How are communities and ecosystems different than “habitat”? Managing for a species invariably means managing its habitat. Habitat (which is derived from the Latin for “it inhabits”) is the place where a particular species lives and grows. It is essentially the environment—at least the physical environment—that surrounds (influences and is utilized by) the species population. The term was originally defined as the physical conditions that surround a species population, or an assemblage of species (Clements and Shelford, 1939). Wildlife managers, in particular, tend to focus on habitat management–identifying and manipulating those environmental factors limiting a targeted population’s size (Leopold 1933, Yoakum and Dasmann. 1971). Scientists often expand the concept of habitat to include an assemblage of many species, living together in the same place. Thus, for example, wildlife managers often work to improve shorebird habitat. The U.S. Fish and Wildlife Service (FWS) has spent many millions of dollars managing for breeding habitat for migratory waterfowl in the prairie pothole region of North America. Ecologists regard the habitat shared by many species to be a biotope—a place where a community of species lives.
The concept of habitat is not synonymous with that of the natural community or ecosystem. A natural community is the assemblage of plants and animals sharing the same biotope and interacting with each other. When one speaks of a natural community, the focus is on the species and their interactions. The biotope, then, is the biophysical stage on which these species and their interactions occur. Communities typically reoccur across a landscape as they track habitat conditions. As such, communities do not occur at a single, specific spatial scale. Vegetation communities are often perceived as the classic community, but one can also describe the smaller community existing within a fallen log, or ephemeral community within a vernal pool.
An ecosystem, then, can be thought of as the whole picture; the combination of a natural community and its habitat (or biotope). As such, an ecosystem can extend far beyond even a large military installation. But ecosystems are more than just a community in its habitat. The concept of the ecosystem includes dynamic ecological processes (see below) and the recognition that species composition (i.e., the community) will change over time as well as over space. Every species within a community responds to the environment differently from the others. Similarly, each species interacts with different suites of other species. As conditions change, as they certainly do within military installations as in other environmental settings, some species become more abundant, while others become rarer.
Natural disturbances, ranging in size from gaps called by fallen trees to massive wildfires, all affect species abundance and distribution differently (Picket and White 1986). Thus, ecosystems are neither static nor homogeneous. Rather, they are composed of “patches” of various sizes and ages, and the relative abundance and distribution of these patches is crucial to maintain the full suite of biodiversity within an area. Maintaining ecological processes, such as fires, floods, and periodic disease epidemics, is the keystone of successful ecosystem conservation. Indeed, the core of the ecosystem-based management approach is the understanding that the persistence of all biodiversity within an area is contingent on the persistence of this crazy-quilt pattern of disturbed and recovering patches. Management, then, needs to focus on the dynamic processes creating this pattern and not on maintaining a static structure and condition. Military activities can mimic some natural disturbances, and thus can often be integrated into a biodiversity management plan.
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Bob Unnasch, Ph.D.
Sound Science LLC