Tipping Points - Lecture 2 (Megafaunal extinctions)

Name 2 species that went extinct

Giant ground sloth ad the woolly mammoth

why did humans move out of Africa

• resource availability

• climate change

• population pressures

• innovation and technology

• social and cultural factors

• hominin biology

• brain thermoregulation

• coevolved zoonotic diseases

where was one of the last places humans discovered

the pacific islands - as they were islands (2500 years ago)

what was the climate doing at the time of humans migrating out of africa?

the climate was changing drastically. more ice, less ice. varied quickly. the temps were similar to what they are today. however, temps decreased until the last glacial maximum. However, there was a large period of warm wet conditions that could have facilitated early waves of human migration. However, the primary out of Africa occurred during a cold and dry period. suggesting push and pull factors may have prompted homo sapiens to coloise eurasia.

how did humans migrate into NA

there was a land bridge connecting asia and north america which allowed humans to cross it into the americas - the date was a lot later as they had to wait for this ice bridge

why is australia a conundrum

humans managed to get into australia quite quickly after africa exit. There was never a land bridge so they HAD to travel across the sea. so they managed to cross the sea before they got to other places!! the oldest sites in australia are 65,000 years ago however only moved out of africa 70,000 years ago - 5,000 years!!

what factors explain the geographic pattern of migration

• they were following the coastline

• possibly were following the sun - why they went east first instead of west

• some mountains were difficult/impossible to traverse so hard to cross from europe to russia

• followed rivers as well

where did neandertals and homoerectus move too

were already in europe, china and inda when homo sapians emerged out of africa

why are larger animals more vulnerable to a range of extinction threate

• exist at a lower pop densities

• intrinsic rate of population increase declines with increasing body mass

• likelihood of extinction was higher for groups with lower reproductive rates

• disproportionate exploited by humans

why would species go extinct

• their habitat is lost and they can’t find refuge

• breeding populations are isolated

• they can evolve fast enough

what is the evidence for the extinction of the megafauna

• Radiocarbon dating directly of megafaunal material, namely bones, teeth, antlers and, more rarely, various soft tissues and dung.

• Extinction dynamics from ancient DNA (aDNA) – E.g. changes in genetic diversity (declines), but some species experienced genetic bottlenecks and survived

• Diets and community structure from stable isotopes

what is the overkill theory

humans caused the extinct of the megafuana due to over hunting them for food.

what are the argumants against overkill

• Scale. Too few humans (initially), and too many animals

• Kills sites only provide evidence for 5 genera (no evidence any of the other 33 genera were preyed upon)

• More evidence now suggesting many of the 33 genera extinctions were staggered

• New evidence suggesting humans arrived c. 1000 years pre-Clovis (but no pre-Clovis kill/scavenging sites)

• Many species found in kill sites have survived – example of bison

• Many other species became extinct that were not hunted (e.g. birds, snakes, spruce trees)

• Survivors experienced range shifts and changes in abundance, i.e. they were impacted

what is the climate change theory

Replacement of vast areas of open ‘mammoth steppe’ (grasses and herbs) by forests as climate changed towards start of Holocene, i.e. loss of habitat

what is the competition for resources theory?

Direct competition for limited resources during periods of pronounced environmental stress

What happened in Eurasia

18/49 species whent extinct (37%) with no evidnece for extinction of carnivores after their prey and lottle evidence for overkill. and it was staggered over any millennia

What happened in North America

38/55 species went extinct (69%). many smaller species also went extinct during the late Pleistocene

what is covis cuture

many sites exhibit black mats in alluvial sequences which are mollic palaeosols and appear to be correlated with Younger Dryas in Europe

What happened in south americA

it was a mixture of both climate and overkill. as the extinctions didnt occur until humans but werent as bad until the climate worsened

what happened in australia

28/55 species went extinct

Human or climate

• Disease seems unlikely – though can’t be discounted.

• Human impact seems to be a factor - but perhaps to varying degrees. Very strong impact on islands – e.g. NZ, Mediterranean. But large continental areas..?

• Direct overkill, competition for resources, an extra stress in the presence of rapid climate change…

• Few examples of remains with weapons. Difficult to explain extinctions in animals (NA sloth) that have very large continental ranges.

• And yet where hominins have lived longest, Africa, the extinctions were low.

what is a hominin

the group consisting of modern humans, extinct human species and all our immediate ancestors

what ape group does hominins have

chimpanzes

when did modern humans evolve in africa

200,000 years ago BP

what is out closest ape cousin and how much dna do we share?

98% of our dna we share

how long ago did humans move out of africa

70,000-50,000 years ago

how long ago did humans move to australia

50,000 years ago

how long ago did humans move to europe

45,000-35,000 years ago

how long ago did humans move to asia

45,000 - 35,000 years ago

how long ago did humans more from asia to the phillapeans

3,500 years ago

how long ago did humans move into north americas

20,000-15,000 years ago

how long ago did humans move into the polynesia

2,500 years ago

how long ago did humans make it to south america

15,000 - 12,000 years ago

how long ago did humans get to russia

25,000 years ago