Effects of local densities and abiotic microenvironments on reproductive outputs of a biennial, Lysimachia mauritiana var. rubida

To understand the relative importance of density‐dependent and density‐independent factors on plant fitness, we examined the effects of local densities and surrounding ground surface conditions on the reproductive output of a monocarpic biennial plant, Lysimachia mauritiana var. rubida in a natural population. Observations were conducted during five successive years in open dry habitats on rocky coastal cliffs of the subtropical B onin ( O gasawara) I slands, J apan. Local density and ground surface conditions, categorized by gravel size, were remarkably heterogeneous in the study population. Therefore, we hypothesized that number of flowers per plant was affected by local density, ground surface condition, and their interaction. During 3 of 5 years, the number of flowers per individual L. mauritiana var. rubida plant was only negatively affected by the local density around the plant. The interaction effects of local density and ground surface conditions were observed in two years. Taken together with the results of previous studies, these results suggest that density effects are dominated survival in the early growing season and reproduction, while the effects of ground conditions are important for seedling recruitment and survival in the late growing season. Thus, interactive effects between density‐dependent and density‐independent factors on the life cycle from germination to reproduction regulate populations of L. mauritiana var. rubida in spatially heterogeneous habitats.