It is intended to capture in a single index the ability of an ecosystem to prevail against disturbance by virtue of its combined organization and size.
Almost half a century earlier, Alfred J. Lotka (1922) had suggested that a system's capacity to prevail in evolution was related to its ability to capture useful power.
In mathematical terms, ascendency is the product of the aggregate amount of material or energy being transferred in an ecosystem times the coherency with which the outputs from the members of the system relate to the set of inputs to the same components (Ulanowicz 1986).
Coherence is gauged by the average mutual information shared between inputs and outputs (Rutledge et al. 1976).
Sensitivity analysis on the components of the ascendency reveals the controlling transfers within the system in the sense of Liebig (Ulanowicz and Baird 1999).