Response to disturbance and change relatively complex

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Response to disturbance and change - Relatively complex trophic hierarchies have been identified form both terrestrial and marine ecosystems - Energy captured by photosynthesis can also be held in plant litter for significant periods of time before being used by decomposers Energy Residence Times - Average length of time energy captured is held Plants: few dyays (open ocean), 3 yrs (grasslands), 22-25 yrs (forests) Plant litter: Trophics : plant litter may release energy in <3 mo. Temperate/boreal: could be as long as >100 years - Litter residence time may be long, but most of energy captured by moves relatively quickly through trophic levels eg. Terrestrial and freshwater ecosystem – photosynthesis- highest trophic levels-a few weeks - The number of trophic levels in most food webs: 3-6 trophic levels - Energy transfer between trophic levels is relatively inefficient – available energy rapidly decreases - ~10% of the energy of any trophic level is passed onto the next trophic level – ‘The 10% rule’ - As a result of the 10% rule, each trophic level is expected to have about 90% less energy available to support it than the preceding trophic level - The decrease in available energy with each trophic level is extremely important in ordering ecosystems Trophic Efficiencies - Birds and mammals (warm-blooded animals) least efficient
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o Assimilate ~3% of energy from food - Insects ~39% - Fish ~10% - Helps to explain o Why the bulk of all biomass (>90%?) on earth are plants o Large carnivores are rare (relative to prey species) o A minimum average of 10 prey organisms to support one predator of equal mass - The structure of pyramids varies widely in practice between ecosystems too; o Panamanian rainforests: ~40,000 g/m^2 of plant biomass to support 14 g/m^2 of primary and secondary consumers and decomposers o Coral reefs: 703 g/m^2 support 132 g/m^2 of herbivores and 11g/m^2 of carnivores o English Channel : 4g/m^2 can support 21 g/m^2 of herbivore biomass (efficiency of copepods harvesting phytoplankton) - We might predict that food webs of insects (high-energy efficiencies) that live in areas of high primary productivity, might contain more trophic levels than other communities – but not the case - Most terrestrial food webs, despite differences in primary productivity and thermal efficiency of the organisms, tend to have three to four trophic levels - Another observation: low primary productivity in oceans but o Many marine communities have 5 trophic levels o Carnivores much more abundant than terrestrial systems - Therefore: energy flow cannot be the only factor limiting the number of trophic levels - Possibility: energy transfer between marine primary producers (microscopic plants) and primary consumers is more efficient than terrestrial energy transfer What is the pyramid representing?
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