Common seed dispersers contribute most to the persistence of a fleshy-fruited tree

A decade-long study into seed dispersal of glossy buckthorn trees by animals in an old-growth Polish forest finds that tree population growth is more positively influenced by a small subset of common generalists rather than specialist frugivores. Mutualistic interactions are by definition beneficial for each contributing partner. However, it is insufficiently understood how mutualistic interactions influence partners throughout their lives. Here, we used animal species-explicit, microhabitat-structured integral projection models to quantify the effect of seed dispersal by 20 animal species on the full life cycle of the tree Frangula alnus in Bialowieza Forest, Eastern Poland. Our analysis showed that animal seed dispersal increased population growth by 2.5%. The effectiveness of animals as seed dispersers was strongly related to the interaction frequency but not the quality of seed dispersal. Consequently, the projected population decline due to simulated species extinction was driven by the loss of common rather than rare mutualist species. Our results support the notion that frequently interacting mutualists contribute most to the persistence of the populations of their partners, underscoring the role of common species for ecosystem functioning and nature conservation.

Automated summary

A decade-long study in an old-growth forest in Poland found that the population growth of glossy buckthorn trees is more influenced by a small subset of common generalists rather than specialist frugivores. The study used animal-specific integral projection models to quantify the effect of seed dispersal by 20 animal species on the tree's life cycle. It was found that animal seed dispersal increased population growth by 2.5%, and the effectiveness was related to interaction frequency rather than dispersal quality.