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Chapter 20

Lecture 16 - Chapter 20.docx

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University of Toronto St. George
Michelle Hilscher

Lecture 16Chapter 20 Consumption efficiency the proportion of available energy that is consumedTypically higher in aquatic ecosystems than in terrestrial ecosystems Also tend to be higher for carnivores than for herbivoresOnce biomass is ingested by the consumer it must be assimilated by the digestive system b4 the energy it contains can be used to produced new biomassAssimilation efficiency The proportion of the ingested food that is assimilatedFood ingested but not assimilated is lost as feces to the env entering the pool of detritusDetermined by the quality of food and the physiology of the consumerThe quality of food available to herbivores and detrivores is generally lower than that of the food available to consumersPlants and detritus are composed of complex componds such as cellulose lignins and humic acids that are not easily digested and they also have low N and P concentrationsAnimal bodies have a carbonnutrient ratio similar to the animal consuming them and are more easily assimilated Assimilation efficiencies for herbivores and detrivores vary bw 2050 for carnivores its about 80 The digestive capacity of consumers is associated with their thermal physiologyEndotherms animals that generate heat internally tend to digest food more completely than ecthotherms animals that rely on heat exchange with the env for thermoregulation and therefore have higher assimilation efficienciesSome herbivores have mutualistic symbionts that help them digest cellulose For ex deer camel cattle have a modified foregut that contains bacteria and protists that increase the breakdown of celluloserich foodsGives ruminants higher assimilation efficiencies than nonruminant herbivores
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