An isolated, yet extensive population of the threatened species Jacobaea paludosa (Asteraceae) shows alarming reproductive constraints

In lowlands, many species have been confined into small and isolated populations due to agricultural and industrial development, leading to constraints in generation turnover which may threaten their survival in the long run. Therefore, studies aimed at identifying such constraints must indeed be carried out. The populations of the hydro-hygrophilous Jacobaea paludosa are decreasing due to progressive habitat loss, water pollution and eutrophication. In order to assess possible reproductive constraints, in this study we have investigated: (a) the species’ self-compatibility and dependency on insect pollination, (b) the occurrence of pollination limitation, (c) differences in reproductive success between the study population and another population subjected to a reinforcement intervention conducted 10 years earlier. We performed a series of field pollination tests, including spontaneous selfing, natural pollination, hand self-pollination and pollen supplementation, as well as assessing reproductive fitness in terms of fruit production, cypselae vitality and seed germination ability. Other than providing insights into the reproductive ecology of the species, our results showed that supplementing capitula with pollen collected from a distinct population benefited seed germination within the study population. Altogether, these results indicate potential inbreeding depression and highlight the importance of focusing on populations as key units for identifying constraints in generation turnover and for implementing targeted conservation measures, thereby optimising resource allocation.