This chapter explain how the first and second laws of thermodynamics apply to ecosystems; define and compare gross primary production, net primary production, and standing crop; explain why energy flows but nutrients cycle within an ecosystem; explain what factors may limit primary production in aquatic ecosystems.
Ch 55 Warm-Up Draw an energy pyramid and label the following trophic levels: ▫ Primary producer ▫ Primary consumer ▫ Secondary consumer ▫ Tertiary consumer What is an example of an organism at each level of the pyramid in #1? If 5000 J of energy is available in producers, how much of that energy would be available to tertiary consumers? Define Ch 55 Terms: Autotroph Heterotroph Detritivore Gross primary production (GPP) Net primary production (NPP) Biogeochemical cycle Nitrogen fixation Chapter 55: Ecosystems You Must Know: • How energy flows through the ecosystem (food chains and food webs) • The difference between gross primary productivity and net primary productivity • The carbon and nitrogen biogeochemical cycles Ecosystems Ecosystem = sum of all the organisms living within its boundaries (biotic community) + abiotic factors with which they interact Involves two unique processes: Energy flow Chemical cycling Overview of energy & nutrient dynamics Energy Flow in an Ecosystem • Energy cannot be recycled must be constantly supplied to an ecosystem (mostly by SUN) SUN • The autotrophs (“self feeders”) are the primary producers, and are usually photosynthetic (plants or algae) ▫ They use light energy to synthesize sugars and other organic compounds • Heterotrophs (“other feeders”) – can’t make own food • Heterotrophs are at trophic levels above the primary producers and depend on their photosynthetic output ▫ Herbivores that eat primary producers are called primary consumers ▫ Carnivores that eat herbivores are called secondary consumers ▫ Carnivores that eat secondary consumers are called tertiary consumers ▫ Another important group of heterotrophs is the detritivores, or decomposers They get energy from detritus, nonliving organic material, and play an important role in material cycling Main decomposers: fungi & prokaryotes Primary Production • Primary production = amt of light energy that is converted to chemical energy • Gross primary production (GPP): total primary production in an ecosystem • Net primary production (NPP) = gross primary production minus the energy used by the primary producers for respiration (R): ▫ NPP = GPP – R • NPP = storage of chemical energy available to consumers in an ecosystem Net primary production of different ecosystems Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and semidesert scrub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Woodland and shrubland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Lake and stream 5.2 0.3 0.1 0.1 4.7 3.5 3.3 2.9 2.7 2.4 1.8 1.7 1.6 1.5 1.3 1.0 0.4 0.4 Key Marine Terrestrial 125 360 65.0 10 20 30 40 50 60 Percentage of Earth’s surface area Freshwater (on continents) 24.4 5.6 1,500 2,500 1.2 0.9 0.1 0.04 0.9 500 3.0 90 22 2,200 7.9 9.1 9.6 5.4 3.5 900 600 800 600 700 140 0.6 7.1 4.9 3.8 2.3 0.3 1,600 1,200 1,300 2,000 250 500 1,000 1,500 2,000 2,500 Average net primary production (g/m2/yr) 10 15 20 25 Percentage of Earth’s net primary production • Primary production affected by: ▫ Light availability (↑ depth, ↓ photosynthesis) ▫ Nutrient availability (N, P in marine env.) • Key factors controlling primary production: ▫ Temperature & moisture • A nutrient-rich lake that supports algae growth is eutrophic Energy transfer between trophic levels is typically only 10% efficient • Production efficiency: only fraction of E stored in food • Energy used in respiration is lost as heat • Energy flows (not cycle!) within ecosystems 10% transfer of energy from one level to next Ecological pyramids give insight to food chains • Loss of energy limits # of top-level carnivores • Most food webs only have or trophic levels Pyramid of Numbers Pyramid of Biomass The dynamics of energy through ecosystems have important implications for the human population Trophic level Secondary consumers Primary consumers Primary producers Matter Cycles in Ecosystem • Biogeochemical cycles: nutrient cycles that contain both biotic and abiotic components • organic inorganic parts of an ecosystem • Nutrient Cycles: water, carbon, nitrogen, phosphorus Water Cycle Carbon Cycle • CO2 removed by photosynthesis, added by burning fossil fuels Nitrogen Cycle • Nitrogen fixation: ▫ N2 plants by bacteria • Nitrification: ▫ ammonium nitrite nitrate ▫ Absorbed by plants • Denitrification: ▫ Release N to atmosphere Phosphorus Cycle Restoration Ecology • Bioremediation: use of organisms (prokaryotes, fungi, plants) to detoxify polluted ecosystems • Bioaugmentation: introduce desirable species (eg nitrogen-fixers) to add essential nutrients Bioremediation of groundwater contaminated with uranium Restoration ecology projects .. .Chapter 55: Ecosystems You Must Know: • How energy flows through the ecosystem (food chains and food webs)... primary productivity and net primary productivity • The carbon and nitrogen biogeochemical cycles Ecosystems Ecosystem = sum of all the organisms living within its boundaries (biotic community)... storage of chemical energy available to consumers in an ecosystem Net primary production of different ecosystems Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert,