Synchronous masting regulates seed-seed interactions for two co-fruiting tree species under the mediation of rodents

Abstract

Knowledge is lacking on how masting regulates seed-seed interactions of sympatric tree species under the mediation of rodents. Here, we compared rodent-mediated seed dispersal between two sympatric tree species (Castanea mollissima and Quercus aliena) in both monospecific and mixed plots, across five successive years in the Qinling Mountains, China. We investigated: (a) whether the rodent-mediated seed dispersal success of each tree species was affected by the presence of the other, and (b) if any effects on dispersal were influenced by either the abundance of rodents present, or by (c) masting (i.e., seed abundance). We found both short-term mutualism and competition occurred between these two sympatric tree species. In non-mast years, the presence of Q. aliena seed reduced predation on C. mollissima seeds and promoted seed caching, which resulted in higher rates of C. mollissima seed dispersal. Synchronous masting enhanced this benefit to C. mollissima seeds, although we detected no clear neighbor or masting benefits for Q. aliena seed dispersal. This shows that inter-specific interactions differ between these masting neighbors, which may relate to either relative species-specific seed abundance or seed traits. We conclude that seed abundance mediates rodents’ seed forging and caching strategies, which may be important for forest regeneration and forest tree species composition.