Seed value influences cache pilfering rates by desert rodents

Authors: VANDER WALL, STEPHEN - University Of Nevada; Dimitri, Lindsay; Longland, William - Bill; WHITE, JOSEPH - University Of Cape Town

Submitted to: Integrative Zoology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2018
Publication Date: 1/30/2019
Citation: Vander Wall, S.B., Dimitri, L.A., Longland, W.S., White, J. 2019. Seed value influences cache pilfering rates by desert rodents. Integrative Zoology. 14(1):75-86. https://doi.org/10.1111/1749-4877.12358.
DOI: https://doi.org/10.1111/1749-4877.12358

Interpretive Summary: Some rodents gather and store seeds. What they do with the seeds that they gather is influenced by characteristics of seeds that affect their desirability or value to rodents. Because seed-caching rodents are important for seed dispersal of several economically important range forage plants, we investigated how seed traits of four different plant species may affect whether rodents find the seeds desirable based on what the animals did with seeds after harvesting them. Piñon pine was the most desirable seed to rodents. Animals removed all piñon pine seeds from experimental caches and either consumed them or transported them long distances, presumably to re-cache them for later use. Desert peach seeds, which are somewhat toxic, were frequently re-cached. Rodents removed Utah juniper and antelope bitterbrush seeds more slowly than other types, sometimes left these seeds behind after digging them up, and moved the ones that they harvested relatively short distances, suggesting that these seeds were of a lower value to animals. Differing traits of seeds clearly influence the way that rodents treat them in nature.

Technical Abstract: Some rodents gather and store seeds. How many seeds they gather and how they treat those seeds is largely determined by seed traits such as mass, nutrient content, hardness of the seed coat, presence of secondary compounds, and germination schedule. Through their consumption and dispersal of seeds, rodents act as agents of natural selection on seed traits, and those traits influence how rodents forage. Many seeds that are scatter-hoarded by rodents are pilfered, or stolen, by other rodents, and seed traits also likely influence pilfering rates and seed fates of pilfered seeds. To clarify coevolutionary relationships between rodents and the plants that they disperse, one needs to understand the role of seed traits in rodent foraging decisions. We compared how the seeds of 4 species of plants that are dispersed by scatter-hoarding animals and that differ in value (singleleaf piñon pine, Pinus monophylla; desert peach, Prunus andersonii; antelope bitterbrush, Purshia tridentata; Utah juniper, Juniperus osteosperma) were pilfered and recached by rodents. One hundred artificial caches of the 4 seed species (25 per species) were prepared, and removal by rodents was monitored. Rodents pilfered high-value seeds more rapidly than the other seeds. Desert peach seeds, which contain toxic secondary compounds, were more frequently recached. Relatively low value seeds like Utah juniper and antelope bitterbrush were pilfered more slowly and were sometimes left at cache sites, and seeds of the latter species were transported shorter distances to new cache sites. The background density of seeds also appeared to influence the relative value of seeds.