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ecology > Lecture 18: Production > Flashcards

Lecture 18: Production Flashcards

1
Q

Ecosystem

A
  • refers to all the components of an ecological system, biotic and abiotic, that influence the flow of energy and elements
  • integrates ecology with other disciplines such as geochemistry, hydrology, and atmospheric science
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2
Q

Primary production

A
  • is the chemical energy generated by autotrophs during photosynthesis and chemosynthesis
  • the rate of primary production
  • Energy assimilated by autotrophs is stored as carbon compounds in plant tissues, thus carbon is the currency used to measure primary production
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3
Q

Gross primary production (GPP)

A
  • total amount of carbon fixed by autotrophs
  • depends on photosynthetic rate
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4
Q

Photosynthetic rate

A
  • is influenced by climate and leaf area index (LAI)—leaf area per unit of ground area
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5
Q

Plants use about half of the carbon fixed in photosynthesis for cellular respiration.

A
  • All plant tissues lose carbon via respiration, but not all tissues are photosynthetic (e.g., tree trunks). Trees tend to have higher respiratory losses.
  • Respiration rate increases with temperature, so tropical forests have higher respiratory losses
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6
Q

Net primary production (NPP)

A

GPP - Respiration
- GPP: all carbon that’s been fixed
- NPP: is the energy left over for plant growth, and for consumption by detritivores and herbivores
- Where water is plentiful (tropics), less NPP to roots, more to shoots to get more light (lots of competition)

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7
Q

Allocation of NPP to storage products (starch)

A
  • provides insurance against loss of tissues to herbivores, disturbances such as fire, and climatic events such as frost
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8
Q

It is important to be able to measure NPP

A
  • NPP is the ultimate source of energy for all organisms in an ecosystem.
  • Variation in NPP is an indication of ecosystem health.
  • Anything put into NPP is pulled out of the atmosphere
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9
Q

Measuring below ground NPP is more difficult

A
  • Fine roots turn over more quickly than shoots—they die and are replaced quickly.
  • Roots may exude carbon into the soil or transfer it to mycorrhizal or bacterial symbionts.
  • Harvests must be more frequent, and additional correction factors are needed
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10
Q

Harvest techniques

A
  • are impractical for large or biologically diverse ecosystems
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11
Q

Chlorophyll concentrations

A
  • Can be a proxy for GPP and NPP. They can be estimated using remote sensing methods that rely on reflection of solar radiation
  • Chlorophyll absorbs blue and red wavelengths and has a characteristic spectral signature.
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12
Q

NDVI (normalized difference vegetation index)

A
  • is measured over large spatial scales and can estimate CO2 uptake and NPP, deforestation, desertification, and other phenomena.
    NDVI = (NIR – red)/ (NIR + red)
    NIR – near-infrared wavelengths (700-1000nm)
    Red = red wavelengths (600-700nm)
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13
Q

High and low NDVI values

A
  • Vegetation has a high NDVI value
  • water and soil have low NDVI values.
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14
Q

NEE (Net ecosystem production or exchange)

A
  • More carbon coming out (source) or is carbon going in (carbon sink)
  • Wants ecosystems to be sinks rather than sources
  • NEE = GPP - (AR + HR)
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15
Q

Eddy correlation or eddy covariance

A
  • NEE is estimated by measuring CO2 at various heights in a plant canopy
  • Instruments are mounted on towers to take continuous CO2 measurements
  • At night, level near plants, soil respiring, lot of CO2
  • Daytime, plants sucking up CO2, see drop in CO2
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16
Q

Phytoplankton

A
  • do most of the photosynthesis in aquatic habitats
  • Phytoplankton have short life spans, so biomass at any given time is low compared with NPP; harvest techniques are not used
17
Q

Environmental controls on NPP

A
  • NPP varies substantially over space and time. Much of the variation is correlated with climate.
  • NPP increases as precipitation increases, up to a point. At very high precipitation levels, there is usually heavy cloud cover, so less light, and wet soils can become hypoxic.
  • NPP increases with increasing average annual temperature
  • ecosystem carbon storage (NEE) does not necessarily increase. Warmer temperature also increase respiration rates and loss of carbon.
18
Q

What nutrient controls NPP in terrestrial ecosystems?

A
  • Nitrogen
  • Phosphorus
  • More nitrogen/phosphorus leads to greater plant growth
    Experiment: Dry and wet meadows
  • In the dry meadow, nitrogen limited NPP.
  • In the wet meadow, both nitrogen and phosphorus limited NPP.
19
Q

Co-limitation

A

two nutrients limiting growth

20
Q

resource-poor vs resource-rich communities

A
  • Plants from resource-poor communities tend to have low growth rates, and require less nutrients, and thus respond less to fertilization, than plants from resource-rich communities.
  • When nutrient-poor communities are fertilized, there is often a change in species composition.
21
Q

NPP in rivers and streams

A
  • NPP is often low. Most of the energy is derived from terrestrial organic matter.
  • Water flow limits phytoplankton growth: most NPP is from macrophytes and attached algae as opposed to free-flowing algae
22
Q

NPP in ocean

A
  • In the open ocean, NPP is mostly limited by nitrogen.
23
Q

Global Patterns of NPP

A

reflect climatic constraints and biome types
- Average rate of NPP for the land surface is higher than for oceans: 54% of carbon is taken up by terrestrial ecosystems, 46% by the oceans.

23
Q

NPP in terrestrial biomes

A

variation is associated mostly with leaf area index and length of growing season.

24
Q

NPP in aquatic ecosystems

A
  • variation is primarily related to variation in nutrient inputs.
  • Upwellings bring nutrient-rich deep water to the surface
24
Q

Herbivores

A

eat plants and algae

24
Q

Secondary production

A
  • Heterotrophs get their energy by consuming organic compounds that were produced by other organisms
25
Q

Carnivores

A

eat other live animals

26
Q

Detritivores

A

eat dead organic matter

27
Q

Omnivores

A

eat both plants and animals

28
Q

Stable isotopes

A
  • used to determine an organism’s diet
29
Q

Net secondary production

A

= Ingestion – Respiration – Egestion
- Not everything converted to energy, some waste products
- depends on the quality of the heterotroph’s food (digestibility and nutrient content), and physiology
- a small fraction of NPP. The fraction is greater in aquatic ecosystems than terrestrial.

ecology (16 decks)

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