Parental Effects on Spatial Patterns of Plants: A Contingency Table Approach

Abstract

We examined the effects of plant size and seed production on the seed shadows and mature offspring patterns of isolated parent plants of six biotypes of Panicum miliaceum. Spatial patterns of offspring were summarized in contingency tables that were classified by distance and orientation from the parent. These tables were analyzed with reciprocal averaging ordination and dispersions profile analysis. The first and second components of the ordination of a detailed data set reflected the distance and orientation, respectively, of the seed shadows from their parents. The mean infructescence height and the mean lateral spread of the parent plants were correlated with the first component of the ordination while the orientation of the parent plants was correlated with the second component. Little support was found for the hypothesis that biotypes with high numbers of seeds produced should have greater dispersal ability. However, when the individuals were grouped by seed production, irrespective of biotype, the more fecund groups had more distant cohorts of mature offspring. This latter trend was partly attributable to the increased density—dependent mortality near fecund parent plants and partly attributable to the larger sizes and hence larger seed shadows of these parents.