Twice as much prey does not lead to twice as many predators, according to Ian Hatton at McGill University in Montreal, Canada, and his colleagues.
In theory, more prey should mean more predators. The authors analysed published data on biomass and numbers of individuals for 2,260 ecosystems in 1,512 locations worldwide. They found that the biomass of predators increased along with the biomass of their prey, but that the ratio of the two values decreased. Across ecosystems from grassland to oceans, the ratio scales with an exponent of around 0.75, rather than scaling by 1 as in a linear relationship.
Similar scaling laws are well known between an organism's body mass and features such as metabolism, growth and reproduction, but had not been identified across whole ecosystems, say the researchers. This indicates an unappreciated degree of ecosystem organization.
Science http://doi.org/7f3 (2015)