Where does constancy collide?

In phytosociology (the Braun-Blanquet school of vegetation classification), constancy is the percentage of sample plots (reléves) of a defined community type in which a given species occurs, grouped into constancy classes (I–V) that help diagnose and distinguish plant associations. Josias Braun-Blanquet established the measure in his vegetation-classification system, and it is set out in Mueller-Dombois and Ellenberg's Aims and Methods of Vegetation Ecology (1974). The referent is the frequency of a species' presence across replicate plots, measured as a percentage, not the perceptual stability of psychology nor the internal steadiness of physiology.[1]

Unit

One species' occurrence frequency across a set of reléves

Recovery means

Tally presence of the species across all reléves of the community type and express as a percentage

Measured by

Percent of plots occupied, binned into constancy classes I–V

In perceptual psychology, constancy is the tendency to perceive the stable properties of an object (its size, shape, lightness, or color) as unchanging even as the retinal image varies with distance, angle, or illumination. Robert Thouless analyzed it quantitatively as ‘phenomenal regression to the real object’ in the British Journal of Psychology (1931). The referent is the mind's correction toward the true object, measured by how far perception departs from the proximal stimulus, distinct from a plant species' plot frequency and from physiological steadiness.[2]

Unit

One perceived property held stable across stimulus changes

Recovery means

Vary viewing distance or illumination and test whether judged size/color stays constant

Measured by

Quantified by a constancy ratio comparing judged to proximal (retinal) values

In physiology, constancy refers to The maintenance of a stable internal environment (temperature, pH, glucose, ion concentrations) against external disturbance, the condition Walter Cannon called homeostasis in his 1929 Physiological Reviews paper ‘Organization for Physiological Homeostasis’, extending Claude Bernard's milieu intérieur. The referent is the regulated steadiness of the body's internal variables, measured as the narrow range they are held within, unrelated to vegetation plot frequency or perceptual correction beyond the shared idea of ‘staying constant’.[3]

Unit

One internal variable held within a regulated range

Recovery means

Perturb the variable and observe regulatory return toward the set point

Measured by

Measured as the maintained range/set point of a physiological variable (e.g., blood glucose, pH)