Flashcards in Lecture 9 Notes Deck (35):
How many groups of megafauna have become extinct?
40 Large mammals
What are 8 examples of the megafauna that have become extinct? (see notes for more details)
1. Wooly mammoth
2. Saiga antelope
3. Ground sloths
4. Giant beaver and moose
6. Saber tooth cat
7. Giant short faced kangaroo
8. Pleistocene marsupial lion
9. Alaska's blue babe (bison priscus)
What are 2 examples of vertebrate remains?
1. Primary teeth
2. Primary bones (more common because chitin is resistant to decay)
What can vertebrate remains tell us?
What does preservation largely depend on?
- needs rapid burial
Why is 14C dating of bones difficult?
Because bones are prone to contamination
Why are bones prone to contamination?
Because they are porous and its easy for bacteria to get in and contaminate it
Why are larger mammals more impacted? (3)
1. They live in smaller groups
2. Reproduce less
3. Larger target
Believed that humans migrated around the globe and hunted any large mammal they encountered
- Paul Martins 1973
- rapid or protracted overhunting
- fast or over a long period of time
- but we know it wasn't rapid
Environmental change hypothesis
- extra terrestrial hypothesis
- volcanic eruptions
- climate change, vegetation change
What are some examples of evidence/arguments in support of the overkill hypothesis? (6)
1. Apparent temporal correlation with human arrival (best evidence)
2. Well documented island extinctions following human settlement (NZ, Madagascar, Australia)
- correlation does not equal causation
3. Non-random extinctions (best evidence)
- hunters favoured larger prey
4. Physical evidence of speared megafauna remains (best evidence)
- mastodon rib with embedded projectile point from coast of Washington ~13,800 calendar years BP
5. More extinctions in America and Australia, where megafauna had no experience with human hunters
6. Cave drawings of bug game hunting
Critiquing the overkill hypothesis (6)
1. Some species went extinct long after human arrival (Africa and Eurasia); some species that were in North America did not go extinct (best critique)
2. Extinctions did not always follow presumed human migration paths
3. Were there really enough humans to hunt to extinctions? Did they have technology to hunt to extinction?
- bow and arrows were developed much later
4. Little direct evidence of overhunting
- few kills or spread remains ... for most species
5. Advantages for managing resources
- early cultures +/- in equilibrium with ecosystems
- wouldnt have taken more than they needed (wouldnt have over killed and managed what they killed)
6. aDNA and fossil evidence suggest megafauna and humans overlapped in North America for thousands of years (best critique)
Archaeological sites with clear evidence for hunting
- few well dated sites associated with hunting
- 27% of all mammoth sites associated with hunting
What is an example of an extra terrestrial impact?
Impact crater (not the explanation)
- major introduction of dust to the atmosphere that blocks the sun and that effects photosynthesis which effects many animals and possibly lead to their extinctions
Why do you need multiple impacts?
Because all extinctions didn't happen all at the same time
What causes a nuclear winter?
Injects of sulphur dioxide in the atmosphere, releasing ash (cool temp and acid rain)
What does nuclear winters disrupt?
Climate on a global scale that can lead to extinction
A period of abnormal cold and darkness predicted to follow a nuclear war, caused by a layer of smoke and dusk in the atmosphere blocking the suns rays
- not the explanation
What do extinctions coincide with? (4)
1. Retreat of conventional ice sheets
2. Drastic fluctuations in climate
3. Vegetation change
4. Habitat loss/alterations
(better explanation because they coincide)
Critiquing the climate/ vegetation hypothesis (3)
1. Many previous glacial cycles and changes in climate not accompanied by extinctions
2. Megafauna would have migrated to more suitable habitats in response to environmental change
3. Non-random extinctions
- if habitats were so drastically altered, why didn't more small mammals also go extinct
- small mammals don't migrate
What does larger size mean?
Where did they not find mammoths?
In higher elevations
When did the extinctions occur?
In the mid holocene
Was dominated by by sedge then switched to what? And what does this implicate?
- switched to grass dominated
- provides evidence that environmental change drove mammoth extinction
What does few plant macrofossils and low productivity mean? And what does it suggest?
There was a major slow increase in burch shrubs in the mid-late holocene period
- suggests warming
- small change in the pollen data
What helps to shed light on Wrangel Island mammoths extinctions?
Genetic variation through time
Wrangle Island mammoths extinctions hypothesis 1
Slow environmental change following LGM reduced carrying capacity
- gradual loss of genetic variation
--> would expect a gradual loss
Wrangle Island mammoths extinctions hypothesis 2
Abrupt environmental change or over hunting
- constant level of genetic variation followed by extinction
--> we would expect constant genetic variation
What causes the bottle neck effect?
Sea levels rising
What are 2 possible examples for extinction of Wrangle Island?
2. Undetected environmental change
- highly unlikely that this caused all extinctions
When did many large mammal species go extinct?
What does non-random extinctions (body size) and general coincidence with human migration suggest?
That humans likely played a role
What are 2 examples of pleistocene extinctions?
2. Climate change (vegetation/habitat change)
- varies in time, space and effects different species
Species distribution model
An associative model relating occurrence of abundance data at known locations of individual species (distribution data) to info on the environmental characteristics of those locations