Biophysical EcologyAn engineer’s view of the

thermal environment

Temperature of the Potentilla varies greatly within the plant, and is mostly higher than air temperature.

A Physics review

1. Stefans Law

E lost = AεσT4

where T = absolute temperature (degrees Kelvin) ε = emissivity,σ = Stefan-Boltzmann constant A = surface area

2. Kirchoff’s Law

Absorptivity = emissivity for a given wavelength of radiation

3. Wein Displacement Law

λmax = c / T

The temperature of an object is a consequence of the balance between energy absorbed and energy lost.

Energy Balance Equation

Esolar + Emetab = Ethermal ± Econd ± Econv ± Eevap - Ephotos ± Estor

Direct solar + skylight + reradiation from environment + reflected solar radiation + Metabolism = Reradiation +/- Convection +/- Conduction + Evaporation +/- Storage

Qabs = ASaSS + (AT/2)ass

+ (AT/2)agrgS + (AT/2)asgrgs

+ (AT/2)aT εσTg4 + (AT/2)aT εsσTs4

Why do turtles bask? The same reason you do!

Compass plants of the prairies orient their leaves so that the broad surfaces face east and west.

Colias butterfly species in the Rocky Mountains have wing pigmentation that varies with elevation. 3300-3600m, 2700-2900m, 1500-1700m. The region of the wings nearest the body make the greatest contribution to body temperature.

Absorptive versus reflectance basking in butterflies.

Pieris butterflies are reflectance baskers. The butterflies on the left hold wings in a broad V whereas the butterflies on the left hold winds in a narrow V.

Why are arctic animals often white?

C = (K/d )(T1-T2)

Conduction

Convection

Free: C = hc[Ts-Ta]

Laminar: C = k(Vm/Dn)(Ts-Ta)

V = velocity, D = Dimension

The turkey oak of the Carolina sandhills has deeply dissected leaves, and holds those leaves at a 90 degree angle to the sky, both adaptations to reduce heat load.

Ear size in rabbits varies with the thermal environment. Compare the pica of the alpine with the jackrabbit of the desert.

E = L ( sρiTi – sρaTa rh) / R

Evaporation

Figure 2.9

Desert plants have many adaptations to the thermal environment. Note especially the limited leave surface area visible in this photograph.

In high-elevation tropical habitats annual temperature variation is low and daily variation is high. Plants in these habitats often have conspicuously furry leaves.