Hoarding of acorns by granivorous mice and its role in the population processes of Pasania edulis (Makino) Makino

In order to evaluate the role of granivorous mice, Apodemus speciosus Temminck and Apodemus argenteus Temminck, in the regeneration of Pasania edulis (Makino) Makino, an evergreen tree, we conducted field studies examining acorn crops, the population dynamics and hoarding behavior of mice and pre- and postdispersal acorn predation in an evergreen broad-leaved forest dominated by P.edulis in Kagoshima, southern Japan. The study was conducted from 1994 to 2000. Apodemus mice selected sound acorns and hoarded them in the soil after transporting them for distances ranging from 5.4 to 19.9m. This behavior appeared to be beneficial to the establishment of seedlings of P.edulis. However, the positive effects were negated by a high rate of recovery of the acorns hoarded by the mice. A life-table analysis of five cohorts of P.edulis indicated that postdispersal predation of acorns by Apodemus mice was a major contributor to annual variation in the number of new seedlings. A considerable number of acorns germinated only in years with a good acorn crop and a low level of resident mice. These results suggest that Apodemus mice are serious acorn predators rather than important dispersers. After germination, acorns were attacked by the acorn borer at a high rate. From these results, we can conclude that acorn production probably makes a smaller contribution to the regeneration of P.edulis than coppice shoot production at the study site.     

Guild structures of seed insects in relation to acorn development in two oak species

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect-infested acorns. In Q. variabilis, two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata, there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild (M. ursulus, C. sikkimensis, Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.     

A record of acorn eating by sika deer in western Japan

The rumen contents of 14 sika deer (Cervus nippon) collected in November 1996 in Yamaguchi Prefecture, the western end of Honshu, Japan, were analyzed by the point-frame method. The contents were composed of high-quality foods like deciduous and evergreen browse and acorns. The composition, which consisted of a significant amount of acorns (27.8 ± 22.5%, mean ± SD), was in contrast to that of northern sika deer populations which exclusively eat graminoid leaves including dwarf bamboos. This is the first record of acorns being a major contributor to diet for wild sika deer. By the point-frame method, acorns were underestimated, and the weight contribution was much greater.     

Extremely long-distance seed dispersal by an overfished Amazonian frugivore

Throughout Amazonia, overfishing has decimated populations of fruit-eating fishes, especially the large-bodied characid, Colossoma macropomum. During lengthy annual floods, frugivorous fishes enter vast Amazonian floodplains, consume massive quantities of fallen fruits and egest viable seeds. Many tree and liana species are clearly specialized for icthyochory, and seed dispersal by fish may be crucial for the maintenance of Amazonian wetland forests. Unlike frugivorous mammals and birds, little is known about seed dispersal effectiveness of fishes. Extensive mobility of frugivorous fish could result in extremely effective, multi-directional, long-distance seed dispersal. Over three annual flood seasons, we tracked fine-scale movement patterns and habitat use of wild Colossoma, and seed retention in the digestive tracts of captive individuals. Our mechanistic model predicts that Colossoma disperses seeds extremely long distances to favourable habitats. Modelled mean dispersal distances of 337-552 m and maximum of 5495 m are among the longest ever reported. At least 5 per cent of seeds are predicted to disperse 1700-2110 m, farther than dispersal by almost all other frugivores reported in the literature. Additionally, seed dispersal distances increased with fish size, but overfishing has biased Colossoma populations to smaller individuals. Thus, overexploitation probably disrupts an ancient coevolutionary relationship between Colossoma and Amazonian plants.     

False phylogenies on wood mice due to cryptic cytochrome-b pseudogene

The phylogeny and phylogeography of the Old World wood mice (subgenus Sylvaemus, genus Apodemus, Muridae) are well-documented. Nevertheless, the distributions of species, such as A. fulvipectus and A. ponticus remain dubious, as well as their phylogenetic relationships with A. sylvaticus. We analysed samples of Apodemus spp. across Europe using the mitochondrial cytochrome-b gene (cyt-b) and compared the DNA and amino-acid compositions of previously published sequences. The main result stemming from this study is the presence of a well-differentiated lineage of Sylvaemus including samples of various species (A. sylvaticus, A. fulvipectus, A. ponticus) from distant locations, which were revealed to be nuclear copies of the mitochondrial cyt-b. The presence of this cryptic pseudogene in published sequences is supported by different pathways. This has led to important errors in previous molecular trees and hence to partial misinterpretations in the phylogeny of Apodemus.     

Quantitative analysis of acorn transportation by rodents using magnetic locator

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.     

Observations of predator-prey interaction on dispersal of an oligochaete prey,Limnodrilus hoffmeisteri

Clumped patches of the oligochaete, Limnodrilus hoffmeisteri, were subjected to predation by the leech, Erpobdella punctata to determine how the dispersion pattern might change. Two separate experiments showed that worms left the patch in 39% and 48% greater numbers when the leech predator was present. This suggests that L. hoffmeisteri uses a antipredatory strategy of dispersal rather than clumping.     

Comparative thermoregulatory adaptations of field mice of the genus Apodemus to habitat challenges

Thermoregulatory abilities, which may play a role in physiological adaptations, were compared between two field mouse species (Apodemus mystacinus and A. hermonensis) from Mount Hermon. While A. hermonensis is common at altitudes above 2100 m, A. mystacinus is common at 1650 m. The following variables were compared in mice acclimated to an ambient temperature of 24°C with a photoperiod of 12L:12D, body temperature during exposure to 4°C for 6 h, O₂ consumption and body temperature at various ambient temperature, non-shivering thermogenesis measured as a response to a noradrenaline injection, and the daily rhythm of body temperature. Both species could regulate their body temperature at ambient temperatures between 6 and 34°C. The thermoneutral zone for A. mystacinus lies between 28 and 32°C, while for A. hermonensis a thermoneutral point is noted at 28°C. Both species increased O₂ consumption and body temperature as a response to noradrenalin. However, maximal VO ₂ consumption as an response to noradrenaline and non-shivering thermogenesis capacity were higher in A. mystacinus, even though A. hermonensis is half the size of A. mystacinus. The body temperature rhythm in A. hermonensis has a clear daily pattern, while A. mystacinus can be considered arhythmic. The results suggest that A. hermonensis is adapted to its environment by an increase in resting metabolic rate but also depends on behavioural thermoregulation. A. mystacinus depends more on an increased non-shivering thermogenesis capacity.Abbreviations C thermal conductance - NA noradrenaline - NST non-shivering thermogenesis - OTC overall thermal conductance - RMR resting metabolic rate - STPD standard temperature and pressure dry - T _a ambient temperature - T _b body temperature - I _b Min minimal T _b , measured before NA iniection - T _b NA maximal - T _b as a response to NA injection - T _lc lower critical point - TNP thermoneutral point - TNZ thermoneutral zone - VO₂ O₂ consumption - VO₂ Min minimal VO₂ measured before NA injection - VO₂NA maximal VO₂, as a response to NA injection     

Seed dispersal of the Korean pine,Pinus koraiensis,by the red squirrel,Sciurus vulgaris

Seed hoarding behavior of the red squirrel,Sciurus vulgaris, was studied in relation to the amount of dispersed seeds of the Korean pine,Pinus koraiensis, and the distribution of its seedlings. After removing a cone from a tree, squirrels sat on the ground and ripped off its cone scales before transporting it. A mean of 3.2 seeds were scatter-hoarded per hole. Of 7.7×10⁴ mature seeds produced in a 0.21 ha planted Korean pine forest, 22% were estimated to be directly eaten by four squirrels, 9% were hoarded by them in the pine forest and 65% were cached outside the forest. Squirrels rediscovered hoarded seeds frequently, until the ground was covered with snow, during the period from snow fall until seed germination the next spring, few hoarded seeds were utilized. Korean pine seedlings were found up to 600 m from their mother trees. Scatter-hoarding by squirrels extensively contributes to seed dispersal to places suitable for the regeneration of the Korean pine. The large size of the cone, the absciss-layer at the cone penduncle, the infrequent dehiscence of cone scales, the large and wingless seeds, and the thick seed-coats have probably all been specialized to facilitate utilization by GenusSciurus.     

Relative importance of ballistic and ant dispersal in two diplochorous Viola species (Violaceae)

Viola is one of the diplochorous plant genera that disperse their seeds in two ways, ballistic and ant dispersal. We compared the seed dispersal of two major Viola species of northern Japan, V. selkirkii and V. verecunda. The mean weight of seed was less in V. verecunda (0.42 ± SD 0.03 mg) than in V. selkirkii (0.61 ± 0.12 mg). The elaiosome of V. selkirkii (0.02 ± 0.004 mg) was larger than in of V. verecunda (0.006 ± 0.0004 mg), whereas the lipid component of elaiosome was not remarkably different between the two species. In ballistic dispersal, the mean dispersal distance was 56.0 ± 17.5 cm in V. verecunda but only 38.3 ± 5.1 cm in V. selkirkii. In ant dispersal, the mean dispersal distance was 28.1 ± 24.9 cm in V. selkirkii and 36.1 ± 33.7 cm in V. verecunda; however, the seed removal frequency of V. selkirkii (15.5%) was much higher than that of V. verecunda (3.0%). These results suggest that V. selkirkii is more dependent on ant dispersal while V. verecunda is more dependent on ballistic dispersal. The effect of seed predation was very serious in both species. In the quadrat census, 99.0% of V. selkirkii seeds and 99.1% of V. verecunda seeds were damaged by ground beetles, spiders, ticks, and others which frequently devoured diaspores. An experiment with V. verecunda seeds demonstrated that the overdispersion of seeds on the forest floor enhanced the frequency of removal by ants and reduced seed damage by predators.     

Local dispersal of maleHelicoverpa zea

Local dispersal ofHelicoverpa zea (Boddie) (Lepidoptera: Noctuidae) males as they emerged following the F₁ and F₂ generations in dent corn was examined in a 4 km diam. area in South Carolina, USA. Males were marked at artificial nectar feeding stations using RbCl, and recovered in traps baited with a synthetic pheromone. Effects of nocturnal boundary layer winds, crop pattern at the pheromone traps, and crop pattern between the marking area and pheromone traps were examined. Local movement of captured male moths was predominantly downwind in both flights in both years of the study. Crop pattern at the traps had no effect on capture of marked moths. During some flights, flowering crops between the marking area and traps had a negative effect on the number of marked moths captured.     

A Phylogenetic View on Species Radiation in Apodemus Inferred from Variation of Nuclear and Mitochondrial Genes

Species of field mice (genus Apodemus) are the most common rodents inhabiting woodlands and forests of the Palaearctic region. We examined the cytochrome b (cyt b) gene in mitochondrial DNA (1140 bp) and the interphotoreceptor retinoid binding protein (IRBP) gene in nuclear DNA (1152 bp) in nine species of Apodemus. Based on the genetic variation, the nine species were grouped into four lineages: (1) Agrarius group (A. agrarius, A. peninsulae, A. semotus, and A. speciosus), (2) Argenteus group (A. argenteus), (3) Gurkha group (A. gurkha), and (4) Sylvaticus group (A. alpicola, A. flavicollis, and A. sylvaticus). It was shown that these four lineages diverged within a short period of evolutionary time, suggestive of a radiation event. Soon after the radiation, the Agrarius group was likely to have differentiated again into the species lineages simultaneously. In contrast, the European clade, the Sylvaticus group, radiated rather recently. The relative ratio of the extent of sequence divergence among the four main lineages to that among the members of the subfamily Murinae (including Mus and Rattus) was calculated to be 72.4% in the cyt b gene with transversional substitutions, and 58.5% in the IRBP gene with all substitutions, using the Kimura two-parameter method. The value for the three European lineages was 27.6% in the cyt b gene and 12.3% in the IRBP gene. These results may have a correlation with the notion that deciduous broadleaf forests remained in Central East Asia through the late Tertiary to the present, while those in Europe to a large extent had disappeared by the Pliocene.     

A Biogeographic View of Apodemus in Asia and Europe Inferred From Nuclear and Mitochondrial Gene Sequences

Sequences of the mitochondrial cyt b gene and nuclear IRBP, RAGI, I7, and vWF genes were used to assess the evolutionary history of major lineages of Apodemus, in particular to better understand dispersal between Asia and Europe. Our data show eight extant lineages of Late Tertiary origin: Apodemus agrarius, A. semotus, A. peninsulae, A. speciosus, A. argenteus, A. gurkha, A. mystacinus, and A. sylvaticus. Monophyly of two European lineages (A. mystacinus and A. sylvaticus) and four Asian lineages (A. agrarius, A. semotus, A. peninsulae, and A. speciosus) was confirmed with high bootstrap support. Together with literature data, the available molecular data depict three crucial evolutionary events: (1) initial wide dispersal and subsequent radiation around 6 million years ago, (2) region-specific radiations in Europe and southern China around 2 million years ago, and (3) westward dispersal of A. agrarius to Europe in the Late Quaternary.     

Germination and water dispersal of seeds from a threatened plant species Penthorum chinense

To conserve a threatened plant species (Penthorum chinense Pursh) in Japan, seed germination responses to pretreatment (imbibition and/or chilled), temperature and light, and seed dispersal by water were examined. The seeds collected from abandoned paddy fields in a warm temperate region, central Japan, germinated in light (14 h photoperiod; light 22°C, dark 21°C) after a moist-chilled treatment. After this pretreatment, the seeds germinated well at 10–25°C (optimum temperature 15°C), but did not germinate in darkness even at the optimum temperature. Most of the seeds floated on distilled water, but 20–60% of the seeds that were collected from several populations sank in distilled water, indicating dimorphism in seed dispersal by water. The floating and sunken seeds did not show significant differences in weight and germination rate within a population. The addition of a surface-active agent in distilled water submerged the seeds, indicating that the buoyancy of the seeds is attributable to an oil coating on the seed surface that enhances the interfacial tension on the seeds. Three times the number of seeds sank in river water collected from a rural area than in distilled water. A greater number of seeds also sank in water that had increasing concentrations of linear alkylbenzenesulfonate, which is a major component of synthetic detergents. This suggests that the water dispersal of this species is suppressed by surface-active agents, including detergents, in river water.     

Adult philopatry and dispersal in the field vol Microtus agrestis

Summary Using mark-recapture data, we related the movements of adult field voles to population density, sex ratio and population growth. Dispersal movements (defined as distances larger than 1 home range diameter) were few in both sexes; 4 out of 197 (2.0%) in males and 8 of 316 (2.5%) in females. The distance moved between sequential trapping periods was similar for males and females; the mean being 10.2 m and 9.0 m respectively. Both males and females moved larger distances during the breeding season than during the nonbreeding period. The distance moved between sequential trapping periods showed a strong negative relation to density, i.e. both sexes moved shorter distances at higher densities, but there were no differences between periods of increasing and declining population densities. These results contradict the dispersal predictions of all major hypotheses proposed to explain population fluctuations in small mammals. The dispersal patterns fit a geometric distribution, suggesting that competition is the primary factor determining the dispersal characteristics of this population.     

Interactions between fire,mycophagous mammals,and dispersal of ectromycorrhizal fungi in Eucalyptus forests

Several species of marsupials in Eucalyptus forests in Australia feed predominantly on the sporocarps of hypogeous fungi. This feeding is apparently beneficial to the fungi as it results in dispersal of spores. As these fungi are in almost all cases ectomycorrhiza-forming species, mycophagy by mammals may play an important role in the maintenance of mycorrhizal symbiosis in Eucalyptus forests. Fire is frequent and a dominant ecological factor in these forests, and this study tested the hypothesis that fire triggers both increased sporocarp production by some hypogeous ectomycorrhizal fungi associated with eucalypts, and increased mycophagy by mammals. Three experimental burns were set in E. tenuiramus forest in southeastern Tasmania. Digging activity (which reflects feeding on hypogeous fungi) by a mycophagous marsupial, the Tasmanian bettong Bettongia gaimardi, increased up to ten-fold after fire, with a peak about 1 month post-fire. This was associated with a similar pattern of increase in sporocarp production, which was due to species in the family Mesophelliaceae (especially Castoreum tasmanicum and Mesophellia spp.). This family appears to have radiated in association with eucalypts and has an exclusively Australasian distribution, unlike many of the other ectomycorrhizal fungi collected in this study which are cosmopolitan and have broad host ranges. No B. gaimardi were killed by fire, and there was no increase in mortality following fire. Population density increased after fire as a result of immigration of adult males. However, body condition and fecundity of individual B. gaimardi were maintained at pre-fire levels. This suggests that the availability of energy to B. gaimardi increased as a result of fire, and the fact that the contribution of fungus to the diet of B. gaimardi was high on burnt relative to control sites suggests further that this increase in energy availability was provided by hypogeous fungi. Effects of fire on hypogeous fungi and B. gaimardi were short-lived; all measured variables returned to control values about 4 months after fire. The capacity of B. gaimardi to survive fire and to harvest the increased sporocarp production triggered by fire provides a mechanism for the rapid dispersal of spores after fire. This should result in the establishment of ectomycorrhizae very early in post-fire succession. Because only some species of ectomycorrhizal fungi fruited in response to burning, fire probably has a strong influence on community structure among ectomycorrhizal fungi.     

Sex-biased dispersal in eastern chipmunks, Tamias striatus

I investigated the effect of male mate competition and inbreeding avoidance on natal dispersal of chipmunks by longitudinally monitoring known individuals from 1986 to 1990. Natal males exhibited greater absolute and effective dispersal distances but dispersed at the same proportion as natal females. Recruitment of juvenile males was negatively affected by density of resident males, but there was no evidence of local mate competition among male kin. Analysis of the spatial distribution of neighbors showed that natal males settled farther from their mothers than did their female siblings and farther than unrelated juvenile males. In addition, mothers apparently tolerated daughters as close neighbors and occasionally shared den sites with grandprogeny. Sexually mature males were never neighbors of their mothers and were never observed at maternal mating bouts. Males may disperse to improve reproductive opportunities by avoiding competition with resident males, and by increasing access to unrelated females. Maternal tolerance of daughters but not sons may result in the close affiliation between mothers and daughters, and indirectly contribute to dispersal of natal males. Hence male-biased dispersal could be a consequence of mate competition and maternal avoidance of incestuous matings. This revised version was published online in July 2006 with corrections to the Cover Date.     

A mark-capture study of Helicoverpa armigera dispersal from pigeonpea in southern India

A method of field application of strontium chloride (SrCl₂) and the assessment of local dispersal of marked Helicoverpa armigera moths in a mark-capture experiment in southern India are described. A 1.7 ha field of pigeonpea sustaining a population of approximately 400,000 larvae was treated with a single application of SrCl₂ plus surfactant at 10 kg/ha, using a motorised high volume sprayer. An estimated 50,400 moths emerging over a 20 day period were unequivocally marked with Sr at a marking efficiency of 55%. Catches of moths in an array of 14 battery operated light traps and 29 pheromone traps, up to 3.5 km distant were analysed by atomic absorption spectrophotometry. Low recaptures of marked moths (7%) in the treated field suggested the rapid exodus of emergent moths, even while the crop remained attractive, and their dilution or replacement by immigrants. The distribution of marked moths in lights and pheromone traps is consistent with a predominantly downwind dispersal close to the ground during the early part of the night and more random movement later on.

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Résumé L'exposé concerne une méthode de traitement en champ des chenilles par le chlorure de strontium (SrCl₂) et de la mesure de la dispersion locale des papillons marqués de H. armigera Hübner (Lépido.: Noctuida) dans le sud de l'Inde. Un champ de 1,7 ha de C. cajan (cultivar ICPL138) qui hébergeait une population d'environ 400 000 chenilles a été traité en une seule fois avec un pulvérisateur motorisé de forte capacité à raison de 10 kg/ha de SrCl₂ additionné de 0,1% Triton X-100 comme surfactant. 55% des 50 400 papillons émergeant sur une période de 20 jours étaient sans ambiguïté marqués au strontium. Les papillons, capturés dans des rangées de 14 pièges lumineux et 33 pièges à phéromones attractifs jusqu'à 3,5 km, ont été examinés au spectrophotomètre à absorption atomique. Les faibles recapturés (7%) dans le champ traité suggèrent un rapide exode des mouches ayant émergé ou leur remplacement par des immigrants. Les captures révèlent, au début de la nuit, une dispersion majoritairement dans le sens du vent, près du sol et, plus tard dans la nuit, un mouvement plus au hasard.