Pilfering of western juniper seed caches by scatter-hoarding rodents varies by microsite and canopy type.

Scatter-hoarding rodents store seeds throughout their home ranges in superficially buried caches which, unlike seeds larder-hoarded in burrows, are difficult to defend. Cached seeds are often pilfered by other scatter-hoarders and either re-cached, eaten or larder-hoarded. Such seed movements can influence seedling recruitment, because only seeds remaining in caches are likely to germinate. Although the importance of scatter-hoarding rodents in the dispersal of western juniper seeds has recently been revealed, the level of pilfering that occurs after initial burial is unknown. Seed traits, soil moisture, and substrate can influence pilfering processes, but less is known about how pilfering varies among caches placed in open versus canopy microsites, or how cache discovery and removal varies among different canopy-types, tree versus shrub. We compared the removal of artificial caches between open and canopy microsites and between tree and shrub canopies at two sites in northeastern California during late spring and fall. We also used trail cameras at one site to monitor artificial cache removal, identify potential pilferers, and illuminate microsite use by scatter-hoarders. Removal of artificial caches was faster in open microsites at both sites during both seasons, and more caches were removed from shrub than tree canopies. California kangaroo rats were the species observed most on cameras, foraging most often in open microsites, which could explain the observed pilfering patterns. This is the first study to document pilfering of western juniper seeds, providing further evidence of the importance of scatter-hoarding rodent foraging behavior in understanding seedling recruitment processes in juniper woodlands.

Phylogenetic Position of a New Trisetacus Mite Species (Nalepellidae) Destroying Seeds of North American Junipers and New Hypotheses on Basal Divergence of Eriophyoidea.

Eriophyoid mites of the genus Trisetacus Keifer are widespread parasites of conifers. A new oligophagous species, T. indelis n. sp., was discovered severely damaging seeds of North American junipers (Juniperus osteosperma, J. occidentalis, and J. californica) in the western USA. It has two codon deletions in the mitochondrial gene Cox1 rarely detected in Eriophyoidea and includes distinct morphological dimorphism of females. A phylogenetic analysis based on amino acid alignment of translated Cox1 sequences using a large set of out-groups (a) determined that two North American congeners, T. batonrougei and T. neoquadrisetus, were the closest known relatives of T. indelis n. sp., and (b) indicated that Old and New World seed-inhabiting Trisetacus from junipers do not form a distinct clade, suggesting a possible independent transition to living in seeds of junipers in America and Eurasia by Trisetacus spp. Our analysis produced a new topology consistent with a scenario assuming gradual reduction of prodorsal shield setation in Eriophyoidea and an ancient switch from gymnosperms to other hosts. Additionally, our analysis did not support monophyly of Trisetacus; recovered a new host-specific, moderately supported clade comprising Trisetacus and Nalepellinae (Nalepella + Setoptus) associated with Pinaceae; and questioned the monophyly of Trisetacus associated with Cupressaceae.

Seed value influences cache pilfering rates by desert rodents.

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.