Answer:
People, polar bears, penguins, and prairie dogs, like most other birds and mammals, are endotherms. Iguanas and rattlesnakes, like most other reptiles—along with most fishes, amphibians, and invertebrates—are ectotherms.
Endotherms generate most of the heat they need internally. When it's cold out, they increase metabolic heat production to keep their body temperature constant. Because of this, the internal body temperature of an endotherm is more or less independent of the temperature of the environment. What is metabolism?
This pattern is shown on the graph below: the mouse maintains a steady body temperature close to 37\,^\circ \text C37
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C37, degrees, start text, C, end text across a wide range of external temperatures.