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General Ecology > Lecture 17: Ecosystems: Energy transfer and Net Primary Production (NPP) > Flashcards

Lecture 17: Ecosystems: Energy transfer and Net Primary Production (NPP) Flashcards

1
Q

define ecosystem

A

Ecological scale at which we see the exchange of common elements among organisms and the environment.

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2
Q

what is the unique process seen at the ecosystem level

A

energy flux and nutrient cycling

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3
Q

what is the primary energy transformation in ecosystems

A

the conversion of light into energy via photosynthesis

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4
Q

Ecosystem _____ and _________________ both increase the amount of energy an ecosystem needs to be sustained

A
  • size
  • speed of energy flow
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5
Q

what is lost with each transfer to a higher trophic level and why

A
  • energy is lost with each transfer to a higher trophic level
  • bc of the work organisms have to do to acquire and use energy
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6
Q

define trophic pyramid

A
  • Graphical representation of the relative energy or biomass at each trophic level
  • visualizes loss of energy between trophic level
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7
Q

Pyramids of energy and biomass in terrestrial systems

A

Energy and biomass pyramids are the same shape (pyramid shape) because of large, relatively long lived primary producers.

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8
Q

Pyramids of energy and biomass in aquatic systems

A
  • energy pyramid is a regular pyramid
  • Biomass pyramid is inverted because of tiny, short-lived primary producers compared to large, long lived consumers.
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9
Q

Tracing energy to reveal real trophic levels

A
  • 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
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10
Q

what does analyzing the isotope ratio reveal

A

reveals trophic level without the need for direct observations

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11
Q

nitrogen isotope ratio ant discovery

A

most canopy ants are herbivores bc they had more 14N (lighter than 15N)

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12
Q

Three main reduction steps

A
  1. Consumption Efficiency
  2. Assimilation Efficiency
  3. Net Production Efficiency
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13
Q

define consumption efficiency

A
  • percentage of energy in a trophic level that is consumed by the next higher trophic level
  • not everything is eaten.
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14
Q

define assimilation efficiency

A
  • 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.
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15
Q

define net production efficiency

A
  • 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
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16
Q

define egested energy

A

indigestible foods that are defecated or regurgitated

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17
Q

define assimilated energy

A
  • What is actually assimilated
  • used to calculate assimilation efficiency
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18
Q

respired energy

A

the component of assimilated energy that is used in respiration

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19
Q

excreted energy

A

the organic waste due to the proportion of assimilated energy that cannot be used bc it is in excess

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20
Q

net production efficiency “equation”

A

Assimilation Efficiency = respiration - excretion

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21
Q

Which plant parts allow for the highest assimilation efficiency?

A

Seeds > Young leaves > Grazing and browsing > Decaying plant material (detritivores)

22
Q

The ________ in food also influences assimilation efficiency and especially the amount of energy lost in excreted energy.

A

balance of nutrients

23
Q

stoichiometry

A

The study of the balance of nutrients in organisms, and ecological systems as a whole

24
Q

Nutrient imbalances in an organism’s diet, and the resulting excess excretion, can greatly reduce assimilation efficiency — but can have ____________________________

A

other (positive) consequences

25
Q

Detritivores form the primary consumers of an additional ________, parallel to the __________ involving herbivores feeding on living plants

A
  • “brown food web”
  • “green food web”
26
Q

Nutrient cycling through the detritivore food web tends to be ______, but _________ for ecosystem stability.

A
  • slower
  • very important
27
Q

since measuring all the energy in an ecosystem is not possible, what do we do instead

A

need to use “proxies” of various kinds that inform us about the properties of the whole ecosystem

28
Q

One good proxy approach for all the energy in an ecosystem is to look at the ____________ through _____________________.

A
  • energy-flow rate
  • part of the ecosystem
29
Q

what do energy flow rates tell us

A

how long energy stays in one trophic level, and therefore how much energy and biomass can accumulate within an ecosystem

30
Q

define energy residence time

A

The length of time energy stays in a given trophic level

31
Q

what can tell us critical things about the functioning of an ecosystem

A

Residence time of energy, biomass, or any key nutrient

32
Q

define primary production

A

the accumulation of energy by plants and other autotrophs

33
Q

define gross primary production

A
  • The measure of all the energy assimilated by the plant
  • much is used in respiration
34
Q

define net primary production

A
  • the energy accumulated as plant biomass
  • the part of primary production available to the next trophic level.
35
Q

3 approaches for practical measures of net primary production to assess energy flow

A
  1. measured by harvesting
  2. measured by recording carbon dioxide uptake rates
  3. measured at large spatial scales using remote sensing
36
Q

practical measures of net primary production - harvesting

A
  • can be measured by harvesting, drying, and weighed biomass produced in particular areas
  • can measure aboveground or below ground
    biomass.
37
Q

practical measures of net primary production - recording carbon dioxide uptake rates

A
  • 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
38
Q

practical measures of net primary production - at large spatial scales using remote sensing

A
  • can be measured at large spatial scales using remote sensing of vegetation cover
  • rapidly advancing method driven by technological development.
39
Q

Global patterns of NPP in terrestrial and aquatic systems using remote sensing data

A
  • terrestrial systems, highest NPP occurs in the tropics
  • Highest NPP in aquatic systems occurs in shallow waters around land
40
Q

what is Net Primary Production influenced by

A
  • the availability of all key inputs to photosynthesis and plant growth:
  • light
  • nutrients
  • water availability and temperature
41
Q

Influences and limits on Net Primary Production - light

A
  • light availability will limit NPP up to the “saturation point”
  • point at which no more light can be used by photosynthetic pigment
42
Q

Influences and limits on Net Primary Production - nutrients

A

Plants are adapted to typically available nutrients, but seasonal or human-driven pulses in nutrients will increase NPP

43
Q

what does low moisture in plants result in

A
  • wilting (water uptake less than loss
    via transpiration)
  • plants close their stomata to reduce water loss.
44
Q

what does a closed stomata do

A

limits carbon dioxide uptake, severely limiting photosynthesis

45
Q

how is production a reflection of water availability

A

Many wild plant species vary little in water use efficiency (~2g used per kg of rainfall)

46
Q

what does water-use efficiency interact with

A

annual rainfall patterns and temperature/annual growing period to determine NPP

47
Q

ideal conditions for high NPP

A

warm temperatures and moderate, consistent rainfall

48
Q

Hotter places have higher NPP, but ______ water reduces nutrient availability (erosion and runoff) and lowers NPP.

A

too much

49
Q

Net secondary productivity

A

the rate of biomass accumulation in consumers

50
Q

what does NPP dictate

A

the net secondary productivity of ecosystems

General Ecology (23 decks)

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