E.Ecosystem09 - Ecosystems THE REALM OF ECOLOGY Biosphere...

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Unformatted text preview: Ecosystems THE REALM OF ECOLOGY Biosphere • Biosphere • Ecosystem Ecology: Ecosystems Interactions between the species in a given habitat and their physical environment. Communities • Community Populations • Population • Organism Factors that Limit Communities SIMPLE TERRESTRIAL ECOSYSTEM • Abiotic (nonliving) Limiting Factors – Temperature – Water – Soil type – Sunlight – Salinity – Wind stress – Altitude, depth • Biotic (living) Limiting Factors – Food source – Competition – Predators – Social factors, mates – Pathogens, parasites – Vegetation Oxygen (O 2) Sun Producer Carbon dioxide (rabbit) Primary consumer (rabbit) Precipitation Falling leaves and twigs Secondary consumer (fox) Producers Soil decomposers Water Energy flow and chemical cycling Organisms Soluble mineral nutrients Energy flow is one-way • Energy enters ecosystems through photosynthesis or chemosynthesis • Some energy is used by producers, some is passed through food chain • All energy eventually dissipates as heat Tertiary consumers Microorganisms and other detritivores Detritus Secondary consumers Primary consumers Primary producers Heat Key Chemical cycling Energy flow Sun Figure 54.2 Chemical materials are recycled Energy flows through the food web • Energy from lower trophic levels is transferred to higher trophic levels • Actual atoms are constantly rearranged into new molecules • Energy needed to form new bonds, but atoms are reused • 5% - 20% of energy consumed is available to next trophic level Tertiary consumers Microorganisms and other detritivores – Carbon cycle – Nitrogen cycle Detritus • Energy returns to the physical environment as heat Secondary consumers Primary consumers Primary producers Heat Key Chemical cycling Energy flow Hardwood forest Sun – Remember thermodynamics! “Energy is neither created nor destroyed!” Figure 54.2 Energy pyramid reflects loss of energy at each trophic level • Only 1% of solar energy reaching Earth is used by living systems • 5% - 20% of energy consumed is available to next trophic level Plant material eaten by caterpillar 200 J Feces 100 J • Oak trees, caterpillars, birds Pyramid of net production 67 J Cellular respiration 33 J Growth (new biomass) Figure 54.10 Energy pyramid reflects loss of energy at each trophic level • Endotherms: 1-3% production efficiency • Ectothermic vertebrates: ~10% • Inverts: as much as 40% – Caterpillar Plant material eaten by caterpillar • Feeding efficiency = growth/consumed = 17% • Production efficiency = growth/assimilated = 33% 200 J Feces 100 J 33 J 67 J Cellular respiration Growth (new biomass) Pyramid of net production Eating high on the food chain is expensive! • Most food webs limited to 4–5 steps • Energetic hypothesis: – Too little energy passed through steps to support another step • Dynamic stability hypothesis: – Even if average 1 °-production sufficient, oscillations & deviations in 1 °-production cause fluctuations in higher steps below minimum viable population. • Less than 10% passed on to next trophic level Biogeochemical cycles: "life-earth-chemical" • Materials enter producers from atmosphere or soil. Pools or Reservoirs of Materials • Pools available: – Abiotic: atmosphere, soil, water, geological • Return to abiotic world through respiration and decomposition. • Materials cycle between pools • Biologically important materials: • Size of pools constant only if entry equals exit – Biotic: living or dead organic matter – Water (H2O) – Carbon (CO2) – Nitrogen (N2, NO3-, NO2-, NH4) Global Water Cycle • Humidity: water in atmosphere • Precipitation: rain, snow • Surface transport: – puddles, groundwater, rivers, oceans • Evaporation: – Transpiration: water loss from plants; helps maintain local humidity – From organisms: sweat, urine, respiration Global Water Cycle Water cycle & NPP • Actual evapotranspiration Net primary production (g/m 2/yr) = annual amount of water evaporated from a landscape and transpired by plants 3,000 Human activity disrupts local water cycles • Diversion of surface transport – Irrigation Tropical forest – Dams • Disruption of soil water retention (watershed disturbance) 2,000 – Clear cutting of forests Temperate forest 1,000 Desert shrubland 0 – Overgrazing Mountain coniferous forest – Also causes loss of minerals through runoff Temperate grassland • Further losses of vegetation Arctic tundra 0 500 1,000 – Desertification 1,500 Actual evapotranspiration (mm H2 O/yr) Figure 54.8 Desertification DESERTIFICATION Ground water removal • May also lead to salt water intrusion Loss of surface vegetation that would retain water 1. 2. Africa U.S. 1930’s Dust Bowl General model of nutrient cycling • the main reservoirs of elements and the processes that transfer elements between reservoirs Reservoir a Organic materials available as nutrients Living organisms, detritus Assimilation, photosynthesis Fossilization Respiration, decomposition, excretion Reservoir c Inorganic materials available as nutrients Atmosphere, soil, water Reservoir b Organic materials unavailable as nutrients Moderate Severe Very Severe Carbon cycle • Carbon dioxide gas (CO2 ) in atmosphere, and bicarbonate (HCO3–) in aquatic media. • Producers use energy (sunlight) to convert CO2 (abiotic pool) into organic biomass (biotic pool) Coal, oil, peat – Carbon fixation Burning of fossil fuels Weathering, erosion Formation of sedimentary rock 6CO2 + 6H2O + energy fi C6H12O6 Reservoir d Inorganic materials unavailable as nutrients Minerals in rocks Figure 54.16 Carbon Cycle Carbon cycle • Consumers eat carbon compounds (sugars, proteins, fats, nucleic acids) made by producers • Produces CO2 as waste; released back into abiotic pool C6H12O6 fi 6CO2 + 6H2O + energy • Carbon fixation tied to energy flow © Biomass trophic pyramid reflects energy pyramid Primary Productivity • The total organic matter (dry mass) produced by all autotrophs in the ecosystem is its Gross Primary Production (GPP). – Global GPP ≈ 1.5 x 10 13 kg [150 billion metric tons]/year • Part of the GPP is used by the producers for their own respiration. • Only the remaining primary production increases the total ecosystem biomass and is available for consumers. = Net Primary Production (NPP) Average net primary productivity of Earth’s biomes Open ocean Continental shelf 5.2 Estuary 0.3 Algal beds and reefs 0.1 Upwelling zones 0.1 Extreme desert, rock, sand, ice 4.7 Desert and semidesert scrub 3.5 Tropical rain forest 3.3 2.9 Savanna 2.7 Cultivated land Boreal forest (taiga) 2.4 Temperate grassland 1.8 Woodland and shrubland 1.7 Tundra 1.6 Tropical seasonal forest 1.5 Temperate deciduous forest 1.3 Temperate evergreen forest 1.0 Swamp and marsh 0.4 Lake and stream 0.4 Key Marine 0 10 125 360 65.0 24.4 5.6 1,500 2,500 1.2 0.9 0.1 0.04 0.9 500 3.0 90 2,200 7.9 9.1 9.6 5.4 3.5 0.6 7.1 4.9 3.8 2.3 0.3 140 1,600 1,200 1,300 2,000 250 20 30 40 50 60 (a) Percentage of Earth ’s surface area 0 500 1,0001,500 2,0002,500 (b) Average net primary production (g/m 2/yr) Tertiary consumers Secondary consumers Primary consumers Primary producers (a) a bog at Silver Springs, Florida. 10 15 20 25 Figure 54.4 • NOTE: pyramid of biomass production – Actual standing crop biomass may differ Dry weight (g/m 2 ) Trophic level 1.5 11 37 Dry weight (g/m 2) Primary consumers (zooplankton) 809 Primary producers (phytoplankton) (b) English Channel marine ecosystem Figure 55.11 • Carbon fixation tied to energy flow © 5 Carbon cycle • NOTE: pyramid of biomass production – Actual standing crop biomass may differ Trophic level 0 (c) Percentage of Earth ’s net primary production Terrestrial Freshwater (on continents) Carbon cycle 22 900 600 800 600 700 Biomass trophic pyramid reflects energy pyramid 21 4 Figure 55.11 • Carbon fixation tied to energy flow © Biomass trophic pyramid reflects energy pyramid Regulation of Trophic Levels Combustion • Bottom-Up Regulation model: ›Nutrients Æ ›Vegetation Æ ›Herbivores Æ ›Predators flNutrients Æ flVegetation Æ flHerbivores Æ flPredators • Top-Down Regulation (trophic cascade) model: ›Predators Æ flHerbivores Æ ›Vegetation Æ flNutrients flPredators Æ ›Herbivores Æ flVegetation Æ ›Nutrients Fossil fuels: Organic litter was transformed into coal or oil • Dead organisms return CO2 to atmosphere when burned – Wood – Fossil fuels • Again: C6H12O6 fi 6CO2 + 6H2O + energy Industrial age combustion Æ excess CO2 in atmosphere Geological pools used faster than they are replaced Global habitat impact: the Greenhouse effect • “Greenhouse gases ” (esp.., CO 2) are transparent to sunlight but absorb infrared radiation trap heat within atmosphere Increase in atmospheric CO2 correlates with increase in global temperature Increase in CO2 Increase in global temperature Nitrogen Cycle Nitrogen cycle Concentric Cycles • Important component of proteins and nucleic acids • N2 forms 79% of atmospheric gas • Nitrogen fixation: N2 gas must be converted to other nitrogen compounds Mutualism: Bacteria are required for nitrogen cycle Legumes and Rhizobium (nitrogen fixing bacteria) • Nitrogen fixating bacteria: ß N2 gas Æ ammonia (NH4+) • Nitrifying bacteria: ß NH4+ Æ nitrite (NO2–) Æ nitrate (NO3–) • Plants use nitrate to make organic amines Nodules on roots Cyanobacteria Without Rhizobium Bacteria return nitrogenous waste to atmosphere • Denitrifying bacteria, decomposers covert NO3– back into N2 gas • Completes cycle With Rhizobium Human influences on nitrogen cycle • Industrially made fertilizers account for 30% of fixed nitrogen • Making fertilizers burns lots of fossil fuels • Deforestation causes loss through run off • Acid rain production Deforestation or over-irrigation increases runoff & nitrogen loss Agriculture and Nitrogen Cycling • Agriculture constantly removes nutrients from ecosystems that would ordinarily be cycled back into the soil • Necessitates adding nitrogen-fertilizers back Figure 54.20 Fig. 36.18C Acid rain Acid rain • North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid • Nitrogen and sulfur compounds (from factory and auto emissions) plus water make nitric acid and sulfuric acid in the atmosphere 4.6 4.3 4.6 4.3 4.6 4.3 4.1 4.6 Figure 54.21 Acid rain North America Mineral nutrient cycles • By the year 2000 the entire contiguous United States was affected by acid precipitation Figure 54.22 Europe • E.g., phosphorus, calcium, potassium, iron Field pH ≥5.3 5.2–5.3 5.1–5.2 5.0–5.1 4.9–5.0 4.8–4.9 4.7–4.8 4.6–4.7 4.5–4.6 4.4–4.5 4.3–4.4 <4.3 • Biological demand is low, but sources usually dependent upon erosion from regional rocks and transport in surface water THE PHOSPHORUS CYCLE Rain Geologic Weathering of rocks uplift Runoff Plants Sedimentation Soil Leaching Consumption Plant uptake of PO43 - Decomposition Figure 54.17 Testing for the limiting nutrient Limiting nutrient • Phytoplankton productivity in three bays along Long Island, NY RESULTS • Nitrogen and phosphorous are the most typical limiting nutrients in many ecosystems Phytoplankton Inorganic phosphorus 2 4 5 1130 15 19 21 Station number Great Moriches South Bay Bay 8 7 6 5 4 3 2 1 0 Shinnecock Bay 30 Phytoplankton (millions of cells per mL ) 8 7 6 5 4 3 2 1 0 Inorganic phosphorus (mg atoms/L) – Carbon, oxygen, & hydrogen are needed in great quantities, but are also tremendously available: \ rarely limiting. – Most trace metals are rare in the environment, but organisms don ’t need much of them: \ seldom limiting. (a) Phytoplankton abundance parallels the abundance of phosphorus in the water. Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. (b) The addition of ammonium (NH 4 +) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO 43+) did not induce algal growth. Phytoplankton (millions of cells/ mL ) • Productivity in a given ecosystem is limited by the availability of all vital nutrients • The particular element whose availability is restricting greater productivity is the limiting nutrient • E.g., 24 Ammonium enriched Phosphate enriched Unenriched control 18 12 6 0 Starting 2 algal density 4 5 11 30 15 19 21 Station number (a) Phytoplankton biomass and phosphorus (b) Phytoplankton response to concentration nutrient enrichment CONCLUSION Since adding phosphorus, which was already in rich supply, had no effect on Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem. Testing for the limiting nutrient Iron-limitation in oceanic ecosystems • Salt marsh EXPERIMENT Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogen to other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls. Adding nitrogen (N) boosts net primary production. RESULTS NOTE: Once N was added, P became limiting! Live, above-ground biomass (g dry wt/m 2) CONCLUSION These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh. 300 N+P 250 200 150 N only 100 Control 50 P only 0 June July August 1980 Experimental plots receiving just phosphorus (P) do not out-produce the unfertilized control plots. Cultural (Anthropogenic) Eutrophication • Sewage or fertilizer runoff adds limiting nutrients to aquatic ecosystems • Algae stimulated to overgrow – Benthic algae overgrow benthic invertebrates – Filamentous algae clog gills – Thick growth dampens flow or reduces mixing – Nocturnal algal respiration consumes all dissolved oxygen • Loss of diversity & community structure • Offshore regions far from terrigenous runoff, isolated from mineral sources ...
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This note was uploaded on 09/02/2011 for the course BIOL 6C taught by Professor Sundram during the Spring '09 term at DeAnza College.

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