In what cases is modification variability especially important for the survival of organisms in nature?

Variability is the ability to acquire new traits or lose old ones. Distinguish between phenotypic (ontogenetic and modification) and genotypic (combinative and mutational) variability.
Modification changes arise in response to the impact of environmental factors (t, illumination, humidity), help to adapt to new conditions and are not inherited. For example, an increase in the number of red blood cells in the mountains, sunburn, muscle gain from physical exertion.
This is important for the survival of organisms in the face of a sharp change in climate or habitat.