Extinctions: past and present
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Transcript of Extinctions: past and present
Extinctions: past and present
Bio 415/615
Questions
1. How do species go extinct?2. How is the ‘background’ extinction
rate calculated?3. What caused mass extinctions in the
geologic record?
How many documented extinctions have there been in
the last 500 years?
~75 plant extinctions
~600 animal extinctions
Some species are more vulnerable to extinction
Species on islands (or isolated habitats)
e.g., ground nesting birds
e.g., ‘naïve’ species: megafauna
Extinction due to predation, not (usually) competition
Raphus cucullatus: extinct mid/late 1600s
TambalacoquTambalacoquee
MauritiusMauritius
Historic extinctions
Species with small geographic ranges
narrowly distributed endemic species
Species with 1 or a few populations
(e.g. Devil’s Hole Pup Fish, Nevada)
Some species are more vulnerable to extinction
Five ways to go extinct
Grey Ducks & Mallards
Extinction via reticulation
Extinction via competition/predation
e.g., extinction on islands, the lighthouse keeper’s cat
Stephens Island Wren (NZ)
Extinction via over-exploitation
NZ moas
Pleistocene megafauna?
Extinction via habitat destruction
Ivory-billed woodpecker (?)
Dusky seaside sparrow: extinct in the wild since 1979, last died in captivity in 1987 (DisneyWorld)
Extinction via changing environmental conditions
Golden toad (Cranopsis periglenes), formerly of Costa Rica
Mass Extinction –
A major episode of extinction for many taxa, occurring fairly suddenly
in the fossil record
5 historic mass extinction events
Mass Extinction Events & Change in diversity
What causes mass extinctions?
Flood basalts and vulcanism
Deccan traps (65 mya)
Siberian traps (250 mya)
Columbia River group (17-14 mya)
Central Atlantic group (180 mya)
Returning to the K-T Boundary:
? Why did Dinosaurs go extinct?
? Why did Mammals and Birds become the dominant terrestrial vertebrates?
Because of,
A. a giant asteroid impact like the movie Armageddon
B. global patterns of cooling
C. the extinction of food the Dinosaurs depended on
Alvarez et al. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208: 1095-1108.
Believed that a giant asteroid had hit the earth, that this had caused a dense cover of particulate matter in the atmosphere that blocked the sun, causing global cooling, and the death of many plants
They predicted that an iridium layer should separate cretaceous from tertiary strata
Swisher et al. 1992, also published in Science, found the asteroid crater on the ocean covered continental shelf of the Yucatan
Mammals and Birds came to dominance after the Dinosaurs went extinct 65 million years ago.
This happened at the boundary between the Cretaceous and Tertiary Periods (or the K-T boundary), which is also the boundary between the Mesozoic and Cenozoic Eras
Mass Extinction – a major episode of extinction for many taxa, occurring fairly suddenly in the fossil record
We don’t know how quickly the extinctions occurred following the
asteroid impact:
Bad weekend versus bad century
(versus bad few million years?)
Either way: a lot of species (millions) went extinct in a relatively short
period of time
Three questions:
1. Have there been more extinctions recently then we expect by chance?
2. What are ‘normal’ background levels of extinctions?
3. Do we expect more rapid extinction events in the near future?
Are human mediated changes in the environment causing another mass extinction?
Background levels of extinction:
Estimates of paleo extinctions derived from wide-ranging marine animals.
Average species may survive for 1-10 million years
If 10 million species on the planet then estimate the loss of a total of 1-10 species per year
So ‘background’ extinction rate is 0.0001-0.00001% of species per year
Current rate of bird and mammal loss is 0.01 % per year
100 – 1000 times greater then background levels
But…
1. Regan (2001) examined estimate and readjusted calculations to 36-78 times background levels
2. Estimates based on wide-ranging taxa may lead to erroneous conclusions
3. Average values calculated on short time intervals (e.g. the last 500 yrs) may lead to erroneous conclusions
Background levels of extinction:
Pimm et al. 2006: birds• About 10,000 bird species known• 129 recorded extinctions since 1500
= 26 extinctions per million species per year(compare to ‘background’ of ~1 E/MSY)
• BUT:– We keep finding new remains of extinct species– Many species are ‘on the verge’ or already gone but
remain on lists– Conservation efforts have prevented many
extinctions
• Added to total, these estimates of more cryptic extinctions yields ~150 E/MSY
• If present habitat loss continues, rate could get to 1500 E/MSY by 2100
Do we expect rates of extinction to accelerate in the near future?
The big question:
Do we expect rates of extinction to accelerate in the near future?
The big question:
We might because of:
1.Habitat destruction
2.Global climate change
Do we expect rates of extinction to accelerate in the near future?
The big question:
We might because of:
1.Habitat destruction
2.Global climate changeBut what if ‘sensitive’ species have already gone extinct?