(3) Unit 7 Topics 10 and 11 Packet

Unit 7: Speciation and Extinction

Definition of Species

• Species: A group of organisms that can interbreed and produce viable, fertile offspring.

  • Viable: Offspring must be living.

  • Fertile: Offspring are capable of producing their own offspring.

Importance of Speciation

• Speciation: The process through which new species arise, contributing to biodiversity.

  • Increased diversity strengthens ecosystems.

Geography and Speciation

• Two primary modes of speciation: Allopatric and Sympatric speciation.

Allopatric Speciation

• Occurs when a population is physically divided.

  • Physical barrier separates populations or a small population becomes isolated (founder effect).

  • Leads to geographic isolation and prevents gene flow.

  • Often triggered by natural disasters causing separation.

Sympatric Speciation

• New species evolve while sharing the same geographic area.

  • Often due to the exploitation of new niches.

  • Example: A finch with a wider beak that can eat larger fruits, leading to a new species.

Reproductive Isolation and Speciation

• Prevents gene flow, essential for speciation.

Types of Reproductive Isolation

1. Prezygotic Barriers: Prevent mating or fertilization before a zygote can form.

   • Types:

     • Habitat Isolation: Species live in different habitats but share the same area.

       • Example: Eastern Bluebird and Mountain Bluebird occupy different elevations.

     • Temporal Isolation: Species breed at different times.

       • Example: Western and Eastern Spotted Skunks breed in different seasons.

     • Behavioral Isolation: Unique behaviors prevent mating.

       • Example: Blue-footed Booby requires specific courtship rituals.

     • Mechanical Isolation: Anatomical differences prevent successful mating.

       • Example: Snails with differently spiraled shells.

     • Gametic Isolation: Sperm and egg of different species can't fuse.

       • Example: Red and purple sea urchins have incompatible proteins.

2. Postzygotic Barriers: Prevent hybrid zygotes from developing into viable, fertile adults.

   • Types:

     • Reduced Hybrid Viability: Hybrid embryos may not develop properly.

       • Example: Domestic sheep and goats can mate, but embryos often die early.

     • Reduced Hybrid Fertility: Hybrids may be sterile.

       • Example: Mules, offspring of horses and donkeys, are sterile.

     • Hybrid Breakdown: Hybrids may be fertile, but their offspring are not.

       • Example: Hybridization in crops may lead to sterile offspring in later generations.

Microevolution vs. Macroevolution

• Microevolution: Changes in allele frequencies within a population.

  • Influenced by natural and sexual selection, genetic drift, and gene flow.

• Macroevolution: Large-scale evolutionary changes over time, including patterns like adaptive radiation and mass extinctions.

• Stasis: Periods of no change, can precede rapid evolution after accumulating genetic changes.

Pace of Evolution

• Punctuated Equilibrium: Rapid evolution occurs after long periods of stasis.

• Gradualism: Evolution occurs slowly over extended periods of time.

Types of Evolution

• Divergent Evolution: Groups with a common ancestor evolve differences to form new species.

• Convergent Evolution: Different species develop similar traits despite having different ancestors (analogous traits).

Extinction

• Extinction: The termination of a species.

  • Five mass extinctions have occurred; a sixth is currently ongoing due to human activity leading to biodiversity loss.

  • Ecological stress from humans affects extinction rates but can lead to new niches being available for exploitation and potentially lead to sympatric speciation.