Resource Partitioning and Competition within a Guild of Fugitive Prairie Plants

Badger disturbances on tall-grass prairies constitute a limiting resource for a guild of fugitive plants. These plants partition the resource along several dimensions. Divergent centers of resource utilization result from different suites of adaptive life-history characteristics important during colonization. While overlap of utilization functions is considerable along single dimensions of the resource, complementary adaptations of species result in reduced overlap along a complex gradient integrating the separate dimensions. We predict that the number, packing, and organization of species into a guild will change as the nature of the limiting resource changes. Specifically, changes in the abundance of the resource alter the heterogeneity of the resource over space, and as a result relationships among the adaptive centers of resource utilization for species also change. Predictions of changes in resource partitioning and guild organization, based upon assumptions concerning competition among species populations, correspond very closely to empirical field observations. In nature, composition of the fugitive species guild is expected to vary locally with changes in the nature and spatial heterogeneity of badger disturbances, and this variation over space also will depend upon the colonization capabilities of the species. Field investigation of competition provided insight into relationships among species comprising the fugitive guild. Competitive interactions are closely related to the adaptive life-history characteristics involved in the colonization of badger disturbances. The type of interaction occurring among individuals on a site depends upon events occurring during the colonization phase of the life cycle, and different types of competitive interactions have different effects upon the likelihood of subsequent site colonization (i.e., reproductive success of interacting individuals). Both the frequency and types of competitive interactions occurring among individuals in fugitive populations are predicted to depend upon the abundance of the limiting resource; the likelihood of colonization will change as the spatial distribution of colonization sites changes. Thus, the effects of changes in the distribution of the resource over space upon the relative colonization rates of species must be known to predict accurately the impact of competition upon resource partitioning and organization of fugitive plant populations into a guild.