American Scientist

When it comes to ecosystems, redundancy can be a very good thing.

An article in American Scientist by SFI Omidyar Fellow Justin Yeakel and SFI VP for Science Jennifer Dunne describes recent studies of modern, historical, and paleontological food webs and reports that over the last half billion years of life on Earth, food webs show a remarkable degree of structural similarity, suggesting we might be able to predict and even influence modern food web responses to perturbations such as species extinctions.

Their essay describes characteristics and patterns that hold for food webs from the Cambrian-era Burgess Shale to present-day Egypt. The scientists draw their evidence from computer simulations they used to reconstruct food web interactions and to quantify ecosystem stability -- the extent to which an ecosystem can restore itself following a disturbance.

In Egypt, Yeakel and Dunne found that a panoply of mid-size herbivores -- such as the gerenuk, sitatunga, ibex, Barbary sheep, and several species of gazelle that populated Egypt roughly 5,500 years ago -- stabilized the ecosystem much in the same way that redundant beams and cables fortify a bridge. When some of those mid-size species vanish, however, an ecosystem can become fragile, sensitive to perturbation, and unable to replenish itself. This is the state of Egypt’s present-day ecosystem, which is down to only four species of mid-size herbivores.

The implications of their findings for modern ecosystems are grim, as many (such as present-day Egypt’s) might have lost the ability to recover from disturbances in the face of rapid extinctions caused by human activities. However, because ecosystems appear to respond to disturbances in similar ways, there may be hope for predicting and thus preventing future extinctions in contemporary animal communities.

“The nature of human-induced impacts on animal communities is qualitatively different today than in the distant past, likely due to the efficiency with which large human populations extract resources from the environment, as well as the degraded condition of contemporary animal communities compared to their historical state,” the researchers write. “Our understanding of modern ecosystems must take these differences into consideration, particularly if we hope to develop a framework for predicting how communities will change in the future.”

Read the article in American Scientist (April 13, 2015, subscription required)