Areas inhabited by black-tailed prairie dogs are subject to continuous and intense disturbance by grazing and burrowing that directly and indirectly alter vegetation composition and structure compared to the surrounding uninhabited areas. Black-tailed prairie dogs serve as prey and provide habitat for a variety of species listed as sensitive, threatened, or endangered (black-footed ferrets, mountain plovers, ferruginous hawks, and swift foxes).
While the general contribution of prairie dog activities to grassland heterogeneity is well recognized, specific information about how that spatial heterogeneity varies across the landscape is limited. Such information will provide valuable insight into the major drivers of vegetation dynamics in response to management and fluctuating environmental conditions. The objective of this study is to evaluate patterns of vegetation heterogeneity within and among prairie dog colonies in the grasslands of the Northern Great Plains.
Prairie dog colonies sampled in this study were highly variable in size, shape, and management history, which was reflected in the variability in species composition and abundance. Of the 154 species recorded, only 2 were found on all 13 colonies. Shortgrass species were recorded on all but one town (i.e., colony). Management and environmental conditions influence species composition and abundance, both native and non-native species, to about the same extent on interior, edge, and off-colony sites.
Edge sites appeared to serve as transition zones between interior- and off-colony sites. Edges contained species of both interior- and off-colony sites with intermediate cover values. However, among colonies, edge sites tended to more closely resemble off-colony sites than interior sites with respect to non-native species. Interior sites showed considerable heterogeneity in non-native species composition and abundance with assemblages that were especially distinct from off-colony sites.
The transitional nature of edges may be a reflection of the response of town boundaries to fluctuating environmental conditions. During dry conditions, colonies reached their maximum recorded size. In comparison to dry conditions, towns mapped during wet years had contracted substantially. Fluctuating boundaries may help maintain species and community level continuity across the landscape and possibly serve as the major source of plant diversity at small and large scales.
Further, preliminary results suggest that boundary dynamics are strongly influenced by the relative dominance of western wheatgrass and shortgrass species. Edge boundaries can be quite large on sites dominated by western wheatgrass and small on colonies dominated by the more grazing and drought resistant shortgrass species.