Yellowstone National Park Policy:  Natural Regulation

What Is Natural Regulation?

Natural regulation is a scientific theory that describes the process by which wildlife populations fluctuate over time. Fluctuation in population abundance is attributed to non-constant birth and death rates, which are affected by a multitude of factors including, winter severity, forage quantity and quality, immigration and emigration, hunting and predation by other wildlife. Yellowstone National Park has adapted natural regulation theory to management policies, affecting elk within the park. For a more complete summary of the science behind natural regulation, the controversy surrounding natural regulation policy, and interviews from biological professionals, visit natural regulation concepts.

What are the necessary assumptions of Natural Regulation?

In order for natural regulation to "work", certain assumptions must be met:

  • The ecosystem must be contained, or function as a complete unit.
  • All flora and fauna components must be represented within the natural range of ecosystem conditions.
  • Human influences on the ecosystem at large must be minimal.

How Does Natural Regulation Affect Elk?

A naturally regulating elk population will exhibit a lower rate of growth, as the population size gets closer to an area carrying capacity. Likewise, as elk population numbers decline, the rate of growth will increase. This cycle is described as a "biofeedback response". Where large numbers of elk are found on the same rangelands, the average condition of individual elk declines. Condition in this sense implies health, or vigor. The amount of fat a cow elk carries would be less if that animal were living on a densely populated rangeland, as opposed to a sparsely populated rangeland. The relationship between elk condition and population density has been documented on elk in Yellowstone. On the northern range, declining pregnancy rates in elk are followed by increasing winter mortality rates of very young and old elk where population numbers are high. Climate and predation are also important to balancing of elk populations under natural regulation. From 1987-1990, a recorded 33% of newborn elk were lost to predation by animals such as: bears, coyotes and golden eagles. Also during this time period, a recorded 20% of the total elk population died each winter due to limited food resources, most of which were very young and old animals.

What Is the Alternative to Natural Regulation?

An alternative to using natural regulation theory to guide elk management in Yellowstone National Park is natural control. "Natural control" was a management strategy used previous to natural regulation in Yellowstone. Under natural control, Yellowstone’s previous management objectives aimed to: "limit park control operations to duplicating the action of natural predation which relieves severe overuse of vegetation and reduce extreme fluctuations in animal numbers." Therefore, the park was more actively involved in maintaining elk at "natural" levels, instead of allowing the natural regulation of elk to occu

Implementing Natural Regulation: 

In the early 1970’s, Yellowstone embarked on a new policy of wildlife management: natural regulation.   At this time, Cole was the superintendent of Yellowstone National Park.  Shortly after, Houston became the new head biologist, and gave complete backing to policy of natural regulation.  By implementing natural regulation policy, Yellowstone was inferring that no human influences would intervene to “control” wildlife.  Ungulate populations in Yellowstone are thought to be “self-regulating”, which allowed the park to comfortably adopt natural regulation as a wildlife management policy.

Landscape Requirements for Natural Regulation:

Wildlife can only self-regulate in the context of a complete ecosystem, under the theory of Natural Regulation.  Yellowstone National Park is not a complete ecosystem, and in fact elk herds, which summer in Yellowstone, have most or part of their winter ranges outside of the park.  However, in the area immediately surrounding the park, a lot of National Forest lands, BLM, and a National Refuge (the National Elk Refuge), create a more continuous landscape.  To the north, the Gallatin National Forest fosters winter rangelands for the migrating Northern Range and Gallatin elk herds.  To the south, Grand Teton National Park and the National Elk Refuge provide wintering range for the Jackson herd.  The Shoshone National Forest provides winter range for both the Carter Mountain herd and the North Fork Shoshone Herd.  The Targhee National Forest is home to the Sand Creek herd in the winter, and to a lesser extent, the Madison-Firehole Herd.   Although the landscape is fairly continuous, with the exception of road systems, intermingled towns and private land, the policy surrounding wildlife management is dramatically different depending on the landownership involved.  It is hard to know if Natural Regulation is an adequate wildlife policy for Yellowstone National Park, because the same elk herds, which are “self-regulating” on Yellowstone property, are being hunted, fed, and influenced by humans in various ways when they cross park boundaries.  The assumption that Yellowstone is a complete ecosystem is not correct in this instance, not necessarily because of inadequate land base surrounding the park, but because of conflicting management policy. 

Elk Management Policy in Regions Surrounding Yellowstone:

Ranches and amenity homes occur just outside the western border of Yellowstone National Park
The management of elk in regions surrounding Yellowstone ranges from winter feed programs on the National Elk Refuge in Jackson, Wyoming, to elk hunting on National Forest and BLM lands, to ranching interaction on private lands.  For a review of the USFS and BLM mission and elk management summaries, visit “Other Federal Agencies”.  For a review of issues surrounding elk and ranching interest interaction, visit, “Ranchers".  The main point is that Yellowstone National Park is not an island, capable of implementing natural regulation policy at the ecosystem scale.  Interagency cooperation and planning is needed to link the continuous landscape to more continuous policy.  Some interagency cooperation is occurring in Yellowstone.  For example, interagency teams exist to promote support between landowners including: federal, state, tribal, private ownership, for grizzly bear management, the northern range fauna (elk a major component), and bison-Brucellosis.  These teams can hopefully overcome some of the issues wildlife face when inhabiting a multi-agency landscape matrix.