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

Biologically relevant properties of light

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:

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 osmotic potential of roots to pull water from soil particles

Increase heat dissipation from leaves by increasing surface area (recall flux equation) by small leaf sizes

Reduce transpiration water loss Drop leaves in drought (e.g.,

tropical dry forest trees)

Reduce transpiration water loss Waxy cuticle

Stomata on leaves control water loss, gas exchange

Reduce transpiration water lossRecessed & hair-filled cavities)

Reduce heat absorption--leaves perpendicular to sun

Reduce heat absorption by leaf surfaces using dense hairs (e.g., pubescent leaves of Enceliopsis, a desert perennial)

Spines both reflect light, & protect precious tissues

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

C3 plant anatomy and biochemistry

Example: Geranium

C4 plant anatomy and biochemistry

Examples: Sorghum vulgare (pictured),

sugar cane

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

Illustration of tradeoffs of C4, C3 plants with temp., CO2 concentration

CAM photosynthesis separates cycles diurnally

Example: Sedum obtusatum

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

Anatomy of countercurrent circulation in fish

Theory of counter-current flow mechanism

Concurrent flow, by contrast, would not allow concentration of O2 in blood of fish

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