According to a review paper titled Trophic Downgrading of Planet Earth, published last week in the journal Science, killing top predators is humankind’s most pervasive influence on nature that has far reaching and devastating effects.
The study was conducted by a team of 24 scientists from around the world who compiled evidence from both experiments and observations to draw conclusions about the decline of top predators and herbivores on land, in the ocean and in freshwater.
“Their findings suggest that ‘trophic downgrading’ — the ecological consequences of losing large apex consumers from nature — causes extensive cascading effects in ecosystems worldwide, especially when exacerbated by factors such as land use practices, climate changes, habitat loss, and pollution,” according to a statement from the Institute for Ocean Conservation Science, which provided major funding for the study, along with Pew Charitable Trust.
Some of the additional consequences noted were changes in vegetation, water quality, the frequency of wildfires, invasive species and the spread of infectious diseases. The review cited examples from the vegetation recovery after wolves were reintroduced at Yellowstone to the increase in intestinal parasites spread from baboons to each other and humans as a result of the loss of lions and leopards in Africa.
“By looking at ecosystems primarily from the bottom up, scientists and resource managers have been focusing on only half of a very complex equation,” said lead author Dr. James A. Estes, professor of ecology and evolution at the University of California at Santa Cruz. “These findings demonstrate that top consumers in the food web are enormous influencers of the structure, function, and biodiversity of most natural ecosystems.”
The report also notes that we are experience the sixth mass extinction in history, but it’s the first to be caused by humans and despite the number of studies that can be conducted while animals are still alive, no one actually knows what the effect will be until they disappear.
“It’s not reporting on any new findings, but I would say its value is that it is a synthesis,” said Matthew Kauffman, a professor at the University of Wyoming, who is not part of the study. “It’s showing us that there are top-down effects of large predators and large herbivores among many different ecosystems, functioning in many different ways. It allows us to see the full scope of the value of having top predators in ecosystems.”
“To the extent that conservation aims toward restoring functional ecosystems, the reestablishment of large animals and their ecological effects is fundamental,” Estes said. “This has huge implications for the scale at which conservation can be done. You can’t restore large apex consumers on an acre of land. These animals roam over large areas, so it’s going to require large-scale approaches.”
Photo credit: Cryptowolf via flickr