Lecture Twenty Two - Extinction

Question 1

What is extinction and why does it occur?

Answer 1

• Perhaps one of the most common of all naturalevolutionaryprocesses
• Perhaps 99.9% of all species that have evolved over the last 3.5 billion years have undergone extinction

Question 2

What is the spatial scale of extinction?

Answer 2

• Local extinction – a species population is
displaced from a habitat
• Regional extinction – e.g. loss of the thylacine from mainland Australia
• Global extinction – a species becomes extinct everywhere`

Question 3

Why are extinction rates so difficult to estimate?

Answer 3

• Species in popular groups (birds, mammals) = much better known.
• Some groups very sparsely sampled, eg. deep sea benthos, fungi, nanoplankton.
• Accurate estimates of species # are difficult for poorly known groups.
• Extinction rates are extrapolations from well-known species.

Question 4

Which species have existed when in the time scale?

Answer 4

Pleistocene: Large mammals & birds (includes human impact).
Cretaceous: reptiles (dinosaurs), many marine species.
Triassic: 35% animal families, many reptiles, marine molluscs.
Permian: 50% animal families, 95% marine species, trees, amphibians.
Devonian: 30% animal families Ordovician: 50% animal families

Question 5

What are some human induced extinctions?

Answer 5

1. 74-86% Megafauna (animals >44 kg ~ 100 lbs) - by prehistoric humans.
   Mammoths:
   • Causes of extinction complex
   • Probably due to combination of improved hunting techniques and ecosystem (steppe) collapse - as the climate warmed.
   • Last known mammoths lived in the Arctic 4000 yrs ago.
2. Since 1600, 2.1% of the world’s mammal and 1.3% of bird species have become extinct.
3. Current extinction rates 100-1000x greater than “natural” rates.
4. Extinction rates for species other than mammals and birds are just rough guesses! e.g. 90% of large predatory fish have been lost from the world’s oceans.

Question 6

What is the ‘sixth’ mass extinction?

Answer 6

The current rate of species extinction is so rapid that it can be compared the past episodes of natural mass extinction known from the Geological record.
• Among scientists, current rate of extinction ranked higher concerns re pollution, global warming, and loss of the ozone layer (American Museum of Natural History) .
• We may be losing 30,000+ species a year. This is much faster than at any time over the last 65 million years.

• NOW - the 1st mass extinction event since the loss of dinosaurs at the start of the Tertiary and the 6th in the four-billion-year history of life.
• Global extinction rate of vertebrate groups could be 15-20% over the next 100 years.
• Up to 50% of species could be wiped out over the next century because of human activities.

Question 7

What is the HIPPOC syndrome?

Answer 7

Human expansion leads to: 
Climate change 
Introductions of species (I).  
Mechanical habitat destruction (H). 
Pollution (P). 
Fishing (over exploitation_ (O). 

These all lead to altered ecosystems.

Question 8

What are the main threats to biodiversity (causes of current extinctions).

Answer 8

• Habitat destruction and fragmentation
• Impacts of introduced species
• Overexploitation (overhunting, overfishing)
• Collecting (for sale, aquaria, private)
• For plants, grazing pressure, altered fire regimes
Most directly or indirectly attributable to growing human Population, increasing at ~ 90 x 106 pa.

HIPPOC effect.

Habitat degradation, destruction and fragmentation are probably the most important causes of extinction today

Question 9

What is overfishing?

Answer 9

• large vertebrates and shellfish - first human
disturbance to coastal ecosystems.
• enormous decrease - biomass and abundance.
• coincided with European colonization of Americas and Pacific.
• started before impact of pollution, eutrophication, habitat destruction, species invasions, climate change

Marine fish - an unsustainable resource:
• 1950-1994: Change in global fisheries from long -lived high trophic level bottom fish to short- lived, low trophic level invertebrates and pelagic fish.
• Driven by changes in fish abundance.
• Implies major changes in marine food webs.
• Continuation of trends will lead to widespread collapse of fisheries.

Question 10

Explain pollution.

Answer 10

Exponential increase in human population the root cause of other impacts and threats.

Key factor driving the extinction vortex:
– Loss of the genetic variation necessary to enable evolutionary responses to environmental change.
What characteristics are common to endangered species approaching extinction?
•Small habitat
•Limited diet
•Long-lived and few young
•Large sized critters ..?
•Commercial value

Extinction vortex:
Small population -> Inbreeding and genetic drift -> Loss of genetic variability -> Reduction of individual fitness and population adaptability -> Lower reproduction and higher mortality -> smaller population etc.