1. Ch 6: Mass Extinction & Global Change

2. Extinction Inevitable Living fossils Rate of extinction not constant
99.9% of species that ever lived have gone extinct
Some species changed enough to be considered a new species
Others were evolutionary dead ends
Living fossils
persist, unchanged for millions of years
Rate of extinction not constant
At least 5 mass extinctions
Are we in the middle of the 6th?

3. History of Life on Earth
Prokaryotes
1.9 BYA: Eukaryotes
600 MYA: Cambrian Explosion
macroscopic organisms!
5 mass extinctions since then
Overall, biodiversity increasing

4. Cretaceous-Tertiary Extinction
315 mya: the amniotic egg
280 mya: reptiles dominate
65 mya: dinosaurs extinct (except birds), mammals dominate
This marks the end of the Cretaceous and the beginning of the Tertiary.
Meteorite strike thought to be root cause
dust blocks solar radiation
tidal waves
fires
acid rain

5. Permian Extinction 251 mya
Four times as many extinctions as the other mass extinction events
only known mass extinction of insects
Root cause unknown
Meteorite
Volcanic activity
Continental drift
Pangea, unstable climate
Drop in sea level dries out shallow marine areas
Low oxygen limits terrestrial life to low elevations
Hypoxic oceans

6. Recovery After Extinctions
Takes tens of millions of years
So while we won’t destroy the planet, we will be extinct before it recovers

7. Estimate the Rate of Extinction
Challenges
Hard to be sure a species is extinct
Most of the world’s species are undescribed
Attempts
World Conservation Monitoring Centre
Most comprehensive list, ~ 90 species of plant, ~ 726 species of animal
Coendangered species ~ those we know little about, but are closely associated with endangered species
Species-Area relationship

8. Species Area Relationship
S = CAz
S, species; C & z, constants depending on taxa and island set; A, area
Combine with an estimate of tropical forest decline
Use that to estimate yearly extinction rate

9. Background Extinction Rate
Typical lifespan of a species is one million years, each year 1 of every million species should go extinct
if 10 million species, 10 species per year
Extinction rate from species-area curve is 27,000 species each year
Assuming human population stabilizes between billion
We may lose between 10-25% of species

10. Global Climate Change What makes glacial and interglacial periods?
Tilt of Earth on its axis 22-25o
Shape of Earth’s orbit
precession of equinoxes, where in orbit solstices and equinoxes occur
Together, a 100,000 year cycle of glacier and inter-glacial periods
Other factors
solar flares/variation in solar output
ocean currents and jet streams
presence of glaciers, CO2, greenhouse gases that affect solar radiation (absorbed) and radiant energy (reflected)
Variations in global and local trends in temperature

11. Historic Responses to Climate Change
Range shifts
toward poles or equator
well-documented in fossil record
Contract range to refugia, remnant habitat
Species tend to respond individually, not by whole-community shifts

12. Future Climate Currently in an interglacial period The role of CO2
enter an extended, super-interglacial period?
The role of CO2
greenhouse gas
concentration rising, 30% over pre-industrial levels
methane has doubled
corresponding rise in temperatures
even if CO2 isn’t the culprit, not a bad idea to curtail use of fossil fuels

13. Adapting to Future Changes
Cycles repeat every 100,000 years, biota survived those changes  evidence of adaptability
Limits to adaptability
populations already stressed by habitat loss, overexploitation…
amount of available habitat limited
barriers to dispersal including roads, urban areas, agricultural lands
Unprecedented changes?
Greater increase in temperature
geographic bottleneck, can only change range so much
mountain-top species
Between the devil and the deep blue sea
Rate of change too fast
mobility, dispersing and sedentary stages, philopatric spp.
Range and phenology changes already detected

15. Between Generational Mobility Key
Mobile Between Generations
Sedentary Between Generations
Mobile as Individuals
Migratory birds
Insects in ephemeral ponds
Pelagic fishes
Philopatric migrants
Insects in deep lakes
Anadramous fishes
Sedentary as Individuals
Territorial fishes with planktonic larvae
Early-successional plants; self-incompatible annuals
Intertidal molluscs
Desert-spring fishes
Late-successional plants; self-compatible perennials
Terrestrial molluscs