When it comes to thermoregulation, ectotherms and endotherms are on opposite ends of the spectrum—Ectotherms rely on their environment and endotherms rely on the production of heat. Heat requires energy, and producing energy requires oxygen. We tested this theory by subjecting an endotherm and an ectotherm to various cold and hot temperatures and recording their level of CO 2 production. We discovered, t the CO 2 rates for ectotherms remain stable in different temeperatures and that typically, the levels of CO 2 production increases during colder temperatures for endotherms. This means that because an ectotherm doesn’t need to control it’s temperature, it doesn’t require energy to maintain heat.