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Energy flow within terrestrial and
aquatic ecosystems Energy available for growth and reproduction (as a
function of food availability):
= GPE - NPE
Tells usamount of energy flow
Not rate at which energy flows
Ecosystem and community development is
regulated by therate of energy flow as well
How fast does available energy flow between
trophic levels
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Second question of energy flow within a system is: how fast does energy transfer occur?
Residence time = inverse of energy transfer rate RT = biomass / net productivity
RT (yr) = energy stored in biomass (kJ m )-2
Net productivity (kJ m yr )-2 -1
Measure of biomass accumulation within any given trophic level
(g(C) m )
(g(C) m yr )
-2
-2 -1or
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Wet tropical rainforest:
Produce about 1800 g m-2 yr-1
andLiving average biomass of 42 000 g m-2
42 000 g m-2
1800 g m-2 yr-1= RT = 23 yr
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Temperate scrubland:
Produce about 600 g m-2 yr-1
and
Living average biomass of 6 000 g m-2
6 000 g m-2
600 g m-2
yr-1
= RT = 10 yr
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Open ocean:
Produce about 125 g m-2 yr-1
andLiving average biomass of 3 g m-2
3 g m-2
125 g m-2 yr-1= RT = 0.02 yr
(About 9 days)
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Ricklefs (1972)
Peat bogs near Root Springs, Concord MA
Herbivores: assimilate energy at a rate of 0.31 J m-2 s-1
Aquatic plants and algae produce 0.09 J m-2 s-1
So, where is the other 0.22 J m-2 s-1 coming from?
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Ecosystems do not exist
individually autochothonous production = energy fixed
within the system
allochothonous production = energy fixed
outside of the system
energy can be from input from external
system
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General Trends
assimilation efficiency increases at higher trophiclevels
NPE decreases at higher trophic levels
GPE decreases at higher trophic levels
Ecological efficiency averages about only 10%
GPE(n) / GPE (n-1) = efficiency of transfer
between specific trophic levels
Aquatic systems typically support more trophic
levels than terrestrial systems
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Nutrient cycles
Biogeochemical sources
Biotic = nutrients released from decomposers
Abiotic = nutrients released from erosion of
substrate or fixed by primary producers Indirect = nutrients stored in soil
Direct = nutrients absorbed directly from
decomposers Indirect = higher nutrient capital
Amount of stored nutrients within the system
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Atmosphere
Primary
producers
ConsumersDead organic
material
Soil
Indirect nutrient cycling
Nutrients can flow from source to source
Length of time at each source dependant
upon source characteristics
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Atmosphere
Primary
producers
ConsumersDead organic
material
Soil
Direct nutrient cycling
Nutrient uptake increased by presence
of mycorrhizae (fungal producers)