Chapter 51

1. Chapter 51 Ecosystems

2. Ecosystems • Population: all the individuals of a certain species that live in a particular area • Community: all the different species that interact together within a particular area • Ecosystems consist of all the organisms that live in an area along with the nonbiological (abiotic) components.

3. Ecosystems • Many global environmental problems have emerged recently. • Ecosystem ecology follows the flow of energy and nutrients through ecosystems • Humans have artificially affected the flow of these components

4. Energy Flow within Ecosystems • Energy enters an ecosystem primarily though sunlight:

5. Energy Flow and Trophic Structure • Species within an ecosystems are classified into different trophic levels: • Primary producers: autotrophs, photosynthetic- plants, algae, some bacteria • Consumers • Primary consumers: herbivores that eat producers (plants)- deer, rabbits, etc. • Secondary consumers: carnivores that eat herbivores: wolf eating a deer • Tertiary consumers: carnivores that eat carnivores: a hawk eating a snake that ate a mouse • Decomposers: fungi, bacteria that break down organic material (dead plants and animals)

6. Different Trophic Levels in an Ecosystem 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

7. Energy Flow in an ecosystem External energy source PRIMARY PRODUCERS CONSUMERS DECOMPOSERS ABIOTIC ENVIRONMENT

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

9. Energy Flow and Trophic Structure • Key points about energy flow through ecosystems. • Plants use only a tiny fraction of the total radiation that isavailable to them. • Most energy fixed during photosynthesis is used for respiration, not synthesis of new tissues. • Only a tiny fraction of fixed energy actually becomes availableto consumers. • Most net primary production that is consumed enters the decomposer food web.

10. Ecological Efficiency: percent of energy transferred from one trophic level to the next 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

11. Ecosystem Processes • Production:rate at which energy/nutrients are converted into growth • Includes Primary Production: growth by autotrophs • Includes Secondary Production - growth by heterotrophs • Consumption - the intake and use of organic material by heterotrophs • Decomposition - the chemical breakdown of organic material

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

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

14. Very little of the energy consumed by primary consumers are used for secondary production 80.7% respiration Energy derived from plants 17.7% excretion 1.6% growth and reproduction

15. Pyramid of productivity 4 Secondary carnivore 3 Carnivore 2 Herbivore 1 Autotroph Productivity Example: 100g of plant becomes 5-20g of grasshopper then 0.25-1g of mouse

16. The Different Trophic levels in an ecosystem is often pictured as a Food chain Pisaster (a sea star) Thais (a snail) Bivalves (clams, mussels)

17. Energy Flow and Trophic Structure • Food chains and food webs • Food chains are typically embedded in more complexfood webs. • Many organisms feed at more than one trophic level

18. Food web Pisaster Thais Limpets Gooseneck barnacles Acorn barnacles Chitons Bivalves

19. 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. • 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.

20. 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

21. 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. • Examples: nitrogen cycle, carbon cycle, phosphorus cycle

22. 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

23. 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.

24. Boreal forest: nutrients are put back into the soil slowly, so organic material builds up

25. Tropical rain forest: decomposition is rapid so there is very little organic build up Result: if living material is removed from tropical rain forests, the soil is nutrient poor to support new growth

26. The rate of nutrient loss is a very important characteristic inany ecosystem. Devegetation experiment Choose two similar watersheds. Document nutrient levels in soil organic matter, plants, and streams.

27. Control Clearcut Devegetate one watershed and leave the other intact. Monitor the amount of dissolved substances in streams.

28. Nutrient export increases dramatically in devegetated plot Nutrient runoff results 1000 800 600 400 200 0 Devegetated Net dissolved substance (kg/ha) Control Year 1965–66 1966–67 1967–68 1968–69 1969–70

29. 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. • Humans are now disrupting almost all biogeochemical cycles. This can have very harmful effects.

30. Humans are adding significant amounts of carbon into the atmosphere 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

31. 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

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

33. THE GLOBAL NITROGEN CYCLE Atmospheric nitrogen (N2) =78% Protein and nucleic acid synthesis Bacteria in mud use N-containing molecules as energy sources, excrete (N2) Lightning and rain Run–off Nitrogen fixing cyanobacteria Nitrogen-fixing bacteria in roots and soil Decomposition of detritus into ammonia Mud • Only nitrogen-fixing bacteria can use N2 • make ammonia (NH3) or nitrate (NO3) • limiting nutrient (demand exceeds supply) for plants • All organisms require nitrogen to make protein • Animals get nitrogen from their diets, not the air Industrial fixation

34. Human activities now fix almost as much nitrogen each year as natural sources 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