Organism Silhouette Area

The function estimates the projected (silhouette) area as a portion of the surface area of the organism as a function of zenith angle. The function is useful for estimating absorbed solar radiation.

proportion_silhouette_area(psi, taxon, raz = 0, posture = "prostrate")

Arguments

psi

numeric zenith angle in degrees between 0 and 360.

taxon

character organism name. Current choices are "lizard", "frog", and "grasshopper".

raz

numeric relative solar azimuth angle (in degrees). Required if taxon = "lizard". This is the horizontal angle of the sun relative to the head and frontal plane of the lizard and options currently include 0 (in front), 90 (to side), and 180 (behind) degrees.

posture

character value describing posture. Required if taxon = "lizard". Options include "prostrate" (default) and "elevated".

Value

numeric silhouette area as a proportion.

Details

Relationships come from

• Lizards: Muth (1977)

• Frogs: Tracy (1976)

• Grasshoppers: Anderson et al. (1979)

References

Anderson RV, Tracy CR, Abramsky Z (1979). “Habitat Selection in Two Species of Short-Horned Grasshoppers. The Role of Thermal and Hydric Stresses.” Oecologia, 38(3), 359--374. doi:10.1007/BF00345194 .

Muth A (1977). “Thermoregulatory Postures and Orientation to the Sun: A Mechanistic Evaluation for the Zebra-Tailed Lizard, Callisaurus draconoides.” Copeia, 4, 710 - 720.

Tracy CR (1976). “A Model of the Dynamic Exchanges of Water and Energy between a Terrestrial Amphibian and Its Environment.” Ecological Monographs, 46(3), 293-326. doi:10.2307/1942256 .

See also

Other allometric functions: mass_from_length(), proportion_silhouette_area_shapes(), surface_area_from_length(), surface_area_from_mass(), surface_area_from_volume(), volume_from_length()

Examples

  proportion_silhouette_area(psi     = 60,   
                             taxon = "frog")
#> [1] 0.2902208
  proportion_silhouette_area(psi     = 60, 
                             taxon = "grasshopper")
#> [1] 0.0862
  proportion_silhouette_area(psi       = 60, 
                             taxon   = "lizard", 
                             posture = "prostrate", 
                             raz     = 90)
#> [1] 0.329857
  proportion_silhouette_area(psi       = 60, 
                             taxon   = "lizard", 
                             posture = "elevated", 
                             raz     = 180)
#> [1] 0.176596