Bio171-F08-Lec11 - Biology 171 Lecture 11 Friday Todays...

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Lecture 11: Friday September 26, 2008 Biology 171 Today’s Topic: Food Chains/Webs and Indirect Effects Announcements Revisit Food Chains Energy Flow to the Deep Sea Food Webs Dominant & Keystone Species Seastars; Urchins; Killer Whales & Sharks Text Reading: Lecture 11: 2 nd ed: Chapter 53 (1229-32); Ch. 54 (1247-52) 3 rd ed: Chapter 53 (1209-12); Ch. 54 (1226-30) Lecture 12: 2 nd ed: Ch. 53 (1232-41) 3 rd ed: Ch. 53 (1213-19) Next Week’s Discussion: Ecology simulations Review Session Sunday Sept. 28th 4-6pm MLB AUD 3 (here)
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Organisms that use the same type of energy source occupy the same trophic level , or position in the food chain A food chain connects the trophic levels in a particular ecosystem and thus describes how energy and material move from one trophic level to another. Fig. 54.5
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Food chains and food webs have only two to seven trophic levels The energy-transfer hypothesis The stability hypothesis The environmental-complexity hypothesis Inefficiencies of energy transfer, environmental stability and/or complexity all influence the number of trophic levels that can be supported in a given ecosystem.
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All ecosystems exhibit a pattern—the pyramid of productivity —in which productivity is greatest at the first (bottom) trophic level and declines at higher levels Fig. 54.7
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The Earth’s Energy Budget Can Support More Herbivores Than Carnivores
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The Hubbard Brook Forest is a model ecosystem for studying energy flow and nutrient cycling.
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16.5% of the energy consumed by this caterpillar is used for growth Why the order of magnitude difference in energy transfer? Secondary Production The amount of chemical energy in consumers food that is converted to their own new biomass during a given time period.
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Occasionally, the biomass of consumers is actually higher than the biomass of producers. This can happen in oceans and lakes where phytoplankton production is high, but turnover (death rate) is also very high
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Phytoplankton <1% of planetary photosynthetic biomass >45% of planet’s primary production can have very short (hours) generation times
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Seawifs June 2000. Marine Chlorophyll Concentration
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Ocean Profile What about the Deep Sea?
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Typical Marine Landscape (2 km depth) total darkness 3˚C 200 atmospheres of pressure
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Deep Sea Echinoderms 1.2 km Depth Until recently, it was generally assumed that the deep sea benthos
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