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Ecology 2483 > Lecture 18 > Flashcards

Lecture 18 Flashcards

1
Q

The Term Ecosystem

A
  • First used by Tansley (1935)
  • refer to all the components of an ecological system (biotic and abiotic) that influence the flow of energy and elements
  • ecosystem integrates ecology with
    geochemistry, hydrology, and atmospheric science
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2
Q

Primary Production

A
  • the chemical energy generated by autotrophs during photosynthesis and chemosynthesis
  • the rate: primary productivity
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3
Q

Energy Assimilated by Autotrophs

A
  • stored as carbon compounds in plant tissues
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4
Q

Carbon

A
  • the currency used to measure primary production
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5
Q

Gross Primary Production (GPP)

A
  • total amount of carbon fixed by autotrophs
  • depends on the photosynthetic rate
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6
Q

Photosynthetic Rate is Influenced By

A
  • climate and leaf area index (LAI)
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7
Q

Leaf Area Index (LAI)

A
  • Leaf area per unit of ground area
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8
Q

LAI Varies Among Biomes

A
  • Less than 0.1 in arctic tundra
  • 12 in boreal and tropical forests
  • Determines how many layers of leaves you can have in a competitive environment
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9
Q

Plants

A
  • Fix a lot of carbon in photosynthesis but lose carbon via respiration
  • Allocate carbon to plants that aren’t photosynthetic
  • Evolve to optimize allocation strategies
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10
Q

Net Primary Production (NPP)

A
  • represents biomass gained by the plant
  • the energy left over for plant growth and for consumption by detritivores and herbivores
  • Total photosynthesis- respiration (NPP=GPP- respiration)
  • the starting point for carbon and energy
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11
Q

Allocation of NPP to Storage Products

A
  • Provides insurance against loss of tissues to herbivores, disturbances such as fire, and climatic events such as frost
  • Substantial amounts of NPP (up to 20% may be allocated to defensive secondary compounds) to avoid being eaten
  • Reproduction and growth are optimized by natural selection
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12
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
  • NPP is associated with the global carbon cycle
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13
Q

Harvest Techniques

A
  • Measure biomass before and after the growing season
  • This is a reasonable estimate of aboveground NPP if corrections are made for herbivory and mortality
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14
Q

Measuring Belowground NPP

A
  • more difficult
  • 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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15
Q

Mechanism for Measuring Belowground NPP

A

minirhizotrons
- pump a clear tube into the ground and it does a 360-degree rotation (the mechanism is the same as those inside a photocopier)
- Allows direct observation of root growth and death
- Have an advanced understanding of belowground production processes

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16
Q

Harvesting Techniques and Chlorophyll

A
  • Impractical for large or biologically diverse ecosystems
  • Chlorophyll concentrations can be a proxy for GPP and NPP
  • Vegetation, dry bare soil, and clear water are present in large landscapes
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17
Q

Normalized Difference Vegetation Index

A
  • NDVI
  • NDVI = (NIR - red) / (NIR + red)
    NIR = near-infrared wavelengths (700-100 nm)
    Red = red wavelengths (600-700 nm)
  • measured over large spatial scales and can estimate CO2 uptake and NPP, deforestation, desertification
18
Q

Example with High NDVI Value

A
  • vegetation
19
Q

Example with Low NDVI Value

A
  • water
  • soil
20
Q

Net Change in CO2

A
  • GPP- total respiration
  • Which can also be referred to as Net ecosystem production or exchange (NEE)
21
Q

Heterotrophic Respiration

A
  • Must be subtracted from NEE to obtain NPP
  • NEE is a more refined estimate of ecosystem carbon storage than NPP
  • NEE = GPP - (AR + HR)
22
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
  • During the day: photosynthesis
  • At night: respiration
23
Q

Phytoplankton

A
  • Do most of the photosynthesis in aquatic habitats
    Short lifespans so biomass at any given time is low compared to NPP; with harvest techniques aren’t used
24
Q

Photosynthesis in Phytoplankton

A
  • measure in a water sample collected and incubated with light
25
Q

Respiration in Phytoplankton

A
  • measure in a water sample collected and incubated without light
26
Q

Environmental Controls on NPP

A
  • NPP varies substantially over space and time
  • NPP increases as precipitation increases up to a point
  • At very high precipitation levels there is usually heavy cloud cover
  • Wet soil can become hypoxic so many organisms can’t survive
  • Need water for plants to produce a lot
  • The warmer you get = the more NPP
27
Q

NEE- Ecosystem Carbon Storage

A
  • Does not necessarily increase with the temperature
  • Warmer temperature also increases respiration rates and loss of carbon
  • This can be indirect by affecting nutrient availability
28
Q

In a Dry Meadow

A
  • nitrogen limited NPP
  • Change in NPP resulted from change in species composition
  • The dominant plant biomass did not increase as much as others
29
Q

In a Wet Meadow

A
  • both nitrogen and phosphorus limited NPP
  • The dominant’s biomass increased more than the others
30
Q

NPP in Lake Ecosystems

A
  • use enclosures called “limnocorrals”
  • NPP is measured as a change in chlorophyll concentrations or the number of phytoplankton cells
31
Q

David Schindler

A
  • Declining water quality in the 1960s motivated him to determine wether inputs of nutrients in wastewater were causing increases in the growth of phytoplankton
32
Q

NPP in the Ocean

A
  • mostly limited by nitrogen
  • NPP in the equatorial Pacific Ocean appears to be limited by iron
  • Large-scale experiments with iron sulphate additions were done in 1993 (suppports the iron limitation hypothesis)
  • Iron is lost quickly from the photic zone
  • Sinking to deeper layers where it is unavailable to support phytoplankton growth
33
Q

Global Patterns of NPP

A
  • reflect climatic constraints and biome types
  • Remote sensing data now provides direct measurements of NPP
  • Global NPP has been estimated to be 105 petagrams (1 Pg = 1015 g) of carbon per year
  • Avg rate of NPP for the land surface is higher than for oceans
34
Q

What % of Carbon is Taken up by Terrestrial Ecosystems

A
  • 54%
35
Q

What % of Carbon is Taken up by the Ocean

A
  • 46%
36
Q

Highest Rates on NPP on Land

A
  • found in the tropics
37
Q

Secondary Production

A
  • Heterotrophs get their energy by consuming organic compounds that were produced by other organisms
38
Q

Heterotrophs

A
  • Herbivores eat plants and algae.
  • Carnivores eat other live animals.
  • Detritivores eat dead organic matter (detritus)
  • Omnivores eat both plants and animals
  • Not all the organic matter consumed by heterotrophs becomes heterotroph biomass.
    some used in respiration and some are egested (lost in urine/feces)
39
Q

Stable Isotopes

A
  • often used to determine an organism’s diet
40
Q

Net Secondary Production

A

ingestion - respiration - egestion
- depends on the quality of the heterotroph’s food, and physiology
- Animals with high respiration rates (endotherms) have less energy left over to allocate to growth

Ecology 2483 (21 decks)

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