Intraspecific variation in seed dispersion of Lepidium campestre (Brassicaceae)

Intraspecific variation in seed dispersion provides the initial context for frequency-dependent and density-dependent processes affecting seed/seedling survival. We examined intraspecific variation in seed dispersion in a ballistically dispersed herbaceous annual. Lepidium campestre, in both the presence/absence of vegetation to determine the magnitude of variation in seed dispersion among parents, the relationship of this variation to parental architecture, and the effect of the presence of vegetation both on the variation and on its relationship to parental architecture. We quantified seed dispersion by placing concentric rings of traps around individual parents out to a distance of 2 m in the presence/absence of vegetation in an old-field plant community. In the absence of vegetation, parents differed in the distance and direction that their seeds traveled. Parental height and infructescence length explained a significant proportion of the variation in mean and standard derivation of seed dispersal distance, its well as skewness and kurtosis of the distribution of seed number as a function of distance. The mean direction that seeds traveled was correlated with all architectural traits. When plants dispersed their seeds in sites with dense vegetation, mean dispersal distance and standard deviation in distance decreased, and dispersal distributions were more right skewed and leptokurtic. The presence/absence of vegetation explained some of the variation among parents in the moments of the distance distribution, but architectural traits also contributed to these descriptive models. Directional components of dispersal were not affceted by vegetation. Correspondence analysis, a multivariate technique that examined distance and direction simultaneously, revealed thai architectural attributes related to variation in dispersion were different from analyses of distance alone. These results suggest that architectural attributes of the parent contribute not only to the distance that seeds travel, but also to other axes of variation, i.e, skewness and kurtosis of the distance distribution or multivariate axes of seed dispersion. Surrounding vegetation alters seed dispersion, but parental attributes can still explain snme of the residual variation. This variation in seed dispersion among parents creates the opportunity for selection on parental dispersal traits.