How predators protect plant biodiversity

Lion in crosshairs
CC BY 2.0 Wikipedia

Last month, we started quite a debate with our article about a group of philosophers who want to turn predators into vegans to end the suffering of herbivores.

The main outcry from the online community was that we need predators to keep the natural order and that humans should not interfere to upset the balance. It's true, many studies show that taking a predator out of an ecosystem causes the whole system to collapse. And now, a new study in Laikepia, Kenya adds further evidence to the pile.

"We're only beginning to understand the linkages between carnivores, their prey, plants and people," said Adam Ford, lead researcher, in a press release.

Predator populations in many parts of the African continent are dropping fast as human expansion eats away at what remains of the wilderness. To see how this affects the landscape, Ford and his team tracked leopards, wild dogs, antelope and impala with GPS collars. They wanted to see whether the ecosystem was different in areas favored by each species.

What they found was surprising - predators were protecting certain plant species with their presence alone. Non-thorny plants did really well in areas where these predators lurked because herbivores avoiding feeding nearby. Where herbivores fed, thorny plants tended to do well because anything that wasn't thorny got eaten away. But with the decline in predators, herbivores have been feeding over larger areas, depleting plant biodiversity and encouraging thorny plant growth.

"Our observations indicate that carnivores – like leopards and wild dogs – shape where herbivores eat," added Ford.

Biodiversity is a critical part of maintaining ecosystem balance. It makes the environment more resilient in the face of irregular weather patterns or natural disasters. In the long run, an overwhelming number of thorny plants will be a problem as herbivores will have nothing left to eat. Maintaining the number of predators will be key in ensuring all animals can thrive.

"Cascading effects of predators on plants has long been known as an important ecological force. It is part and parcel of the complex biodiversity that we now understand is central for the long term persistence of ecosystems. Take out a piece of the complexity and you never really know what will happen," Dr. John Vandermeer from the University of Michigan told Treeehugger. "Eliminating predators, besides being a reduction in biodiversity in and of itself, can have knock on effects by changing competitive relationships among herbivores giving rise to yet further biodiversity reductions at a distinct level, which, in turn, can have indirect consequences on the structure of the plant biodiversity."

Ford and his team also found that herbivores avoid all plants with thorns - no matter what the species. He and his team artificially added thorns to non-thorny plants and found that impalas and antelopes steered clear.

Three quarters of the predators of the world are in decline, so this study adds further evidence that conservation efforts need to take predators into account.

"Ultimately we all depend on nature for the services that it provides, from crop pollination to climate regulation," Stuart Butchart, of Birdlife International told TreeHugger. "Healthy ecosystems, with intact habitats and natural population levels and species diversity, underpin these services. We risk our future and that of future generations when we destroy nature."

How predators protect plant biodiversity
Herbivores are having a field day Kenya.