Endotherm vs ectotherm: the central separation

An endotherm DEFENDS an internal temperature setpoint; an ectotherm TRACKS the environment. In R19 this is one parameter: basin depth. A deep basin (high loop gain) pins the setpoint against an ambient drive; a shallow one follows it. Under the same ambient sweep the endotherm barely moves (sensitivity 0.054) while the ectotherm tracks (1.394).

The separation is mechanistic, not a label. A defended setpoint is a deep R19 attractor whose basin resists an ambient drive; a tracked one is shallow. The discriminant is exact: a loop defends iff spinodal(g) > ambient drive amplitude; else it tracks.

One parameter: basin depth

Sweeping an ambient drive across both loops, the endotherm setpoint stays pinned and the ectotherm state follows the drive almost one-to-one -- a sensitivity ratio of about 26x. Nothing here requires a special gene; it requires a basin deep enough that the ambient drive amplitude stays below the spinodal.

The discriminant

A loop defends its setpoint if and only if its spinodal exceeds the ambient drive amplitude; otherwise it tracks. Sensitivity falls monotonically as the barrier deepens (confirmed), so 'defend vs track' is a continuous consequence of one R19 quantity.

Three questions, three chapters

Q1 -- the GENE-LEVEL criterion (next: a present, drivable effector-command pair, not a γ value). Q2 -- how and how much the strategies differ (basin depth here, plus the thermostat and cost chapters). Q3 -- over how large a RANGE (the cost and continuum chapters: a metabolic factor of ~5-10x plus a discontinuous regime boundary).