The zone where organisms survive but with reduced reproduction is:
A tolerance curve usually has an optimum near its centre, where physiological performance, growth, and reproduction are greatest. Moving toward either the lower or upper limit enters a zone of physiological stress. Organisms can remain alive there, but energy must be diverted to homeostasis, leaving less for growth and reproduction; abundance consequently tends to be low. Beyond the tolerance limits lies the zone of intolerance, where individuals cannot survive for long and the species is absent. The “zone of extinction” is not the standard segment of a Shelford tolerance curve, while an optim
Ref: Evolutionary Analysis, Herron & Freeman, 5th Ed., Ch. 10