Biogeography: 

Biogeography: 

  • Biosphere is the whole are of earth’s surface
  • The biosphere is made up of the atmosphere (air), lithosphere (land), hydrosphere (water)
  • The process of drifting apart is known as continental drift; major factor in determining the current distribution of species
  • Biosphere can be divided into a number of biogeographical regions – continents and islands; inhabited by distinctive species of animals and plants –
  • Organisms can move freely from place to place within each region but not from one region to another
  • Terrestrial biogeographical regions include the Nearctic (North America); Eurasia (Palaearctic); South America (Neotropic); Africa (Afrotropic); Australian; Indomalayan; Oceanic and Antarctica
  • Biogeographical regions are related to land masses and not to climate


Diversity within each biogeographical region or continent: 

  • Each region has a large diversity of its own


Diversity between different biogeographical regions: 

  • Diversity between the land masses/ biogeographical regions more striking than the diversity of each region
  • Each region has a group of organisms that are more closely related to each other than to organisms in other biogeographical regions – because of local diversification by speciation/ the dispersal of species within a biogeographical region
  • Organisms in a region are descendants from the ancestors that were previously there


What is biogeography?

  • The study of the past/present distribution of the worlds many species
  • Biogeographers combine information from a very broad range of fields – ecology, evolution, palaeontology, climatology

 Biogeographers attempt to answer various questions:

  • Which species occur
  • Where do they occur
  • Why did the species get to where they are
  • How have they adapted
  • Why and how are distributions changing
  • Why is a species not there


Alfred Russel Wallace; 19th century British naturalist, explorer, geographer, anthropologist, biologist – helped found modern science of biogeography


What areas are studied in biogeographical? 

  • Dispersal: Movement of populations away from their point of origin
  • Evolution: Change in genetic composition of a population
  • Extinction: Disappearance of a species


Biogeographical – Plate tectonics/continental drift: 

  • Biogeographical has been one of the central fields of study of evolutionary biology


Biogeographical distributions of species: 

  • Explorers were aware of broad global patterns of animal/plant distributions – they discovered new lands; found previously unknown varieties of plants/animals


Darwin’s explanation of biogeographical distribution of species: 

  • Beagle Darwin made a careful study of the biogeographical patterns of the existing species by collecting first-hand evidence
  • From these studies he developed his biogeographic ideas about which he wrote his book
  • Darwin felt he had to reject the orthodox story firmly embraced by European science – time of the Beagle Voyage
  • Theory proposed that all species remain unchanged – discontinues in the distribution patterns of species were due to separate multiple creations


Darwin’s explanation of how species came to be distributions: 

  • Distribution patterns of a species could be explained by each species having its origin in a single centre of origin
  • Species then dispersed, passively or actively – centre of origin
  • Ancestors of each species became extinct in the ‘single centre of origin’
  • Populations became isolated from their ancestors – result of being dispersed
  • Separate populations colonised new areas the species adapted to conditions – became different, forming new species
  • Darwin observed that some species in adjacent geographical areas tended to have more features in common than those living further apart
  • Darwin observed that individual islands have species of the same genus that are slightly different


Worldwide distributions of large flightless birds: 

  • Lost the ability of flight as they adapted to a new environmental circumstances
  • Most flightless birds below to the order Struthioniformes – commonly known as ratites


What are ratites?

  • A family of flightless birds
  • One of the largest birds of all time, the extinct moa/ extant ratites such as the ostrich, emu and rhea
  • They resemble each other, similar modes of life in each landmass

Extant: Living

Where are ratites? 

Found on the continents that were all part of what was Gondwanaland

  • Ostrich: Northern, Eastern, Southern Africa
  • Rheas: South America
  • Emus: Australia
  • Moas: New Zealand  

What are the physical characteristics of ratites? 

  • Flat sternum (breastbone)
  • Small wings
  • Large bodies
  • Heavy leg bone
  • Thick, strong feet
  • Specialized toe structure/ no opposable first toe


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