The distinct fruit size and physical defense promote divergent secondary seed dispersal strategies of three oak species

Secondary seed dispersal is one of the most important factors contributing to the co-existence of plant species. Variations in fruit properties including fruit size, physical defense and chemical composition influence seed foraging and secondary dispersal, but the details remain unclear. Here, we focused on three common nut-bearing tree species (Quercus aliena Blume, Q. dentata Thunb., and Q. variabilis Blume), which often co-occur in mixed deciduous forest in northern China. We estimated their acorn properties and evaluated their effects on the secondary dispersal patterns. We found similar chemical profiles but different acorn sizes and physical defense among these three species. Moreover, we detected distinct secondary seed dispersal strategies in relation to their acorn properties: Q. dentata produced the smallest-sized acorns with the lowest physical defense, which had shorter dispersal range but the highest survival rate; Q. variabilis generated the largest-sized acorns with the highest physical defense, which suffered the lowest survival rate but benefited from the longer dispersal range; and an intermediate survival rate existed in Q. alienawith the intermediate-sized acorns. In addition, Père David's rock squirrel (Sciurotamias davidianus Milne-Edwards, Sciuridae) and brown rat (Rattus norvegicus Berkenhout, Muridae) are secondary seed dispersal agents for three oak species. Brown rats not only disperse more acorns than Père David's rock squirrels, they also create different dispersal distance for the acorns of three species, which enhance three species’ niche separation. Our results therefore revealed that differentiations in acorn properties have derived distinct trade-offs in secondary seed dispersal strategies, likely facilitating the coexistence of the three examined species.