#21 - Food Webs - Trophic efficiencies The proportions of...

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1 Trophic efficiencies The proportions of the NPP that move through the pathways of a food web is determined by a set of three transfer efficiencies: – Consumption efficiency (CE) CE = (I n / P n-1 ) x 100 – Assimilation efficiency (AE) • (A n / I n ) x 100 – Production efficiency (PE) • (P n / A n ) x 100 Consumption efficiency CE is the proportion of the total production at one trophic level that is consumed by the next highest level. Level 1 barb2right 2 Level 2 barb2right 3 CE = (I n / P n-1 ) x 100 Assimilation efficiency AE is the proportion of the food energy taken in by a consumer that is assimilated (moved across the gut wall). This is the energy that is available to be used by the consumer. – used for work (e.g., running, immune response) – used for growth – used for reproduction (A n / I n ) x 100 Assimilation Efficiencies Herbivore AE ~ 20-50% plant physical & chemical defenses high proportion of cellulose & lignin Carnivore AE as much as 80% Microbe decomposers AE ~ 100%? Plant parts may differ substantially in their digestibility by herbivores seeds & fruits AE ~ 60-70% leaves ~ 40-50% wood ~ 10-15%
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2 Production efficiency PE is the proportion of assimilated energy that is turned into new biomass of the consumer (P n / A n ) x 100 Probably varies considerably across seasons in most organisms... Production efficiencies Invertebrate herbivores, PE ~ 30-40% • Ectothermic vertebrates, PE ~ 10% Endothermic vertebrates, PE ~ 1-2% PE of endotherms tends to be lowest for the smallest species (shrews, mice, hummingbirds) and greatest for the largest species (elephants, blue whale) Original work by
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