Forest rodents provide directed dispersal of Jeffrey pine seeds

Abstract

Some species of animals provide directed dispersal of plant seeds by transporting them nonrandomly to microsites where their chances of producing healthy seedlings are enhanced. We investigated whether this mutualistic interaction occurs between granivorous rodents and Jeffrey pine (Pinus jeffreyi) in the eastern Sierra Nevada by comparing the effectiveness of random abiotic seed dispersal with the dispersal performed by four species of rodents: deer mice (Peromyscus maniculatus), yellow-pine and long-eared chipmunks (Tamias amoenus and T. quadrimaculatus), and golden-mantled ground squirrels (Spermophilus lateralis). We conducted two caching studies using radio-labeled seeds, the first with individual animals in field enclosures and the second with a community of rodents in open forest. We used artificial caches to compare the fates of seeds placed at the range of microsites and depths used by animals with the fates of seeds dispersed abiotically. Finally, we examined the distribution and survival of naturally establishing seedlings over an eight-year period. Several lines of evidence suggested that this community of rodents provided directed dispersal. Animals preferred to cache seeds in microsites that were favorable for emergence or survival of seedlings and avoided caching in microsites in which seedlings fared worst. Seeds buried at depths typical of animal caches (5-25 mm) produced at least five times more seedlings than did seeds on the forest floor. The four species of rodents differed in the quality of dispersal they provided. Small, shallow caches made by deer mice most resembled seeds dispersed by abiotic processes, whereas many of the large caches made by ground squirrels were buried too deeply for successful emergence of seedlings. Chipmunks made the greatest number of caches within the range of depths and microsites favorable for establishment of pine seedlings. Directed dispersal is an important element of the population dynamics of Jeffrey pine, a dominant tree species in the eastern Sierra Nevada. Quantifying the occurrence and dynamics of directed dispersal in this and other cases will contribute to better understanding of mutualistic coevolution of plants and animals and to more effective management of ecosystems in which directed dispersal is a keystone process.

Seed predation by rodents results in directed dispersal of viable seed fragments of an endangered desert shrub

“…The mechanism proposed to explain the persistence of these species is that seed dispersal by scatter-hoarding rodents may have substituted the services provided by the original dispersers (Guimarães et al 2008). Scatter-hoarding rodents bury intact seeds in shallow caches, and those seeds that are not retrieved by the animals, are protected from invertebrate predation, and can germinate and establish (Briggs et al 2009. Thus, seed dispersal by scatter-hoarding rodents results from forgotten cached or re-cached intact seeds.…”

Patterns of seed dispersal syndromes on serpentine soils: examining the roles of habitat patchiness, soil infertility and correlated functional traits

“…Thus, species that are restricted to highly patchy habitats may require dispersal methods that are especially efficient at dispersing to those patches (directed dispersal). Birds and mammals have been found to preferentially disperse seeds to favourable microsites for germination (Wenny and Levey 1998;Dean and Milton 2000;Purves and Dushoff 2005;Briggs et al 2009). Therefore, in patchy habitats directed vertebrate dispersal may be expected to be more common, whilst the frequency of less directed dispersal syndromes, such as wind dispersal, may be lower (Howe and Smallwood 1982;Wenny 2001;Spiegel and Nathan 2010).…”

Pine seed removal in fragments of three temperate plant communities

“…The removal is motivated by seed traits such as the nutritional quality, size and the presence of secondary compounds that vary among a large number of plants (Shimada & Saitoh 2003, Hulme & Kollmann 2005, Wang et al 2012, including pines (Lobo et al 2009), and intervene in their evolution process (Hulme & Benkman 2002). In temperate forests, rodents exert a significant impact on the establishment and permanence of different pine species (Briggs et al 2009). Pines carry out their seed dispersal processes during the dry season March-June (Perry 2009, Cortés-Flores et al 2013) and the phenological overlap among them occur (Hulme & Kollmann 2005, Martínez & González-Taboada 2009, while in subalpine grassland the seed availability is almost all year (Peterson & Rieseberg 1987, Herrera-Arrieta 2007.…”