n ecosystems around the world, big guys eat littler guys, who in turn eat plants and other organisms at the base of the food web. A study now finds that removing top predators in freshwater environments allows their prey to flourish and overgraze on plants and algae. The result of the missing plant matter: a 90 percent reduction in uptake and storage of carbon dioxide.
Several research teams have explored the importance of predators in protecting organisms that store carbon, notes ecologist James Estes of the University of California, Santa Cruz, who was not involved in the new research. The new study is particularly strong, he says, because it demonstrates predators' influence across a broad range of ecosystems. It therefore suggests “that the phenomenon may be fairly general.”
When pesticide runoff, overfishing or other human activities impact ecosystems, the first species to disappear are usually the bigger, top predators, notes freshwater ecologist John Richardson of the University of British Columbia in Vancouver and coauthor of the study, published online February 17 in Nature Geoscience. The new work shows that predator losses have effects beyond the loss of biodiversity: “We can see climate effects as well,” he says. “We start seeing a higher flux of carbon dioxide into the atmosphere.”
Study leader Trisha Atwood, then also at the University of British Columbia, and colleagues simulated three freshwater ecosystems outdoors to study the effects lower in the food web of predator loss at the top. They diverted water from streams near Vancouver into six channels they had constructed. Those channels accumulated critters and debris for about six weeks.