by a meteorite impact, Wiped out 75% of marine species and 50% of genera
• Short term impacts of K-P Mass Extinction

  • Cooling and darkening
  • Generation of SO2 and acid rain
  • Dust clouds
  • Widespread fires
• Long term impacts of K-P Mass Extinction

  • Increased CO2 leads to warming
  • Force of impact: massive earthquakes
• Evolutionary implications of mass extinctions: Many lineages lost, Less diverse habitats, Less affected lineages, More diverse habitats
• Species-Area Curve

  Species with smaller geographic ranges are more at risk of extinction
• Drivers of human-induced extinction

  • Human population growth
  • Per capita consumption
• Biogeography

  Global distributions of lineages and diversity
• Alfred Russel Wallace: the "father of biogeography", Traveled the world documenting species distributions, supported through collections
• Biogeographic regions

  Six regions corresponding to the six major tectonic plates
• Factors determining the geographical distribution of a given clade (Weins and Donoghue 2004)

  • The ancestral ecological niche of the clade
  • The geographical starting point for dispersal
  • Limitations to this dispersal imposed by abiotic conditions and other species
  • Opportunities for niche evolution that are afforded to individual species by their geographical location
  • The amount of time since the origin of the clade, during which niche evolution and dispersal could occur
• Why are there more species in the tropics? Tropics occurred over large extents so more clades originated in the tropics, Many clades and species are specialized for the tropical niche
• Carrying capacity

  The amount of individuals that can survive with a given amount of resources
• Net reproductive rate (R0)

  R0 < 1: decreasing population, R0 = 1: stable population, R0 > 1: increasing population
• Intrinsic rate of growth (r)

  r < 1: decreasing population, r = 1: stable population, r > 1: increasing population
• Capture-Mark-Release-Recapture

  Method to estimate population size
• Metapopulations

  Organisms live in a semi-connected network of subpopulations
• Types of population distributions

  • Random
  • Clumped
  • Uniform
• Spatial scale affects population distribution: Small spatial extent - uniform distribution, Large spatial extent - clumped distribution
• Density

  Population size divided by range
• Allee effect

  High population density can improve the survival rate of individuals
• Wolves make roadways safer because they control the population of deer
• Problems with Biological Species Concept


  Can only be studied experimentally, Can't be tested in fossils, Does not apply to asexual, pathogenic species
• Problems with Phylogenetic Species Concept


  Not many "good" phylogenies, Are seemingly trivial diagnostic traits biologically meaningful?, Could cause the number of described species to more than double
• Problem with Morphological Species Concept

  Is useful for fossils but can be misleading - individuals with similar forms can be different