Table 1

Parameters used

SymbolMeaningValue*Units
αLight attenuation coefficient100cm−1
C Concentration of a chemical1  ×  1016molecules⋅cm−3
d Distance between positions in a gradientcm
D Diffusion coefficient for chemicals1  ×  10−5cm2⋅s−1
D 0 Diffusion coefficient of a non-motile organismcm2⋅s−1
D m Diffusion coefficient of a motile organismcm2⋅s−1
f Fraction of light absorbed by photoreceptor0.0003
ηViscosity of the environment0.01poise = erg⋅s⋅cm−3
H c Heat capacity per unit volume4.2  ×  107erg⋅cm−3⋅K−1
H T Thermal conductivity6.2  ×  104erg⋅s−1⋅cm−1⋅K−1
I Light intensity1  ×  1016photons⋅s−1⋅cm−2
k Boltzmann’s constant1.4  ×  10−16erg⋅K−1
L Decay length of spatial gradientcm
P V Specific mechanical power30erg⋅cm−3⋅s−1
r Radius of organismcm
T Absolute temperature293°K
u Speed relative to size20radii⋅s−1
10diameters⋅s−1
v Speed of swimmingcm⋅s−1
  • * Indicates the specific values assumed in making the standard estimates of Table 2

  • A value of 0.1 cm for chemical and light stimuli; 5 × 105 cm for temperature.