Effects of intraspecific competition on size variation and reproductive allocation in a clonal plant

Clonal plants grow in diameter rather than height, and therefore competitio n among genets is likely to be symmetric and to result in smaller variation in size of genets than in non-clonal plants. Moreover, clonal plants can r eproduce both sexually and vegetatively. We studied the effects of density on the size of rosettes and of clones, variation in the size of rosettes an d of clones, and allocation to sexual and vegetative reproduction in the cl onal herb Ranunculus reptans. We grew plants from an artificial population of R. reptans in 32 trays at two densities. After four months, differences in density were still apparent, although clones in,the low-density treatmen t had on average 155% more rosettes and 227% more rooted rosettes than clon es in the high-density treatment. The coefficient of variation of these mea sures of clone size was 15% and 83% higher, respectively, in the low-densit y treatment. This indicates that intraspecific: competition among clones of R. reptans is symmetric and increases the effective population size. Roote d rosettes were larger and varied more in size in the low-density treatment . The relative allocation of the populations to sexual and to vegetative re production was 19% and 13% higher, respectively, in the high-density treatm ent. Moreover, seeds produced in the high-density treatment had a 24% highe r mass and a 7% higher germination percentage. This suggests that with incr easing density, allocation to sexual reproduction increases more than alloc ation to vegetative reproduction in R. reptans, which corresponds to the re sponse of some other species with a spreading growth form but not of specie s with a compact growth form. We conclude that intraspecific competition is an important factor in the life-history evolution of R. reptans because in traspecific competition affects its clonal life-history traits and may affe ct evolutionary processes such as genetic drift and selection through its e ffect on the effective population size.