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Chapter 51

Chapter 51. Ecosystems. Chapter 51. Ecosystems. Many global environmental problems have emerged recently. Ecosystems consist of all the organisms that live in an area along with the nonbiological components. Energy and nutrient flows link the biotic and abiotic environments. .

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Chapter 51

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  1. Chapter 51 Ecosystems

  2. Chapter 51

  3. Ecosystems • Many global environmental problems have emerged recently. • Ecosystems consist of all the organisms that live in an area along with the nonbiological components. • Energy and nutrient flows link the biotic and abiotic environments.

  4. Energy Flow and Trophic Structure • All ecosystems consist of four components that are linkedby the flow of energy: • Primary producers • Consumers • Decomposers • Abiotic environment (Fig. 51.1)

  5. Figure 51.1 External energy source PRIMARY PRODUCERS CONSUMERS DECOMPOSERS ABIOTIC ENVIRONMENT

  6. Figure 51.1 CONSUMERS DECOMPOSERS External energy source PRIMARY PRODUCERS ABIOTIC ENVIRONMENT

  7. Energy Flow and Trophic Structure • Key points about energy flow through ecosystems. • Energy enters ecosystems in the form of sunlight that is usedin photosynthesis by producers. • Plants use only a tiny fraction of the total radiation that isavailable to them. • Only a tiny fraction of fixed energy actually becomes availableto consumers.

  8. Energy Flow and Trophic Structure • Key points about energy flow through ecosystems. • Most net primary production that is consumed enters the decomposer food web. • From there, only a small fraction is used for secondaryproduction by herbivores and carnivores. • Most energy fixed during photosynthesis is used for respiration, not synthesis of new tissues. (Fig. 51.2)

  9. Figure 51.2 Energy source: 1,254,000 kcal/m2/year 0.8% energy captured by photosynthesis. Of this... …55% lostto respiration …45% supports growth (Net primary production) …34% enters decomposer food web as dead material …11% entersgrazing food web

  10. Figure 51.2 0.8% energy captured by photosynthesis. Of this... …55% lost to respiration …45% supports growth (Net primary production) …34% enters decomposer food web as dead material …11% enters grazing food web Energy source: 1,254,000 kcal/m2/year

  11. Figure 51.3a Terrestrial productivity 0–100 100–200 200–400 400–600 600–800 >800 Productivity ranges (g/m2/yr)

  12. Figure 51.3b Marine productivity <35 35–55 55–90 >90 Productivity ranges (g/m2/yr)

  13. Figure 51.4 80.7% respiration Energy derived from plants 17.7% excretion 1.6% growth and reproduction

  14. Figure 51.5 49.4 µm 305 nm Predators of decomposers: Spider Salamander Centipede Puffball Puffball Mushroom Earthworm Millipede Nematodes Primary decomposers: Bacteria and archaea Pillbugs

  15. Energy Flow and Trophic Structure • Trophic structure • Organisms that obtain their energy from the same type ofsource occupy the same trophic level. • Each feeding level within an ecosystem represents a trophiclevel.

  16. Energy Flow and Trophic Structure • Trophic structure • Organisms at the top trophic level are not eaten by any other organisms. • Productivity is highest at the lowest trophic level. (Fig. 51.6a,b)

  17. Figure 51.6a Trophic levels Trophic level 4 3 2 1 Feeding strategy Secondary carnivore Carnivore Herbivore Autotroph Decomposer food chain Grazing food chain Cooper’s hawk Owl Shrew Earthworm Dead maple leaves Robin Cricket Maple tree leaves

  18. Figure 51.6b Pyramid of productivity 4 Secondary carnivore 3 Carnivore 2 Herbivore 1 Autotroph Productivity

  19. Energy Flow and Trophic Structure • Food chains and food webs • Food chains are typically embedded in more complexfood webs. (Fig. 51.7a,b)

  20. Figure 51.7a Food chain Pisaster (a sea star) Thais (a snail) Bivalves (clams, mussels)

  21. Figure 51.7b Food web Pisaster Thais Limpets Gooseneck barnacles Acorn barnacles Chitons Bivalves

  22. Energy Flow and Trophic Structure • Food chains and food webs • The maximum number of links in any food chain or web ranges from 1 to 6. (Fig. 51.7c) • Hypotheses offered to explain this: • Energy transfer may limit food-chain length. • Long food chains may be more fragile. • Food-chain length may depend on environmental complexity.

  23. Figure 51.7c 1 2 3 4 5 6 Food chains tend to have few links. 10 8 6 4 2 0 Streams Lakes Terrestrial Average number of links = 3.5 Number of observations Number of links in food chain

  24. Biogeochemical Cycles • The path an element takes as it moves from abiotic systems through living organisms and back again is referred to asits biogeochemical cycle. (Fig. 51.8)

  25. Figure 51.8 Plants Consumption Herbivore Assimilation Feces or urine Death Death Detritus Uptake Soil nutrient pool Decomposer food web Loss to erosion or leaching into groundwater

  26. Figure 51.9 upper Boreal forest

  27. Figure 51.9 lower Tropical rain forest

  28. Biogeochemical Cycles • A key feature in all cycles is that nutrients are recycledand reused. • The overall rate of nutrient movement is limited most by decomposition of detritus. • The rate of nutrient loss is a very important characteristic inany ecosystem. (Fig. 51.10a,b)

  29. Figure 51.10a upper Devegetation experiment Choose two similar watersheds. Document nutrient levels in soil organic matter, plants, and streams.

  30. Figure 51.10a lower Control Clearcut Devegetate one watershed and leave the other intact. Monitor the amount of dissolved substances in streams.

  31. Figure 51.10b 1965–66 1966–67 1967–68 1968–69 1969–70 Nutrient runoff results 1000 800 600 400 200 0 Devegetated Net dissolved substance (kg/ha) Control Year

  32. Biogeochemical Cycles • Nutrient flow among ecosystems links local cycles into one massive global biogeochemical cycle. • The carbon cycle and the nitrogen cycle are examples of major, global biogeochemical cycles. (Fig. 51.11, 51.13a) • Humans are now disrupting almost all biogeochemical cycles. This can have very harmful effects. (Fig. 51.12a,b; 51.13b)

  33. Figure 51.11 THE GLOBAL CARBON CYCLE All values in gigatons of carbon per year Atmosphere: 750 (in 1990) +3.5 per year Photosynthesis: 102 Respiration: 50 Fossilfuel use: 6.0 Deforestation: 1.5 Physical and chemical processes: 92 Decomposition: 50 Physical and chemical processes: 90 Land, biota, soil, litter, peat: 2000 2 Rivers: 1 Ocean: 40,000 Aquatic ecosystems Terrestrial ecosystems Human–induced changes

  34. Figure 51.13a THE GLOBAL NITROGEN CYCLE Atmospheric nitrogen (N2) Protein and nucleic acid synthesis Bacteria in mud use N-containing molecules as energy sources, excrete (N2) Lightning and rain Run–off Industrial fixation Nitrogen fixing cyanobacteria Decomposition of detritus into ammonia Nitrogen-fixing bacteria in roots and soil Mud

  35. Figure 51.12a 1860 1880 1900 1920 1940 1960 1980 Human-induced increases in CO2 flux over time 6 5 4 3 2 1 0 Fossil fuel use Annual flux of carbon (1015g) Land use Year

  36. Figure 51.12b 360 350 340 330 320 310 Atmospheric CO2 CO2 concentration (ppm) 1960 1970 1980 1990 Year

  37. Figure 51.13b Sources of nitrogen fixation 160 140 120 100 8060 40 20 0 Lightning Fossil fuels Nitrogen-fixing crops Amount of nitrogen (gigatons/year) Biologicalfixation Nitrogenfertilizer Natural sources Human sources

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