The second of our formal journal responses was published today in PNAS! It is reproduced below:
Increasing preference for beef magnifies human impact on world’s food web
Kenneth J. Feeley & Brian Machovina
Bonhommeau et al.’s paper, “Eating up the world’s food web and the human trophic level,” (1) provides a valuable perspective on the role of human food consumption within the global ecosystem. However, the ranking of human beings at a similar trophic level as other animal species downplays the effects that humans have on the Earth in comparison to other species. The sheer volume of food consumed by humans and our growing preference for inefficient food sources cause us to have increasingly disproportionate impacts on the global ecosystem in relation to other species, even of the same trophic level.
The importance of dietary preference is exemplified by differences between China and the USA. China’s HTL increased from 2.1 in 1989 to 2.2 in 2009. This increase in HTL was driven by a more than doubling of pork consumption in China over the past two decades. Over the same period total beef consumption in China increased six-fold – from approximately 1 million tonnes in 1989 to >6 million tonnes in 2009 (2). Beef is an extremely inefficient food source; the land area required to produce a kilogram is beef is >2.5 times greater than required for pork and >3 times greater than for poultry (3, 4). As such, the area of land required to meet China’s food demands is growing at a faster rate than required based on population growth and increasing HTL alone. Roughly three times as much land area was required to meet China’s demand for meat in 2009 as in 1989 (approximately 470,000km2 in 1989 vs. 1,380,000km2 in 2009; estimates based on annual consumption of beef, pork and poultry  and global average land requirements for production ). Over this period, China’s population increased by approximately 18% and per capita meat consumption increased by 135%. Together these two factors account for roughly 90% of the increase in required land area. An additional 71,000km2 of increased land demand is due to a doubling in the relative consumption of beef (beef constituted 4% of meat consumed in 1989 and 9% in 2009). In the USA, population size increased by 22% and per capita meat consumption increased by 6% (2). These two factors alone would have resulted in a 30% increase in the area of land required for meat production. However, in contrast to China, the USA has decreased relative consumption of beef (beef accounted for 40% of meat consumed in 1989 and 33% in 2009). Consequently, the total land area required to fulfill the USA’s food demands increased by only 21%.
Despite a relatively-low HTL (1), humans have a dominant role in the world’s food web, appropriating approximately 10% of total net primary productivity for food production purposes alone (1, 5). This amount will almost invariably increase in the future due to growing population sizes and concurrent increases in the HTL; this pressure on the Earth’s systems can be further magnified by a rapidly-growing preference for beef and other inefficient food sources.
Reply by Bonhommeau et al.
1. Bonhommeau S, et al. (2013) Eating up the world’s food web and the human trophic level. Proceedings of the National Academy of Sciences.
2. Food and Agriculture Organization of the United Nations (2013) FAOSTAT database. (http://faostat3.fao.org/faostat-gateway/go/to/home/E).
3. Elferink EV & Nonhebel S (2007) Variations in land requirements for meat production. Journal of Cleaner Production 15(18):1778-1786.
4. Gerbens-Leenes PW, Nonhebel S, & Ivens WPMF (2002) A method to determine land requirements relating to food consumption patterns. Agriculture, Ecosystems & Environment 90(1):47-58.
5. Imhoff ML, et al. (2004) Global patterns in human consumption of net primary production. Nature 429(6994):870-873.