Pilfering ability of four seed-caching rodents in the Sierra Nevada

Background/Question/Methods

Resource partitioning may allow many species of seed-caching rodents to coexist through temporal or spatial differences in resource harvesting. However, no study to date has shown that such partitioning can fully explain how multiple species of rodents coexist. Another potentially important behavior among seed-caching rodents, cache pilfering, could allow rodents to partition a resource through their ability to defend and pilfer caches. A rodent’s ability to pilfer or defend a cache is likely strongly related to their food storage behavior, either larder- or scatter-hoarding. In this study, we hypothesized that differences in pilfering ability among seed-caching rodents may explain observed coexistence and is likely linked to their food storage behavior. To address this question, we examined the pilfering ability of four coexisting seed-caching rodent species: Tamias amoenus, T. quadrimaculatus, Peromyscus maniculatus, and Spermophilus lateralis. Both species of Tamias and P. maniculatus are scatter-hoarders while S. lateralis is a larder-hoarder. In 2009 and 2012, forty trials of pair-wise comparisons were conducted to determine the ability of naïve individuals to locate and retrieve caches created by other rodents inside an enclosure. A Geiger counter was used to locate radioactively labeled Pinus jeffreyi seeds that were cached by rodents. 

Results/Conclusions

No significant differences were observed between the pilfering ability of either Tamias spp., P. maniculatus, or S. lateralis (F = 0.863, P = 0.469). However, Variance among species differed slightly with T. quadrimaculatus finding caches less consistently than T. amoenus and P. maniculatus. Species were also able to find caches made by rodents of the same species more consistently than caches created by other species. Despite no overall difference among study species, only one S. lateralis individual was able to pilfer caches. Inability to detect caches, as seen in the other trials, is the likely result for S. lateralis. Larder-hoarders should spend most of their time harvesting seeds and defending caches, spending little if any time pilfering. As scatter-hoarders, it is not surprising that Tamias spp. and P. maniculatus have similar abilities to pilfer, finding approximately 39% of caches. If a species had an advantage in their pilfering ability, they could potentially out-compete ecologically similar rodents and eventually extirpate them. It is unlikely that this scenario of unequal pilfering could lead to the diversity and coexistence witnessed in rodent communities of the western United States.