Dispersal syndrome differentiation of Pinus armandii in Southwest China: Key elements of a potential selection mosaic

Pinus armandii is a species of pine native to China with a wide geographical distribution and large-wingless seeds (about 300 mg). The study is to determine the variation in seed dispersal traits among populations within a relative small geographic scale and furthermore to explore if the trait differentiation results in the differences in dispersers, in particular nutcrackers (Nucifraga caryocatactes) and scatter-hoarding rodents. We conducted studies at five sites at different elevations in northwest Yunnan Province. The study sites are separated by 10–200 km and divided into populations partly isolated by mountains and rivers. The cone and seed traits diverged significantly among the five study sites while the traits among individual trees at each site did not differ significantly. Nutcrackers and scatter-hoarding rodents presented conflicting preference in cone and seed traits: nutcrackers preferred smaller cones with smaller seeds, which increased the foraging efficiency of nutcrackers; while scatter-hoarding rodents tended to cache larger seeds. Consistent with variation in preferences by nutcrackers and scatter-hoarding rodents, in nutcracker-dominated sites, pines were characterized by smaller cones, smaller seeds, and thinner seed coats; while in sites where nutcrackers were not abundant, pines had relatively larger cones with larger seeds, which could enhance caching activities by scatter-hoarding rodents. The study provided some key elements for potential selection mosaic on cone and seed traits of a long-lived perennial tree among populations with limited geographical range.