Lecture 17: Ecosystems: Energy transfer and Net Primary Production (NPP) Flashcards
define ecosystem
Ecological scale at which we see the exchange of common elements among organisms and the environment.
what is the unique process seen at the ecosystem level
energy flux and nutrient cycling
what is the primary energy transformation in ecosystems
the conversion of light into energy via photosynthesis
Ecosystem _____ and _________________ both increase the amount of energy an ecosystem needs to be sustained
- size
- speed of energy flow
what is lost with each transfer to a higher trophic level and why
- energy is lost with each transfer to a higher trophic level
- bc of the work organisms have to do to acquire and use energy
define trophic pyramid
- Graphical representation of the relative energy or biomass at each trophic level
- visualizes loss of energy between trophic level
Pyramids of energy and biomass in terrestrial systems
Energy and biomass pyramids are the same shape (pyramid shape) because of large, relatively long lived primary producers.
Pyramids of energy and biomass in aquatic systems
- energy pyramid is a regular pyramid
- Biomass pyramid is inverted because of tiny, short-lived primary producers compared to large, long lived consumers.
Tracing energy to reveal real trophic levels
- Ratio of different Nitrogen isotopes (15N/14N) changes with trophic level
- more of the heavier isotope means nitrogen was acquired from a higher trophic level
what does analyzing the isotope ratio reveal
reveals trophic level without the need for direct observations
nitrogen isotope ratio ant discovery
most canopy ants are herbivores bc they had more 14N (lighter than 15N)
Three main reduction steps
- Consumption Efficiency
- Assimilation Efficiency
- Net Production Efficiency
define consumption efficiency
- percentage of energy in a trophic level that is consumed by the next higher trophic level
- not everything is eaten.
define assimilation efficiency
- percentage of consumed energy that is assimilated into the organisms in the consumer trophic level
- not everything that is eaten is used by the organism.
define net production efficiency
- percentage of assimilated energy directed to growth and reproduction of the consumer trophic level
- not everything used by the organism contributes to growth and reproduction
define egested energy
indigestible foods that are defecated or regurgitated
define assimilated energy
- What is actually assimilated
- used to calculate assimilation efficiency
respired energy
the component of assimilated energy that is used in respiration
excreted energy
the organic waste due to the proportion of assimilated energy that cannot be used bc it is in excess
net production efficiency “equation”
Assimilation Efficiency = respiration - excretion
Which plant parts allow for the highest assimilation efficiency?
Seeds > Young leaves > Grazing and browsing > Decaying plant material (detritivores)
The ________ in food also influences assimilation efficiency and especially the amount of energy lost in excreted energy.
balance of nutrients
stoichiometry
The study of the balance of nutrients in organisms, and ecological systems as a whole
Nutrient imbalances in an organism’s diet, and the resulting excess excretion, can greatly reduce assimilation efficiency — but can have ____________________________
other (positive) consequences
Detritivores form the primary consumers of an additional ________, parallel to the __________ involving herbivores feeding on living plants
- “brown food web”
- “green food web”
Nutrient cycling through the detritivore food web tends to be ______, but _________ for ecosystem stability.
- slower
- very important
since measuring all the energy in an ecosystem is not possible, what do we do instead
need to use “proxies” of various kinds that inform us about the properties of the whole ecosystem
One good proxy approach for all the energy in an ecosystem is to look at the ____________ through _____________________.
- energy-flow rate
- part of the ecosystem
what do energy flow rates tell us
how long energy stays in one trophic level, and therefore how much energy and biomass can accumulate within an ecosystem
define energy residence time
The length of time energy stays in a given trophic level
what can tell us critical things about the functioning of an ecosystem
Residence time of energy, biomass, or any key nutrient
define primary production
the accumulation of energy by plants and other autotrophs
define gross primary production
- The measure of all the energy assimilated by the plant
- much is used in respiration
define net primary production
- the energy accumulated as plant biomass
- the part of primary production available to the next trophic level.
3 approaches for practical measures of net primary production to assess energy flow
- measured by harvesting
- measured by recording carbon dioxide uptake rates
- measured at large spatial scales using remote sensing
practical measures of net primary production - harvesting
- can be measured by harvesting, drying, and weighed biomass produced in particular areas
- can measure aboveground or below ground
biomass.
practical measures of net primary production - recording carbon dioxide uptake rates
- can be measured by recording carbon dioxide uptake rates under small-scale, controlled conditions — a direct measure of photosynthesis and ultimate biomass accumulation
- oxygen uptake and release rates are used in aquatic systems
practical measures of net primary production - at large spatial scales using remote sensing
- can be measured at large spatial scales using remote sensing of vegetation cover
- rapidly advancing method driven by technological development.
Global patterns of NPP in terrestrial and aquatic systems using remote sensing data
- terrestrial systems, highest NPP occurs in the tropics
- Highest NPP in aquatic systems occurs in shallow waters around land
what is Net Primary Production influenced by
- the availability of all key inputs to photosynthesis and plant growth:
- light
- nutrients
- water availability and temperature
Influences and limits on Net Primary Production - light
- light availability will limit NPP up to the “saturation point”
- point at which no more light can be used by photosynthetic pigment
Influences and limits on Net Primary Production - nutrients
Plants are adapted to typically available nutrients, but seasonal or human-driven pulses in nutrients will increase NPP
what does low moisture in plants result in
- wilting (water uptake less than loss
via transpiration) - plants close their stomata to reduce water loss.
what does a closed stomata do
limits carbon dioxide uptake, severely limiting photosynthesis
how is production a reflection of water availability
Many wild plant species vary little in water use efficiency (~2g used per kg of rainfall)
what does water-use efficiency interact with
annual rainfall patterns and temperature/annual growing period to determine NPP
ideal conditions for high NPP
warm temperatures and moderate, consistent rainfall
Hotter places have higher NPP, but ______ water reduces nutrient availability (erosion and runoff) and lowers NPP.
too much
Net secondary productivity
the rate of biomass accumulation in consumers
what does NPP dictate
the net secondary productivity of ecosystems
