1. Chapter 51 Ecosystems

2. Chapter 51

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

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

5. External energy source PRIMARY PRODUCERS CONSUMERSDECOMPOSERS ABIOTIC ENVIRONMENT Figure 51.1

6. External energy source PRIMARY PRODUCERS CONSUMERSDECOMPOSERS ABIOTIC ENVIRONMENT Figure 51.1

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

8. Energy Flow and Trophic Structure n 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 secondary production by herbivores and carnivores. Most energy fixed during photosynthesis is used for respiration, not synthesis of new tissues. (Fig. 51.2)

9. Energy source: 1,254,000 kcal/m 2 /year 0.8% energy captured by photosynthesis. Of this... …45% supports growth (Net primary production) …11% enters grazing food web …34% enters decomposer food web as dead material …55% lost to respiration Figure 51.2

10. Energy source: 1,254,000 kcal/m 2 /year …11% enters grazing food web …34% enters decomposer food web as dead material 0.8% energy captured by photosynthesis. Of this... …45% supports growth (Net primary production) …55% lost to respiration Figure 51.2

11. 0–100 100–200 200–400 400–600 600–800 >800 Productivity ranges (g/m 2 /yr) Figure 51.3a Terrestrial productivity

12. <35 35–55 55–90 >90 Productivity ranges (g/m 2 /yr) Figure 51.3b Marine productivity

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

14. Predators of decomposers: Spider Centipede Mushroom Earthworm Primary decomposers: Bacteria and archaea Millipede Nematodes Pillbugs Salamander 305 nm49.4 µm Figure 51.5 Puffball

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

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

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

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

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

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

22. Energy Flow and Trophic Structure n 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. Number of observations Number of links in food chain 10 8 6 4 2 0 123456 Streams Lakes Terrestrial Figure 51.7c Food chains tend to have few links. Average number of links = 3.5

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

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

26. Boreal forest Figure 51.9 upper

27. Tropical rain forest Figure 51.9 lower

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

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

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

31. Devegetated Net dissolved substance (kg/ha) 1965–661966–671967–681968–691969–70 Control 1000 800 600 400 200 0 Year Figure 51.10b Nutrient runoff results

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

34. THE GLOBAL NITROGEN CYCLE Nitrogen fixing cyanobacteria Mud Decomposition of detritus into ammonia Nitrogen-fixing bacteria in roots and soil Industrial fixation Protein and nucleic acid synthesis Atmospheric nitrogen (N 2 ) Bacteria in mud use N-containing molecules as energy sources, excrete (N 2 ) Run–off Lightning and rain Figure 51.13a

35. Land use Fossil fuel use Year Annual flux of carbon (10 15 g) 65432106543210 1860188019001920194019601980 Figure 51.12a Human-induced increases in CO 2 flux over time

36. Year CO 2 concentration (ppm) 360 350 340 330 320 310 1960197019801990 Figure 51.12b Atmospheric CO 2

37. Natural sourcesHuman sources Amount of nitrogen (gigatons/year) 160 140 120 100 80 60 40 20 0 Sources of nitrogen fixation Lightning Biological fixation Fossil fuels Nitrogen fertilizer Nitrogen- fixing crops Figure 51.13b