Megalania, which was 5 meters long and weighed 600 kilograms. This too is no more. The trend continues to this day: Fish stocks of large-bodied, slow-growing species are slower to recover from fishing and so more vulnerable to overfishing. Big charismatic animals are the poster children of conservation. We study them more intensively, bias our conservation efforts in their direction, and value them aesthetically and spiritually, but it hasn’t done them much good.

So when we plan where to spend scarce conservation money, working out which species are most likely to be at risk of extinction, there is a good case for biasing our efforts toward large species. And when we find a new species or population, we should be more concerned for its future if it is an ape or a deer than if it is a rodent.

The Insurance Man

When Jim Brown and Brian Enquist began thinking about metabolism, they were more interested in explaining nature than saving it. The search for general principles that apply across the living world, the pair believed, should focus on a combination of energy and allometry. This call to make energy the center of ecology was not unprecedented. Ecology is the study of nature’s economy, and energy has long been one of the currencies tracked by ecologists, through food webs, for example, to explain how much life a habitat can support or as a way to understand why animals prefer to eat certain foods. Ecology has also been one of the areas of biology most receptive to ideas from physics. Around the turn of the twentieth century, ecologists seized on concepts then influential in chemistry, such as equilibrium and thermodynamic descriptions of energy flow, and applied them as metaphors for explaining ecological phenomena such as the stability of populations and the coexistence of species.

The person who did the most to get ecologists thinking like physicists was Alfred Lotka, born in Austria in 1880. Lotka did nearly all his scientific work in his spare time. He trained as a physical chemist and emigrated to the United States in 1902. There he worked at the General Chemical Company, in a patent office, at the U.S. Bureau of Standards, and as a science journalist. He ended his working life, following a brief



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