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Chapter 12

BIOL150 Chapter Notes - Chapter 12: Decomposer, Primary Producers

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Rebecca Rooney

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Biology 150 Chapter 12 Ecosystem Energetics
Organismal and Evolutionary Ecology Reading notes
12.8 Food Chains
- Primary producer autotrophs, first trophic level
- Secondary producer heterotrophs/consumers
- Among the secondary producers, first-level consumers (herbivores), second trophic
level; and second-level consumers (first-order carnivores), third trophic level
- Grazing food chain: the herbivores are biophagus that consume living plant biomass
- Detrital (decomposer) food chain: the herbivores are saprophagus that consume
dead organic matter (detritus)
- Herbivores in each chain are the energy source for carnivores, and the source of
energy for the detrital chain is dead organic matter and wastes from the grazing
food chain
- Energy is not recycled in the detrital chain, because the second law of
thermodynamics states that energy can only flow one way. However, the detrital
food chain can recycle its matter until it is all used up, whereas the grazing food
chain which involves only living tissues, cannot.
- The distinction between grazer and detrital food chains is blurred at higher trophic
levels because even highly selective carnivores rarely distinguish whether their prey
are members of a grazing or a detrital food chain
12.9 Pyramid Models
- Energy flowing into a trophic level decreases with each successive level in a food
- Energy pyramid: constructed of the total energy processed at each trophic level is
thus pyramidal in shape, with the slope reflecting the efficiency of energy transfer
- The more efficient the transfer, the steeper the slope, because
(1) Not all energy is consumed between one level and the next
(2) Of the energy consumed, not all is transformed into production to be consumed
by the next level (2nd law of thermodynamics)
- 10-percent rule: only 10% of the energy consumed as biomass in a given trophic
level is converted to biomass at the next trophic level; assumes all animal tissue is
- In real life, ecosystems are not governed by a simple principle that dictates a
constant proportion of energy reaching successive level
- Trophic efficiency (TE): the overall measure for quantifying energy transfer between
levels; the ratio of productivity in a given trophic level (Pn) to the productivity of the
level it feeds on (Pn-1). TE= Pn/ Pn-1= CE X GPE
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