A method for finding distribution of metabolic energy between organismal functions: application to birds' energy expenditures to counteract gravity and to support steady and short flights

Production of energy (metabolism) and its distribution is vital for living organisms, both at individual level - between different functions of an organism, as well as between species of communities at different organizational levels, including food chains. Here, a new general method for finding distribution of metabolic energy between different organismal functions is proposed. The method is based on earlier discoveries (in two independent studies, for multicellular and unicellular organisms) that metabolic allometric scaling is the result of natural selection guided by optimization of distribution of common resources between the species of a food chain. This distribution is established in such a way that it secures amount of resources for each species to reproduce in sufficient quantities (sufficient for preservation of a food chain), while not allowing some species acquiring too many resources to jeopardize existence of other species they prey on or share common resources with. The introduced method was applied to birds, including both steady and short flights modes. Birds' metabolism has specifics, because besides other functions, it has to compensate force of gravity during the flight. However, this parameter is difficult to find, while such data is important for ecological studies at population and individual levels. We discovered increase of fraction of metabolic power required to compensate force of gravity with mass increase, which is a principal factor, restricting maximum possible mass of flying animals. The obtained results show efficiency of a proposed method for detailed studies of animals' metabolism, physiology, and of population ecology.