Female Reproductive Success of Narrow Endemic Erodium Paularense in Contrasting Microhabitats

In 1996, we investigated the female reproductive success of the narrow endemic Erodium paularense in a population with a mixture of rock and lithosol microhabitats. The main purposes of this study were to determine the main factors that affected reproductive success and whether these factors were influenced by differences in the two contrasting microhabitats. In both microhabitats, fruit set was low, and seed abortion rates were very high. Lithosol plants were larger and had higher flower, fruit, and seed production than rock plants. We used structural equation modeling (SEM) to analyze the effects of plant size, phenological variables, competition, and flowering synchrony on fecundity and to compare path coefficients among microhabitats. In both microhabitats reproductive success was strongly predicted by plant size and to a lesser extent by flowering synchrony. Flowering moment and intensity did not have a significant effect on fruit set, suggesting that pollinator availability is not a limiting factor in total seed production. This was further corroborated by hand-pollination experiments. Resource limitations, inbreeding depression, and environmental restrictions may be responsible for the high rates of seed abortion. Multisample comparison of path coefficients for the two microhabitats rejected the possibility that reproductive patterns could be described by one single model. The main divergences in both microhabitat models were related to competition. Reproductive data from 1995, a year with below-average rainfall, showed remarkably lower seed production at the lithosol microhabitat and similar values at the rock microhabitat as compared to 1996. The variation of the reproductive parameters between the two years was evaluated by multisample analyses in which 1995 data were fed into the 1996 models. At the lithosol microhabitat, two constrained paths involving seed production produced a significant decrease in fit, whereas at the rock microhabitat, significant differences were found in three paths involving only phenological variables. Thus, the lithosol microhabitat may contribute to greater seed production in favorable years while the rock microhabitat may provide more stable conditions over time.