A biodiversity crisis: food webs are collapsing worldwide

The scale of the biodiversity crisis is illustrated by recreating 130,000-year-old mammalian food webs.

A recent study published in the journal Scienceprovides the clearest picture yet of the long-term effects of land mammal decline on food webs.

It’s not a pretty sight.

“While about 6% of land mammals went extinct during that time, we estimate that more than 50% of mammalian food webs have disappeared,” said ecologist Evan Fricke, lead author of the study. “And the mammals most likely to decline, both in the past and today, hold the key to the complexity of the mammalian food web.”

A food web consists of all the connections between predators and their prey in a given region. Complex food webs are essential to manage populations in a way that allows more species to coexist, thus promoting biodiversity and ecosystem stability. But animal losses can reduce this complexity, thereby reducing an ecosystem’s resilience.

Mapping of all mammalian species that would live today in central Colombia (left), southern California (center), and New South Wales, Australia (right) were it not for human-caused range reduction and extinction from the late Pleistocene to the present. Photo credit: Oscar Sanisidro/University of Alcalá

Although mammalian declines are a well-documented aspect of the biodiversity crisis, with many animals either becoming extinct or surviving in a small portion of their historical geographic ranges, the extent to which these losses have impacted the world’s food webs has remained unclear.

To understand what has been lost through food webs connecting land mammals, Fricke led a team of scientists from the United States, Denmark, the United Kingdom and Spain to use the latest machine learning techniques to determine “who ate whom has” from 130,000 years ago to today. Fricke conducted the research while on a faculty fellowship at Rice University and is currently a Research Scientist at the Massachusetts Institute of Technology.

A predator-prey interaction between cheetahs and an impala in Kruger National Park, South Africa in June 2015. Photo credit: Evan Fricke

Using data from modern observations of predator-prey interactions, Fricke and colleagues trained their machine learning system to determine how species traits affect the likelihood that one species would prey on another. Once trained, the model could predict predator-prey interactions between pairs of species that were not seen directly.

“This approach can tell us who is eating who 90% of the time today.

” data-gt-translate-attributes=”[{” attribute=””>accuracy,” said Rice ecologist Lydia Beaudrot, the study’s senior author. “That is better than previous approaches have been able to do, and it enabled us to model predator-prey interactions for extinct species.”

The research offers an unprecedented global view into the food web that linked ice age mammals, Fricke said, as well as what food webs would look like today if saber-toothed cats, giant ground sloths, marsupial lions, and wooly rhinos still roamed alongside surviving mammals.

“Although fossils can tell us where and when certain species lived, this modeling gives us a richer picture of how those species interacted with each other,” Beaudrot said.

By charting changes in food webs over time, the analysis revealed that food webs worldwide are collapsing because of animal declines.

“The modeling showed that land mammal food webs have degraded much more than would be expected if random species had gone extinct,” Fricke said. “Rather than resilience under extinction pressure, these results show a slow-motion food web collapse caused by selective loss of species with central food web roles.”

The study also showed all is not lost. While extinctions caused about half of the reported food web declines, the rest stemmed from contractions in the geographic ranges of existing species.

“Restoring those species to their historic ranges holds great potential to reverse these declines,” Fricke said.

He said efforts to recover native predator or prey species, such as the reintroduction of lynx in Colorado, European bison in Romania, and fishers in Washington state, are important for restoring food web complexity.

“When an animal disappears from an ecosystem, its loss reverberates across the web of connections that link all species in that ecosystem,” Fricke said. “Our work presents new tools for measuring what’s been lost, what more we stand to lose if endangered species go extinct and the ecological complexity we can restore through species recovery.”

Reference: “Collapse of terrestrial mammal food webs since the Late Pleistocene” by Evan C. Fricke, Chia Hsieh, Owen Middleton, Daniel Gorczynski, Caroline D. Cappello, Oscar Sanisidro, John Rowan, Jens-Christian Svenning and Lydia Beaudrot, 25 August 2022, Science.
DOI: 10.1126/science.abn4012

The study was funded by Rice University, the Villum Fonden, and the Independent Research Fund Denmark.