1. Factors Limiting Distribution: Temperature, Moisture, And Other Physical-Chemical Factors – Chapter 6

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

3. Insolation – Solar Radiation
Amount of heat delivered to the poles is only about 40% that at the equator.

4. 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)

5. World Distribution Of Mean Annual Precipitation
Equator

6. 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.

7. 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

8. Climatic Diagrams: Relationship between temperature and precipitation
Temperature Limiting
Moisture Limiting

9. 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
Population size
Low
High
Temperature
Zone of
intolerance
physiological stress
Optimum range No
organisms
Few
Lower limit
of tolerance
Abundance of organisms
Upper limit

10. 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

11. What aspect is limiting distribution? No rule of thumb.
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

12. 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

13. 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.

14. 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

15. 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.

16. Timberline
Wind Beaten Trees

17. Latitude and Altitude Alpine Tundra Tropical Forest Tropical Forest
Temperate Deciduous Forest
Northern Coniferous Forest
Arctic Tundra
Low
High
Moisture Availability
Elevation
Montane
Coniferous
Forest
Deciduous
Forest

18. 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?

19. 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.

20. Mean height (cm) in garden
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

21. 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

22. 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

23. 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!

24. 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

25. Proposed model for the effects of light intensity.
Relationship of thallus morphology to depth for seven species of sargassum.

26. 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.

27. C3 Versus C4
C4 plants do not reach saturation levels even under the brightest sunlight.

28. C3 C4
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

29. C3 Versus C4 C3 plants are much more common in cooler habitats

30. 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).

31. 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.
6.5°C
4.5°C