The number and size of seeds in common versus restricted woodland herbaceous species in central Iowa, USA

Abstract

Mabry, C. M. 2004. The number and size of seeds in common versus restricted woodland herbaceous species in central Iowa, USA. Á/ Oikos 107: 497 Á/504.Few plants have widespread distributions and occur wherever there is suitable habitat. Most species are absent from seemingly suitable sites because of limited colonizing ability. At a landscape scale colonization is limited by lack of seeds or suitable microsites, and this limit is likely to be exacerbated by current human alteration of the landscape. To test the hypothesis that species with restricted distributions have a more limited capacity for dispersal compared to common species, I compared seed number in a group of seven common woodland herbaceous species compared to seven species in the same genus or family with more restricted distributions. Restricted species had nearly an order of magnitude fewer seeds compared to closely related common species. They also produced over an order of magnitude larger seeds. These results support dispersal limitation. The ability to detect these differences was reduced when taxonomic information was not included. The data suggest that these species can not maximize both seed size and seed number. The results are interpreted in light of the human disturbance history that has had an overriding influence on the Iowa landscape and has likely favored species with an output advantage of abundant seeds over species with far fewer seeds.

Species traits as generalized predictors of forest community response to human disturbance

“…Similarly, the association between undisturbed sites and basal phyllotaxy probably reflects the presence of ferns in these areas. The association between undisturbed sites, solitary flowers, and dehiscent fruits with 4-20 seeds suggests low reproductive output, which is consistent with other studies (Matlack, 1994;Dupré and Ehrlé n, 2002;Mabry, 2004). However, other traits that have also been associated with low dispersal capacity -lack of vegetative spread, few seeds/fruit, large seeds -were associated with disturbance for at least one of our two study areas.…”

“…For example, a study in Iowa using taxonomically paired species showed that less common species had larger seeds than closely related common species (Mabry, 2004). However, without the paired design that allowed species' relatedness to be factored out, these patterns would not have been evident.…”

Determinants of local abundance and range size in forest vascular plants

“…There was, however, no relationship between the dispersal capacity of species (as deduced from diaspore type and number) and their geographical range, which appears to be consistent with previous work (Eriksson & Jakobsson, 1998;Thompson et al, 1999;Jacquemyn et al, 2003), but contrary to findings of other studies (e.g. Eriksson & Jakobsson, 1998;Murray et al, 2002;Mabry, 2004). On the other hand, perennials with no or only limited clonal growth produced more diaspores per plant than strongly clonal species, which may confer a higher dispersal capacity.…”

Previous land use alters plant allocation and growth in forest herbs

“…Sowing and transplant experiments have also demonstrated that the absence of many species is caused by seed limitation (Eriksson & Ehrlen 1992; Turnbull et al . 2000; Mabry 2004). Thus, propagule availability has probably influenced the plant community in our farmed stands, even though the communities in logged stands show few long‐term effects on diversity (Pearson et al .…”

“…Similarly, species with rapid clonal expansion and large numbers of seeds tend to be more frequent in altered stands (Eriksson 1995; Singleton et al . 2001; Mabry 2004). Stand age and distance from source habitat can interact with dispersal and further limit the colonization of altered stands (Matlack 1994).…”