Ecology through time 2

Question 1

Megafauna

Answer 1

• Megafauna onset of the Quaternary, the definition of it varies typically >40/44kg
• In every region except Africa almost every large animal was lost; mammoth, thunderbirds etc

Question 2

Overkill Hypothesis

Answer 2

• Proposed that Pleistocene megafauna extinction driven by the arrival of Homo sapiens
• Extinctions don’t consider with global-scale climate change but coincide with the arrival of humans

Question 3

Why is Africa different?

Answer 3

• Homo spaiens migrated out of Africa -180k and 110ka
• Homo sapiens arrived in South America 12ka
• Homo genus evolved in Africa 2.6Ma
• The most widely accepted view is that the coevolution of megafauna and humans in Africa allowed large animals to adapt to human hunting pressures

Question 4

Broader ecological impacts

Answer 4

• Johnson (2009) Evidence from modern ecosystems indicates that megafauna have the following impacts
  a) reduce vegetation density
  b) increase gaps
  c) disperse seeds
  d) reduce fire (reduce fuel build-up, create fire-breaks)
  e) accelerate nutrient cycling

Question 5

Extinction of the mammoth steppe

Answer 5

• Extinction of mammoths profoundly changed the vegetation
• Absence of grazers led to a rise in the water table which benefits mosses
• Low productivity and low transpiration - soils remain waterlogged
• Lack of grazing allows the establishment if wet-tolerant shrubs and trees

Question 6

Megafauna in Amazonia

Answer 6

• Population declines of large-seeded animal-dispersed trees
• These trees tend to be large and carbon-dense so knock on Carbon dynamics
• Profound effect on nutrient cycling

Question 7

Megafauna extinction and wildfire

Answer 7

• Fire history can be reconstructed from charcoal deposits in Peat or sediments
• Dating fossils can provide estimates of extinction dates - but is challenging where fossil preservation is poor

Question 8

What is Linnaean shortfall?

Answer 8

• It is the discrepancy between the total number of species and those described by science

Question 9

How quickly are we losing species?

Answer 9

• 35% of mangroves lost
• 20% of coral reefs lost
• Nature of habitat destruction varies - variable drivers
• A very small proportion of species known to have gone extinct - 0.01% of known marine species, 0.2% of known freshwater species
• More than 42,100 species are threatened with extinction

Question 10

Is this the whole story for extinction?

Answer 10

• 0.00007% of recorded species
• <1000 recorded extinctions over the last 500 years (IUNC)
• In fossil record, it is impossible to distinguish between rarity and extinction - If species becomes rare, it is very unlikely to be recorded in fossil record

Question 11

Functional Extinction?

Answer 11

• Javan rhinoceros once found across SE Asia, important ecosystem engineer
• No extinct yet but no longer performing key ecosystem function - nutrient cycling

Question 12

Ecological impacts of (functional extinction)

Answer 12

• Cascading effects on ecosystem (trophic cascades)
• 80% of wild plants depend on insects for pollination
• Nutrient cycling in the soil - key role in soil fauna
• 60% of birds use insects as a food source
• Reintroduction of keystone species → Wolves in Yellowstone (Kate’s lecture)
  → Extinction of megafauna
  → Pleistocene Park

Question 13

Human disruption of ecosystems: alien and invasive species

Answer 13

• Alien invasive species: A species established outside of its natural disturbiton whose introduction threatens biological diversity
• Alien species have been introduced by humans they are not native, introduced may be intentional or accidental