1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 58 LECTURE SLIDES

2. 2 Dynamics of Ecosystems Chapter 58

3. Biogeochemical Cycles Ecosystem –Includes all the organisms that live in a particular place, plus the abiotic environment in which they live and interact Biogeochemical cycles –Chemicals moving through ecosystems –Biotic and abiotic processes Biogeochemical cycles usually cross the boundaries of ecosystem –One ecosystem might import or export chemicals to another 3

4. Biogeochemical Cycles Carbon cycle –Carbon is a major constituent of the bodies of organisms –Carbon fixation: metabolic reactions that make nongaseous compounds from gaseous ones –Aerobic cellular respiration releases CO 2 –Methanogens: produce methane (CH 4 ) by anaerobic cellular respiration 4

5. 5 Carbon cycle

6. Biogeochemical Cycles Over time, globally, the carbon cycle may proceed faster in one direction –This can cause large consequences if continued for many years –Earth’s present reserves of coal, and other fossil fuels were built up over geological time –Human burning of fossil fuels is creating large imbalances in the carbon cycle –The concentration of CO 2 in the atmosphere is going up year by year 6

7. Biogeochemical Cycles Water Cycle –All life depends on the presence of water –60% of the adult human body weight is water –Amount of water available determines the nature and abundance of organisms present –It can be synthesized and broken down Synthesized during cellular respiration Broken down during photosynthesis 7

8. Biogeochemical Cycles Basic water cycle –Liquid water from the Earth’s surface evaporates into the atmosphere –Occurs directly from the surfaces of oceans, lakes, and rivers –Terrestrial ecosystems: 90% of evaporation is through plants –Water in the atmosphere is a gas –Cools and falls to the surface as precipitation 8

9. 9 Water cycle

10. Biogeochemical Cycles Groundwater: under ground water –Aquifers: permeable, underground layers of rock, sand, and gravel saturated with water –Important reservoir: 95% of fresh water used in United States –Two subparts: Upper layers constitute the water table Lower layer can be tapped by wells 10

11. Biogeochemical Cycles Changes in the supply of water to an ecosystem can radically alter the nature of the ecosystem Deforestation disrupts the local water cycle 11 Water that falls as rain drains away Tropical rain forest  semiarid desert

12. Biogeochemical Cycles Nitrogen Cycle –Nitrogen is a component of all proteins and nucleic acids –Usually the element in shortest supply –Atmosphere is 78% nitrogen –Availability Most plants and animals cannot use N 2 (gas) Use instead NH 3, and NO 3 – 12

13. Biogeochemical Cycles Nitrogen fixation: synthesis of nitrogen containing compounds from N 2 –Nitrification: N 2 → NH 3 → NO 3 – –Denitrification: NO 3 – → N 2 –Both processes are carried out by microbes: free or living on plant roots –Nitrogenous wastes and fertilizer use radically alter the global nitrogen cycle –Humans have doubled the rate of transfer of N 2 in usable forms into soils and water 13

14. 14 Nitrogen Cycle

15. Biogeochemical Cycles Phosphorus cycle –Phosphorus is required by all organisms Occurs in nucleic acids, membranes, ATP –No significant gas form –Exists as PO 4 3– in ecosystems –Plants and algae use free inorganic phosphorus; animals eat plants to obtain their phosphorus 15

16. 16 Phosphorus cycle

17. Biogeochemical Cycles Limiting nutrient –Weak link in an ecosystem; shortest supply relative to the needs of organisms –Nitrogen and phosphorus can also be limiting nutrients for both terrestrial and aquatic ecosystems –Iron is the limiting nutrient for algal populations in about 1/3 of world’s oceans 17

18. 18 When wind brings in iron-rich dust, algal populations proliferate, provided the iron is in a usable chemical form In this way, sand storms in the Sahara Desert, by increasing the dust in global winds, can increase algal productivity in Pacific waters

19. Biogeochemical Cycles Biogeochemical cycling in a forest ecosystem – Hubbard Brook Experiment –Undisturbed forests are efficient at retaining nutrients –Disturbed (cut trees down) – amount of water runoff increased by 40% Loss of calcium increased ninefold Loss of phosphorus did not increase Loss of NO 3 – at rate of 53 kg/hectare/yr 19

20. 20 The Hubbard Brook Experiment Orange curve shows nitrate concentration in the runoff water from the deforested watershed; green curve shows the nitrate concentration in runoff from an undisturbed watershed

21. Flow of Energy in Ecosystems Energy is never recycled Energy exists as: –Light –Chemical-bond energy –Motion –Heat First Law of Thermodynamics: energy is neither created nor destroyed; it changes forms 21

22. Flow of Energy in Ecosystems Second Law of Thermodynamics: whenever organisms use chemical- bond or light energy some is converted to heat (entropy) Earth functions as an open system for energy Sun is our major source of energy 22

23. Flow of Energy in Ecosystems Earth’s incoming and outgoing flows of radiant energy must be equal for global temperatures to stay constant Human activities are changing the composition of the atmosphere Greenhouse effect: heat accumulating on Earth, causing global warming 23

24. Flow of Energy in Ecosystems Trophic levels: which level an organism “feeds” at Autotrophs: “self-feeders” synthesize the organic compounds of their bodies from inorganic precursors –Photoautotrophs: light as energy source –Chemoautotrophs: energy from inorganic oxidation reactions (prokaryotic) Heterotrophs: cannot synthesize organic compounds from inorganic precursors –Animals that eat plants and other animals 24

25. Flow of Energy in Ecosystems Trophic levels –Primary producers: autotrophs –Consumers: heterotrophs Herbivores: first consumer level Primary carnivores: eat herbivores Secondary carnivores: eat primary carnivores or herbivores Detritivores: eat decaying matter –Decomposers: microbes that break up dead matter 25

26. 26 Trophic levels within an ecosystem

27. Flow of Energy in Ecosystems Productivity: the rate at which the organisms in the trophic level collectively synthesize new organic matter –Primary productivity: productivity of the primary producers –Respiration: rate at which primary producers break down organic compounds 27

28. Flow of Energy in Ecosystems Gross primary productivity (GPP): raw rate at which primary producers synthesize new organic matter Net primary productivity (NPP): is the GPP less the respiration of the primary producers Secondary productivity: productivity of a heterotroph trophic level 28

29. Flow of Energy in Ecosystems Fraction of incoming solar radiant energy captured by producers –Something around 1% per year –Primary producers capture this in chemical bond energy Carry out their own respiration Losses to heat –Heterotrophs have only chemical- bond energy left in primary producers 29

30. 17% growth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31. 17% growth 33% cellular respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

32. 32 Amount of chemical-bond energy decreases as energy is passed from one trophic level to the next –50% of chemical-bond energy is not assimilated and is egested in feces –33% of ingested energy is used for cellular respiration –17% ingested energy is converted into insect biomass Some is available to next consumer 17% growth 50% feces 33% cellular respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. Ecologists figure as a rule of thumb that the amount of chemical-bond energy available to a trophic level over time is about 10% of that available to the preceding level over the same period of time 33

34. 34 Ecosystems vary considerably in their NPP

35. Flow of Energy in Ecosystems Number of trophic levels is limited by energy availability –Limits on top carnivores: exponential decline of chemical-bond energy limits the lengths of trophic chains and the numbers of top carnivores an ecosystem can support Only about 1/1000 of the energy captured by photosynthesis passes all the way through to secondary carnivores 35

36. 36 Flow of energy through the trophic levels of Cayuga Lake Flow of Energy in Ecosystems

37. Ecological pyramids –Pyramid of energy flow or pyramid of productivity –Pyramid of biomass May be inverted –Pyramid of numbers 37

38. 38

39. Trophic-level interactions Trophic cascade: process by which effects exerted at an upper level flow down to influence two or more lower levels –Top-down effects: when effects flow down –Bottom-up effects: when effect flows up through a trophic chain 39

40. 40 Top-down effects Enclosures with brown trout had fewer herbivorous invertebrates and more algae than ones without trout

41. 41 Top-down effects Stream enclosures with large carnivorous fish have fewer primary carnivores, more herbivorous insects, and a lower level of algae

42. 42 Trophic cascade in a large-scale ecosystem Along the West Coast of North America, the sea otter/sea urchin/kelp system exists with low or high sea otter populations

43. Flow of Energy in Ecosystems Human removal of carnivores produces top-down effects –Aldo Leopold: posited effects long before scientific hypothesis articulated –Overfishing of cod – 10% their previous numbers Prey of cod have become more abundant –Jaguars and mountain lions absent on Barro Colorado Island Smaller predators become abundant 43

44. Flow of Energy in Ecosystems To predict bottom-up effects, must take into account life history of the organisms –When primary productivity is low, producer populations cannot support herbivore populations –As primary productivity increases, herbivore populations increase –Increased herbivore populations lead to carnivore populations increasing 44

45. 45 Bottom-up effects model Experimental study

46. 46 Biodiversity and Stability David Tilman: species richness may increase stability of an ecosystem Plots with more species showed less year- to-year variation in biomass Drought: decline in biomass negatively related to species richness

47. Biodiversity and Stability Tilman’s conclusion not accepted by all ecologists Critics question the validity and relevance: –When more species are added to a plot, the greater the probability that one species will be highly productive –Plots would have to exhibit “overyielding” 47

48. Biodiversity and Stability Species richness is influenced by ecosystem characteristics –Primary productivity –Habitat heterogeneity Accommodate more species –Climatic factors More species might be expected to coexist in seasonal environment 48

49. 49 Factors that affect species richness Biodiversity and Stability

50. Tropical regions have the highest diversity –Species diversity cline: biogeographic gradient in number of species correlated with latitude Reported for plants and animals –Evolutionary age of tropical regions –Increased productivity –Stability/constancy of conditions –Predation –Spatial heterogeneity 50

51. 51 Latitudinal cline in species richness Biodiversity and Stability

52. Island Biogeography Robert MacArthur and Edward O. Wilson proposed that species–area relationship was a result of the effect of geographic area and isolation –Islands have a tendency to accumulate more and more species through dispersion –Rate of colonization must decrease as the pool of potential colonizing species becomes depleted –The rate of extinction should increase with more species on an island 52

53. Island Biogeography At some point, extinctions and colonizations should be equal MacArthur and Wilson equilibrium model –Island species richness is a dynamic equilibrium between colonization and extinction –Island size and distance from the mainland would affect colonization and extinction 53

54. 54 Long-term experimental field studies are suggesting that the situation is more complicated than first believed Equilibrium model