Effects Of Predators On Carbon Cycle
June 18, 2013

Study Shows Dramatic Effects Of Predators On Carbon Cycle

April Flowers for redOrbit.com - Your Universe Online

The predator-prey relationship can affect the flow of carbon through an ecosystem, according to a new study from the Yale School of Forestry & Environmental Studies. The findings, published in Proceedings of the National Academy of Sciences, may offer a new way of looking at biodiversity management and carbon storage for climate change.

The study examines the relationship between grasshoppers (herbivores) and spiders (predators) in the food chain, and how that relationship affects the movement of carbon through a grassland ecosystem. Carbon is the basic building block of all organic matter, and it moves through the food chain at varying speeds depending on whether it's being consumed or being stored in the bodies of plants. In terms of specific animal responses, such as fear from predation, this pathway is seldom looked at.

"We're discovering that predators are having important effects on shaping the make-up of ecosystems," says Dr. Oswald Schmitz, professor of ecology. "But we've not really spent a lot of time measuring how that translates into other functions like nutrient cycling and recycling."

To understand how the levels of carbon would change over time, the team manipulated the food chains of a grassland ecosystem. Several controlled ecosystems were created; some that contained only native grasses and herbs, others that had plants and an herbivore grasshopper, and some others that had plants and herbivores along with a carnivorous spider species — all three tiers of the food chain. A form of traceable carbon dioxide was injected into sample cages covered with Plexiglas as well, allowing the team to track the carbon levels by periodically taking samples from leaves, roots and dead animals.

The team found the rate of carbon uptake by the plants was driven up by the presence of spiders approximately 1.4 times higher than when just grasshoppers alone were present and by 1.2 times higher than when no animals were present. The findings also revealed the presence of both herbivores and carnivores could change the pattern of carbon storage in the plants. The grasshoppers, apparently afraid of being eaten, consumed less plant matter when the spiders were present. There was also a shift by the grasshoppers toward eating more herbs instead of grasses in fearful scenarios.

When both herbivores and carnivores were present, the grasses stored more carbon in their roots as a response to lower levels of disturbance. When only herbivores were present, the plants stored less carbon overall, likely in response to the more intense eating habits of the herbivores that put pressure on plants to reduce their storage and release more carbon. Both the plants and herbivores changed their behaviors which affected, in turn, the composition of their local environment in response to the stress impacts.

Although this study was conducted on a small scale, it has significance for biodiversity conservation and ecosystem management, as it could inform practices done in much larger areas.“¯The Alaskan wilderness, for example, is home to animals that have the same predator-prey dynamics that drive the carbon cycle, so protecting lands and storing carbon could be linked within a broader conservation strategy. Given that top predators are declining at rates faster than many other species in worldwide biodiversity loss trends, appreciating the role of predators is very important.

"It's going to force some thinking about the vital roles of animals in regulating carbon," concludes Dr. Schmitz, pointing to the fact the UN's body of scientific experts who study climate change don't consider these multiplier effects in their models. "People are arguing for a paradigm change."