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