Recaching of Jeffrey pine (Pinus jeffreyi) seeds by yellow pine chipmunks (Tamias amoenus): potential effects on plant reproductive success

Abstract

Animals that scatter-hoard seeds frequently dig up and recache them at new locations. The effect of the recaching of seeds on plant reproductive success was studied in the Sierra Nevada of western Nevada. The fate of 1000 individually marked Jeffrey pine (Pinus jeffreyi) seeds initially placed in 100 primary caches in a 10 x 10 array was monitored during autumn 1995 and spring 1996. Yellow pine chipmunks (Tamias amoenus) quickly removed nearly all of the seeds and recached many of them in 377 secondary caches containing 727 seeds. Later, rodents dug up most of these caches and transferred them to 213 tertiary caches (283 seeds), 75 quaternary caches (92 seeds), and 13 quintic (fifth order) caches (13 seeds). Overall, rodents ate 15.3% of the seeds they took from primary through quintic caches, and an additional 71.1% of the seeds disappeared, probably to underground runways and larders. During our spring survey of the study site, 133 seeds (13.6%) from 84 caches had germinated or were about to germinate. As rodents moved seeds from cache site to cache site, several changes occurred that potentially influenced the distribution and survival of Jeffrey pine seedlings. First, the number of seeds per cache decreased. Second, cached seeds were gradually moved farther from the source area. Third, the dispersal distance between successive cache sites decreased. Fourth, the distribution of cached seeds became more even. Lastly, more seeds were cached beneath shrubs, which serve as nurse plants for Jeffrey pine seedlings. Consequently, the movement of seeds between cache sites by chipmunks may increase the probability that Jeffrey pine seedlings will establish from rodent caches.