Great Ideas in Science: Lecture 14 – Ecosystems

1. Great Ideas in Science:Lecture 14 – Ecosystems Professor Robert Hazen UNIV 301 All living systems live in ecosystems of many interacting organisms.

2. Three Definitions of Evolution • Evolution as Change: Life on Earth has changed over time • Common descent: All living things on Earth descended from a common ancestor. • Natural selection: The process by which life evolved is Darwinian natural selection

3. First Definition of Evolution: Change Over Time Observational evidence overwhelmingly supports the theory that life originated on Earth billions of years ago as a single cell, and has been changing ever since. • Fossils • Molecular Biology • Cellular biology • Genetics • Comparative anatomy • Observations of nature and of breeding

4. Extinct Animals

5. If you accept observational evidence, then the unambiguous conclusion is that life has changed over time. TRILOBITES

6. Three Related Terms • Creationism • Young Earth Creationism • Scientific Creationism

7. 1. Creationism • Creationists believe that God created the universe and life. • Many creationists accept the Bible’s creation story as a metaphor; they rely on empirical evidence (Psalm 19). • Many scientists are also creationists in this sense.

8. 2. Young Earth Creationism • Young-Earth creationists believe in a literal reading of Genesis. • Earth is about 10,000 years old. • Geology features caused by Noah’s Flood. • All species created in modern form. • Minor evolutionary changes only. • For many young-Earth creationists, the findings of science are irrelevant at best, and possibly dangerous and subversive.

9. 3. Scientific Creationism • Scientific creationists search for empirical evidence that supports the tenets of young-Earth creationism. • SC is not science, because its basic tenets are not subject to change based on empirical evidence. • Even if its tenets conformed to observational evidence, “scientific” creationism would not be science. • Should creationism be taught in the science classroom?

10. Second Definition of Evolution: Common Descent • Common descent means that all living things descended from the first living cell. • Tree diagrams reveal ancestral relationships.

11. Second Definition of Evolution: Common Descent • Common descent means that all living things descended from the first living cell. • Tree diagrams reveal ancestral relationships. • The search for fossil intermediates supports common descent.

12. Fossils Fossils prove that life on Earth has changed over time; most extinct. Fossils demonstrate that these changes are gradual and progressive (simple to complex) All known fossils fit into a pattern of continuous evolution.

13. Geological Time

14. Fossils Strata Younger = higher

15. Gradual Evolution

16. Objections to Common Descent “Darwinists rarely mention the whale because it presents them with one of their most insoluble problems. They believe that somehow a whale must have evolved from an ordinary land-dwelling animal, which took to the sea and lost its legs. … A land mammal that was in the process of becoming a whale would fall between two stools – it would not be fitted for life on land or sea, and would have no hope of survival.” Alan Haywood, 1985

17. Whale Evolution Ambulocetus

18. Whale Evolution Ambulocetus

19. Whale Evolution Rodhocetus

20. Whale Evolution Basilosaurus

21. Whale Evolution The power of the theory of evolution by natural selection is its predictive power. If we see a gap in the fossil record, then we can predict what kind of rock and what age of rock to search, and we can make a good guess as to what kind of fossil we’re likely to find.

22. From DNA to Protein • Transcription: Use DNA to make mRNA • Attach mRNA to ribosome • Translation: RNA to amino acids • Fold amino acids into protein

23. The Genetic Code

24. The Cell Theory, 1839 • All living things are composed of cells • The cell is the fundamental unit of life • All cells arise from previous cells

25. CONCLUSIONS: Observational evidence overwhelmingly supports the hypothesis of common descent for all known life forms, living and fossil, on Earth.

26. Third Definition of Evolution: Natural Selection (Darwin) • Populations exhibit variation. • More individuals are born than will survive. • The most fit individuals are more likely to reproduce.

27. Charles Darwin (1809-1882)

28. Charles Darwin:The Beagle at Galapagos

29. Microevolution Phacops trilobites: Almost unchanged from 440 to 370 million years!

30. Microevolution

31. Unanswered Questions about Evolution How does macroevolution occur? Why are some species static? What is the rate of evolution? What is the rate of extinction? What causes mass extinctions?

32. Macroevolution How did such an amazing diversity of trilobites arise?

33. Eye Evolution “To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree …” Charles Darwin, On the Origin of Species

35. Eye Evolution Selection rules for model eye evolution: 1. Vary curvature, aperture, and central refractive index randomly by 1%. 2. If visual acuity (spatial resolution) increases, then retain that variation. D. Nilsson & S. Pelger, “A pessimistic estimate for the time required for an eye to evolve.”Proc. R. Soc. Lond. B 256, 53-58 (1994).

36. Eye Evolution This evolutionary sequence is continuously driven by selection.

37. What is the Rate of Evolution? Punctuated Equilibria (a) versus Gradualism (b)

38. Mass Extinctions

39. Mass Extinctions and the Rate of Evolution • Rate of extinction • 10%-20% extinct in 5-6 million years • Mass extinctions • 30%-90% extinct • At least 5 episodes • Mechanisms • Asteroids • volcanoes

40. Mass Extinctions Evidence from the Fossil Record

41. Mass Extinctions Evidence from Iridium

42. Mass Extinctions Evidence from Foraminifera

43. What Causes Mass Extinctions? Human Activities

44. What Causes Mass Extinctions? Human Activities

45. Ecology and Ecosystems Ecology: The study of natural living systems Ecosystems: Consist of biotic and abiotic components Community: All organisms in an ecosystem • Producers • Consumers • Decomposers

46. Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms • Ecosystems consist of both living and nonliving parts • Energy flows through • Matter is recycled • Every organism occupies an ecological niche (two species cannot occupy same niche) • Stable ecosystems achieve balance among populations • Ecosystems can be disrupted

47. Every Ecosystem Consists of Both Living and Nonliving Parts Abiotic: The chemical and physical environment Biotic: All living organisms that form the ecological community

48. Energy Flows Through Ecosystems • Food Web • Interactions of organisms • Trophic Levels • Photosynthetic plants • Herbivores • Carnivores • Decomposers • Most energy is lost as heat • 10% is transferred from one level to the next.

49. Matter is Recycled by Ecosystems Carbon: Atoms continuously cycle

50. Stable Ecosystems Achieve a Balance Among Their Populations Homeostasis is a balance among populations. Resources are always limited. While we observe some variation in populations, overall they are relatively constant.