(at high elevations, in remote areas, and above natural barriers) harbor native populations. Introduced rainbow and brown trout also have reduced the range of the native brook trout.
In Great Smoky Mountains National Park, an inventory of black bear populations showed that only about 500 bears were present, far fewer than expected in the ecosystem, so managers were motivated to develop a regional management plan. When population monitoring showed unexpectedly low bear populations in several sections of the park, illegal hunting was suspected, and an enforcement program was instituted. A multi-agency state and federal operation led to the arrests of several persons allegedly involved in exporting bear parts to the Orient.
Defining cause-and-effect relationships, in particular, requires sustained, interdisciplinary research at a variety of spatial and temporal scales. Because change is universal in nature, research must determine whether a given amount of change represents natural fluctuation around a steady state or a net trajectory in a desirable or undesirable direction. In Yellowstone National Park, for instance, the deteriorating condition of the northern range continues to create controversy. Scientists external to the park say the deterioration is caused by excessive populations of elk; research by park biologists, however, indicates that the changes are natural and caused, in part, by climatic changes. The controversy stems in large part from the lack of long-term data. Since ecosystems operate under fluctuations in climate, the need to detect actual directional change in resources poses a significant challenge that requires a substantial and sustained research effort. Such efforts require sophisticated and sensitive research techniques. Because the parks often lack even the most basic inventory of resources and baseline data, research often must start from an inadequate data base for the design of key studies.
The population dynamics and interactions among gray wolves, moose, and vegetation at Isle Royale National Park