2Trophic structure is a key factor in community dynamics Every community has a trophic structureA pattern of feeding relationships consisting of several different levelsThe sequence of food transfer from producer to consumer is called a food chain.Producers are autotrophs (“self feed”)Consumers are heterotrophs (“different feed”)
3Food chains interconnect, forming food webs A food webA network of interconnecting food chainsArrows indicate direction of nutrient transferSeveral 1° Consumers depend on same producerSome eat at multiple levelsFigure 37.10
4Includes a community and the abiotic factors with which it interacts. Ecosystem ecology emphasizes the processesenergy flow and chemical cyclingTransfer substances through trophic levels. But one flows out the other cycles within.An ecosystemIncludes a community and the abiotic factors with which it interacts.ChemicalcyclingEnergyflowLightenergyChemical elementsHeatFigure 37.11
5Each day Earth receives energy from the sun Each day Earth receives energy from the sun equivalent to 100 million atomic bombs…Most is absorbed, scattered, and reflected by our atmosphere or by the Earths surface.Only 1% of all the light energy the Earth receives is converted into chemical energy by primary producers through photosynthesis (the process of changing light into sugar and other foods/chemical energy).However, on a global scale this is enough to produce170 billion tons of organic material per year.
6The amount of living organic material in an ecosystem is its Biomass. The amount of solar energy converted to chemical energy (organic material) by producers in a given area at a given time is called primary production.Primary production
7Primary production sets the energy budget for ecosystems Is the rate at which producers convert sunlight to chemical energy in organic matter (biomass)Open oceanEstuaryAlgal beds and coral reefsTundraTemperate grasslandCultivated landBoreal forest (taiga)SavannaTemperate deciduous forestTropical rain forest5001,0001,5002,0002,500Average net primary productivity (g/m2/yr)Figure 37.12Desert and semidesert scrubContributes most to Earth’s total net production due to its size
8Energy supply limits the length of food chains A pyramid of productionShows the flow of energy from producers to primary consumers and to higher trophic levels1/1000 of the sun’s energy makes it this farTertiaryconsumersSecondary consumersPrimaryProducers10 kcal100 kcal1,000 kcal10,000 kcal1,000,000 kcal of sunlightCan’t eat allCan’t digest all2/3 digested used by cellsRest to mass (growth)Only this can be eaten by next level.(1% of sun’s energy)Figure 37.13
9Limited by availability of energy Only about 10% of the energy stored at each trophic level is available to the next levelOnly a tiny amount of the energy converted by primary producers flows through he food chain to the top consumerThis is why top level consumers require so much territory…It takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production.Also why food chains are limited in sizeLimited by availability of energy
10CONNECTIONA production pyramid explains why meat is a luxury for humansA field of cornCan support many more human vegetarians than meat-eaters (less energy is wasted)Trophic levelSecondary consumersPrimary consumersProducersHumanvegetariansCornmeat-eatersCattleFigure 37.14
11Chemicals are recycled between organic matter (organisms) and abiotic reservoirs Biogeochemical cycleConsumersProducersNutrientsavailableto producersAbiotic reservoirDetritivores3214DecomposersFigure 37.15Soil
12Water moves through the biosphere in a global cycle Transport over landSolar energyNet movement of water vapor by windRunoff andgroundwaterPercolationthrough soilPrecipitation over landEvaporation andtranspiration fromlandPrecipitationover oceanEvaporation from oceanSolar heatdrives the global water cycle throughprecipitation, evaporation, and transpirationFigure 37.16
13Human activity affects the global water cycle Important source of atmospheric water is transpiration, so destruction of the rain forests will change amount of water in the atmosphere and can alter local and global weather patterns.2) Pumping large amounts of ground water to the surface for irrigation can increase evaporation and deplete ground water supplies.
14The carbon cycle relies on photosynthesis, respiration, and decomposition Carbon compounds (organic) are consumed.Respiration returns CO2 to the atmosphere.Photosynthesis = RespirationBurning fossil fuels is increasing CO2 levels and is causing global warming.
15The nitrogen cycle relies heavily on bacteria Nitrogen is a constituent of DNA and proteins…is essential for life.Various bacteria in soil convert gaseous N2 to compounds that plants use:ammonium (NH4+) and nitrate (NO3–)Detritivores decompose organic matter and recycle nitrogen to plants.Figure 37.18
16Humans are altering the nitrogen cycle Humans are altering the nitrogen cycleSewage treatment facilities often empty large amounts of nitrogen into rivers and streams2) Fertilizer is routinely appliedThese nitrogen sources continue to fertilize when they enter lakes and streams causing algae bloomsNitrates enter ground water used as drinking water and can be toxic
17The phosphorus cycle depends on rock weathering Phosphorus is needed for nucleic acids (DNA), phospholipids (cell membranes), bones and ATP (energy)It and other soil minerals are recycled locally.Weathering is a slow process so phosphorus is limited.Figure 37.19
18In aquatic systems that have not been altered by humans the limited amount of phosphorus keeps algae to a minimum.In areas affected by humans (sewage, fertilizers, pesticides) phosphate pollution leads to heavy algal growth.Major algae blooms can kill aquatic organisms and be toxic to humans.