Production efficiency differences between poikilotherms and homeotherms have little to do with metabolic rate.

The idea that homeothermic populations have a much lower production efficiency than poikilothermic populations, because warm-blooded individuals exhibit a higher metabolic rate per gram of body weight, is widespread. Using Dynamic Energy Budget (DEB) theory, in combination with a modelling exercise based on empirical data for over 1000 different species, I show that this idea is wrong. Production efficiency of homeothermic individuals can be as high or even higher than that of poikilotherms. Differences observed are merely the result of different energy allocation and life-history strategies. Birds, for example have evolved to invest a large proportion of the assimilated energy in somatic growth and maintenance and to mature at a relatively large size. Therefore, their production efficiency as an adult is low. This low reproduction efficiency combined with a low mortality rate causes the low production efficiency of bird (and other homeothermic) populations.