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Ecosystem • all the organisms living in a community, as well as the abiotic factors with which they interact Energy Flow and Chemical Recycling • Energy flows through ecosystems, whereas matter cycles within them Energy Flow • Energy: the ability to do work • Behavior describe by: • 1st Law of Thermodynamics Energy may be transformed from one type into another but is never created or destroyed. 2nd Law of Thermodynamics States that when energy is transferred or transformed, part of the energy assumes a form that can not pass on any further. This means…. With the passage of time, closed systems tend to move toward maximum entropy, eventually no energy available to do work. But… Living systems, like us, are open systems with a constant input of energy. Energy, Mass, and Trophic Levels • Energy in – from the Sun – captured by autotrophs = producers (plants) • Energy through – food chain • transfer of energy from autotrophs to heterotrophs (herbivores to carnivores) • heterotrophs = consumers – herbivores – carnivores 2005-2006 Figure 42.4 Sun Key Chemical cycling Energy flow Heat Primary producers Primary consumers Secondary and tertiary consumers Detritus Microorganisms and other detritivores Figure 42.3 Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter. Prokaryotes and fungi are important detritivores Primary Production • The amount of light energy converted to chemical energy by an ecosystem’s autotrophs in a given time period. • Sets the budget for the ecosystem. • Only 1% of the energy striking the earth is converted to chemical energy. Energetics • Study of how energy get from the sun to organisms Energetics • Chemosynthesis Productivity Figure 42.6 Where are the most productive areas on Earth? Net primary production (kg carbon/m2 • yr) 3 2 1 0 What do you notice about Primary Production in the Oceans? Gross and Net Primary Production – Total primary production is known as gross primary production (GPP). • This is the amount of light energy that is converted into chemical energy in an ecosystem. – The net primary production (NPP) is equal to gross primary production minus the energy used by the primary producers for respiration (R): • NPP = GPP – Ra • NPP is expressed as – Energy per unit area per unit time (J/m2 yr), or – Biomass added per unit area per unit time (g/m2 yr) • Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period • NEP is gross primary production minus the total respiration of all organisms (producers and consumers) in an ecosystem (RT) NEP = GPP − RT In aquatic ecosystems, light and nutrients limit primary production • Production in Marine ecosystems. – Light is the first variable to control primary production in oceans, since solar radiation can only penetrate to a certain depth (photic zone). 2005-2006 •In the open ocean, nitrogen and phosphorous levels are very low in the photic zone, but high in deeper water where light does not penetrate. Phytoplankton density (millions of cells per mL) Which nutrient limits phytoplankton? 30 Ammonium enriched 24 Phosphate enriched 18 Unenriched control Ecologists use the term limiting nutrient to define the nutrient that must be added for production to increase. 12 6 0 A B C D E Collection site F G • Upwelling of nutrient-rich waters in parts of the oceans contributes to regions of high primary production • Production in Freshwater Ecosystems. – Solar radiation and temperature are closely linked to primary production in freshwater lakes. – During the 1970s, sewage and fertilizer pollution added nutrients to lakes, which shifted many lakes from having phytoplankton communities to those dominated by cyanobacteria. 2005-2006 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • This process is called eutrophication, and which can lead to loss of most fish species 2005-2006 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Primary Production in Terrestrial Ecosystems • In terrestrial ecosystems, temperature and moisture affect primary production on a large scale • Primary production increases with moisture Figure 42.8 Net annual primary production (above ground, dry g/m2 • yr) 1,400 1,200 1,000 800 600 400 200 0 20 40 60 80 100 120 140 160 180 200 Mean annual precipitation (cm) • Actual evapotranspiration is the water transpired by plants and evaporated from a landscape • It is affected by precipitation, temperature, and solar energy • Actual evapotranspiration can be used as a predictor of net primary production • Soil nutrients are often the limiting factors in primary production (nitrogen and phosphorus) – adaptations help plants access limiting nutrients from soil. • Nitrogen Fixing Bacteria • mycorrhizal fungi – these fungi supply plants with phosphorus and other limiting elements • Roots have root hairs that increase surface area • Many plants release enzymes that increase the availability of limiting nutrients. • Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time Net secondary production is the energy stored in biomass An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration Energy transfer between trophic levels is typically only 10% efficient Trophic structure • Food chains – feeding relationships – food chain usually 4 or 5 links = trophic levels – length of food chain limited by inefficiency of energy transfer 2005-2006 Why are big, fierce animals rare? The nitrogen cycle The phosphorous cycle The carbon cycle The water cycle