An animal that regulates its internal body temperature throughout a wide range of temperatures, frequently in response to changes in the ambient temperature is known as poikilotherms.
"Ectotherms" or "cold-blooded creatures" are alternate terms for poikilotherms.
A minor change in body temperature has little effect on poikilotherms.
Poikilothermic organisms are often known as ectotherms.