This Article was published by The Huffiington Post: Wolves in a Tangled Bank
For decades scientists have been investigating the ecological role of wolves. In his 1940s game surveys, Aldo Leopold found ungulates wiping out vegetation wherever wolves had been removed. He concluded that by controlling ungulates, wolves could restore plant communities and create healthier habitat for other species, such as birds.
Since Leopold’s time, many scientists have studied food web relationships between top predators and their prey–called trophic cascades. In the 1960s and 1970s Robert Paine, working with sea stars, and James Estes, working with sea otters, showed that ecosystems without top predators begin to unravel. Paine created the metaphorical term keystone species to refer to top predators and noted that when you remove the keystone, arches and ecosystems collapse. Over the years ecologists found trophic cascades–also called top-down effects–ubiquitous from coral reefs to prairies to polar regions.
In the mid-1800s in his book The Origin of Species, Charles Darwin presciently described nature as a “tangled bank.” Nature’s complexity results from myriad species and their relationships with other species and all the things that can possibly affect them, such as disease, disturbance, and competition for food. Science works incrementally, taking us ever deeper into nature’s tangled bank as we investigate ecological questions. Each study answers some questions and begets new ones. Sometimes we find contradictory results. Learning how nature works requires that we keep searching for answers amid the clues nature gives us, such as the bitten-off stem of an aspen next to a stream where there are no wolves.
Trophic cascades science that focuses on wolves is still in its infancy, with huge knowledge gaps. For example, we’ve linked wolves to strong effects that cascade through multiple food web levels. However, we’re just starting to parse how context can influence these effects. Some Yellowstone studies have found that wolves have powerful indirect effects on the plants that elk eat, such as aspens, due to fear of predation. With wolves around, elk have to keep moving to stay alive, which reduces browsing pressure.
It’s human nature to try to find simple solutions. Today we are grappling with monumental environmental problems such as climate change. Due to the wolf’s iconic status and our need to fix broken ecosystems, the environmental community and the media have run with the science that shows a strong wolf effect. This has inspired other scientists to work hard to prove that ecosystems are more complex than that. These dissenting studies demonstrate that the wolf dwells in a tangled bank, working alongside many ecological forces.
In my own research I’ve found that wolves need another keystone force–fire–to drive trophic cascades. In my previous work in Glacier National Park, Montana and in our ongoing Earthwatch research in Waterton Lakes National Park, Alberta, we are experimenting with fire in a wolf-dominated system.
Our first five years of data show that with wolves and fire present, elk herbivory drops, aspens thrive, and biodiversity soars due to the healthy habitat created by young, vigorously saplings. Parsing these relationships has involved gathering data on 35 ecological variables and building 72 statistical models.