Ecosystems

Ecosystems Ecosystem = sum of all the organisms living within its boundaries (biotic community) + abiotic factors with which they interact. -involves energy flow and chemical cycling Energy Flow in an Ecosystem-overview: sun à primary producers à primary consumers à secondary and tertiary consumers à decomposers/microorganisms/detritivores-energy cannot be recycled à must be constantly supplied to an ecosystem (mostly by 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) – cannot make own food-heterotrophs are at trophic levels above the primary producers and depend on their photosynthetic output.-primary consumers = herbivores that eat primary producers-secondary consumers = carnivores (or omnivores) that eat herbivores-tertiary consumers = carnivores (or omnivores) secondary consumers-another important group of heterotrophs is the detritivores or decomposers = get energy from detritus, nonliving organic material, and play an important role in material recycling -main decomposers – fungi and prokaryotes (bacteria) Primary Production-Primary production = the amount of light E that is converted to chemical E-Gross primary production (GPP) = total primary production in an ecosystem-Net primary production (NPP) = gross primart production minus the E used by the primary producers for respiration (R): -- so then, NPP = GPP –R-NPP = storage of chemical energy available to consumers in an ecosystem-primary production affected by: -light availability (increased depth, decreased photosynthesis) -nutrient availability (N and P in marine environments)-key factors controlling primary production: temperature and 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 (it does not cycle) within ecosystemsex: 1,000,000 J sunlight à 10,000 J primary producers (grass) à 1,000 J primary consumers (grasshopper) à 100 J secondary consumers (mouse) à 10 J tertiary consumers (owl) Ecological pyramids give insight to food chains-loss of E limits # of top-level carnivores-most food webs only have 4-5 trophic levels The dynamics of energy through ecosystems have important implications for the human population:-we can be primary consumers (plant-based diets) or secondary consumers (diets heavy in animal foods) Matter cycles in ecosystems-Biogeochemical cycles: nutrient cycles that contain both biotic and abiotic components-goes back and forth from organic to inorganic parts and vice versa-nutrient cycles: water, carbon, nitrogen, phosphorous-water: evaporation/transpiration, condensation, precipitation-carbon: atmosphere, photosynthesis, plants/animals, respiration/decomposition, atmosphere.---CO2 removed by photosynthesis, added by burning fossil fuels.-nitrogen: N-fixation (N2 à plants by bacteria), nitrification (ammonium à nitrite à nitrate, absorbed by plants), denitrification (release N to atmosphere)-phosphorous: rocks/soil, plants/animals, decomposition Restoration Ecology-Bioremediation: use of organisms (prokaryotes, fungi, plants) to detoxify polluted ecosystems -ex: bioremediation of groundwater contaminated w uranium-Bioaugmentation: introduce desirable species (ex: N-fixers) to add essential nutrients

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