ECOSYSTEMS AND ENERGY FLOW CH 55

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Energy flows through ecosystems while matter cycles through ecosystems

I. Ecosystems and Physics (what?!)

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ecosystems involve matter and energy transformations

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NRG can’t be created or destroyed, only transformed

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solar NRG→chemical NRG→heat

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NRG transfers increase entropy therefore they are inefficient and NRG is lost as heat

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Matter can’t be created

II. Trophic Structure, Food Chains And Food Webs

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Food chains link trophic levels together

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Food webs are branching food chains with more complex interactions

III. Energy and Productivity in Ecosystems

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In most ecosystems, primary production is the amount of solar energy converted to chemical energy (the rate of photosynthesis)

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How much photosynthesis occurs, sets how much energy is available in that ecosystem

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A. Gross and Net Production Gross primary production (GPP): amount of photosynthesis in a given time. The amount of carbon fixed into organic molecules

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Net primary production (NPP): what is left over for consumers. It is the amount of new biomass added by autotrophs

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What do autotrophs do with the organic molecules produced?

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Use it in cell respiration

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Store it as new biomass

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How do you measure net primary production?

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Gross production – cell respiration = net production

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Tropical rainforests and coral reefs are the most productive while marine ecosystems are the least Terrestrial and aquatic ecosystems have different limitations to their primary production

Measuring NPP in terrestrial ecosystems

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Terrestrial ecosystem: forest, grassland

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Measure the increase in biomass

Measuring NPP in aquatic ecosystems

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Measure rates of photosynthesis and respiration

B. Primary Production and Eutrophication

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Excessive addition of nutrients like phosphorus and nitrogen to aquatic ecosystems causes eutrophication

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Excess nutrients cause algal bloom

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As algae die, decomposers use up oxygen decaying them

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This limits oxygen available to fish at deeper levels

IV. Energy Transfer Between Trophic Levels

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Is inefficient with only about 10% from one trophic level is available to next Depending on organism, 10-30% of energy obtained is converted to new biomass = secondary production The rest is used for cell respiration or is lost as waste

Production efficiency = secondary production/amount assimilated

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This inefficient energy transfer creates ecological pyramids

V. Biogeochemical Cycling in Ecosystems

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Life depends on recycling of matter

A. Water cycle

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The water from oceans evaporates into the atmosphere Water from plants evaporates to the atmosphere by transpiration Water precipitates from the atmosphere to the earth Most of the water enters into the oceans Some of the water is taken up by living organisms

B. The Carbon cycle

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CO2 in the atmosphere is fixed by photosynthetic organisms animals eat the photosynthetic organisms animals respire and put CO2 back into the atmosphere animals die and their remains become fossil fuels fossil fuels are burned and CO2 is deposited in the atmosphere

C. The nitrogen cycle

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atmospheric N2 is fixed by nitrogen fixing bacteria and used by plants herbivores eat the plants herbivores pee, poop and die returning nitrogen to the soil which is then fixed by nitrogen fixing bacteria in plants Carnivores eat herbivores Carnivores pee, poop, and die returning nitrogen to the soil to be fixed some bacteria in the soil take the soil nitrogen and restore it to atmospheric nitrogen