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Comparative Ecology of the Narrow Endemic Echinacea tennesseensis and Two Geographically Widespread Congeners: Relative Competitive Ability and Growth Characteristics

Using a multiple de Wit replacement series, we tested the hypothesis that the middle Tennessee cedar glade endemic, Echinacea tennesseensis, is a poor competitor compared with its geographically widespread close relatives, Echinacea angustifolia var. angustifolia and Echinacea pallida. In the competition experiment, all pairwise combinations of the three Echinacea taxa were grown under greenhouse conditions at several densities and proportions for 175 d. Classical and functional growth analyses were performed on the three taxa to quantify physiological and morphological characteristics that influence competitive ability. The hierarchy of competitive ability (based on relative yield and aggressivity), plant dry mass, and leaf area was E. pallida > E. tennesseensis > E. angustifolia. However, neither relative growth rate, net assimilation rate, leaf area ratio, nor specific leaf weight differed significantly among the three species (protected least significant difference [PLSD], P > .05). We conclude that lack of competitive ability per se cannot account for the narrow endemism of E. tennesseensis.