Natural seed deposition patterns and their effects on post-dispersal seed fate are critical to tropical tree recruitment. The major dispersal agents of the large-seeded tree Canarium euphyllum in Khao Yai National Park, Thailand, are large frugivorous birds such as hornbills, which generated spatially heterogeneous seed deposition patterns because they regurgitated seeds at perching trees and conspecific and heterospecific feeding trees. We investigated the fate of seeds dispersed in this manner using seed removal experiments and automatic camera trapping. Seeds placed experimentally around conspecific feeding trees had higher removal rates than seeds placed elsewhere. These effects were likely mediated by two seed-eating rodents, the Indochinese ground squirrel (Menetes berdmorei) and the giant long-tailed rat (Leopoldamys sabanus). Consequently, the spatial patterns generated by hornbills had consequences for post-dispersal seed fates, particularly whether or not the seeds were removed by rodents. Primary dispersal by hornbills does alter seed fate by altering the probability of rodent–seed interaction, but the ultimate impact of dispersal by hornbills will depend on how important rodent scatterhoarding is to seed germination and seedlings. Given that major seed dispersers of C. euphyllum are now absent or rare in degraded forests in tropical Asia, it is becoming increasingly important to understand the roles of scatterhoarding rodents in these altered habitats in this region.

Mast seeding is a common phenomenon, and has important effects on seed dispersal and hoarding by animals. At population level, the predator satiation hypothesis proposes that the satiating effect of a large amount of seeds on a relatively small number of predators benefits seed survival in mast-seeding years. However, the effect of mast seeding on the scatter-hoarding of rodents at the individual level is largely unknown. In this study, we investigated the effects of seed abundance (by simulating mast seeding and non-mast seeding) on the removal, consumption and scatter-hoarding of seeds of Camellia oleifera (Theaceae) by Edward’s rat Leopoldamys edwardsi (Muridae) in seminatural enclosures in southwest China. We wanted to test the masting-enhanced hoarding hypothesis, which suggests that rodents tend to scatter-hoard more seeds in mast-seeding years in order to occupy more food resources. Our results indicate that L. edwardsi tended to disperse and scatter-hoard more seeds of C. oleifera per night with increasing seed abundance, and to eat less seeds per night when there was a high level of seed abundance in the enclosure experiments. These results support the masting-enhanced hoarding hypothesis. This capacity of rodents may be an evolutionary adaptation to the mast-seeding phenomenon. Our results suggest that mast seeding benefits forest regeneration not only through the predator satiation effect at the population level, but also through increased hoarding by animals at the individual level.

A variety of nut-producing plants have mutualistic seed-dispersal interactions with animals (rodents and corvids) that scatter hoard their nuts in the soil. The goals of this review are to summarize the widespread horticultural, botanical, and ecological literature pertaining to nut dispersal inJuglans, Carya, Quercus, Fagus, Castanae, Castanopsis, Lithocarpus, Corylus, Aesculus, andPrunus; to examine the evolutionary histories of these mutualistic interactions; and to identify the traits of nut-bearing plants and nut-dispersing rodents and jays that influence the success of the mutualism. These interactions appear to have originated as early as the Paleocene, about 60 million years ago. Most nuts appear to have evolved from ancestors with wind-dispersed seeds, but the ancestral form of dispersal in almonds (Prunus spp.) was by frugivorous animals that ingested fruit.

Nut-producing species have evolved a number of traits that facilitate nut dispersal by certain rodents and corvids while serving to exclude other animals that act as parasites of the mutualism. Nuts are nutritious food sources, often with high levels of lipids or proteins and a caloric value ranging from 5.7 to 153.5 kJ per propagule, 10–1000 times greater than most wind-dispersed seeds. These traits make nuts highly attractive food items for dispersers and nut predators. The course of nut development tends to reduce losses of nuts to insects, microbes, and nondispersing animals, but despite these measures predispersal and postdispersal nut mortality is generally high. Chemical defenses (e.g., tannins) in the cotyledons or the husk surrounding the nut discourage some nut predators. Masting of nuts (periodic, synchronous production of large nut crops) appears to reduce losses to insects and to increase the number of nuts dispersed by animals, and it may increase cross-pollination. Scatter hoarding by rodents and corvids removes nuts from other sources of nut predation, moves nuts away from source trees where density-dependent mortality is high (sometimes to habitats or microhabitats that favor seedling establishment), and buries nuts in the soil (which reduces rates of predation and helps to maintain nut viability). The large nutrient reserves of nuts not only attract animal dispersers but also permit seedlings to establish a large photosynthetic surface or extensive root system, making them especially competitive in low-light environments (e.g., deciduous forest) and semi-arid environments (e.g., dry mountains, Mediterranean climates). The most important postestablishment causes of seedling failure are drought, insufficient light, browsing by vertebrate herbivores, and competition with forbs and grasses. Because of the nutritional qualities of nuts and the synchronous production of large nut crops by a species throughout a region, nut trees can have pervasive impacts on other members of ecological communities. Nut-bearing trees have undergone dramatic changes in distribution during the last 16,000 years, following the glacial retreat from northern North America and Europe, and the current dispersers of nuts (i.e., squirrels, jays, and their relatives) appear to have been responsible for these movements.

Seed predation and seed dispersal are key factors that determine plant recruitment. In this study, we compared the role of small (<200 g) and ‘large’ mammals as predators of Araucariaangustifolia (Araucariaceae) seeds in the Brazilian Araucaria Forest. We also investigated the effect of deposition site, namely open grassland, forest edge or forest interior (>50 m from the edge) on seed-removal rates. We conducted field experiments on seed removal in July 2003 and 2004. We compared the habitat types using two exclusion treatments: semi-permeable exclosure (exclusive access of small rodents) and an open control (access of all mammal groups). We considered proportion of seeds removed after 15 days to investigate the effect of year, habitat type, and exclusion treatment on seed removal by using three-factor permutational ANOVA. We also evaluated seed fate and seed consumers by using spool-and-line devices attached to seeds and camera trapping. The results showed that seed removal differed significantly between years and among habitat types, but not between exclusion treatments. Removal rates were higher in 2004 than in 2003 and also were significantly lower in the open field when compared with both forested types (edge or interior) in both years. There was also a significant interaction between ‘year’ and ‘habitat’ which was driven by an increase in 2004 removal rates in the open field compared to the previous year. Our combination of manipulative experiments, camera-trapping survey, and spool-and-line seed tracking demonstrated that small rodents are responsible for the majority of seed removal of A. angustifolia in the study area. The low removal rates in open habitats indicate that they could serve as safe sites for A. angustifolia seeds. The results also suggested a potential role of small rodents as seed dispersers (about 4% of removed seeds were not consumed). The knowledge of how fragmentation affects pattern of seed predation and establishment of A. angustifolia through changes in abundance of different-sized mammals is essential for the conservation of the Brazilian Araucaria Forest and its most characteristic species.

Seeds of the Japanese walnut, Juglans ailanthifolia, are usually scatter-hoarded by two rodent species, the Japanese squirrel Sciurus lis and the field mouse Apodemus speciosus, but only by the latter in several areas where S. lis is absent. We examined seed-size-mediated interactions of these three species across a wide geographic range. Field tracking of walnuts with miniature radio-transmitters revealed that squirrels hoarded larger seeds more frequently and at greater distances than smaller seeds. In contrast, mice hoarded smaller seeds more frequently and transported them farther than larger seeds. These seed dispersers could affect the evolution of seed size because seeds hoarded at sites farther from source trees are known to survive better until germination and as seedlings. We expect that larger seeds may be advantageous in regeneration if the main seed dispersers are squirrels, whereas smaller seeds may be advantageous if mice are the dominant dispersers. These predictions were supported by the fact that seed size was smaller on islands inhabited only by mice and at the edge of the squirrel distribution, compared to areas where mice and squirrels are both common.

Transported distance and mortality of acorns scattered by rodents were investigated with magnets inserted into acorns (40 of Quercus serrata and 20 of Quercus acutissima) and a magnetic locator in a natural forest stand. All the treated acorns were transported, and 60% of them were discovered again with a magnetic locator from autumn to the next spring. Most transported acorns suffered predation within one month after the start of the experiment. Several acorns were rehoarded at least two or three times. Average transported distance of scattered acorns was 22.1±8.9 m (max=38.5 m) and the survival rate was 3.0%. The magnet method is one of the most effective methods for tracking acorns through the winter.

This is the first study to investigate whether scatter-hoarding behavior, a conditional mutualism, can be disrupted by forest fragmentation. We examined whether acouchies (Myoprocta acouchy, Rodentia) and agoutis (Dasyprocta leporina, Rodentia) changed scatter-hoarding behavior toward seeds of Astrocaryum aculeatum (Arecaceae) as a consequence of a decrease in forest-patch area. Our study was conducted at the 30-year-old Biological Dynamics of Forest Fragments Project, in central Amazon, Brazil. We tested whether forest size affected the number of Astrocaryum seeds removed and scatter-hoarded (and likely dispersed) by acouchies and agoutis, as well as the distance that the seeds were hoarded. The study extended over three seasons: the peak of the rainy season (March–April), the transition between the rainy and the dry season (May–June), and the peak of the dry season (August–September). Our results revealed that the number of seeds removed was larger in smaller fragments, but that the percentage of seeds hoarded was much lower, and seeds eaten much higher, in 1-ha fragments. Moreover, fewer seeds were taken longer distances in fragments than in the continuous forest. Site affected the number of seeds removed and season affected the percentage of seeds hoarded: more seeds were removed from stations in one site than in two others, and hoarding was more important in April and September than in June. Our study reveals that scatter-hoarding behavior is affected by forest fragmentation, with the most important disruption in very small fragments. Fragmentation converts a largely mutualistic relationship between the rodents and this palm in large forest patches into seed predation in small fragments.

The effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin-binding salivary proteins and tannase-producing bacteria, whereas such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns between the three species may be due to differences in their physiological tolerance to tannins.

Ecological experiments often accumulate data by carrying out many replicate trials, each containing a limited number of observations, which are then pooled and analysed in the search for a pattern. Replicating trials may be the only way to obtain sufficient data, yet lumping disregards the possibility of differences in experimental conditions influencing the overall pattern. This paper discusses how to deal with this dilemma in model selection. Three methods of model selection are introduced: likelihood-ratio testing, the Akaike Information Criterion (AIC) with or without small-sample correction and the Bayesian Information Criterion (BIC). Subsequently, we apply the AICc method to an example on size-dependent seed dispersal by scatterhoarding rodents.

The example involves binary data on the selection and removal of Carapa procera (Meliaceae) seeds by scatterhoarding rodents in replicate trials during years of different ambient seed abundance. The question is whether there is an optimum size for seeds to be removed and dispersed by the rodents. We fit five models, varying from no effect of seed mass to an optimum seed mass. We show that lumping the data produces the expected pattern but gives a poor fit compared to analyses in which grouping levels are taken into account. Three methods of grouping were used: per group a fixed parameter value; per group a randomly drawn parameter value; and some parameters fixed per group and others constant for all groups. Model fitting with some parameters fixed for all groups, and others depending on the trial give the best fit. The general pattern is however rather weak.

We explore how far models must differ in order to be able to discriminate between them, using the minimum Kullback-Leibler distance as a measure for the difference. We then show by simulation that the differences are too small to discriminate at all between the five models tested at the level of replicate trials.

We recommend a combined approach in which the level of lumping trials is chosen by the amount of variation explained in comparison to an analysis at the trial level. It is shown that combining data from different trials only leads to an increase in the probability of identifying the correct model with the AIC criterion if the distance of all simpler (=less extended models) to the simulated model is sufficiently large in each trial. Otherwise, increasing the number of replicate trials might even lead to a decrease in the power of the AIC.