Historical biogeography Flashcards
Dispersion of animals across the globe in random. True or false?
False, there are underlying geological patterns.
List 4 factors that affect our understanding of species distribution.
- Dispersal
- Vicariance
- Extinction
- Missing data
Explain the two main types of dispersal, with examples.
- Jump dispersal: a species overcomes a physical barrier due to the evolution of a new character OR by a chance event, e.g. pterosaurs blown over a mountain range to colonise the other side
- Geodispersal: a physical barrier disappears, e.g. an ocean closes up
What is meant by a barrier in dispersal?
A physical barrier, like a mountain range or ocean, as well as things like climate and sea level etc. Basically abiotic factors of the environment.
Define vicariance.
When a physical barrier forms in an organism’s environment.
Vicariance is often visible in evolutionary trees. How?
Speciation mirrors separations of landmass etc.
Give 2 historical examples of vicariance.
- Dinosaurs evolved in South Africa when the continents were joined as Pangea. When Pangea split the dinosaurs were globally distributed.
- The Turgai Sea opened up in the middle Jurassic. Asia became separated from all the other continents, leading to the evolution of unique fauna.
Why is it that Europe and North America did not have different dinosaur species until the cretaceous?
There was no vicariance, so species could freely cross between the 2 places, until the Atlantic opened up.
How does extinction shape distribution?
It removes whole groups, e.g. Marsupials used to be globally distributed.
How does missing data affect our understanding of species distribution? Give an example.
Incomplete records are misleading: was thought that titanosaurs were confined to South America from the late cretaceous. This was until footprints were found in Oxfordshire in the UK, dating to the middle-Jurassic (earlier).
There are major fluctuations in diversity over time, but this may be due to an incomplete fossil record. How?
Specimens have been destroyed by geological processes OR some specimens have not been found yet.
Sampling bias also affects our understanding of diversity. Give an example of this.
Evidence suggests dinosaur diversity, particularly in saurischians, peaked before the End Cretaceous mass extinction. However scientists may have over-sampled this period of geological time as they wanted to discover why the dinosaurs went extinct or where birds came from, thus we have more specimens and data from that time period which is misrepresentative.
