IN THE REVIEW “STATUS AND ECOLOGICAL EFFECTS OF THE WORLD’S LARGEST CARNIVORES” (10 January, DOI: 10.1126/science.1241484), W. J. Ripple et al. claim that meat consumption by humans is one of many threats to carnivores and biodiversity. We argue that human carnivory is in fact the single greatest threat to overall biodiversity.
Livestock production accounts for up to 75% of all agricultural lands and 30% of Earth’s land surface, making it the single largest anthropogenic land use (1). Meat and feedstock production is rapidly rising in biodiversity-rich developing countries. For example, in China, animal products currently constitute ~20% of diets, but this amount is expected to increase to ~30% or higher over the next two decades (2). For China to attain a level of carnivory similar to the United States, its projected 1.5 billion inhabitants would increase consumption of animal products by almost 30% (3). Given current trends, 1 billion additional hectares of natural habitats—an area larger than the United States—will be converted to agriculture by 2050 (4).
Free ranging cattle in Galicia, NW of Iberian Peninsula.
Substituting meat with soy protein could reduce total human biomass appropriation in 2050 by 94% below 2000 baseline levels (5) and greatly reduce other environmental impacts related to use of water, fertilizer, fossil fuel, and biocides. Soy protein production for global livestock markets is the second leading cause of Amazonian deforestation after pasture creation. Eliminating livestock and instead growing crops, including soy protein, only for direct human consumption could negate future agricultural land expansion, while increasing the number of calories available for human consumption by as much as 70% (6)— enough to feed an additional 4 billion people, exceeding the projected global population growth of 2 to 3 billion (6). This savings in land and calories is due to eliminating the loss of ~90% of the energy available in plants during the conversion to livestock (7).
We argue that reducing and maintaining animal products to even 10% of the global human diet would enable the future global population to be fed on just the current area of agricultural lands. Without a global decrease in per capita meat consumption by humans, the loss of natural habitats, large carnivores, and biodiversity is certain to continue.
BRIAN MACHOVINA* AND KENNETH J. FEELEY
Florida International University, Miami, FL 33199, USA. *Corresponding author. E-mail: email@example.com
edited by Jennifer Sills
1. Food and Agriculture Organization, “Livestock’s long shadow: Environmental issues and
options” (FAO, Rome, 2006); http://www.fao.org/docrep/010/a0701e/a0701e00.HTM.
2. M. A. Keyzer, M. D. Merbis, I. F. P. W. Pavel, C. F. A. van Wesenbeeck, Ecol. Econ. 55, 187
3. S. Bonhommeau et al., Proc. Natl. Acad. Sci. U.S.A. 110, 20617 (2013).
4. D. Tilman et al., Science 292, 281 (2001).
5. N. Pelletier, P. Tyedmers, Proc. Natl. Acad. Sci. U.S.A. 107, 18371 (2010).
6. E. Cassidy, P. C. West, J. S. Gerber, J. A. Foley, Environ. Res. Lett. 8, 8 (2013).
7. H. Charles et al., Science 327, 812 (2010).
Downloaded from http://www.sciencemag.org on February 21, 2014