Previous studies on Chinese white pine (Pinus armandii) have shown that larger seeds had greater dispersal success by rodents than smaller ones. However, the effects of mean seed mass at the scale of individual trees on seed dispersal success by rodents are poorly understood. 

Dr. WANG Bo and his colleague of Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences conducted a study to investigate how variation in seed mass and number among tree individuals affects the behavior of animal dispersers and in turn the component of tree fitness involving dispersal of seeds away from the mother tree. The study was conducted in a pine forest in the Hengduanshan Mountains in Shangri-La County, Yunnan Province. 

The researchers first surveyed intraspecific variation in seed production in a natural Chinese white pine population. They then investigated how the variation affected seed predation and dispersal by scatter-hoarding rodents, which were the primary seed dispersers/predators. 

They found that the mass of individual seeds affected almost every step in their discovery, consumption, and dispersal by scatter-hording rodents. Rodents were more likely to harvest larger seeds under trees and to remove them rather than eat them in situ, and were more likely to cache and re-cache them.

At the individual tree level, the mean seed mass conferred no advantage for successful dispersal. After initial harvesting, seed mass did not increase the chances of successful dispersal. 

In addition to tree-to-tree variation in the effects of seed mass, the researchers also investigated rodent predation and dispersal behavior between 2 years: when seed production was high in 2012, and when it was low in 2013 and they used commercial seeds for experiments. 

They showed that despite seed size affecting rodent decisions, variation among trees in dispersal success associated with mean seed size was small once seeds were harvested. It possibly explained the very high variation (0.038–0.361 g) in mean seed mass among trees.

The results emphasized that it is necessary to look at the scale of individual trees, in order to investigate the potential fitness consequences of seed size for dispersal. 

The study entitled “Tree-to-tree variation in seed size and its consequences for seed dispersal versus predation by rodents” has been published online in Oecologia.