Animals having a built-in thermostat to maintain constant body temperature are known as

How does the kangaroo rat in North American deserts meet all its water requirements?

$A$: Some organisms can maintain internal homeostasis by means of physiological processes and are called 'Regulators'.
$R$: 'Regulators' can maintain internal homeostasis only up to a limit of stressful conditions.

Mammals from colder climates generally have shorter ears and limbs to minimize heat loss. This is known as:

Which of the following pairs is mismatched?

Animals living in colder regions have shorter tails and ears compared to animals living in warmer regions. This phenomenon is called: