Impacts of moderateness and cobalancedness in seed mass and coat thickness on seed dispersal effectiveness of Quercus variabilis by rodents

Seed traits are important factors in determining the fitness of seeds under seed dispersal and predation by animals, but the combined effects of conflicting traits (e.g., defense and attraction traits) of seeds on the hoarding behavior of animals and then the seed fates have never been investigated. In this study, by measuring seed mass (representing attraction trait to rodents) and coat thickness (representing defense trait to rodents), we examined the impacts of moderateness (medium defensive and attractive trait values) and cobalancedness (positive association between defensive and attractive trait values) in seed mass and coat thickness on the fates of Quercus variabilis acorns which were hoarded mainly by rodents in 2019 and 2021. We found acorns with more moderate seed mass and coat thickness had a higher final survival probability by the end of the 2 months of study, supporting the Moderateness Hypothesis. Seed mass was positively correlated with the seed coat thickness, supporting the Cobalancedness Hypothesis. We also found attraction-biased acorns and co-balanced acorns showed higher final survival probability than defense-biased acorns, partially supporting the Cobalancedness Hypothesis and suggesting the co-balance between seed mass and coat thickness may have not been fully achieved. Our results suggest that the moderateness and cobalancedness between conflicting traits (e.g., seed attraction and defense traits) may play a crucial role in influencing rodent-mediated seed fate, and then trait evolution of seeds under rodent dispersal and predation.