Lecture 14

Question 1

Extinction

Answer 1

• 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

Question 2

Passenger Pigeons

Answer 2

• huge populations
• exterminated by human hunting
• population crashed under hunting pressure because they need large populations to reproduce

Question 3

Background Extinction

Answer 3

-constant toll of species

Question 4

Mass Extinction

Answer 4

• 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

Question 5

Causes of Extinction

Answer 5

• 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)

Question 6

Ordovician Mass Extinction

Answer 6

• caused by worldwide cooling and glacial period so collapse of tropical organisms
• 86% of species
• 443 mya

Question 7

Devonian Mass Extinction

Answer 7

• global cooling
• mainly affected coral reefs
• 74% of species
• 359 mya

Question 8

Permian Mass Extinction

Answer 8

• 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

Question 9

Triassic Mass Extinction

Answer 9

• CO2 levels rise, heating, pH drop
• sea and land affected
• 86% of species
• 200 mya

Question 10

Cretaceous Mass Extinction

Answer 10

• asteroid
• most famous; dinosaurs and marine animals become extinct
• 76% of species
• 65 mya

Question 11

Pleistocene Mass Extinction

Answer 11

• recent extinction
• large mammals, plants, amphibians, likely coral reefs, rain forests and more
• possible triggers: climate warming and ecological changes or humans (overkill hypothesis)

Question 12

Most Notorious Extinction-End Cretaceous

Answer 12

• 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

Question 13

Where are the craters?

Answer 13

• 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

Question 14

Permian Extinction-Rock Layers

Answer 14

• 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

Question 15

Humans

Answer 15

-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

Question 16

Linear Events

Answer 16

-CO2 rises so temperature also rises because CO2 is a major greenhouse gas

Question 17

Non-Linear Event

Answer 17

• 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

Question 18

Response to Mass Extinction

Answer 18

• 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

Question 19

Fragmentation of Habitats

Answer 19

• 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

Question 20

Evidence of Asteroid in Cretaceous

Answer 20

• Ir spike
• shocked quartz
• soot
• Chicxlub crater

Question 21

Biotic Effects of Asteroid

Answer 21

• 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

Question 22

Potential Trigger of Permian Extinction

Answer 22

-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)

Question 23

Secondary Causes of Mass Extinctions

Answer 23

• must be independent cause

- downstream effects

Question 24

Secondary Cause Permian

Answer 24

-positive feedbacks, CO2 and methane combine with reduction in O2 levels as photosynthesis drops

Question 25

Secondary Cause Cretaceous

Answer 25

-fall out of hot fragments from collision, massive fires, plant ie off also affects animals. Global cooling from dust clouds high in atmosphere

Question 26

Secondary Cause Pleistocene

Answer 26

- overkill fragments populations, genetic loss, populations fall below recovery levels - climate change adds stress though changes in plant communities - forest replaces cold grasslands

Question 27

End Permian Conditions

Answer 27

- 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

Question 28

Diversity of Life Through Time

Answer 28

- 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

Question 29

Long-Range Patterns

Answer 29

- 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

Question 30

Causes of Modern Extinctions

Answer 30

- 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

Question 31

Extinctions and Human Wellbeing

Answer 31

- 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

Question 32

Induced Rats and Island Extinctions

Answer 32

- 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

Question 33

Recovery for Lord Howe Island

Answer 33

- 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