Final answer:
Small desert mammals primarily maintain water balance by reducing water losses, using adaptations such as concentrating their urine and feces, using metabolic water efficiently, and exhibiting behaviors to minimize water expenditure.
Step-by-step explanation:
Small desert mammals maintain water balance primarily by reducing water losses compared to humidic mammals. Desert mammals exhibit several adaptations that assist in minimizing water loss. These adaptations include having more concentrated urine and drier feces, which reduce the amount of water excreted. Additionally, they may have behaviors such as being nocturnal to avoid the heat of the day, and physiological mechanisms like efficient use of metabolic water. Metabolic water is the water produced during metabolic processes like the hydrolysis of adenosine triphosphate (ATP) or during the breakdown of food in cellular respiration. Unlike desert mammals, humidic mammals do not face the same environmental pressures to conserve water and thus may not have as many or as efficient water-saving adaptations.