In the heart of the North American Rocky Mountains is an island of immense ecological complexity. The island, Yellowstone National Park, is the core of a greater Yellowstone ecosystem and, like other great ecosystems of the world, is stellar place to come to terms with the earth’s natural processes, the web of life, and the role of humans in the natural world. In Yellowstone National Park, those lessons are writ large across a landscape that, in 1872, was designated the world’s first national park.
Central to the establishment of Yellowstone was the preservation of the spectacular geothermal features, landscapes, and animal populations so iconic to the park today. The geysers and hot springs that give Yellowstone its name were originally thought to be a myth fabricated by early visitors to the region. When the first scientific expedition to the area was launched in 1863, scientists found not only the largest geothermal system in the world, they found a region inhabited by terrifying predators and large herds of grazing animals that migrated across large expanses of wilderness.
The idea of a national park was to preserve those natural wonders while providing for the use and enjoyment of resources for future generations. It is a balancing act still played out every day in Yellowstone by its managers and resource experts.
The park is home to key predator species (grizzly and black bear, grey wolf, mountain lion), prey species (elk, deer, moose), and a host of birds and smaller mammals. A mosaic of vegetation including coniferous forests, arid shrub and grasslands add to the ecological complexity. Snowmelt from the park flows to the Mississippi, the Colorado, and the Columbia Rivers. Over 3.5 million tourists visit the park each year. Sit for a few minutes at the boardwalk near Old Faithful geyser and you will hear a dozen languages and see people from all walks of life. Yellowstone is indeed a global destination.
The concept of the park as an island within a larger context is important. The term Greater Yellowstone Ecosystem is a term first used by Frank Craighead in a document he and his brother John wrote in 1972; he also referred to it in a report to the Congressional Research Service in 1986. The park is clearly an artificial social construct meant to delineate administrative boundaries; wild animals, grizzlies and wolves included, do not respect such borders and freely move from parkland to national forest and private land. Enlightened management of large wide-ranging animals required acknowledgement of those movements and reconciliation of the differing administrative missions of the National Park Service and the US Forest Service would need to be considered.
The figure below shows the outer edge of their grizzly locations and so the expected historical range of the bear. Based on these data, the Craigheads introduced the concept of the Greater Yellowstone Ecosystem. The idea became central to bear management in the region and is still used 40 years later.
Public displays of nature and natural history were popular in 18th century Europe and America but conservation of biodiversity as a management concept came much later. The romanticism of early American conservationists like Thoreau, Roosevelt, and Muir inevitably gave way to rationalists in the mold of Pinchot, Leopold, and, in Yellowstone, John and Frank Craighead. In 1978, at a conference at the University of San Diego, scientists advocated for a discipline that would place conservation of large natural systems at the center of research and policy; it became known as conservation biology.
The science of conservation biology stems from the English tradition of the management of nature in all its forms. Like other institutional frameworks, conservation biology comes with a prejudice. In this case it places an emphasis on biological surveys that document the assembly of species and their interactions across multiple scales. Conservation biologists believe it is not enough to simply protect animals and their habitat, what is important is to preserve landscape scale processes; preserve the ecological interactions among the parts and you preserve multiple species and, the whole. Biodiversity, measured by number of species functioning in a given system, is the metric by which management is judged.
By extension, the bias reflected in conservation management is that if we can get the science right the maintenance and restoration of biological diversity will follow. Conservation biology is a prescriptive in the sense that the goal is a management plan for the conservation of biological diversity at every level of the natural community. Michael Soulé, the father of conservation biology, describes it as a “crisis discipline.” He refers to a disciplinary focus on the rapidity of ecosystem change, the increasing rate of biological extinctions, and the global loss of biodiversity; conservation lacks the luxury of time if it is preserve the natural world. This is why initiatives like restoration of predator/prey relationships takes on a sense of urgency and ultimately – scientific advocacy.
Ecosystems are just that -- systems. The parts— species, habitats, and nutrients—connect with one another directly and indirectly at multiple trophic levels. Changes in one part of the ecosystem can affect other parts. Resiliency is the degree to which a system can tolerate disturbance to those connections such as loss of a key predator or limiting the ecological fire regime. It is a measure of how much disturbance a system can withstand without changing self-organized processes and structures that make up the whole. Ecological resilience is maintained by keystone structuring processes across a number of scales and metrics but fundamental is the idea of functional biodiversity. In the Greater Yellowstone, the keystone process is the predator/prey relationship where the major actors are wolves, bears, elk, and bison. The logic is that if these keystone species are intact within the loose boundaries of the Greater Yellowstone, most of the rest of the ecosystem will remain functional and healthy. The key ecological question for many scientists and policy makers is how far these processes can deviate from “the norm” before system collapse. When faced with choices about the makeup and number of predators or letting wildfires burn, park superintendents weigh scientific, political, and agency costs and benefits. This is the management dilemma faced by virtually all public lands managers the world over. A key to preserving biodiversity lies in the inherent complexity of ecosystems. Complexity can be found in the landscape in the form of “patchiness”, the idea that other things being equal, larger patches of potential habitat tend to support more biodiversity than smaller patches and, structurally complex patches tend to be more important for habitat than homogeneous landscapes.
Predator/prey relationships across and between trophic levels provide the necessary stability for almost infinite numbers of species to exist in ecosystems. Predators keep the size of species populations in check at supportable levels and so, encourage resource efficiency. When prey numbers are high, predators increase and reduce their numbers. When predator numbers are high, prey decrease and thus reduce the number of predators through starvation and lower fecundity. There is no true "balance of nature" rather, ecosystems are subject to active dynamic processes at all trophic levels.
The Yellowstone landscape is powered by predator/prey interactions. Living organisms exist within webs of interactions with other living creatures, the most important of which involve eating or being eaten. Complex interactions among several species are called food webs while simpler linear ones within a particular food web are called food chains. Sometimes, major disturbances can result in cascading effects, either positive or negative, between tropic levels.
The Greater Yellowstone Ecosystem is well understood to be ecologically complex but, in reality, no more so than other ecosystems such as Serengeti in Tanzania, the rain forests of Brazil, or even Central Park in the heart of New York City. In this respect Yellowstone is simply one of many spectacular ecosystems found on every continent. What sets places like Yellowstone apart is the mosaic of large numbers of predator and prey species resident on ecologically functional landscapes and credible institutions that allow for management decisions to play out on those landscapes. One reason land managers in places like Yellowstone can conduct large scale experiments with wildfire and wolves is that robust institutions exist. National parks operate under a Congressional mandate, courts and nonprofits monitor their progress, the science community is invited onto the landscape. These sometimes competing forces help safeguard the efficacy of ecological experimentation.