National parks are not secure islands unto themselves. Living organisms and the natural processes which bind them together are not confined by the lines that people have drawn on maps. Acknowledging these ecological truths, park scientists and resources managers have increasingly looked beyond legal park boundaries for relationships and connections. With the parks as the core elements, they have defined larger ecosystems which include neighboring lands and communities. The concept of greater ecosystems more aptly conveys a sense of the non-insular nature of natural preserves.

Lands and communities adjacent to parks represent the "ghost acreage," or the additional external acreage necessary for energy flow and exchange with living communities within the parks. For example, the welfare of certain animal populations is dependent on the availability and ecological health of areas to which they periodically migrate. The quality and quantity of water flowing into a park from beyond its boundaries can significantly alter the park's ecological balance. Air pollution generated in adjacent communities can threaten the welfare of park wildlife.

Yellowstone and Everglades are good examples of national parks where the greater ecosystem management concept is practiced,