Why might the distribution of a species (its realized niche) be less expansive than its fundamental niche (i. e. fundamental niche: the range that the species would be capable of living in in the absence of biotic interactions)

a symbiotic relationship with the mitochondria

bal is blood alcohol level. bac will normally be higher in a person with more body fat. so the answer to your question would be, as body fat decreases, the increasing rate of bal decreases.