Mammal body size and heart energy efficiency : an inverse relationship

Abstract

A groundbreaking study undertaken by researchers from the University of Pretoria’s (UP) Faculty of Veterinary Science has revealed that the heart operates with declining energy efficiency as body size increases among mammals. This means that larger mammals have hearts that lose relatively more energy as heat, rather than directing that energy to the blood so that it circulates around the body. A tiny shrew, therefore, has a more efficient heart than that of a large elephant. The implication is that eventually an upper limit on body size will be reached, where the heart is so inefficient at pumping blood, that it is no longer viable to do so. A gigantic 100-tonne sauropod, or any large-sized member of the dinosaur group Sauropoda, may represent this upper limit on body size. The UP-led study, which was published today in the Proceedings of the Royal Society B, was conducted in collaboration with scientists from the University of Adelaide and Monash University in Australia, and the University of British Columbia in Canada.