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Factors Limiting Distribution:
Temperature, Moisture, And Other PhysicalChemical Factors
– Chapter 6
Climatology
• Large temperature differentials over Earth are
the result of two basic variables: incoming
solar radiation and distributions of land and
water.
Insolation – Solar Radiation
Amount of heat delivered to the poles is only
about 40% that at the equator.
• 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)
World Distribution Of Mean Annual
Precipitation
Equator
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.
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
Climatic Diagrams:
Relationship
between
temperature and
precipitation
Moisture Limiting
Temperature
Limiting
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.
– Shelford’s Law of Tolerance
– Organism’s can acclimate to some conditions
Lower limit
of tolerance
Abundance of organisms
Few
No
organismsorganisms
Population size
No
Few
organismsorganisms
Upper limit
of tolerance
Zone of
Zone of
intolerance
physiological stress
Low
Optimum range
Temperature
Zone of
Zone of
physiological stress
intolerance
High
• 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
• 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
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
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.
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
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.
Timberline
Wind Beaten Trees
Latitude and Altitude
High
Alpine
Tundra
Elevation
Montane
Coniferous
Forest
Deciduous
Forest
Low
Tropical
Forest
Tropical Forest
High
Temperate
Deciduous Forest
Northern
Coniferous Forest
Moisture Availability
Arctic Tundra
Low
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?
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.
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
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
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
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!
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
Proposed model for the
effects of light intensity.
Relationship of thallus
morphology to depth for
seven species of
sargassum.
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.
C3 Versus C4
• C4 plants do not reach saturation levels even
under the brightest sunlight.
C3
C3 Versus C4
• C4 plants physically
separate CO2 fixation
and the Calvin cycle
C4
• 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
C3 Versus C4
• C3 plants are
much more
common in
cooler habitats
% C4 plants
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).
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 Earth’s biota.
4.5°C
6.5°C