A Biodiversity Crisis: Food Webs Worldwide Are Collapsing

The long-term implications of declining land mammals on food webs are now best understood according to a new study that was published in the journal Science.

It's a hideous sight.

"We estimate that more than 50% of mammal food web links have perished in that time, but only approximately 6% of terrestrial mammals have gone extinct," said ecologist Evan Fricke, the study's primary author. "And the complexity of the mammal food web depends on the mammals that are most likely to decline, both historically and currently."

All the relationships between predators and their prey in a specific area are known as a food web. Complex food webs are necessary for population control in a way that permits more species to coexist, hence enhancing ecosystem diversity and stability. However, animal extinctions might lessen this complexity, which would make an ecosystem less resilient.

Illustration showing every mammal species that, if not for range contractions and extinctions due to humans from the Late Pleistocene to the present, would live in central Colombia (left), Southern California (middle), and New South Wales, Australia (right), respectively, today. Credit: University of Alcala/Oscar Sanisidro ́

The extent to which these losses have influenced the world's food webs is still unknown, despite the fact that decreases in mammals are a well-documented element of the biodiversity problem, with many creatures either going extinct or only remaining in a small portion of their historical geographic ranges.

Fricke led a team of scientists from the United States, Denmark, the United Kingdom, and Spain in applying the most recent machine learning techniques to establish "who ate who" from 130,000 years ago to the present in order to understand what has been lost from food webs connecting land animals. Fricke, who is currently a research scientist at the Massachusetts Institute of Technology, carried out the study while holding a faculty fellowship at Rice University.

Fricke and colleagues trained their machine learning system to identify how species features affected the likelihood that one species would prey on another using data from contemporary observations of predator-prey interactions. After being trained, the model can forecast predator-prey interactions between species that haven't been explicitly seen.

According to principal author of the paper and Rice ecologist Lydia Beaudrot, "this approach can tell us who eats whom today with 90% accuracy." "That is better than what prior methods could do, and it allowed us to model predator-prey relationships for ancient animals," the researcher said.

According to Fricke, the study provides a previously unattainable global perspective on the food chain that connected ice age mammals. It also provides a glimpse into what modern food chains would look like if saber-toothed cats, giant ground sloths, marsupial lions, and wooly rhinos coexisted with living mammals.

"This simulation offers us a deeper picture of how those species interacted with one another," Beaudrot said. "While fossils can tell us where and when specific species lived, they cannot tell us how they interacted."

The investigation showed that food webs are collapsing globally as a result of animal losses by tracking changes in food webs across time.

According to Fricke's simulation, terrestrial mammal food webs have deteriorated significantly more than would be predicted if a random species had died out. These findings demonstrate a slow-motion food web collapse brought on by the selective extinction of species with key food web roles, as opposed to resilience under extinction pressure.

The findings also demonstrated that hope is not lost. About half of the reported food web reductions were attributed to extinctions; the remaining percentage was due to the geographic ranges of already extant species contracting.

The potential to stop these decreases is very high, according to Fricke, if those species are returned to their former habitats.

According to him, restoring the complexity of the food web depends on attempts to rehabilitate native predator or prey species, such as the reintroduction of lynx in Colorado, European bison in Romania, and fishers in Washington State.

According to Fricke, "the loss of an animal from an environment ripples across the web of links that binds all species in that ecosystem." "Our work offers new techniques for quantifying what has been lost, what more we risk losing if endangered species become extinct, and the ecological complexity we can restore through species recovery," the authors write.

The Independent Research Fund Denmark, the Villum Fonden, and Rice University all provided funding for the study.

By RICE UNIVERSITY