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Reasons for Rarity
The Natural Heritage Inventory tracks the location and status of rare plant and animal species in Arkansas. Technically, these area species are known as "species of special concern" and can be considered to be rare for a number of reasons.
Endemics: species that are only known to occur in a relatively small area. A number of plant and animal species occur in Arkansas and nowhere else in the world. The Caddo Mountain salamander (Plethodon caddoensis) is only found in certain areas of the Ouachita Mountains of Arkansas.
Disjuncts: species whose populations occur in widely separated areas. Such an example is sand cherry (Prunus pumila), a plant primarily found in the northern United States. Isolated populations of this plant also occur in the Grand Prairie of Arkansas.
Relicts: relicts are plants and animals that were probably once more common when the climate of Arkansas was much different than it is today. As the climate changed, populations of these species died out. However, small populations of some species continue to cling to appropriate habitat in the state. A number of such species occur on Mt. Magazine in western Arkansas.
Peripherals: as species reach the edge of their range they tend to become less common and may ultimately qualify as being rare. The plains harvest mouse (Reithrodontomys montanus) is found throughout the Great Plains but becomes progressively rare southward into Arkansas.
Habitat Specificity: Certain species are limited geographically by their habitat requirements. For instance, the filmy fern (Trichomanes boschianum) is only found in damp limestone grottoes or sandstone overhangs in deep canyons of the Boston Mountains of Arkansas.
Human-induced Rarity: Some species have become rare as a result of human activities. Loss of native habitat to such things as agricultural production and urban development has resulted in the decline of a number of species that were once more common in Arkansas. The prairie mole cricket (Gryllotalpa major) is a species dependent upon tallgrass prairie. As prairies in Arkansas were plowed under for crop production, this species has become progressively rare and is now restricted to isolated fragments of remaining prairie habitat.
Besides habitat loss, degradation of habitat from pollution can also lead to species declining to the point of becoming rare. A significant number of freshwater mussel species that occur in the rivers and streams of Arkansas are dependent upon high water-quality. Alterations of river courses through channelization, urban and agricultural run-off, and increased sediment loads all have had a negative impact on a number of these species.
