Food Webs (Week 7)
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This 5 page Class Notes was uploaded by Erica on Sunday October 25, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 25 views.
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Date Created: 10/25/15
Food Webs 1 Definitions Pelagic the water column environment Benthic the sea oor environment includes coral reefs and rocky intertidal Plankton unable to swim horizontally against ocean currents but may move vertically in the water column phytoplankton zooplankton Nekton able to swim against ocean currents fish squid sea turtles 2 Zooplankton Groups Holoplankton Planktonic organisms that live their entire life in uid suspension Examples Copepods shrimp arrow worms Meroplankton Planktonic organisms that live spend only part life in uid suspension Examples Crabs barnacles oysters fish larvae Pelagic Food Chains Complex food webs are simplified by grouping the species into small broad categories Grouping depends on I Main food sources of the organism Autotroph Group Carbon growth comes from nonorganic sources Heterotroph Group Carbon growth comes from previously formed organic carbon material Trophic Level Nutritional feeding level within a food chain web I Main predators of the organism Simpli ed Pelagic Food Chain Conceptualization Top Tropic Level Second Tropic Level First Tropic Level Assigning Organisms to Trophic Levels Is the organism Autotrophic or heterotrophic 9 Does the organism contain chlorophyll yes autotroph no heterotroph o Heterotrophic 9 is the organism a primarysecondarytertiary consumer 3 SizeStructured Food Webs Size determines almost everything about an organism s position on the community Prey size is often 11 0 the consumer s size Marine food webs are strongly SizeStructured 4 Trophic Pyramid Trophic Transfer Efficiency Trophic Transfer Efficiency depends on exploitation efficiency amp gross production efficiency Trophic Transfer Efficiency Exploitation Efficiency x Gross Production Efficiency Trophic Transfer Ef ciency T T Sunlight Carbon Dioxide Exploitation Ef ciency The efficiency with which a consumer population is able to find capture and ingest all potential prey present in the environment quotA game of hide and seekquot Strategies for detecting and capturing prey o Locomotion I Cruising relying on own locomotion I Ambush relying on the locomotion of your prey to come to you 0 Perception I Visual perception I Mechanosensory I Chemosensory o Raptorial grasp prey with appendages 0 Direct Interception bump into prey and engulf o Filtering sieve large volumes of water 0 Entanglement set net or trap Counter strategies to avoid detection and frustrate capture 0 Avoid encounters or detection remain motionless be transparent separate by time and or space I Die Vertical Migration migrate up to surface layer at night to feed in the dark migrate down during the day for safety of darkness 0 Frustrate the capture process spines mechanical defense escape response schooling Bioluminescence Examples 0 Spring Blooms in the Temperate North Atlantic Region 0 Exploitation efficiency is very low much of phytoplankton is not found by grazers and instead sinks into the deep ocean as dead phytoplankton cells 0 Tropical Environments o Exploitation efficiency is very high almost all phytoplankton is found and consumed by grazers Gross Production Ef ciency Gross Growth Production Efficiency amount of consumer biomass produced amount of prey ingested This efficiency ranges between 20 60 T rophic Transfer E ficiency Summary Trophic transfer efficiency is a function of exploitation efficiency 10 to 90 and gross production efficiency 20 to 60 The combined effect of both exploitation and gross production efficiencies yields an overall trophic transfer efficiency of about 10 to 20 10 trophic transfer efficiency 5 Consequences of Food Chain Length on Harvestable Fish production Small cells have the growth advantage at low nutrient conditions This is important Open oceanregion there are a lot of trophic steps 7 steps to get to harvestable fish Costal region 2 trophic steps 0 Very efficient transfer of carbon from primary producer to harvestable fish 0 This region is the most productive for fish The upper limit on the total biomass of harvestable fish in an ocean province is determined by o Intensity of primary production per square meter in the ocean province and areal extent of the ocean province 0 Number of trophic levels between primary producers and the harvestable fish in the ocean province and the trophic transfer efficiencies between each of trophic levels
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