Competition does not come at the expense of colonization in seed morphs with increased size and dispersal

Abstract

PREMISE OF THE STUDY: Seed-level trade-offs of heterocarpic species remain poorly understood. We propose that seedlings emerging from seeds with apermanent pappus (dispersing seeds) are stronger competitors than those emerging from seeds without a pappus (nondispersing seeds) because dispersingseeds are larger and germinate faster than nondispersing seeds in Centaurea solstitialis .METHODS: We conducted a competition experiment with both seed morphs, in which we recorded emergence rate and proportion, estimated seed dispersalby wind (anemochory) and by mammals (exozoochory), and measured size and abundance of seed morphs.KEY RESULTS: We found that seedlings from pappus seeds had greater competitive abilities than those from non-pappus seeds. Similarly, pappus seedlingsemerged at much faster rates and larger proportions than non-pappus seedlings. Pappus seeds were larger, were more numerous, and displayed improvedexozoochory compared to non-pappus seeds. Anemochory was poor for both seed morphs.CONCLUSIONS: We found support for our hypothesis, raising in turn the possibility that competition and colonization are positively associated in seedmorphs of heterocarpic species with enhanced exozoochory of larger seeds. These fi ndings are not consistent with those from heterocarpic species withenhanced anemochory of smaller seeds or slower-germinating seeds. Our results additionally suggest that pappus and non-pappus seeds of C. solstitialisdisplay a task-division strategy in which pappus morphs colonize and preempt unoccupied sites through improved dispersal and fast and large emergenceof seedlings with increased competitive abilities, whereas non-pappus morphs promote site persistence through delayed germination and dormancy.This strategy may contribute to the success of C. solstitialis in highly variable environments.