Acorn dispersal by rodents: The importance of re-dispersal and distance to shelter

Abstract

Factors affecting the ecological balance between seed predation and effective seed dispersal remain unclear. We studied the contribution of scatter-hoarding rodents to effective acorn dispersal by labeling acorns and tracking their fates. Seventy percent of the seeds were re-dispersed from their initial fates with up to five successive dispersal movements, revealing that acorn fate is dynamic along time. Dispersal distances were not affected by the slope and acorns were dispersed farther when heavier. However, we found that successive dispersal movements (re-dispersal of seeds) and distance to rodent shelter (shrub cover) are more important factors than acorn weight to determine dispersal distances and acorn survival. Dispersal distances increased with the number of successive dispersal movements, attaining a total of up to 132 m. Seed re-dispersal enhances the redistribution of seeds, moving the seeds farther from the mother plants and increasing the ability of oaks to colonize. However, high numbers of dispersal movements decreased the probability of seed survival. Surprisingly, open microhabitat was found to increase dispersal distances and seed survival (higher when farther from shelter). More seeds were dispersed to shelter but had shorter dispersal distances and higher predation rates. Despite this, shelter is needed to ensure rodent presence and seed caching, so that structurally complex habitats with open microhabitats and shrub cover will favour oak regeneration. This study also underlines the contribution of rodents to effective seed dispersal (with 36.4% of surviving acorns in favourable caches at the end of autumn and 3.4% in next spring). Both the repeated movement of seeds and distance to shelter are two main factors determining seed dispersal by rodents and should be taken into account in further studies.