17.4 - Patterns of Evolution

• Extinction

  • More than 99% of all species that ever lived on Earth are now extinct
  • Several times in Earth's history where there has been mass extinctions that whipped out entire ecosystems
  • Each mass extinction left habitats open and provided ecological opportunities for those organisms that survived
• Adaptive Radiation (Divergent Evolution)

  • Occurs when a single species or small group of species has evolved through natural selection into diverse forms that live in different ways
  • Darwin's finches evolved from a single species
  • Diverge in response to types of food and different habitats
• Convergent Evolution

  • Some organisms look like they're related, but they're really not
  • Similar environments can make similar phenotypes more fit
  • Ex: sharks, penguins, and dolphins
  • They all have streamlined bodies and appendages that help them to move through water
• Coevolution

  • The change of two or more species in close association with each other
  • Predator and prey can coevolve
  • Parasites and host can coevolve
  • Can be beneficial o both organisms, as in bees and plants - the poisonous newt & garter snake
• Punctuated Equilibrium

  • Darwin believed that populations of organisms changed gradually over time (gradualism)
  • Punctuated equilibrium is a term used by scientists to describe a pattern of long, stable periods interrupted by brief periods or more rapid changes
  • Rapid evolution can occur for several reasons:
  • When a small population becomes isolated
  • Mass extinctions can open many ecological niches and provide new opportunities for the organisms that survive