Biogeography is the study of the distributions of plants and animals on Earth in both space and time.

Questions addressed in Biogeography

• What species are found where and why?
• What historical events ( plate tectonics, glaciation, climatic change), contributed to the distribution of species?
• What are the roles of the environment and interactions with other organisms in the definition of a range for a species?
• Why are the animals and plants of large, isolated regions ( Australia, Madagascar) so distinctive?
• Why is the diversity of species lowest on isolated oceanic islands and how are these islands colonized?

Some organisms are cosmopolitan and are distributed all over the Earth. Most organisms are endemic, that means they are restricted to certain geographic areas. Same Species inhabiting similar habitats on different continents may be more closely related to nearby species than they are related to each other.

• Historical causes of biogeographic distributions
  Vicariant events in the past determine present day distribution of organism, e.g. the formation of major barriers which let to the dispersal of species, such as plate tectonics , sea level changes or major climate changes.
  For example the breakup of Gondwana during the Mesozoic led to the dispersal of a number of the ancient groups of plants and animals:
  ratites ( elephantbird, egg) ; Kauri
  Marsupials .
  The fossil record reveals that marsupials were widely distributed during the mesozoic era . By the end of the Cretaceous, marsupials were nearly extinct in NA . Marsupials appear in Antarctica and Australia in the late Eocene (35 mya). The connection between Australia and South America was completely severed by about 40 mya. Marsupials are now found primarily in Australia ( marsupial wolf , Tasmania) and South America. The opossum, the only marsupial in North America, is a recent immigrant from the SA.

  Another example for the disperal of species caused by the breakup of Gondwanaland is the plant family of Proteaceae , Fig. 57.3 .
  Plate tectonics also explain the distribution of a weevil species in New Zealand Fig. 57.2

  The ability to disperse varies greatly from and depends on the mobility of an organisms. Phylogenies can often be used to interprete a present distribution pattern. Fig. 57.1-1 , Fig. 57.1-2 , Przewalski horse

• Ecological Biogeography
  Species distribution determined ecological factors such as the interaction between organisms and their environments.

• Island Biogeography
  Species diversity is determined by the distance of the island from the mainland, the size of the island, the type and number of new colonizers, and extinction events (Krakatoa) .
  Model of species diversity : Fig. 57.5 , Fig. 57.6

• Biogeographic zones
  Based on geographic histories, evolutionary links, climate and dominant species (flora and fauna) seven biogeographic areas can be distinguished. This division represents the highest level of biogeographical structuring. Fig. 57.4
  
  • North America and Greenland (Nearctic)
  • Europe, Northern Asia, Middle East and Extreme North Africa (Palearctic)
  • Central and South America (Neotropical)
  • Madagascar and most of Africa (Ethiopian)
  • South Asia and Indonesia (Oriental)
  • Australia and New Zealand (Australasian)
  • Oceanic Islands

• Biome
  The next lower level of biogeographical structuring is the division into biomes. Ecosystems can be classified according to the distribution of species which inhabit them. These ecosystems, referred to as biomes are dominated by characteristic vegetation and populations of animals which have adapted certain reproductive, growth and feeding strategies and have established close links to the prevailing physical conditions of the environment.

  Major biomes are : Tropical forests, temperate forests, boreal forests , Savannah, temperate grasslands, deserts, tundra. Fig. 57.3 .
  Species diversity increases with decreasing latitude, Fig. 57.8

• Oceanic biogeography
  Oceanic environment also can be divided into zones, based on circulation patterns and currents in the ocean. Fig. 57.11 , Fig. 57.12 , Fig. 57.13