Lecture 4: Energy Transfers Flashcards
Leaf photosynthetic ability - why isn’t production always maximized?
- photosynthetic capacity = photosynthetic rate/biomass unit of leaves under facorable conditions = C-gaining potential/biomass united invested in leaves
- Leaf N + photosynthetic potential positively correlated
- persistent trade-off between traits that maximize photosynthesis vs. leaf longevity
- long-lived leaves are more typical in N-limited conditions (max. longevity: predation, toughness)
What traits might maximize leaf longevity?
- higher proportion of complex C-containing compounds (cellulose, lignin)
- high C content is byproduct of continuing photosynthesis/C-fixation w/ conversion to other end-products (surface area, amino acids) constrained by absence of other resources (N)
- resource-poor environments (each leaf more expensive) –> lower turnover
- leaves less susceptible to herbivory
- more likely to give plant “carbon return on investment” over longer leaf lifespan
Why does the efficiency of energy transformations matter?
- efficiency of autotrophic primary production determines available chemical energy to fuel primary producer populations –> higher trophic levels
- basis for carrying capacity K (amount of biomass that can be supported by amount of incoming energy)
Egested energy
portion of consumed energy that is excreted/regurgitated
Assimilated energy
portion of energy a consumer digests and absorbs (analogous to GPP for producers)
Respired energy
portion of assimilated energy a consumer uses for respiration
* remaining energy can be used for growth and reproduction (net secondary productivity)
Net secondary productivity
rate of consumer biomass accumulation in a given area (analogous to NPP for producers)
Trophic transfers
Rule of thumb: trophic efficiency is 5-20% (~10%)
Energy order of events
1) Ingested
2) Assimilated/feces
3) Respiration/production
4) Biomass
5) Predation/mortality
Consumption efficiency
- percentage of energy/biomass in trophic level that is consumed by next higher level
consumption efficiency = consumed energy/net production energy of the next trophic level
Assimilation efficiency
- percentage of consumed energy that is assimilated (ex. bones)
assimilated efficiency = assimilated energy/consumed energy
Do you expect primary consumers or secondary consumers to have higher assimilation efficiency? Why?
Secondary
* most tough materials and non-digestible parts have been elminated by the primary consumer so that a larger proportion of the consumed energy can be assimilated (instead of excreted)
Do you expect endotherms of ectotherms to have higher production efficiency?
Ectotherms
* “spend” less of their assimilated energy on metabolism/respiration to regulate body temperature
Ecological efficiency (trophic efficiency: one trophic level to the next) equation
E(consump) x E(assim) x E(prod) = Prod(n)/Prod(n-1)
Trophic & biomass pyramids
Secondary - 2.4%
Primary - 11.5%
Producers - 86.1%
Which type of ecosystem (terrestrial vs. aquatic) has higher ecological efficiency?
Aquatic
* more assimilated energy available per lvl
* producers easily accessible
* less fight w/ gravity
–> more tropic levels than terrestrial (~5 vs. 3-4)
Traits of aquatic producers
Small, highly-palatable, short-lived
Traits of terrestrial producers
lignin, cellulose, desfense compounds, long-lived
Energy residence times
- length of time energy spends in a given trophic lvl (longer time = greater energy accumulation)
Energy residence time (years) = energy present in a trophic lvl (J/m2) / Net productivity (J/m2/year)
Biomass residence time
- length of time biomass spends in a given trophic lvl
Biomass residence time (years) = biomass present in trophic lvl (kg/m2) / Net productivity (kg/m2/year)
Residence times
- Energy & biomass residence times X account for dead organic matter residence time (consumed by scavengers, detritivores, and decomposers)
= dead organic matter present in trophic lvl (kg.m2)/ dead organic matter productivity (kg/m2/year)
- Dead matter residence time lower in humid tropical ecosystems vs. temperate and boreal forests (water limitation)
Prior to the evolution of living organisms and their proliferation, did the Earth have stores of organic chemical energy?
Nope
Carbon bonds
energy currency of life
Examples of human alteration of C-cycle
1) Greenhouse effect & planetary warning
2) Ocean acidification (not warming, CO2 concentration)
3) Thermodynamics & energy availability
