Chapter 21: Energy in Ecosystems

what does ecology quantify

ecology quantifies the flow of matter and energy through ecosystems

why do we consider energy flow

species interactions involve energy, determines biomass in trophic levels, energy efficiency, community resilience

primary productivity

the rate at which solar energy is captured and converted into chemical bonds by photosynthesis

photosynthesis equation

6 CO2 + 6H2O + photons —> C6H12O6 + 6O2

gross primary productivity

the rate at which energy is captured and assimilated by producers

net primary productivity

the rate of energy that is assimilated by produces and converted into producer biomass; includes all energy that is not respired

how much terrestrial NPP do humans use

over 20%

standing crop

the biomass of produces in a given area at a particular time

what do ecosystems with high primary productivity not have

a high standing crop because consumers may eat it quickly

how can NPP be measured

as the change in producer biomass over time (i.e., growing season) - NPP is a rate

what happens to plant mass

it is harvested, dried, and weighed

what can herbivory or tissue mortality lead to

underestimation of NPP

what kind of biomass is often collected

aboveground

what do producers do during gas exchange

take up CO2 during photosynthesis and produce CO2 during respiration

where are leaves placed

in a sealed chamber with CO2 sensor

what occurs in light

photosynthesis and respiration occur; the net uptake of CO2 represent NPP

what occurs in the dark

only respiration occurs, then GPP can be measured

GPP equation

GPP = NPP + Respiration

isotopes

CO2 with 14C added to sealed container with plant and traced

eddy flux covariance

CO2 uptake and release measured with towers that sample CO2 concentrations at different heights above ground

remote sensing

analysis of conditions of a large area using satellite or airplane photos

what does chlorophyll absorb

red and blue wavelengths but reflect wavelengths

how are high standing crops shown

green

primary production

production by producers

secondary production

production by herbivores

what do herbivores consume

only a fraction of producer biomass and they only digest a portion of energy consumed

egested energy

the portion of consumed energy that is expelled without being digested

assimilated energy

the portion of energy that a consumer digests and absorbs; analogous to GPP for producers

net secondary productivity

the rate of consumer biomass accumulation; analogous to NPP for producers

what does net secondary productivity depend on

primary productivity for energy

what is NPP positively correlated with

net secondary productivity

how does NPP vary

with latitude and across terrestrial and aquatic biomes

what is NPP also positively correlated with

annual temperature

what is mean annual precipitation related with

NPP until 3m of annual precipitation

nutrients

particularly nitrogen and phosphorus can strongly affect NPP in terrestrial ecosystems

what can both nitrogen and phosphorous limit

NPP of aquatic ecosystems

what can excess nutrients cause

eutrophication

nutrient limitation in the open ocean

in the open ocean other elements limit productivity, diatoms are often limited by silicon, iron is also limiting: when researchers added iron to the ocean, concentrations of phytoplankton tripled - photosynthesis by algae and respiration by consumers both increased with no net change in CO2 uptake

trophic pyramid

a chart of the amount of energy or biomass in each trophic group

in terrestrial systems

pyramids of biomass and energy look similar

in aquatic systems

there are low standing crops - inverted biomass pyramid

efficiency

the amount used compared to the amount lost

what is is important to study efficiency

important for understanding energy flow and use, ecosystem function

ecological efficiency (food chain efficiency)

the percentage of net production from one trophic level camped to the next lower trophic level

ecological efficiency equation

net production energy of a trophic level (J) / net production energy of the next lower trophic level (J)

what does ecological efficiency incorporate

consumption, assimilation, and net production

why is ecological efficiency about 10%

because energy is lost at each step

what does low ecological efficiency make difficult

to have long food chains; there is little energy to support higher trophic levels

what does eating lower on the food chain require

less energy

ecological stoichiometry

the study of the balance of nutrients in ecological interactions, such as between an herbivore and a plant

example of ecological stoichiometry

fast growing water fleas (top) need more P relative to N than slow growing copepods (bottom). if the ratio of ingested nutrients to required nutrients is low, consumers must eat more food. higher consumption leads to higher rates of excretion which lowers ecological efficiency

in terms of the net primary productivity, where are most productive ecosystems found

near the equator

of the energy assimilated by an organism, some is used for growth and reproduction and the rest is termed

respired energy

which of the following factors can limit the number of trophic levels in a food web

a limited amount of sunlight

in aquatic systems, why is the pyramid of energy the opposite shape compared to the pyramid of biomass

the producers are microscopic and reproduce quickly