Lecture 20- trophic cascades-posted

Lecture 20- trophic cascades-posted - Testing the...

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Time since disturbance % cover of Gigartina control Ulva removed inhibition tolerance facilitation Testing the alternatives: What happens when you remove Ulva?
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The food “chain” and “web” abstractions Primary Producer (plants) Primary consumer (herbivore) Secondary consumer (predator) Omnivore Eat on both Part of food Chain, eating Across a food level Trophic level : all the organisms whose energy source has passed through the same number of steps to reach them
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Keystone Species – a species that has a disproportionate effect on its environment relative to its biomass/abundance____ Paine 1969 Before After Removal Removal # of Species 0 15 Tatoosh Island, Washington state Keystone predators prevent competitive exclusion
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Architectural metaphors in ecology: Keystones vs. Foundations QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Foundations have a big effect because of their abundance / size Foundations have a big effect because of their size/abundance
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Indirect effects – the effect one species on another via its effects on a third species e.g, keystone species e.g, foundation species + -- --
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The trophic cascade Piscivore(large fish) herbivore_____ (planktonic crustacean) Planktivore(small fish) phytoplankton lo hi Piscivore biomass Biomass Planktivore Herbivore phytoplankton Well known in lakes
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Trophic cascades in local systems: Mary Power, UC Berkeley… Eel River, CA Small fish Herbivorous insects Steelhead present Steelhead absent Predatory insects
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Trophic cascades in kelp forests… Urchins can overgraze kelps, leaving nothing but crustose coralline algae that are grazer- resistant. When otters are present, urchin densities are reduced, increasing kelp biomass Humans hunted otters to near extinction in much of California in the 1700’s but they have made a comeback in central California
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Otters maintain high population densities in much of Alaska, but recently some populations have declined… why?
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Killer whales
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Adding another trophic level to the cascade Estes et al. 1998 Where otters are declining…
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Why are orcas suddenly eating otters?
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This note was uploaded on 11/29/2010 for the course BIOLOGY 1211 taught by Professor Patricelli during the Spring '10 term at UC Davis.

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Lecture 20- trophic cascades-posted - Testing the...

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