Abundance, distribution and life histories of grassland plants: a comparative study of 81 species

1 This study examines the abundance and distribution of grassland plant spe cies in particular relation to features affecting colonization. Seed produc tion (inversely related to seed size) and recruitment success (positively r elated) affect colonization ability, suggesting that seed size can be used as a key trait. 2 Data on seed size, dispersal mode, life form, geographical range size and abundance were gathered for 81 grassland plant species in a field study ar ea in Sweden. Seed production and plant size were estimated for 69 of these species. Analyses were performed both across species, with species treated as independent data points, and for 43 'phylogenetically independent contr asts'. 3 The cross-species analyses suggested that local abundance was related to life forms but not dispersal or plant size. Perennials were generally most abundant, as were clonal species. If abundance reflects colonization we pre dicted that species with intermediately sized seeds (or intermediate seed p roduction) would be most abundant, and this was supported by the phylogenet ic contrast but not by cross-species analyses. In the former analysis, a hi gh abundance of species was significantly associated with a small seed size deviation land seed number deviation) from the median values of these trai ts in the community. 4 Local abundance, seed production and seed size deviation from the communi ty median value were positively related to geographical range size in the c ross-species analysis, but no relationships were seen in the phylogenetic c ontrast analysis. 5 We conclude that colonization processes do have a significant influence o n abundance patterns in grasslands. Seed size is a key trait for colonizing ability, and the effects of the trade-off of seed size vs. seed number mus t be considered. No single mechanism can be identified that influences both abundance and geographical distribution range.