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Consumption Efficiency• CE = food ingested/food produced
• How much of prey population that consumer eats
• For herbivores – 5% in forests, 25% in grasslands, 50% in phytoplankton ecosystems
• For vertebrate predators – up to 50-100% vertebrate prey; 5% invertebrate prey
• For invertebrate predators – 25% invertebrate prey
Assimilation Efficiency
• AE = food assimilated/food ingested
• How much of prey eaten is digested
• AE usually low for herbivores, microbivores, detritivores – 20-50%
• AE usually high for carnivores – 80%
Production Efficiency
• PE = new biomass produced/food assimilated
• How much of prey digested is converted to consumer biomass and used in reproduction – rest is lost as respiratory heat
• PE high for invertebrates – 30-40%
• Intermediate for ectotherm vertebrates – 10-20%
• Low for endotherm vertebrates – 1-2%
Efficiency of Energy Transfer (Production Efficiency)
E = P/(P + R)
where
E = efficiency
P = net production
R = respiration
• Some representative efficiency values are as follows:
• birds 1.3%
• small mammals 1.5%
• large mammals 3.1%
• fish 10.0%
• herbivorous insects 39%
• carnivorous insects 56%
• detritivore insects 47%
Lindeman’s Efficiency
• LE = assimilation at trophic level n
assimilation at trophic level n – 1
LE examines efficiency of transfer between trophic levels – often assumed to be 10% but…is actually more complex
Decomposition
• Role in ecosystems – decomposition is gradual disintegration of dead organic matter and is brought about by both physical and biological agents
• decomposers - organisms which convert organic elements to inorganic form - mostly bacteria and fungi
• detritivores - animals that consume dead organic matter
• only decomposers can break down complex organic material releasing nutrients to soil - other organisms can do limited breakdown, but not enough to efficiently recycle nutrients
Resources for decomposers and detritivores
• not just dead bodies of plants and animals, but also shed dead body parts such as skin cells (food for mites on humans), feathers, horns, leaves, twigs
• loss of cells from root caps creates rhizosphere which is resource rich place for soil bacteria
• plant tissues are leaky and release soluble sugars and nitrogen compounds on leaf surface creating rich environment for bacteria and fungi on leaves called phyllosphere
Donor Control
• Decomposers and detritivores live in world where resource supply is donor controlled - the donor controls density (population size) of the recipient, but the reverse does not happen - there is no direct feedback between consumer population and resource
• In contrast, plants and predators do exert a direct effect on their resources because they reduce amount of resources (population size of the prey) in the environment
Important Terms for Decomposition Cycle
• Immobilization - inorganic nutrient element is incorporated into organic form, usually through the growth of green plants - thus not available to other plants
• Mineralization - conversion of elements from organic to inorganic form by decomposition