Biology: The Dynamic Science, Peter J. Russell, Paul E. Hertz, Beverly McMillan, pp. 1058, Cengage Learning, 2011, ISBN 978-0-538-49374-1, ... most ectotherms are unable to maintain optimal body temperature when the temperature of their surroundings departs too far from that optimum ... endotherms require a nearly constant supply of energy to maintain their body temperatures. Because that energy is provided by food, endotherms typically consume much more food than ectotherms of equivalent size ...
