Download lecture 7 ch 2+3 physical environment: constraints and

LECTURE 4 CH 2+3 PHYSICAL ENVIRONMENT: CONSTRAINTS AND
SOLUTIONS
Background
Physical laws set limits on life.
Life exists out of equilibrium with physical world; uses energy to counteract.
Life tolerates extreme conditions.
Adaptations evolved in response to physical environment.
Shelford’s ‘Law of Tolerance’
Individual’s physical responses show optimum and limits of tolerance.
Tolerance limits affect individual’s performance and survival/reproduction.
Distribution of species controlled by tolerance limits.
More than 1 factor may limit distribution.
Tolerance is related to functioning of enzymes.
Physical factors organisms face
1) Water
Why is it the ideal medium for life?
How do constraints of water account for adaptation of form?
What are thermal properties of water?
Buoyancy and viscosity
Limits of water determine distribution of deserts (coupled with high T in hot deserts)
Adaptations of animals to aridity (e.g. kangaroo rat)
Vary body temperature
Concentrated urine and dry feces
Nocturnal activity; use burrows in day
Food provides metabolic water
Adaptations of plants to aridity
How do plants obtain water?
Soil – plant – atmosphere continuum
Soil - roots via osmosis
Movement upward in plant aided by cohesion and adhesion
Transpiration pull from atmosphere to leaf to xylem water column
Water gradient (in to out) is very steep
CO2 gradient (out to in) is very shallow
>>>>Water loss relative to CO2 gain
Structural adaptations: hairs, sunken stomates
Photosynthetic adaptations
C3: Problem = Rubisco has higher affinity for O2 than CO2;
Especially at high temp and low H2O; less CO2 fixed
C4: Solution = Spatial separation of CO2 uptake from Rubisco; keep O2 low
CAM: Problem = High water loss with stomates open in day to take in CO2
Solution = Temporal separation of CO2 uptake (night; high humidity)
and CO2 fixation by Rubisco (day; low humidity); save water
When and where did C3 vs. C4 evolved relative to CO2 conc.?
2) Dissolved solutes and nutrients
Water as powerful solvent; contains solutes
Solutes reflect bedrock chemistry
Plants obtain mineral nutrients from soil water
Root:shoot ratio > in low nutrients
Ionic conc. in soils affects plant distributions
Evolution of tolerance to heavy metals
3) Dissolved solutes: Salt and water balance
High or low conc. of ions in water  osmotic strain
Hyperosmotic: gain water, increase pressure in cell; lose solutes
Hypoosmotic: lose water, cells collapse; gain solutes
Fish in fresh water: retain water and excrete ions
Fish in salt water: retain ions and excrete excess water
Animals excrete excess nitrogen in urine
Plants in salt (e.g. mangroves) actively excrete salt.