Transcript Ecosystems
Ecosystems Chapter 48 Ecosystems Open systems through which energy flows and materials are recycled Require energy and nutrient input and generate energy and nutrient output Modes of Nutrition Autotrophs Capture sunlight or chemical energy Producers Heterotrophs Extract energy from other organisms or organic wastes Consumers, decomposers, detritivores Simple Ecosystem Model energy input from sun PHOTOAUTOTROPHS (plants, other producers) nutrient cycling HETEROTROPHS (consumers, decomposers) energy output (mainly heat) Consumers Herbivores Carnivores SPRING fruits insects Parasites rodents, rabbits birds Omnivores Decomposers Fungi, bacteria Detritivores Small invertebrates SUMMER fruits rodents, rabbits insects birds Seasonal variation in the diet of an omnivore (red fox) Trophic Levels Who Eats Whom? All the organisms at a trophic level are the same number of steps away from the energy input into the system Producers are closest to the energy input and are the first trophic level Trophic Levels in Prairie Fourth-level consumers (heterotrophs): 5th Top carnivores, parasites, detritivores, decomposers 4th Third-level consumers (heterotrophs): Carnivores, parasites, detritivores, decomposers Second-level consumers (heterotrophs): 3rd Carnivores, parasites, detritivores, decomposers First-level consumers (heterotrophs): 2nd Herbivores, parasites, detritivores, decomposers Primary producers (autotrophs): 1st Photoautotrophs, chemoautotrophs Food Chain A straight-line sequence marsh hawk upland sandpiper of who eats whom Simple food chains are garter snake rare in nature cutworm plants Tall-Grass Prairie Food Web marsh hawk sandpiper crow snake frog weasel badger coyote spider sparrow earthworms, insects vole pocket gopher grasses, composites ground squirrel Energy Losses Energy transfers are never 100 percent efficient Some energy is lost at each step How? Heat Limits the number of trophic levels in an ecosystem Grazing Food Web Detrital Food Web Input: Two Types of Food Energy Webs Energy Input: Transfers: Transfers: Producers (photosynthesizers) Producers (photosynthesizers) energy in organic wastes, remains herbivores carnivores decomposers Energy Output energy losses as metabolic heat & as net export from ecosystem energy in organic wastes, remains Energy Output decomposers decomposers detritivores detritivores energy losses as metabolic heat & as net export from ecosystem Figure 48.7 Page 871 Biological Magnification A nondegradable or slowly degradable substance becomes more and more concentrated in the tissues of organisms at higher trophic levels of a food web DDT in Food Webs Effective chemical for killing mosquitoes Accumulates in fatty tissues Synthetic pesticide banned in United States since the 1970s Still persist in sediments Birds that are carnivores accumulate DDT in their tissues, produce brittle egg shells DDT in an Estuary (1967) DDT Residues (ppm wet weight of whole live organism) Ring-billed gull fledgling (Larus delawarensis) Herring gull (Larus argentatus) Osprey (Pandion haliaetus) Green heron (Butorides virescens) Atlantic needlefish (Strongylira marina) Summer flounder (Paralychthys dentatus) Sheepshead minnow (Cyprinodon variegatus) Hard clam (Mercenaria mercenaria) Marsh grass shoots (Spartina patens) Flying insects (mostly flies) Mud snail (Nassarius obsoletus) Shrimps (composite of several samples) Green alga (Cladophora gracilis) Plankton (mostly zooplankton) Water 75.5 18.5 13.8 3.57 2.07 1.28 0.94 0.42 0.33 0.30 0.26 0.16 0.083 0.040 0.00005 Primary Productivity Gross primary productivity is ecosystem’s total rate of photosynthesis for the ecosystem during an interval Net primary productivity is rate at which producers store energy in tissues in excess of their aerobic respiration NPP accounts for the organic mass of plants (growth) and represents storage of chemical energy available to consumers. NPP = GPP - Respiration Primary Productivity Varies Seasonal variation Variation by habitat The harsher the environment, the slower plant growth, the lower the primary productivity Ecological Pyramids Biomass Pyramid has tiers symbolizing the total dry weight of all organisms in an ecosystem's levels at any given time. Biomass represents chemical energy stored in the organic matter of a trophic level. Most narrow sharply from producers at the base to top-level carnivores at the top. Silver Springs Study Aquatic ecosystem in Florida Site of a long-term study of a grazing food web g/m2 decomposers, detritivores (bacteria, crayfish) 5 1.5 third-level carnivores (gar, large-mouth bass) 1.1 second-level consumers (fishes, invertebrates) 37 first-level consumers (herbivorous fishes, turtles, invertebrates) 809 primary producers (algae, eelgrass, rooted plants) Energy Pyramid Reflects trophic structure most accurately because it is based on energy looses at each level Pyramid of Energy Flow Primary producers trapped about 1.2 percent of the solar energy that entered the ecosystem 6-16% passed on to next level (10%) 21 top carnivores decomposers + detritivores = 5,080 carnivores herbivores 383 3,368 producers 20,810 kilocalories/square meter/year Figure 48.11 Page 874 ENERGY INPUT: Incoming solar Energy Flow In energy not 1,700,000 kilocalories harnessed: Silver Springs 1,679,190 (98.8%) 20,810 (1.2%) Energy in organic wastes and remains: 4,245 Energy losses as metabolic heat & as net export Producers from To next trophic level: ecosystem: 3,368 13,197 Herbivores 720 383 Carnivores 90 21 Top carnivores 5 Figure 48.12 Page 874 2,265 272 16 Decomposers, detritivores 5,060 ENERGY OUTPUT: 20,810 Total annual energy flow: 1,679,190 1,700,000 (100%) All Heat in the End At each trophic level, the bulk of the energy received from the previous level is used in metabolism This energy is released as heat energy and lost to the ecosystem Eventually all energy is released as heat Biogeochemical Cycle Influence the availability of essential elements in ecosystems The amount of nutrients cycling is greater than those entering or leaving Main reservoir for the nutrient is in the environment Environmental Inputs Environmental Outputs of Nutrients of Nutrients Precipitation Runoff Metabolism Evaporation Weathering Three Categories Hydrologic cycle Atmospheric cycles Water Nitrogen and carbon Sedimentary cycles Phosphorus and sulfur Hydrologic Cycle Atmosphere wind-driven water vapor 40,000 evaporation precipitation from ocean into ocean 425,000 385,000 precipitation onto land 111,000 evaporation from land plants (evapotranspiration) 71,000 surface and groundwater flow 40,000 Ocean Land Figure 48.14 Page 876 Hubbard Brook Experiment A watershed was experimentally stripped of vegetation All surface water draining from watershed was measured Removal of vegetation caused a six-fold increase in the calcium content of the runoff water Hubbard Brook Experiment losses from disturbed watershed time of deforestation losses from undisturbed watershed Figure 48.15 Page 877 Carbon Cycle Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, and rocks Sediments and rocks are the main reservoir diffusion between atmosphere and ocean bicarbonate and carbonate in ocean water photosynthesis combustion of fossil fuels aerobic respiration marine food webs death, incorporation sedimentation into sediments uplifting sedimentation marine sediments Carbon Cycle - Marine Figure 48.16 Page 878 atmosphere combustion of fossil fuels volcanic action terrestrial rocks weathering photosynthesis aerobic combustion respiration of wood sedimentation land food webs soil water leaching, runoff death, burial, compaction over geologic time Carbon Cycle - Land peat, fossil fuels Figure 48.16 Page 878 Carbon in the Oceans Most carbon in the ocean is dissolved carbonate and bicarbonate Ocean currents carry dissolved carbon Carbon in Atmosphere Atmospheric carbon is mainly carbon dioxide Carbon dioxide is added to atmosphere Aerobic respiration, volcanic action, burning fossil fuels Removed by photosynthesis Greenhouse Effect Greenhouse gases impede the escape of heat from Earth’s surface Figure 48.18, Page 880 Global Warming Long-term increase in the temperature of Earth’s lower atmosphere Figure 48.19, Page 881 Carbon Dioxide Increase Carbon dioxide levels fluctuate seasonally The average level is steadily increasing Burning of fossil fuels and deforestation are contributing to the increase Other Greenhouse Gases CFCs - synthetic gases used in plastics and in refrigeration Methane - produced by termites and bacteria Nitrous oxide - released by bacteria, fertilizers, and animal wastes Nitrogen Cycle Nitrogen is used in amino acids and nucleic acids Main reservoir is nitrogen gas in the atmosphere Nitrogen Cycle gaseous nitrogen (N2) in atmosphere nitrogen fixation by industry food webs on land uptake by excretion, death, uptake by fertilizers autotrophs decomposition autotrophs nitrogen fixation NH3-,NH4+ in soil leaching nitrogenous wastes, remains NO3in soil dentrification ammonification 2. Nitrification 1. Nitrification NO2in soil leaching Figure 48.21 Page 882 Nitrogen Fixation Plants cannot use nitrogen gas Nitrogen-fixing bacteria convert nitrogen gas into ammonia (NH3) Ammonia and ammonium can be taken up by plants Ammonification & Nitrification Bacteria and fungi carry out ammonification conversion of nitrogenous wastes to ammonia Nitrifying bacteria convert ammonium to nitrites and nitrates Nitrogen Loss Nitrogen is often a limiting factor in ecosystems Nitrogen is lost from soils via leaching and runoff Denitrifying bacteria convert nitrates and nitrites to nitrogen gas Human Effects Humans increase rate of nitrogen loss by clearing forests and grasslands Humans increase nitrogen in water and air by using fertilizers and by burning fossil fuels Too much or too little nitrogen can compromise plant health Phosphorus Cycle Phosphorus is part of phospholipids and all nucleotides It is the most prevalent limiting factor in ecosystems Main reservoir is Earth’s crust; no gaseous phase Phosphorus Cycle mining FERTILIZER GUANO excretion agriculture uptake by autotrophs MARINE FOOD WEBS weathering DISSOLVED IN OCEAN WATER uptake by autotrophs weathering DISSOLVED IN SOILWATER, LAKES, RIVERS death, decomposition sedimentation LAND FOOD WEBS death, decomposition settling out leaching, runoff uplifting TERRESTRIAL ROCKS MARINE SEDIMENTS over geologic time Figure 48.23, Page 884 Human Effects In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils In developed countries, phosphorus runoff is causing eutrophication of waterways