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 Heterotrophs 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 Parasites Omnivores Decomposers Fungi, bacteria Detritivores Small invertebrates SPRING fruits insects rodents, rabbits birds 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 Third-level consumers (heterotrophs): 4th 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 of who eats whom marsh hawk A straight-line sequence of who eats whom Simple food chains are rare in nature upland sandpiper garter snake cutworm plants

Tall-Grass Prairie Food Web marsh hawk sandpiper crow snake frog weasel badger coyote spider sparrow pocket gopher ground squirrel vole earthworms, insects grasses, composites

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

Two Types of Food Webs Grazing Food Web Detrital Food Web Energy Input: Energy Input: Transfers: Transfers: Producers (photosynthesizers) Producers (photosynthesizers) energy losses as metabolic heat & as net export from ecosystem energy in organic wastes, remains energy losses as metabolic heat & as net export from ecosystem energy in organic wastes, remains herbivores decomposers decomposers carnivores detritivores detritivores decomposers Energy Output Energy Output 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 third-level carnivores (gar, large-mouth bass) 1.5 second-level consumers (fishes, invertebrates) decomposers, detritivores (bacteria, crayfish) 1.1 first-level consumers (herbivorous fishes, turtles, invertebrates) 37 primary producers (algae, eelgrass, rooted plants) 809 5

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%) top carnivores 21 decomposers + detritivores = 5,080 carnivores 383 herbivores 3,368 producers 20,810 kilocalories/square meter/year Figure 48.11 Page 874

Energy Flow In Silver Springs Incoming solar energy not harnessed: 1,679,190 (98.8%) ENERGY INPUT: 1,700,000 kilocalories 20,810 (1.2%) Producers To next trophic level: Energy in organic wastes and remains: Energy losses as metabolic heat & as net export from ecosystem: Herbivores Carnivores Top carnivores Decomposers, detritivores 4,245 720 5 90 3,368 383 21 13,197 2,265 272 16 5,060 ENERGY OUTPUT: Total annual energy flow: 1,700,000 (100%) Energy Flow In Silver Springs 20,810 1,679,190 Figure 48.12 Page 874

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 of Nutrients Precipitation Metabolism Weathering Environmental Outputs of Nutrients Runoff Evaporation

Three Categories Hydrologic cycle Atmospheric cycles Water Atmospheric cycles Nitrogen and carbon Sedimentary cycles Phosphorus and sulfur

Hydrologic Cycle Atmosphere precipitation onto land 111,000 wind-driven water vapor 40,000 evaporation from ocean 425,000 precipitation into ocean 385,000 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

bicarbonate and carbonate in ocean water diffusion between atmosphere and ocean combustion of fossil fuels bicarbonate and carbonate in ocean water photosynthesis aerobic respiration marine food webs death, sedimentation incorporation into sediments uplifting sedimentation marine sediments Carbon Cycle - Marine Figure 48.16  Page 878

combustion of fossil fuels atmosphere volcanic action combustion of fossil fuels photosynthesis aerobic respiration combustion of wood terrestrial rocks sedimentation weathering land food webs soil water peat, fossil fuels death, burial, compaction over geologic time leaching, runoff Carbon Cycle - Land 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

Long-term increase in the temperature of Earth’s lower atmosphere 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

excretion, death, decomposition nitrogenous wastes, remains Nitrogen Cycle gaseous nitrogen (N2) in atmosphere nitrogen fixation by industry food webs on land uptake by autotrophs excretion, death, decomposition uptake by autotrophs fertilizers nitrogenous wastes, remains NO3- in soil nitrogen fixation dentrification NH3-,NH4+ in soil ammonification 2. Nitrification NO2- in soil leaching 1. Nitrification 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

DISSOLVED IN OCEAN WATER DISSOLVED IN SOILWATER, LAKES, RIVERS Phosphorus Cycle GUANO FERTILIZER TERRESTRIAL ROCKS LAND FOOD WEBS DISSOLVED IN OCEAN WATER MARINE FOOD WEBS MARINE SEDIMENTS excretion weathering mining agriculture uptake by autotrophs death, decomposition sedimentation settling out leaching, runoff uplifting over geologic time DISSOLVED IN SOILWATER, LAKES, RIVERS 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