Cut Down to Size

Water-dwelling animals will shrink more than land animals in response to climate change, scientists say in the Proceedings of the National Academy of Sciences.

Animals that rely on their environment for heat generally don’t grow as big in warmer conditions. So as the climate changes, many species are expected to shift to smaller sizes. But scientists have never been quite sure why some animals grow smaller as the temperature climbs.

One possibility is that it’s harder for larger animals to get enough oxygen. Aquatic animals would struggle even more than land animals, since water has less available oxygen than air.

The study authors reviewed experiments performed on 169 species that tested how the organisms’ mass changed with temperature. With each 1-degree Celsius increase in temperature, aquatic animals that were 100 milligrams reduced their body mass by 5 percent. But land animals of the same size reduced their mass by only 0.5 percent, the team found.

The results suggest that oxygen requirements drive the relationship between temperature and size, though organisms smaller than 0.01 milligrams appear to be exempt from this rule. Scientists trying to predict the effect of shrinking animals “must consider the stark differences between environments we have demonstrated in the temperature-size responses of species,” the authors write. Roberta Kwok | 5 November 2012

Source: Forster, J., A.G. Hirst, and D. Atkinson. 2012. Warming-induced reductions in body size are greater in aquatic than terrestrial species. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1210460109.

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