What factor can cause a specific takin population to trend toward the lower end (100 cm) of the accepted shoulder height range?

Answer

Harsher, high-altitude conditions with sparser resources

Environmental pressures from high-altitude habitats with limited forage availability can cause individuals to develop smaller body frames, leading measurements to trend toward the lower end of the species' height spectrum.

What factor can cause a specific takin population to trend toward the lower end (100 cm) of the accepted shoulder height range?
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