Factors Limiting Distribution: Temperature, Moisture, And Other Physical-Chemical Factors

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Factors Limiting Distribution Temperature,
Moisture, And Other Physical-Chemical Factors
Chapter 6
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Climatology

• Large temperature differentials over Earth are
  the result of two basic variables incoming solar
  radiation and distributions of land and water.

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Insolation Solar Radiation
Amount of heat delivered to the poles is only
about 40 that at the equator.
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• Land heats and cools much more rapid than does
  water, so land-controlled climates have large
  daily and seasonal temperature fluctuations.

Average Annual Temperature Range (C) Monthly
mean warmest monthly mean coldest (?15C ?27F)
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World Distribution Of Mean Annual Precipitation
Equator
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Moisture Circulation

• Of the water that falls on land, about 30 is
  returned via runoff.
• The rest (70) of the moisture returns back to
  the atmosphere by evaporation and transpiration
  from plants.
• Transpiration is the loss of water through plant
  leaves
• Evaporation and transpiration (combined -
  evapotranspiration) depends primarily on
  temperature.
• Evaporation is high in arid areas.

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Evapotranspiration

• Potential evapotranspiration - Usually measured
  as a function of temperature.
• Amount of water that would be lost given an
  unlimited amount of rainfall
• Actual evapotranspiration the evaporative water
  loss from a site covered by a standard crop,
  given the precipitation

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Climatic Diagrams Relationship between
temperature and precipitation
Temperature Limiting
Moisture Limiting
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Tolerating Temperature and Moisture

• Organisms either tolerate the conditions as they
  are or escape via some evolutionary adaptation.
• Organisms have upper and lower lethal limits.
• Shelfords Law of Tolerance
• Organisms can acclimate to some conditions

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• Temperature and moisture may act on any stage of
  the life cycle and can limit the distribution of
  a species through their effects on one or more of
  the following
• Survival
• Reproduction
• Development of Young Organisms
• Interactions of other organisms (competition,
  predation, parasitism, disease) near the limits
  of temperature or moisture tolerance

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• What aspect is limiting distribution?
• Maximums, minimums, averages, or the level of
  variability
• No rule of thumb.
• Plants and animals respond differently during
  different stages of their life cycle
• How to show that temp or moisture is limiting
• Determine which phase of the life cycle is most
  sensitive to temperature or moisture
• Identify the physiological tolerance range of the
  organism for this life cycle phase
• Show that the temperature or moisture range in
  the microclimate where the organism lives is
  permissible for sites within the geographical
  range, and lethal for sites outside the normal
  geographic range

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Drought

• How can plants resist drought (evolutionarily)?
• Improvement of water uptake by roots
• Reduction of water loss by stomatal closing,
  reduction of cuticular respiration, reduction of
  leaf surface area
• Photosynthesis Solar Energy CO2 H2 O ?
  C6H12O6 O2
• Respiration C6H12O6 O2 ? CO2 H2 O Energy
• Storage of water
• Xerophytes plants that live in dry areas.
• Most have the above adaptations

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Temperature and Moisture Interaction

• Soil drought deficiency in soil moisture
• absolute shortage of water in soil
• Frost drought present water is unavailable due
  to low temperatures
• Relative shortage of water
• Low temperatures can produce the symptoms of
  drought
• Many of the distributional effects attributed to
  temperature may in fact operate through the water
  balance in plants.

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The rate of water uptake in loblolly pine
decreases rapidly at lower temperatures.
Predicted range based on temperature and
moisture strongly correlates with actual range
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Timberline

• Moving up a mountain, there is an altitudinal
  limit to the presence of trees this is called
  the tree line or timberline.
• Strong illustration of physical limitations to
  plant growth
• Nine factors that may affect the location of a
  timberline
• Lack of soil, desiccation of leaves in cold
  weather, short growing season, lack of snow
  (exposing plants to winter drying), excessive
  snow lasting through the summer, mechanical
  effects of high winds, rapid heat loss at night,
  excessive soil temperatures during the day,
  drought
• Above can be boiled down to three factors
  temperature, moisture, and wind.

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Timberline
Wind Beaten Trees
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Latitude and Altitude
Montane Coniferous Forest
Deciduous Forest
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Adaptation

• We know that genetic and physiological uniformity
  does not occur throughout a species entire
  range.
• Ecotype subspecies or race that is especially
  adapted to a particular set of environmental
  conditions.
• describes genetic variability within a species.
• For example, Plantago maritima grows tall in
  marshes and as a dwarf on the coast
• Are ecotypes the result of environmental or
  genetic differences, or a mixture of both?

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Common Garden

• A common garden experiment can be used to
  separate the phenotypic (environmental) from the
  genotypic (genotype) components of variation.
• Plants of the same species but growing in a
  diversity of habitats are grown in the same
  environment.
• Any differences in phenotype can then be
  attributed to genotype differences
• Common garden experiments are also used for
  animal studies.
• Temp tolerance, salinity tolerance, reproductive
  differences etc.

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Plantago maritima

• Marsh normal height 30 40 cm
• Cliff normal height 5 10 cm
• Each grown in a common garden

Plantago maritima Source Mean height (cm) in garden
Marsh Population 31.5
Cliff Population 20.7
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Morphological and Physiological Differences

• Diverse phenotypes can be explained three ways
• All differences are phenotypic, and seeds
  transplanted from one situation to the other will
  respond exactly as the resident species
• All differences are genotypic, the mature plants
  will retain the form and physiology typical of
  their original habitat
• Some combination of phenotypic and genotypic
  determination produces an intermediate result

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Light As A Limiting Factor

• Photoperiod presence of light during a 24 hour
  period
• Can influence seasonal physiology / behavior
• Increasing/decreasing day length
• Essential for photosynthesis conversion of CO2
  to organic compounds
• Shade tolerant versus shade intolerant plants
• Metabolic rate differences

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Important principle in evolutionary
ecology Individuals of a species cannot do
everything in the best possible way! Adaptations
to live in one type of habitat make it difficult
or impossible to live in another type of habitat
there are no superanimals or superplants!
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Seaweeds

• Light is attenuated very fast in water (less
  light available the deeper you are).
• Two general types of seaweed occur
• Flat wide monolayered thalli
• Highly dissected narrow multilayered thalli

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Proposed model for the effects of light intensity.
Relationship of thallus morphology to depth for
seven species of sargassum.
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C3, C4, and CAM Photosynthesis

• Plants have evolved different types of
  photosynthesis as an adaptation to different
  habitat types.
• During photosynthesis CO2 is fixed to an
  organic molecule.
• C3 CO2 is fixed to a three carbon molecule
• C4 CO2 is fixed to a four carbon molecule
• CAM crassulacean acid metabolism
• CO2 taken in at night and stored as malic acid,
  which is then used to complete photosynthesis
  during the day.

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C3 Versus C4

• C4 plants do not reach saturation levels even
  under the brightest sunlight.

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C3 Versus C4

• C4 plants physically separate CO2 fixation and
  the Calvin cycle
• They are more efficient at recycling CO2 through
  respiration and and use a different enzyme to fix
  CO2

C3 ? RuDP Carboxylase to fix CO2, is inhibited by
O2 C4 ? PEP Carboxylase to fix CO2, not
inhibited by O2
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C3 Versus C4

• C3 plants are much more common in cooler habitats
• C4 plants

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CAM Plants

• Open their stomata at night to take up CO2,
  presumably to conserve water.
• Segregate photosynthesis by time.
• These plants are found in very dry areas like
  deserts (cacti are CAM plants).

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Climate Change And Species Distribution

• If temperature and moisture are the master
  limiting factors for the geographical range of
  animals and plants, the climatic warming that is
  now occurring will have profound effects on the
  Earths biota.

?6.5C
?4.5C