Within crowded natural plant populations, the traditional prediction is that most of the offspring from which future generations are drawn will be contributed by the relatively few individuals belonging to the larger size classes. Yet, the extent to which this is true should depend on the extent to which the inevitably more numerous, but relatively small suppressed plants within the same population manage not only to survive suppression, but also to reproduce before death. We recorded the above-ground dry mass for mature reproductive plants from natural populations of 21 species of herbaceous angiosperms. Relative reproductive output per plant size decile was estimated as the relative total plant mass per decile (i.e. relative to the grand total plant mass of the entire population sample), scaled between 0 and 1.0. Frequency distributions of estimated relative reproductive output for the ten plant size deciles were then generated for each species based on the assumption that total seed production is proportional to total plant mass. As a test of this assumption, in addition to total above-ground dry mass, we counted the total number of seeds produced per plant for the population sample obtained for Cardamine parviflora.
Results/Conclusions
Fecundity in Cardamine parviflora was directly proportional to plant size, i.e. a 10-fold increase in individual plant size was associated with a 10-fold increase in individual seed production (r 2 = 0.96). Plant size distributions for all species were strongly right-skewed, as expected. Surprisingly however, in every case, the vast majority of the estimated offspring production within the population was contributed by the three, four, or five smallest deciles of the plant size distribution. For seven of the species, most of the total estimated offspring production was derived from just the two smallest plant size class deciles. Our data suggest, in contrast with traditional theory, that most of the coexisting species within crowded vegetation are successful residents not because they are relatively large, but because they produce numerous descendants from numerous offspring that have ‘reproductive economy’ — i.e. offspring with the ability, despite suppression to a very small size, to also produce offspring of their own for the next generation.
