Trait Hierarchy and Interactive Effects Govern Seed Fate in Rodent-Mediated Dispersal: Insights from Coat Thickness, Nutrients, and Tannins.

Seed traits play a pivotal role in shaping rodent-mediated seed dispersal, a key process driving forest regeneration. However, disentangling the independent and interactive effects of physical (coat thickness), nutritional, and chemical (tannin) traits remains challenging due to their natural covariation. Using artificial seeds in enclosures, we quantified how these traits influence foraging decisions by Leopoldamys edwardsi, a dominant scatter-hoarding rodent in subtropical forests. Our results revealed a hierarchical order of trait importance: nutrient content > tannin content > coat thickness. High-nutrient seeds were preferentially consumed, while moderately nutrient-rich seeds (50% peanut powder) were most frequently scatter-hoarded, balancing immediate energy gain and long-term storage. Tannins exerted a dual effect: low concentrations (0.5%) enhanced consumption, likely due to reduced microbial decay, whereas high concentrations (7%) deterred both consumption and hoarding by impairing digestibility. Coat thickness had weaker effects but interacted with nutrients, as thin-coated, high-nutrient seeds were favored for both consumption and hoarding. Interactive effects highlighted a "benefit-first" decision framework, where rodents prioritize energy gain (nutrients), then modulate behavior to preserve benefits (tannins aiding storage), and finally account for handling costs (coat thickness). These findings illuminate coevolutionary dynamics between rodents and seeds, emphasizing how trait combinations shape mutualistic interactions critical for forest dynamics. Our study provides a mechanistic basis for predicting how shifts in seed traits may disrupt these interactions, with implications for ecosystem management.