1. Reading Assignments BSCI – Chapter 7 CONS – Chapters 4-5

2. Deterministic vs. Extrinsic Stochastic Threats Frequency Mean Growth Rate

3. Stochastic Threats and Population Size time ln(N) time ln(N)

4. “Quiz” time ln(N)

5. The aspen sunflower

6. Environmental Variation

7. Good years...

8. Bad years

9. Snowpack and Frost Damage

10. How might climate change affect this sunflower?

13. Species / Population B Species / Population A Extinction by genetic swamping Hybridization Species B’ Causes of Extinction (Genetic Swamping) Time

14. What IS Causing Extinction? Habitat Destruction73 Introduced species68 Chemical pollutants 38 Hybridization38 Overharvesting15 Extinction Threats for North American Freshwater Fishes (IUCN)

15. Topics: Historical Extinctions What is the background rate of extinctions? What are mass extinctions? How long does recovery from mass extinctions take? Causes of select prehistoric extinctions. What is the current rate of extinctions?

16. “Pseudo-extinction” CladogenesisAnagenesis

17. Sideling Hill, MD

18. Stratigraphic Geology (study of layered rock) Sedimentation Stratum (singular) Beds = strata > 1 cm Lamina(e) = stratum(a) < 1 cm Lithification Fossils

20. Characteristics of a ME Brief relative to the expected duration of the taxa Involve considerable numbers of taxa

21. Proposed Agents of Mass Extinctions Changes in climate and sea level (marine regression). Asteroid impacts (especially K/T).

22. Stanley’s research on bivalves during Pleistocene cold adapted: no change warm adapted: no change Gulf stream cold adapted: no change warm adapted: declined Glacier Climate Change

23. Marine Regression Continental shelf: loss of habitat refuges Current sea level Conical island: no loss of habitat

24. Marine Regression 87% of recent marine families have > 1 species in shallows. Expected extinction with refuges: 100 - 87 = 13%. Observed extinction of families: 52% (Permian). Conclusion: marine regression is not the only cause of mass extinction (Jablonski).

25. Climate Change Evidence There were major glaciations at the beginning of the Ordovician and Devonian ME’s. No major glaciations accompanied the Permian, Triassic and Cretaceous ME’s. Another major glaciation, ca. 300 million years ago, and lasting 90 million yrs, did not result in an ME. Tentative Conclusion: glaciations might cause extinctions in marine invertebrates, but are not currently regarded as a necessary cause for ME’s.