Environmental Engineering Reference
In-Depth Information
In 1557, Pieter van der Heyden engraved Pieter Brueghel the Elder's illustration of the proverb
“big i sh eat little i sh.” This picaresque image illustrates both a long tradition of harvesting
marine zoomass and the increasing sizes of species at the top of the trophic pyramid.
to produce new zoomass (Golley 1968; Humphreys 1979; Currie and Fritz 1993).
With respective means at 2% and 15%, an even split of the consumed phytomass
(assuming 10% of 55 Gt C of the global net primary production, or NPP) would
result in net herbivore production of some 470 Mt C/year—while Whittaker
and Likens (1973) calculated what they considered to be a high estimate of about
370 Mt C/year. Global meat production (carcass weight) in 2010 was about 290
Mt; reverse application of typical live weight/dressed carcass factors (Smil 2000)
yields at least 450 Mt of slaughtered live weight, or at least 90 Mt C. The annual
slaughter of domestic animals would thus account for 20-25% of net secondary
production.
Animal domestication in general, and modern mass-scale commercial breeding
and production in particular, pose a different set of energetic challenges. Little can
be done about changing the metabolic efi ciencies of individual species (for example,
pigs are inherently more efi cient converters of feed than cattle), but higher produc-
tivities can be achieved by supplying adequate amounts of optimally selected feeds.
As a result, modern varieties of meat-producing heterotrophs mature faster and
reach higher slaughter weights sooner than the traditional breeds and require less
