Pollination niche overlap contributes to the maintenance of rare flowering species in alpine grasslands.

Abstract

Pollinator-mediated interactions shape the assembly and diversity of plant communities reliant on animal pollination. Such interactions can provide rare species with fitness advantages through facilitation while increasing intraspecific competition among abundant species. However, the roles of pollination generalisation and pollinator sharing in these dynamics remain unclear. To address this, we examined how plant rarity and pollination niche structure (breadth and overlap) influence pollination outcomes across 44 co-flowering species in Qinghai-Tibetan alpine grasslands. We measured plant abundance, floral traits, pollinator visitation, stigmatic pollen deposition, and seed production. Our results showed that rarer species exhibited broader pollination niches and greater niche overlap with co-flowering species, both associated with higher visitation and increased pollination outcomes. Pollination niche overlap, enhanced by greater floral trait similarity, emerged as a key mechanism promoting the persistence of rarer species through pollinator-mediated facilitation. Furthermore, asymmetric facilitation allowed rarer species to gain disproportionate conspecific pollen while abundant species experienced stronger intraspecific competition. Together, these results show that trait-mediated pollinator sharing enhances the persistence of rare species in pollinator-limited ecosystems and contributes to the maintenance of plant diversity.