Announcements

1. Announcements • Check your syllabus with the one online to make sure it is the right one! • No reading assignment for section this week • Focus on your textbook

2. Two-minute Quiz Imagine that you are a wetland ecologist. It is early summer, and you and your limnologist best friend are mapping a system of streams, rivers, and wetlands near the coast in northern Siberia. • You ford a small, rocky, fast moving stream. True or false: Most of the litter in this stream is likely to be highly processed. • You follow the water downstream until it slows and pools in an area filled with sedges and accumulated organic matter. Are there many trees in this biome? • You hike overland to a large river that empties into the sea. You taste the water and it is brackish. The birding is great. Where are you now? (multiple answers possible for this one)

3. Summary from Wednesday • aquatic ecosystems • differences between low & high order streams • production vs. biomass pyramids • lakes • light penetration • thermal stratification and O2 content • phytoplankton and abiotic factors over the year • oligotrophic vs. eutrophic • wetlands • biogeochemistry

4. Wetland Biogeochemistry • When land is flooded, O2 gets used up by decomposers and the soil becomes anaerobic • Demand for O2 is still high • Other minerals containing oxygen get reduced • Reduction is when a compound gains an electron- in this case by giving up an O2 atom • Some molecules release O2 more easily than others • If the water level drops, O2 enters the soil again, and the reduced substances can get oxidized O2  NO3-  Fe(OH)3  MnO2  SO42-  CO2

5. Saltwater vs. Freshwater Systems • Salt marshes • sulfur cycling important CO2 H2S SO42- organic matter SO42-

6. Saltwater vs. Freshwater Systems • Freshwater systems • decomposition is slow • organic matter accumulates • storage of carbon • reduction of CO2 produces methane (CH4) O2  NO3-  Fe(OH)3  MnO2  SO42-  CO2

7. Environmental Concerns in Wetlands • Drainage • either for agriculture and development, or to use the available water • Pollution • wetlands are in low-lying areas

8. The open ocean is most like… • a temperate rain forest • the chaparral • the desert • a Mediterranean grassland …with regard to productivity.

9. Where is the ocean most productive? Where nutrients are available: • near the coast • rivers bring nutrients • in upwelling zones

10. Coastal Upwelling

11. Coastal Upwelling Off-shore winds blow southward.

12. Coastal Upwelling Friction and the effects of the Earth's rotation cause the surface layer of the ocean to move away from the coast.

13. Coastal Upwelling As the surface water moves offshore, cold, nutrient-rich water comes up from below, replacing it.

14. Euphotic zone Aphotic zone Sediment Why are nutrients down deep? Why are surface waters low in nutrients? Dead material sinks to the bottom, where it is dark and photosynthesis is not taking place

15. Coral reefs • Coral reefs are extremely productive • Visibility is great! • But we know that nutrient-rich water is murky How is this possible? Where are the nutrients?

16. Coral reefs • Efficient cycling of nutrients • Complex relationships between organisms • zooxanthellae in coral • intricate food webs

17. Ecology subfields: • Population Ecology: • the study of individuals of a certain species occupying a defined area during a specific time

18. Population Ecology • Population density • # of individuals of a certain species in a given area • Population demography • a way of assessing well-being • proportion of males to females • birth rates • death rates • replacement of parents by next generation (fitness) • life expectancy

19. The Tools of Population Ecology • Modeling • Creation of Life Tables

20. Why are models powerful? You can use them to: • synthesize information • look at a system quantitatively • test your understanding • predict system dynamics • make management decisions

21. Population Growth • t= time • N = population size (number of individuals) • dN = change in population size • dt = change in time • dN/dt= rate in change of population size • r = growth constant; maximum rate of population increase • K = carrying capacity; maximum population size

22. dN dt Population Growth • Assume a fixed rate of reproduction per individual • for starters, let’s assume no limits on growth • change in number of individuals over time would be equal to the number of individuals multiplied by a growth constant = r * N • exponential growth

23. Population size (N) Time (t)

24. Can the population really grow forever? Population size (N) Time (t)

25. Can the population really grow forever? What should this curve look like to be more realistic? Population size (N) Time (t)

26. Population Growth • logistic growth • assume that as a population increases, it becomes limited by resources • growth rate should decline when the population size gets large • symmetrical S-shaped curve with an upper asymptote

28. Announcements • Women in Science and Engineering • “Applying to Graduate School in Sciences” workshop and lunch Oct. 27th • Check your syllabus with the one online to make sure it is the right one! • No additional reading assignment for section this week • Focus on your textbook reading • Bring your calculator to section

29. dN dt • = r * N Summary from Monday • Wetland biogeochemistry • H2S production in brackish wetlands • Methane (CH4) production in freshwater wetlands • Open oceans vs. coastal areas • Population ecology • The power of modeling • Modeling exponential growth • Logitstic growth • Resources limit population growth N t

31. dN dt Population Growth • How do you model logistic growth? • How do you write an equation to fit that S-shaped curve? • Start with exponential growth • = r * N

32. N K dN dt Population Growth • How do you model logistic growth? • How do you write an equation to fit that S-shaped curve? • Start with exponential growth • = r * N (1 – )

33. N K dN dt Population Growth • logistic growth • = r * N (1 – )

34. ≈ 0 N K N K dN dt dN dt • = r * N (1 – 0) Population Growth • logistic growth • so, when N is much smaller than K • = r * N (1 – ) exponential growth

36. ≈ 0 ≈ 1 N K N K N K dN dt dN dt dN dt • = r * N (1 – 0) • = r * N (1 – 1) Population Growth • logistic growth • so, when N is much smaller than K • when N is equal to K • = r * N (1 – ) exponential growth no growth

38. > 1 ≈ 1 ≈ 0 N K N K N K N K dN dt dN dt dN dt dN dt • = r * N (1 – 0) • = r * N (1 – 2) • = r * N (1 – 1) Population Growth • logistic growth • so, when N is much smaller than K • when N is equal to K • when N is much larger than K • = r * N (1 – ) exponential growth no growth population shrinks

40. What is carrying capacity? • where births = deaths • number of individuals an area can support through the most unfavorable time of year • population an area can support without degradation of the habitat

41. What limits populations? • Density-dependent factors: • intra-specific competition • food • space • contagious disease • waste production • Density-independent factors: • disturbance, environmental conditions • fire • flood • colder than normal winter

42. = r * N (1 – ) N K N K K K K-N K dN dt dN dt dN dt • = r * N ( ) Species interactions • How do we model them? • Start with logistic growth • = r * N ( - ) Use this equation for 2 different species

43. dN1 dt dN2 dt K1-N1 K1 K2-N2 K2 Species interactions • Population 1  N1 • Population 2  N2 • But the growth of one population should have an effect the size of the other population • = r1 * N1 ( ) • = r2 * N2 ( )

44. Species interactions • New term for interactions a12 effect of population 2 on population 1 a21 effect of population 1 on population 2 • Multiply new term by population size the larger population 2 is, the larger its effect on population 1 (and vice versa) a12 * N2 a21 * N1

45. dN1 dt dN2 dt Species interactions • If two species are competing, the growth of one population should reduce the size of the other • Population 1  N1 • Population 2  N2 K1 - N1 - a12 N2 K1 • = r1 * N1 K2 - N2 - a21 N1 K2 • = r2 * N2

46. dN1 dt dN2 dt Species interactions • If two species are competing, the growth of one population should reduce the size of the other • Population 1  N1 • Population 2  N2 Because this is a negative term, K is reduced K1 - N1 - a12 N2 K1 • = r1 * N1 K2 - N2 - a21 N1 K2 • = r2 * N2

47. dN1 dt dN2 dt Species interactions • If it is a predator-prey relationship, then the two populations have opposite effects on one another • Prey (N1) • Predator (N2) Because this is a negative term, K is reduced K1 - N1 - a12 N2 K1 • = r1 * N1 Because this is a positive term, K is increased K2 - N2 + a21 N1 K2 • = r2 * N2

48. dN1 dt dN2 dt Species interactions • If it is a mutually beneficial relationship, then the two populations increase each other’s size • Population 1  N1 • Population 2  N2 Because this is a positive term, K is increased K1 - N1 + a12 N2 K1 • = r1 * N1 Because this is a positive term, K is increased K2 - N2 + a21 N1 K2 • = r2 * N2

49. Problems with simple logistic growth • births and deaths not separated • you might want to look at these processes separately • predation may have no effect on birth rate • no age structure • when is a fish just a fish?

50. Announcements • Check your syllabus with the one online to make sure it is the right one! • Bring your calculator to section