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.
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ABSTRACT: We examined the effects of soil water content (SWC) on scatter-hoarding decisions of Siberian chipmunks, Tamias sibiricus, when caching acorns of Quercus mongolica. We hypothesized that higher SWC, which favours germination in this and similar oaks, would also be favoured for caching and cache recovery in this rodent. We conducted three sets of experiments: one in small arenas, a second in larger seminatural enclosures, and a third in the field with free-ranging chipmunks in a temperate forest of the Xiaoxing’anling Mountains of northeast China. Siberian chipmunks selectively cached acorns in soil of higher SWC and recovered more observer-made artificial caches where SWC was higher. We argue the selective scatter hoarding in soil of higher SWC represents a form of directed dispersal that may be relatively common in other systems, especially where SWC is unevenly distributed, and further suggest that this may represent an important rodenteseed interaction that varies with climate.Animal Behaviour. 10/2013;
Conference Paper: Deer Mice (Peromyscus spp.) Biology, Damage and Management: A Review[Show abstract] [Hide abstract]
ABSTRACT: AbstrAct: The deer mouse is the most widely distributed and abundant small mammal in North America. They use a wide array of habitats, are very adaptable, and have a high reproductive potential. They play a number of roles in ecosystems, but can cause damage to orchards, forests, agriculture crops, and rangelands primarily through seed and newly-emerged seedling consumption. They also cause damage similar to house mice when they occupy buildings or other structures. Deer mice are important components in disease transmission especially of hantaviruses and Lyme disease. Damage reduction methods generally involve lethal control to reduce numbers using rodenticides and traps. Improvements in control methods are needed, especially in some agricultural crop types.Vertebrate Pest Conference, University of California, Davis; 01/2012
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ABSTRACT: The water-impermeable seed coat of ‘hard’ seeds is commonly considered a dormancy trait. Seed smell is, however, strongly correlated with seed water content, and hard seeds are therefore olfactionally cryptic to foraging rodents. This is the rationale for the crypsis hypothesis, which proposes that the primary functions of hard seeds are to reduce seed predation and promote rodent seed dispersal.We use a mechanistic model to describe seed survival success of plants with different dimorphic soft and hard seed strategies. The model is based on established empirical ecological relationships of moisture requirements for germination and benefits of seed dispersal, and on experimentally demonstrated relationships between seed volatile emission, predation and predator escape.We find that water impermeable seed coats can reduce seed predation under a wide range of natural humidity conditions. Plants with rodent dispersed seeds benefit from producing dimorphic soft and hard seeds at ratios where the anti-predator advantages of hard seeds are balanced by the dispersal benefits gained by producing some soft seeds.The seed pathway predicted from the model is similar to those of experimental seed tracking studies. This validates the relevance and realism of the ecological mechanisms and relationships incorporated in the model.Synthesis: Rodent seed predators are often also important seed dispersers and have the potential to exert strong selective pressures on seeds to evolve methods of avoiding detection, and hard seeds seem to do just that. This work suggests that water-impermeable hard seeds may evolve in the absence of a dormancy function and that optimal seed survival in many environments with rodent seed predators are obtained by plants having a dimorphic soft and hard seed strategy.This article is protected by copyright. All rights reserved.Journal of Ecology 08/2014; · 5.69 Impact Factor