Trophic Dynamics
Systems Ecology:
emeryand biomass flow- one way to heat
Food chains-Food
Webs
Diagramatic
Representation by species becomes a nightmare
Trophic levels:
functional groups
Producers,
Consumers, Decomposers
Energy Flow
Energy Subsides:
Tides
Air/water
currents driven by themal redistribution
Hydrologic cycle
Energy flow
diagram in heterotrophs
Pyramid of
numbers/biomass as a community structural element
If each trophic
step reduces energy by 10% and 1 herbivore supported on one acre, then
carinvore needs 10 acres, secondary carnivore needs 100
Top predators
rare, require large territories
2 people per
square mile can live on trout, 2000, must eat rice
Trophic levels
limited by production: 4-5 max, but
Trophic ³levels²
blurred on an organism basis
Grazer food
chains
Detritus food
chains
community
production - community metabolism
Measure of net
community production P/R ratios
Streams
dominated by detritus food chains: heterotrophic community: most energy
imported
Early
successional plant communities: autotrophic: most energy stored, not respired
Steady State:
Climax
communities tend to have P/R ratios near 1,
despite constant
turnover within
Production/Biomass
ratio (P/B) Flow/flux rates
P/B high for
immature forests:accumulating biomass
P/B low for
climax forest: estimates turnover rate
P/B high with TD
short, small body size
P/B low with TD
long, large body size
Communities
dominated by annuals have high P/B
Aquatic
communites P/B several orders of magnitude higher
Ecological Efficiency:
transformation of energy and matter
NPP (Plant)
efficiency
autotrophic
respiration 20-75% of GPP
High for
communities with low P/B ratios: cost of maintaining biomass
low for
grasslands, aquatic communities
Forests < 50%
Grass/aquatics
> 50%
Herbivore
consumption:
<5% for
climax forest
>30% for
ungulates on grasslands
20-40% for
aquatic communities
Bacteria
20-30% of PP
Assimilation:
depends on food quality
cockroaches on
sugar and yeast 100%
Detritivores 10%
Browser/grazers
30-60%
Carnivores 60-90%
Tissue growth:
depends on maintenance/cost of free existence
feedlot beef 50%
elephants 1%
Poikilotherms
20-50%
Homeotherms 1-3%
Ecological
Growth Efficiencies
Herbivores
Homotherms
0.3-1.5%
Poikilotherms
9-25%
Carnivores
Homotherms
0.6-1.8%
Poikilotherms
12-35%
Protozoans:
10-50%
most energy flow
in global ecosystem through poikilotherms:
10-20%
for total trophic level