(September 03, 2015) --

In studying different ecosystems, whether on land or in the water, much has been made about the differences and diversity of habitats and the animals that occupy them. Dr. Just Cebrian, Senior Marine Scientist, Dauphin Island Sea Lab, and Professor, Marine Sciences, University of South Alabama, has recently published an “Insights” paper in the prestigious journal Science that highlights a remarkable similarity across ecosystems published by Hatton et al. (4 Sept. 2015, Volume 349, Issue 6252): as the quantity of prey increases largely, the amount of food produced for predators does not keep pace with it, and as a result predator abundance increases only slightly.

For the past century, much of ecological science has focused on trying to elucidate what regulates the flow of energy and matter in ecosystems. This is of utmost importance for an understanding of the goods and benefits that ecosystems provide to humans, such as the production of harvestable food and energy, and the storage of greenhouse gases and mitigation of climate change.

Recent research published in Science by Hatton et al. (2015) shows ecosystems with more abundant prey do not transfer proportionally higher quantities of food to predators. Rather, food production levels off in ecosystems with more abundant prey, and as a result, predator abundance increases little, despite large prey availability. Potential reasons include prey growth metabolical constraints and/or density-dependent inhibitory processes, which may result in little additional growth as prey availability increases.

“These results are striking because they indicate that the quantity of harvestable predators, for example, commercial fisheries that feed on marine prey, increase little despite large increases in prey. Clearly more productive ecosystems are inefficient when it comes to transferring energy up the food chain. Hatton et al. generalize this for all ecosystems on Earth and quantify the inefficient rate at which energy is transferred up the food chain” Dr. Cebrian says.

Interestingly, another recent report by Lafferty et al published in Science (21 Aug. 2015, Volume 349, Issue 6250) indicates that trophic inefficiency leading to small increases in predator abundance with large increases in prey abundance may likely apply not only to classical examples, such as lions and wildebeest, or copepods and phytoplankton, but also to all other types of consumers, such as micropredators, parasites and parasitoids, and their specific resources.

Dr. Cebrian points out that ecosystems with more prey also retain carbon for a longer time, since they slowly turn over their carbon from prey to predator biomass. “Ecosystems with more prey are larger carbon reservoirs. Ecosystems accumulate prey because it is not lost to predators or senescence. In ecosystems with more prey, these losses are less prevalent and, thus, there is a larger carbon pool. This is why ecosystems with more prey can help better mitigate climate change,” Dr. Cebrian concludes.

Together, these results bring an improved understanding of carbon flow and storage in ecosystems that has important implications for managers. Trophic transfer is inefficient, and increased prey may translate in little gain in predator commercial harvest. Such allometry needs to be considered in production/yield models. Oppositely, ecosystems with more prey are prominent carbon reservoirs. As prey increases, the role that ecosystems play as carbon pools contrasts with that as producers of harvestable predator biomass.

Media Contact: Dr. Just Cebrian – jcebrian@disl.org; 251-861-2141 x7568.
More information, including a copy of the paper, can be found online at the Science press package at http://www.eurekalert.org/jrnls/sci. You will need your user ID and password to access this information. You can also email scipak@aaas.org.