Do All Organisms Burn Energy at Approximately the Same Rate?

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Elephants, bacteria, and trees may not have much in common besides their status as living organisms that consume energy to power their basic life functions, but a new study has found a remarkable similarity within that commonality. A team of researchers examined over 3,000 organisms from different branches of the tree of life and found that while creatures may vary enormously in size and complexity, their metabolisms use energy at roughly the same rate. The researchers examined the at-rest metabolisms of all the species and compared their energy usage, pound for pound. While there were some outliers, most species fell within a narrow range, using between 1 and 10 watts per kilogram of biomass. Study coauthor Anastassia Makarieva says that since such a large number of species falls within this narrow range, she hypothesises there may be an optimum metabolic rate for all organisms. "Organisms that lie close to this value may be the fittest to survive," she says [New Scientist].

The researchers found no correlation between organisms' size and their metabolic rate, which contradicts an influential study published in 1997 in which ecologists found a strong correlation between the size of an animal and its metabolism. Under their rubric, small creatures used energy efficiently while large creatures did not. As organisms grow larger, they produce less energy relative to their bulk. The … ecologists claimed that this relationship between size and metabolic rate, known as allometric or power scaling, was a general law of life that resulted from the difficulty of transporting nutrients around larger and larger bodies [Wired News].

But in the new study, which will be published in this week's Proceedings of the National Academy of Sciences [subscription required], researchers didn't just compare species within a related group, but looked at an extraordinarily diverse set of species. The findings were remarkably consistent, study coauthor Peter Reich says. For example, an elephant is one trillion million times larger than a single-celled bacterium — that's 20 orders of magnitude — but their metabolisms fall roughly within an order of magnitude. "If there was power scaling, you'd have a 4000-fold metabolic variation. Whereas we only see a 30-fold variation," Reich said. "They're not even anywhere in the ballpark of power scaling" [Wired News].

http://blogs.discovermagazine.com/80beats/2008/10/14/do-all-organisms-burn-energy-at-approximately-the-same-rate/