“Less than 30 cm” for what is the average precipitation in deserts. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Terrestrial biomes are distinguished primarily by long-term temperature and precipitation regimes, their seasonality, and the vegetation physiognomy those conditions support. Latitude is informative only because it often covaries with climate. The remaining alternatives—“10-20 cm”, “20-30 cm”, “More than 50 cm”—refer to different states, processes, or scales and therefore do not expr
Ref:
Campbell Biology, Urry et al., 12th Ed., Ch. 52