Elevational patterns in plant breeding systems and pollen limitation in Afrotropical montane grasslands

Plant reproduction along elevational gradients may be limited by insufficient pollination service, variation in selfing capacity or post-pollination constraints, yet these mechanisms are rarely studied together across multiple co-occurring species. We examined how seed production, pollen limitation and selfing capacity vary along the full elevational gradient of Afromontane grasslands on Mount Cameroon. We combined a hand-pollination experiment with recordings of flower visitors at four elevations above the timberline (2300-3800 m a.s.l.). In seven zoogamous species, we quantified natural seed production, pollen limitation and indices of autonomous and facilitated selfing from controlled pollination treatments, while independently measuring visitation frequency and visitor diversity on unmanipulated plants. Natural seed production peaked at intermediate elevation and declined sharply towards the summit, where the pollen-limitation index was highest. At the highest elevation, some species produced few or no seeds even after supplemental outcrossing. Autonomous and geitonogamous selfing capacities showed no consistent elevational trends despite partial self-compatibility in several species. Visitation frequency and diversity declined towards the summit, and natural seed production increased with visitation frequency, whereas pollen limitation and selfing indices showed no clear relationships with visitation metrics. Together, our results indicate that elevational variation in reproductive success is linked to changes in pollination service, but that pollen limitation and selfing capacity do not track visitation in a simple way. No increase in selfing capacity towards the summit suggests limited potential for increased reproductive assurance through selfing under high-elevation conditions, while additional processes after pollen delivery may also constrain seed production near upper vegetation limits.