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Lecture 2: Ecological Limiting Factors
Reading: Economy of Nature, pp. 34-59.
Conditions
 not
consumed or used-up by other organisms
not
made unavailable or less available by other organisms
climate
and weather, physical environment, abiotic environmental factors
temperature
relative
humidity (RH)
hydrogen
ion concentration (pH)
salinity
wind speed
stream water
flow velocity
pollutant
concentration
Resources
|
something
consumed, used, or incorporated or transformed |
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something
eaten, incorporated in biomass |
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using it
makes it unavailable or unusable for other organisms |
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reuse may
occur after a period of use by another organism
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water |
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nutrients
(C, N, S, K, P) |
|
minerals |
|
food |
|
mates |
|
shelter |
|
solar
radiation |
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Major nutrients
required by organisms (Ricklefs, 1996, p 41, Table 2.1)
| Element |
Function |
| Nitrogen
(N) |
Structural
component of proteins and nucleic acids |
| Phosphorus
(P) |
Structural
component of nucleic acids, phospholipids, and bone |
| Sulfur (S) |
Structural
component of many proteins |
| Potassium
(K) |
Major solute
in animal cells |
| Calcium (Ca) |
Structural
component of bone and of material between woody plant cells; regulator
of cell permeability |
| Magnesium
(Mg) |
Structural
component of chlorophyll; involved in the function of many enzymes |
| Iron (Fe) |
Structural
component of hemoglobin and many enzymes |
| Sodium (Na) |
Major solute
in extracellular fluids of animals |
Solar radiation: a critical resource
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arriving
energy varies with latitude
highest at the equator
(see Ricklefs, 1996, pp 80 and 81, Fig. 4.1 and 4.2)
varies with degree of atmospheric
scattering and reflection
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at leaf
surface light can be
reflected
filtered and transmitted
absorbed
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eukaryotic
chloroplasts absorb light between 380nm and 710nm
visible light spectrum
56% of incident radiation
is outside visible range
photosynthetically active
radiation (PAR) (~400nm - 700nm)
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prokaryotic
chlorophylls: absorption peaks at 800nm, 850nm, and 870-890nm |
Spectral distribution of sunlight (Ricklefs,
1996, p 45, Fig. 2.13)
Biological energy flow is an open system,
not a cycle
Major energy transformation processes
Cellular respiration
Photosynthesis
Light intensity (energy/unit time/unit
area) (Ricklefs, 1993, p 39, Table 2.2)
| Measurement |
Units |
Typical
Value |
| langley (ly) |
1 cal cm
¯2 |
700 ly d
¯1 |
| watt (W) |
1 J s ¯1 |
1000 W m
¯2 |
| einstein
(E) |
6 X 10 23
photons |
2000 µE
m ¯2 s ¯1 |
| Source: M.G.
Barbour, J. H. Burk, and W. D. Pitts, Terrestrial Plant Ecology, Benjamin
Cummings, Menlo Park, California (1980). |
Photosynthesis rate as a function of
light intensity. The compensation point is the light intensity at which
the rate of photosynthesis just compensates for the maintenance needs
of the organism (cell respiration rate) (Ricklefs, 1996, p 46, Fig.
2.15).
Water absorbs light energy and scatters
light
In sea water: At 10m, the energy
of visible light decreases 50%
At 100m, the energy of visible light decreases to <7%
|
Red is
absorbed first |
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Blue and
violet scatter easily |
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Green
penetrates water best |
Euphotic zone: Depth to which photosynthesis
exceeds respiration in water.
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Rarely
the compensation point, the bottom of the euphotic
zone, is as deep as 100m. Examples, very clear ocean or
lakes near equator. |
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In highly
turbid waters, the compensation point may be
reached at 1m. |
Major Essential Elements
|
Calcium
(Ca), Iron (Fe), Nitrogen (N), Magnesium (Mg), Potassium (K),
Phosphorus (P), Sodium (Na), Sulfur (S) |
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Limiting
Nutrient Elements
In aquatic (freshwater)
environments: nitrogen and phosphorus
In marine (saltwater)
environments: iron
In terrestrial environments:
nitrogen and phosphorus (calcium) |
Other Essential Resources
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Carbon
Dioxide: Not limiting |
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Oxygen:
Can be limiting in water |
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Water:
Often limiting in terrestrial environments |
Limitations for one essential resources
can influence the availability of other essential resources. This
is the case among terrestrial plants for the relationships between
photosynthetic rates, water loss, and gas exchange.
Photosynthetic Capacity and Water Conservation
Photosynthesis rate varies widely among
species (100x) even with light saturation and all other resources
in abundance. This variation is due in part to differences between
plant species in the biochemistry of carbon fixation in photosynthesis
(Calvin Cycle). Plants can be categorized as having C3, C4, or CAM
metabolism.
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