Weed flower dilemma: competitiveness with few costly flowers or
ruderality with numerous cheap flowers?
Abstract
Weed species are ecological models that recently received considerable
attention due to their particular strategies linked to their
ruderal-competitive traits. They are known to have the potential to
provide additional floral resources for insects in flower-poor
agroecosystems. However, their floral traits are much more scarcely
studied than those of plants found in other habitats, such as
grasslands. The aim of this study was to describe the floral phenotype
of weeds and to determine to what extent their floral traits match their
ecological strategies as described on the basis of leaf traits. We
therefore cultivated 19 forb weeds from perennial agroecosystems,
previously identified in Mediterranean fields, in a greenhouse for seven
months and collected data on 12 floral and 5 leaf traits. We tested
whether these traits covaried and whether they exhibited an ecological
strategy at the phenotype scale. We found that in matters of flower
production, weed species face a trade-off: either numerous small,
low-stature flowers with small quantities of pollen and nectar, or few,
large, higher-held flowers with more pollen and nectar. The floral
traits were found to reflect Grime’s CSR strategies: the weed species
producing fewer but costlier flowers belonged to C-strategy species,
whereas those producing more but less costly flowers belonged to species
dominated by an R strategy These findings indicate that the potential of
weeds as floral resources for insects is related to their ecological
strategies, which are known to be affected by agricultural practices
that filter species composition. This implies that, as for the provision
of other ecosystem services, weed communities can be managed so as to
select species with interesting floral traits for pollinators.