From Ricklefs, R.E. Ecology, 3rd Ed., W.H. Freeman
loam
Water availability to plants depends on surface tension, soil structure Different soil types,
with different particle sizes (and size distributions) have different soil water availability
Different plant pigments absorb light in different parts of electromagnetic spectrum--and reflect colors that they don’t absorb: chlorophylls green, carotenoids yellow-red
Water tends to absorb longer wavelengths, scatter shorter ones; thus greens penetrate deepest
Surface plant such as green alga (Ulva) thus has pigments like terrestrial plants; deeper water red alga (e.g., Porphyra) absorbs most efficiently in the green wavelengths
Biologically relevant properties of air Air less viscous, less buoyant than water (organisms
move easily thru it, but need more support) Composed of different substances: 78% N2, 21% O2,
0.03% CO2, traces of CH4, N2O, etc. Diffusion of gases much more rapid in air than water
O2 diffuses rapidly in air (solubility 0.21 cm3/cm3 air); slowly in water (solubility 0.01 cm3 O2
/cm3 water) O2 often limits organisms in water-saturated
environments, especially where decay organisms (heterotrophs like bacteria) take up O2
This leads to anoxic conditions (like sulfur-stink of mucks in Lafitte Park)
CO2, by contrast, is rare, often limiting, in air (0.03%); dissolves readily in water (carbonic acid, bicarbonate)
Many plants tend to have great difficulty getting enough CO2, when stomata are open enough to transpire water; this is particular problem in desert environments (see next lecture)
•Reduction reaction less favorable energetically than oxidation--former requires energy from sun via chlorophyll molecules as energy-absorbers;
•energy of living things stored in reduced carbon bonds, e.g., carbohydrates
Respiration is reverse of photosynthesis
Respiration involves coupled oxidation & reduction (redox) half reactions, the reverse of those in photosynthesis O2 + 4e- + C4+ = CO2; Reduction half-reaction (oxygen is
reduced by gain of electrons) CH2O = C4+ + H2O + 4e-; Oxidation half-reaction (carbon is
oxidized) Coupled together: CH2O + O2 = CO2 + H2O
Overall reaction is favorable (net release of energy) because reduction of oxygen (top step) releases more energy than reduction of carbon; and oxidation of carbon (bottom step) releases more energy than reduction of oxygen requires
Temperatures of living things Temperatures of living things determined by range of
temperatures at which water is in liquid phase Few organisms can survive temperatures > 45ºC,
because of protein denaturation at high temperatures Some organisms can exist at higher temperatures due
to particularly heat-stable proteins Most organisms cannot tolerate body (cell)
temperatures below freezing, because of damage to cells from ice crystals Some organisms can exist at slightly lower
temperatures using antifreezes such as salts, glycerol Increased temperature sets higher rate of chemical
reactions (2-4 times increase in rate per 10ºC)
Physiological ecology: adaptations to the physical environment
Selected adaptations to physical environment Plant adaptations for CO2 uptake, water use
efficiency Animal adaptations for water conservation Animal adaptations for gas, heat exchange
Tradeoffs involved in adaptations
Plant adaptations to hot, dry environments (e.g., deserts)
Gas exchange challenges faced by plants:
Water loss Water diffusion gradient
steeper than CO2 gradient High metabolic rates Shortage of soil water Herbivory
Increase heat dissipation from leaves by increasing surface area (recall flux equation) by small leaf sizes
Reduce heat absorption by leaf surfaces using dense hairs (e.g., pubescent leaves of Enceliopsis, a desert perennial)
Important set of adaptations for water conservation involve photosynthesis:
C3 plants the norm in cool, moist climates
C4 plants adapted to hot, dry climates because of efficiency of CO2 uptake
CAM plants are another fundamental variation on C4 plants, also adapted to hot, dry climates
C4 photosynthesis has advantages, costs
Advantages: CO2 in high concentration Water loss reduced
Costs and tradeoffs: Recovering PEP from Pyruvate expensive Less leaf tissue devoted to photosynthesis Not beneficial in cool climates
Review of variations on theme of photosynthesis
Adaptations involve multiple levels of organization Tradeoffs evident--no one adaptation best in all
environments; specialization comes with costs Plant adaptations to desert environments illustrate
modification of flux components: area, conductance, gradient
Animals also modify components of flux equation to obtain materials--e.g., countercurrent exchange mechanisms Countercurrent circulation in fish allows
concentration of O2 from water into blood stream Blood flows across gill lamellae (of gill filaments) in
vessels that flow opposite to direction of water flowing across gills
This countercurrent maintains a concentration gradient for absorption of O2 throughout gills
According to physical laws O2 diffuses from areas of higher concentration to lower
Some birds use countercurrent mechanism to cool extremities, so as to minimize gradient (and thus minimize heat loss) to cold environment; heat flows from artery to vein along length of leg, to conserve heat proximal to body
Figure 3.17
Minimize water-loss gradient by nocturnal activity-- illustrates importance of behavior
Large surface area of nasal passages conserves H2O Inhalation of hot, dry air evaporates H2O, cools surfaces Exhalation of moist, warm air condenses on cooled
surfaces, retains water Large & small intestines resorb water efficiently
Kangaroo rats of SW deserts illustrate variety of mechanisms to minimize water loss
Conclusions: Physiological adaptations covers a huge topic--we’ve
just skimmed surface with a few examples Re-emphasizes the constraints imposed by physical
environment Every specialization comes with costs
Jack of all trades is master of none Corollaries: “A master of one is master of no others”
and “there’s no free lunch” Adaptations can be observed at many levels of
organization--e.g., biochemistry, cell and tissue anatomy, whole-organism anatomy and behavior
Most organisms have many, diverse adaptations to physical environment