Science 7th Grade - Mr. Hankins

Study Section 3 of Chapter 22 - Biogeography (see study notes posted below)

Biogeography - The study of where organisms live (bio=life, geo=earth, graphy=description of)

Key terms:
Biogeography:    The study of where organisms live
Continental drift:    The very slow motion of continents
Dispersal:        The movement of organisms from one place to another
Exotic species:    An organism that is carried into a new location by people
Climate:        The typical weather pattern in an area over a long period of time    


Key points:

Continental drift:

• Drift (a slow or gradual movement or change from one place to another)
  
• What led to worldwide distribution of species?
  
• One factor is continental drift.
  
• Continents are part of huge blocks of solid rock, called plates, that make up Earth’s surface.
  
• These plates move very slowly over millions of years… or “drift” over time.
  
• The continents used to be part of one land mass called the Pangea (approx 225 million years ago).
  
• Over millions of years, the land masses drifted apart. Therefore, species in one location were separated by oceans of space.
  

Dispersal:

• Caused by three things:
  

1. Wind
   
2. Water
   
3. Living things
   

• Many animals move into new areas on their own, but plants and small animals need assistance.
  
• Wind can disperse seeds, the spores (a cell made by some plants that is like a seed and can produce a new plant) of fungi, insects, and other small light organisms.
  
• Water transports objects that float, such as coconuts, branches and leaves. This acts as boats or rafts for dispersal.
  
• Living things can act as dispersal agents (a person or thing that causes something to happen) for other organisms. I.e., a bird eats berries in one area and deposit the seed via it’s waste in another area.
  
• Humans can act as dispersal agents either intentionally or unintentionally. Ie., when humans bring corn or tomato plants to another area. Or “exotic” insects or mammals are carried unintentionally on human transportation vehicles.
  

Limits to Dispersal:

• Three factors:
  

1. Physical Barriers:    ie, water, mountains, and deserts. They are hard to cross and limit movement.
   
2. Competition:        a new species must compete with existing species in their new area. They must find their niche. In some cases, the species can’t coexist and one species become extinct or displaced.
   
3. Climate:        the weather of an area (see figure 12 on page 755) can limit dispersal. Ie. certain organisms can exist in cold and windy climates. Other organisms cannot disperse to these areas because they can’t exist in the climate.