Allopatric Speciation

• Biological Species Concept

  Genetically isolated group with its own gene pool
• Speciation 


  Formation of new species - the process of 1 species splitting into 2 or more species
• Adaptive Radiation 


  The process where a species rapidly diversifies from an ancestral species to form new species with differing adaptations
• Reproductive Isolation 


  When a single population becomes 2 separate populations that are unable to interbreed due to physical, biological, or bahvioural habits
• Morphological Species Concept

  Defines a species by structural features - individuals of the same species are morphologically similar
• Isolating Mechanisms 


  A mechanism that separates 2 groups, preventing them from mating or producing viable/fertile offspring

  • these mechanisms can operate before or after reproduction
  • the organisms become so genetically different that they form 2 new species - they can then no longer interbreed, even if the populations come back together
• Pre-Reproductive Isolating Mechanisms 


  Biological or ecological mechanisms that prevent organisms from being able to interact to reproduce

  • temporal (time) mechanisms: individuals breed during different seasons or times
  • behavioural mechanisms: individuals have different mating patterns
  • morphological mechanisms: individuals have different reproductive structures
• Post-Reproductive Isolating Mechanisms

  Don't prevent mating but prevent young from being produced

  • gamete mortality: gametes don't survive
  • zygote mortality: zygote forms but doesn't survive
  • hybrid mortality: adult offspring are formed but are infertile, usually because they've received a different number or type of chromosome from each species
• Micro-evolution

  • a change in the frequency of various alleles within a population
  • change below the species level
  • small-scale changes in the gene pool of a population due to the mechanisms of evolution
• Macro-evolution

  • changes in allele frequency in more than 1 population/species
  • major evolutionary changes above the species level
  • large-scale changes resulting from an accumulation of micro-evolutionary changes over many generations
• Allopatric Speciation

  • gene flow is disrupted when populations become physically separated through geological isolation
  • populations diverge - may be due to different selection pressures acting on the 2 populations, or due to other random processes such as genetic drift
  • physical barriers that can separate a sub-population from its original population: water (lakes, rivers), land, mountains
  • new physical barriers can arise: continental drift, rising sea levels, climate change)
• Step: Variation 


  A range of alleles are available in a single population
• Step: Isolation

  • geographical isolation (allopatric) - physical barriers (rivers, mountains etc.)
  • gene pool splits - subpopulations form
  • no gene flow between the 2 separate populations
• Step: Selection Pressures

  • different selection pressures cause changes to gene pools
  • micro-evolutionary changes create small differences
  • predation, competition, disease
  • there are more members in the population than the environment can support
• Step: Survive

  • increase in frequency of favourable alleles
  • individuals with favourable alleles survive in higher numbers
• Step: Reproduce

  • higher frequency of favourable alleles
  • pass on alleles in higher proportion
• Step: Change in Allele Frequency

  • decreases variation
  • differences in the gene pool prevent gene flow even when they're united
• Step: Speciation

  • 2 different species are formed
  • only occurs if they don't mix too soon
  • can't interbreed to produce fertile offspring
• Allopatric Speciation Steps

  1. Variation
  2. Isolation
  3. Selection Pressures
  4. Survive
  5. Reproduce
  6. Change in Allele Frequency
  7. Speciation