Lecture 14 Flashcards
1
Q
Extinction
A
- complete disappearance of an entire species from the face of the Earth
- can still have extinct species even though some are still alive
- i.e. white rhinos half a dozen left but none of reproductive age so they will be all gone soon
2
Q
Passenger Pigeons
A
- huge populations
- exterminated by human hunting
- population crashed under hunting pressure because they need large populations to reproduce
3
Q
Background Extinction
A
-constant toll of species
4
Q
Mass Extinction
A
- thousands of species becoming extinct at once
- perhaps whole ecosystem collapsed
- important for setting a new direction of life
- dominant organisms now aren’t there so non-dominant organisms can radiate and fill niches
5
Q
Causes of Extinction
A
- competition: Darwin’s idea (natural selection) but there’s more to it; Not just that survivors are better than those that go extinct
- biological: new predators, disease, loss other members of biosphere
- physical environmental change-associated with large mass extinctions; doesn’t mean that organisms weren’t good enough competitively
- accident: small populations particularly vulnerable (survivors not necessarily superior to victims)
6
Q
Ordovician Mass Extinction
A
- caused by worldwide cooling and glacial period so collapse of tropical organisms
- 86% of species
- 443 mya
7
Q
Devonian Mass Extinction
A
- global cooling
- mainly affected coral reefs
- 74% of species
- 359 mya
8
Q
Permian Mass Extinction
A
- siberian volcanism, global warming, and toxic gasses
- 96% of species
- most deadly seen
- 252 mya
- After extinction comes biological recovery (after Cretaceous this was almost instantaneous (and by instantaneous I mean a few million years)) this took a very long time-almost half of Triassic
- marked by geological events and atmospheric composition changes
9
Q
Triassic Mass Extinction
A
- CO2 levels rise, heating, pH drop
- sea and land affected
- 86% of species
- 200 mya
10
Q
Cretaceous Mass Extinction
A
- asteroid
- most famous; dinosaurs and marine animals become extinct
- 76% of species
- 65 mya
11
Q
Pleistocene Mass Extinction
A
- recent extinction
- large mammals, plants, amphibians, likely coral reefs, rain forests and more
- possible triggers: climate warming and ecological changes or humans (overkill hypothesis)
12
Q
Most Notorious Extinction-End Cretaceous
A
- Walter and Luis Alvarez went out hunting for cause of the extinction. found rock layers with boundaries between Cretaceous and Cenozoic and there’s a little layer of clay defining the boundary. Investigated chemistry of this layer and discovered there was an iridium spike
- how do you get this spike?-asteroids; calculated the size of the asteroid that would have led to this outcome and it was 6 miles wide
- only extinction caused by an asteroid
13
Q
Where are the craters?
A
- very active weathering on earth so they quickly erode away
- twin lakes in Ontario are the result of meteors
- the one from the mass extinction is near the Yucatan Peninsula which is invisible on the surface but is 120 mi in diameter
- only detectable by drilling and magnetic fields
14
Q
Permian Extinction-Rock Layers
A
- in china that take you through this extinction; very well preserved
- could date beds that are the extinction beds
- able to do good lead and uranium dating
- extinction interval was less than 60 thousand years which is tiny compared to the span of dates of earth history so it could have been a week or a day or a few thousand years
- very extreme precision dating in something so old
15
Q
Humans
A
-arose in Africa but there were animals all over the world so when humans migrated to these other parts animals had never seen them before and were much more vulnerable to being hunted
16
Q
Linear Events
A
-CO2 rises so temperature also rises because CO2 is a major greenhouse gas
17
Q
Non-Linear Event
A
- at some point methane is released from methane hydrate stores
- methane is much more potent greenhouse gas than CO2
- sudden temperature jump
- permafrost is as important as the ocean for methane storage
- huge craters in Siberia are appearing because of this effect
18
Q
Response to Mass Extinction
A
- lot has nothing to do with Darwinian selection but luck
- survivor ship is non random-favors generalists in their habitats and have a wide range geographically-better chance of survival
- not related to species richness of clades (doesn’t mean that the families with the most species are the ones that are going to survive)
- rapid radiation among surviving groups because all environments are now present and unoccupied by anything that excludes you
- ripple effects among other organisms
19
Q
Fragmentation of Habitats
A
- when you put a farm down in the middle of a forest you split the forest up so there is less flexibility of habitats in this situation
- diminishes range of species and habitat
20
Q
Evidence of Asteroid in Cretaceous
A
- Ir spike
- shocked quartz
- soot
- Chicxlub crater
21
Q
Biotic Effects of Asteroid
A
- large land animals
- marine plankton
- marine reptiles, ammonites
- temporary replacement of forests by ferns
- survivors that populate a changed world in the recovery phase-recovery rapid-radiations in 5myr
22
Q
Potential Trigger of Permian Extinction
A
-Permian: large volcanic eruptions, causing release of CO2, and methane release from marine methane hydrates-global warming, anoxia, toxic gasses form in seas as a result (H2S)
23
Q
Secondary Causes of Mass Extinctions
A
- must be independent cause
- downstream effects
24
Q
Secondary Cause Permian
A
-positive feedbacks, CO2 and methane combine with reduction in O2 levels as photosynthesis drops
25
Secondary Cause Cretaceous
-fall out of hot fragments from collision, massive fires, plant ie off also affects animals. Global cooling from dust clouds high in atmosphere
26
Secondary Cause Pleistocene
- overkill fragments populations, genetic loss, populations fall below recovery levels
- climate change adds stress though changes in plant communities
- forest replaces cold grasslands
27
End Permian Conditions
- siberian massive eruptions of lava-CO2 release-->global warming
- methane release from methane hydrates as sea warms-->global warming FAST
- warming dries forests, lowered photosynthesis-->O2 levels drop
- stratified oceans are present which have anaerobic deep water, releases H2S to shallow water and atmosphere
- combo results in mass extinction
28
Diversity of Life Through Time
- long term trends
- steady state levels maintained by origins vs. extinctions
- mass extinctions punctuate, but in an odd way. Replace selection by the "field of bullets"
- something new: human generated extinction-already enormous
29
Long-Range Patterns
- phyla established in Cambrian. few or now extinctions, no new phyla since
- extinct classes, orders, etc. Larger groups are more likely to survive. All species die out relatively rapidly
- overall shifts of faunas long term
- causes of extinctions not always clear. Long range patterns have a lot of randomness
30
Causes of Modern Extinctions
- human-generated extinction increasing rapidly
- habitat destruction, human population growth
- overfishing, hunting, collecting
- climate change
- fragmentation of habitats
- introduction of disease organisms
- introduction of alien species
- environmental degradation
31
Extinctions and Human Wellbeing
- rivets and plane analogy
- how many can we pop and still have the plane held together
- environmental services: absorption of CO2, production of O2
- richest habitats at risk are the centers of diversity
- coral reefs, and tropical forests are great sources of speciation. Now rapidly being destroyed.
- Amphibians-30% threatened with extinction
32
Induced Rats and Island Extinctions
- islands are evolutionary labs but also fragile-vulnerable to introduced cats, rats, goats, pigs
- rats accidentally introduced to islands have destroyed over 100 unique island species
- many more species are in danger
- new techniques for rat eradication are now being applied
33
Recovery for Lord Howe Island
- rats introduced and killed off stick insects
- now survivors from Ball's Pyramid are being bred in captivity
- Hope is now to persuade Lord Howe Islanders to allow a rat eradication and a stick insect re-introduction
