Announcements

1. Announcements • Fisheries problem is due now • No class on Wednesday • Problem set is due in your TA’s box by 10am on Wednesday, November 24th

2. Summary from Friday • Economics of fishing • What causes overfishing • Biological magnification • Aquaculture

3. Two minute quiz • With regard to fisheries, how is cost related to effort? How is effort related to population size? • How can government subsidies lead to overfishing? • Why are cheap fisheries more likely to be unsustainable than more expensive fisheries?

4. harvest (benefit or income) benefit matches cost at this point cost Rate of harvest (benefit or income) Cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

5. Government subsidies maintain jobs, provide protein, but lead to over- fishing Unsubsidized cost Rate of harvest (benefit or income) Subsidized or Unsubsidized cost Subsidized cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

6. Expensive fishery only profitable when population sizes are large, likely to be sustainable cost benefit matches cost at this point Rate of harvest (benefit or income) Cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

7. Cheap fishery profitable at small population size, likely to be unsustainable benefit matches cost at this point Rate of harvest (benefit or income) Cost cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

8. Case Study: Salmon Farming • People like salmon • Wild populations are threatened • Farming used as a solution for providing people with the fish they want to eat

9. Case Study: Salmon Farming • problems with salmon farming: • escapes • interbreeding with wild population • genetic engineering • competing with wild populations • farmed salmon are fed wild-caught fish • 3 pounds of wild fish for 1 pound of farmed salmon • pollution from waste and left-over food • disease spread • high density of fish in cages • aesthetics

10. Marine Reserves • Prime fish are larger and older • Normal fishing removes the largest fish • eventually all big fish are caught • quality of fish goes down • reproductive success of fish goes down • Reserves allow some fish to grow to maturity • Fishing improves protected area unprotected area

11. Agriculture • Costs and Benefits • Ecosystem Dynamics vs. Food Production • Ecological Problems associated with: • tillage • use of chemical pesticides, herbicides, etc. • irrigation

12. Agriculture • Like fisheries: similar concerns of balancing yield and sustainability • Environmental impacts can be large • Goal is to maximize productivity plant growth is usually nutrient limited yield nutrient supply

13. Agriculture • Benefit from crops = yield • Cost goes up with fertilizer application benefit cheap fertilizer expensive fertilizer yield nutrient supply

14. Fate of fertilizer • Taken up by plants • Leached from the system • enters systems downstream • Denitrified and converted into N gasses

15. Ecosystem Dynamics • A crop field is an ecosystem! • all natural biological processes can occur: • competition • herbivory • disease • why would a farmer care?

16. Ecosystem Dynamics • A crop field is an ecosystem! • all natural biological processes can occur: • competition • herbivory • disease • why would a farmer care? • achieving peak yield requires that these processes be limited

17. Ecosystem Dynamics • Monoculture= one species of plant • encourages competition, herbivory, and disease • fertilization  enhances growth of all plants, but crops are bred to be poor competitors • energy is allocated to the portions that people eat…not to roots for uptake • specialist herbivores do well in monoculture • disease can spread easily if all plants are the same species

18. Food Production • The goal of agriculture is to produce food • Farmers use many techniques to limit competition, herbivory and disease • tillage • herbicides • insecticides • fungicides • These things increase yields, but also have environmental impacts

19. Tillage • Plowing has been used for thousands of years • kill weeds • prepare the seed bed • stimulate nutrient mineralization

20. Tillage • Plowing is a powerful tool for maximizing crop production • Drawback: • loose, bare soil is vulnerable to erosion by wind and water

21. What is topsoil? • Topsoil is a semi-renewable resource • A horizon • Good water retention • Easy root penetration • Rich in organic matter • Can be 50-60 cm thick in prairie • Forms on the order of millimeters per year • About 1/3 has been lost from Midwest since European settlement

22. Announcements • This week we will: • Finish up Agriculture • Cover Conservation • Go over the midterm • Review for the final • Fill out evaluations • Have a science ethics discussion?

23. Two-minute quiz A. True or false: • A crop field is an ecosystem. • All of the fertilizer applied to a field is taken up by plants and used for growth. • The “dead zone” in the Gulf of Mexico is primarily caused by overfishing. B. Name three problems associated with aquaculture.

24. Summary from Friday • Salmon as an aquaculture case study • Marine Reserves • Agriculture • Costs and Benefits • Ecosystem Dynamics vs. Food Production • Ecological Problems associated with: • tillage  erosion

25. What is topsoil? • Topsoil is a semi-renewable resource • A horizon • Good water retention • Easy root penetration • Rich in organic matter • Can be 50-60 cm thick in prairie • Forms on the order of millimeters per year • About 1/3 has been lost from Midwest since European settlement

26. How much is topsoil worth? • Assume a loss of 1 inch of topsoil over 1 acre • 1” = 2.54 cm • 1 m2 = 10,000 cm2 • 1 acre = 4070 m2 • bulk density of topsoil = 1.4 g/cm3 • 1” over 1 acre = • 103,378,000 cm3 = 144,729,200 g = 145 Tons • Topsoil costs $20 per yard3 = 0.85 Tons • 145 Tons equals a cash loss of $3,412.00 • A 50 cm thick A horizon would be worth $67,000 per acre.

27. Can topsoil be replaced? • “Topsoil” from a nursery is usually compost + subsoil (B horizon) • where does the compost come from? • Would dredging the Mississippi Delta work? • A horizon has a mix of sand, silt, and clay • river or wind transports particles at different rates • how to put them back together? • how would you pay for dredging and transport • what about salinity?

28. Off-site costs of erosion • Sedimentation • fills up reservoirs, rivers, and lakes • 4 billion tons/year deposited in the U.S. • Effects: • loss of water storages • loss of fishing grounds • loss of wetlands and estuaries • loss of offshore reefs

29. How to limit erosion • Contour plowing: across a slope • creates lots of micro-dams • Cover-cropping: • plant something during the non-growing season to keep soil from eroding • No-till agriculture: don’t plow at all • seeds are drilled directly into soil • problems?

30. Use of Pesticides/Herbicides • Cost • expensive to buy and disperse • Health • many are toxic to humans • Ecological Effects • when washed downstream, can affect other ecosystems • can select for resistant strains of pests

31. Irrigation • Crops grow well in warm climates • sunlight • appropriate temperatures • good soil • Water often limits growth  irrigation

32. Salinization • Common result of irrigation • Salts precipitate out of solution in soil • Occurs when: • climate is warm and dry • water table is high • salts are present • Problem: too much salt kills plants • primary cause: plants are unable to take up water • secondary cause: toxicity of Na+ and Cl-

33. Mechanism of Salinization • Irrigation: most water contains a small amount of salt • accumulation over time • Surface soils dry up, and water from deeper soil moves upwards • Evaporation: leaves salts on surface

34. Food Production • How can farmers reduce environmental impacts while still keeping yields high? • limit monoculture • intercrop or rotate crops • plant a variety of genotypes • currently, some fields have a single clone of corn • control pests with natural predators • use ladybugs to control aphids • use chemicals only when necessary

35. Conservation • Long term management plans can be used to conserve resources • Resource Management can include: • management of materials • management of plants or animals that are used for food, fiber, or other purposes

36. Resource management There are 3 different classes of resources: • Renewable • air • Semi-renewable: renewable if not over-harvested • water • soil • fish populations • Non-renewable • fossil fuels • certain minerals

37. Resource management • Biological resources are fragile! • Populations can easily be over-harvested • fisheries are often over-fished

38. Conservation • keystone species • “flagship species” • long-term land protection: reserves single-species management

39. Announcements • Professor Levine’s announcement • This week we will: • Finish up Conservation • Go over the midterm • Review for the final • Fill out evaluations • Have a science ethics discussion?

40. Two-minute quiz A. True or false: • A flagship species must be a keystone species. • Coal is a renewable resource. • Cover cropping can reduce erosion during the non-growing season. B. Name two problems caused by sedimentation.

41. Summary from Monday • Replacement of Topsoil • cost • feasibility • Sedimentation • Limiting Erosion • Pesticides and Herbicides • Irrigation and Salinization • Resource Management and Conservation

42. Designing a reserve • Shape and Size • determine minimum viable area (MVA) needed for each population • estimates of energy use by trophic level • territoriality • landscape structure • one large or several small?

43. A larger area can support more animals

44. Edge effect • circular reserves have less edge • edge effects include gradients in: • light • moisture • wind • noise • pollution • outside may be unprotected

45. Shape determines edge effect

46. minimize edge effects more complete food chains lower risk of inbreeding BUT… at risk from environmental disaster and disease may be easier to accomplish politically can create corridors so than animals can interbreed One largeor several small?

47. = full protection = limited protection