Physical controls on the distribution of organisms Flashcards
Light
variation in light intensity is a key control in distribution of plant species within an ecosystem
Heliophytes
- sun plants
- plants which grow best in full sunlight
- shade intolerant
Sciophytes
- shade plants
- plants which grow best in shade
- shade tolerant
C4 photosynthesis
- more efficient use of CO2
- no photorespiration
- chloroplasts concentrated within bundle sheath cells
- but expensive!
- tropical grasses
- good water-use efficiency
- efficient at high temp and low CO2
Transpiration
evaporation from the leaf
Evapotranspiration
evaporation from leaf plus soil
C3 plants
inefficient at high temp and low CO2
- increased photorespiration
- poor water-use efficiency
- physiological drought
CAM photosynthesis
Crassulacean Acid Metabolism
- carbon fixation pathway that evolved in some plants as an adaptation to arid conditions.
- closes leaves at night to reduce evapotranspiration and open at night to collect CO2
Photoinhibition
shrinking of chloroplasts, loss of chlorophyll, loss of CO2 due to ‘photo-oxidation’
Photo-respiration
- as a result from photo-oxidation
- CO2 released but not utilisable by plant
- only occurs in C3 plants
Rate of photorespiration
positively correlated with light intensity and temperature
Sun leaves
- thicker, more cell layers
- thicker cuticle
- leaves more dissected
Shade leaves
- thinner, fewer cell layers
- thinner cuticle
- leaves less dissected§
Perennials
live for more than 1 year
shade tolerant plants
annuals
not enough light in shady conditions to support them
must germinate, grow, flower and set seed in 1 year
phenology
The timing of changes in growth of plant e.g.
- flowering in spring
- Shedding leaves in Autumn
Triggered by changes in duration of daylight
Photoperiodism
relationship between phenology and light
Key points about plants and light
- too little light is bad, but too much light is also bad
- plants have evolved a range strategies to grow under low and high light intensities
Temperature
geographic distribution of plants strongly linked to temperature
- metabolic and physical damage by extreme heat and cold
Chilling stress
- damage to cold temp above 0 degrees
Chilling sensitive
Damage by temp <10 degrees
Chilling resistant
survive < 10 degrees but damaged by ice formation
Frost resistant
survive to -15 degrees
Frost tolerant
Survive to -40 degrees
Cold tolerant
survive below -40 degrees
Damage caused by chilling stress
- above 0 degrees, but may be 15-20 for some tropical plant species
- infertile pollen or seeds
- low growth rate
- leaf discolouration
- stem/leaf dieback
- lesions on fruit
- young plants affected more than older/larger plants
Frost hardening
- frost resistance only possible if cooling gradual
- period of physiological preparation required
Poikilotherms
- cold blooded animals
- Ectotherms
- fish, reptiles, amphibians, insects
Homeotherms
- warm blooded animals
- Endotherms
- birds, mammals
- metabolic generation fo heat
Ectotherms
- body temp = ambient temp of environment
Endotherms
- above ambient temp of environment
Temperature Range
- when active, body temp must be in a narrow range
- most cannot survive close to freezing or near 40 degrees
Eurythermic
species that can tolerate a broad temperature range
Stenothermic
species with a restricted temperature range
Why does metabolic rate decline rapidly above 40°C?
- Enzyme activity slows
- Proteins break down
- Cell membranes destroyed
- Rates of oxygen intake no longer match respiratory needs
Allens rule
the shorter an animals erctremitites are relative to body mass, the lower the rate of heat loss
Moisture and plants
Xerophystes
mesophytes
hydrophytes
Desert annuals
- 8 day life cycle
- very high rates of photosynthesis
Tropical Deciduous trees
- drop leaves in dry season
- store water in trunk
- photosynthetic bark
Conclusion
- form related to function
- different strategies (avoidance versus adaptation)
- interaction of physical factors
