Factors Limiting Distribution: Temperature, Moisture, And Other Physical-Chemical 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 Temperature Limiting Moisture 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 Population size Low High Temperature Zone of intolerance physiological stress Optimum range No organisms Few Lower limit of tolerance Abundance of organisms Upper limit

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? 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

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 Alpine Tundra Tropical Forest Tropical Forest Temperate Deciduous Forest Northern Coniferous Forest Arctic Tundra Low High Moisture Availability Elevation Montane Coniferous Forest Deciduous Forest

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.

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

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 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

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

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. 6.5°C 4.5°C