Charles Darwin
- graduated 1831
- naturalist on Beagle on round the world trip
- 22 when left, returned when 27 in 1836
- last long trip
South America
- Darwin saw giant mammal fossils
- important, did not recognize importance until he got home and identified the specimens
- read Malthus in 1838 clearly looking for a mechanism
Darwin’s tools to study evolution
- travel, collections, observation
- geographic distribution of organisms
- morphology and classification
- geology
- simple experiments
Biogeography
- the study of geographic distribution of organisms
- in his early reasoning based on his travels this is what he used
- key to making him realize that evolution had to have occurred
Role of biogeography in establishing evolution
-Darwin: relationships of living and extinct South American mammals. Species distributions in the Galapagos Islands-birds and tortoises
Wallace: Wallace’s line in East Asia
-biogeography plus paleontology were crucial to Darwin’s inference of evolution
Key point from South America
-fossil glyptodons-related to living armadillos
Ground sloths
- related to living tree sloths
- groups native to South America
- fossil species not identical to the living
- fossils are related to living groups native to same region which indicates a genetic link between the extinct and living species in regions of the world (ground sloth DNA is similar to that of living tree sloths)
Other examples of genetic link
-cacti new world vs. euphorbs old world
Other example from biogeography
- Tasmanian wolf
- dog-like but not related to dogs
- has a pouch and is a marsupial related to possums and kangaroos
- DNA links it to other Australian marsupials
- all other original mammals in Australia are marsupials
- how do we account for this dog like carnivore–>Darwin (and) Wallace fact best explained by the hypothesis of local evolution in various regions of the Earth
- resemblance to wolf is convergence between unrelated carnivores
Mexican blind cave fish
- analogous case under modern study
- not relate to blind cave on other continents
- related to fish with eyes that linve in above ground streams near the caves-can be hybridized in lab
- eye loss is linked to genes that enlarge the jaws for feeding on cave floor. loss of eyes is incidental
Conclusion
-evolution is taking place locally, with direct genetic link between an ancestral population and a derived population
Generalizations from biogeography
- fossil forms related to the living in various regions
- similar environments have similar forms, but related to local species
- island faunas have peculiarities that can only be explained by migrations of ancestors from elsewhere, followed by local evolution and speciation
Darwin in the Galapagos
- disharmony: reptiles in mammalian roles
- species unique to the islands but closest relatives in South America
- species unique to each island, but closely related to those on the other Galapagos islands
- Adaptive spectrum of birds but within a small group of finches, rather than among several bird groups (these other groups are absent from the islands
- Conclusion: these observations make more sense given evolution than creation
Tortoises in Galapagos
-every island in the Galapagos had a different species of tortoise and very few species survived. All related to each other and all related to tortoises in South America in the new world
Alfred Russell Wallace
- also made disturbing observations like Darwin
- travels to Indonesian island ins 1850’s
- Bali and Lombok are 20 miles apart
- Bali: tigers, monkeys, orangs, rhinos, bears, Asian birds
- Lombok: marsupials, birds of paradise, cocatoos
Why do evolutionary biologists study islands?
- semi isolated evolutionary laboratories
- fewer species, simpler evolutionary histories
- products of colonization followed by speciation
- each island is unique, but general rules apply across islands
- e.g. accidental sampling of colonists that may not represent outside world (reptiles dominate Galapagos), islands effects like dwarfing, evolution of endemics, convergence
Island biogeography
- dispersal
- species/area
- adaptive radiation and convergence
Effects of geography on past life
- plate tectonics
- paleobiogeography
- vicariance
Results of low dispersal rates to islands
- disharmony of faunas e.g. no mammals on the Galapagos Islands. Mammals never got there , so reptiles dominate what would be mammalian niches
- endemics: colonizing species evolve into unique forms in isolation
Area effect
- area of an island determines the number of species that are present (so of course so does dispersal)
- number of species on an island is an interaction between number of new species introduced and number of species that go extinct
Archipelago Effect:
-species coming from outside survives on an island and gives rise to a new species which then migrates to a new island and gives rise to a new species which then migrates back to the first island and so on
Adaptive radiation and convergence
- colonizing organisms evolve to fill empty niches
- convergence results when unrelated organisms in different locations evolve similar adaptations or structures
- islands provide numerous examples of both, and have been viewed as evolutionary laboratories
Plate tectonics
- has rearranged positions of contacts between continents over time
- ancient distribution of animals and plants provide evidence
- influences evolution, and the present distribution of some organisms has resulted from continental movement-called vicariance e.g. flightless bird
-endemics
colonizing species evolve into unique forms in isolation
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