Lecture 15 - extinction Flashcards
What are the 2 types of extinction?
- contemporary
- geological
What are the 2 contemporary types of extinction?
- local extinction
- species extinction
What are the 3 geological types of extinction?
- background extinction
- extinction events
- mass extinction events
What % of species are threatened with extinction?
25%
Give an example of local extinction
loss of population from a particular area - e.g. wolves from Britain
Describe extinction in the fossil record
- extinction is a feature of life on Earth
- because of current concerns we tend to focus on species/local extinctions & forget extinction has been happening since life on Earth began
- 99% of all species that ever existed have give extinct
What is background extinction?
the sum of all normal species terminations during a defined time interval
What are extinction events?
times where many species go extinct for a shared reason, typically regional rather than global in scale, but pertaining to selective extinction of clades
What are mass extinction events?
times of geologically rapid global disappearance of much of life, when many species of wide ecological range died out worldwide
Describe the mass extinction events
- End-Ordovician (444 mya) - glaciation
- Late Devonian (372 mya) - Large Igneous Province (LIP), ocean anoxia
- End Permian (252 mya) - LIP
- End - Triassic (201 mya) - LIP
End-Cretaceous (66 mya) - Meteorite impact
Describe after mass extinctions
- survivors of mass extinctions are not random
- often share ‘generalist’ characteristics
- sometimes referred to as ‘disaster laxa’
What is species senescence?
suggestion that species undergo a lifecycle like individuals:
- birth
- development
- reproduction
- death
What is orthogenesis?
change in organisms was due not to natural selection, but to unchecked directional trends within a lineage
Why did Irish Elk (giant deer) go extinct? (SUPPOSEDLY - ACCORDING TO ORTHOGENESIS)
- evolved on an irreversible trajectory towards larger & larger antlers
- Irish elk went extinct when antlers became too large
- could no longer hold up their heads
- got entangled in the trees
Why is evidence for species senescence weak?
- no mechanism for Orthogenesis
- completely at odds with natural selection
- species don’t have ‘allotted’ lifespans
How did Irish Elk actually go extinct?
- sexual selection favoured large antlers and large body size
- natural selection favoured smaller size in response to rapid changing towards warmer, more temperature climates at the end of the last ice age
What causes only some species to go extinct?
- competition & the Red Queen (biotic factors)
- environment - the Court Jester (abiotic factors)
What are factors explaining the probability of speciation?
- species age
- species diversity
- climate
- ecology
What drives speciation in Planktonic foraminifera?
diversity (competition)
What drives extinction in Planktonic foraminifera?
climate
What drives the probability of speciation?
biotic factors (the red queen)
What drives the probability of extinction?
abiotic factors (environmental factors - the court jester)
What is species selection?
the idea that some lineages (or species) have characteristics that make them more likely to speciate or less likely to go extinct
- e.g. species that are large might be just as likely to go extinct, but more likely to speciate
