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.     

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.     

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.     

荒漠孑遗植物裸果木种子时空扩散特性

裸果木(Gymnocarpos przewalskii)是亚洲中部荒漠区少有的第三纪孑遗物种,由于气候变化及人为干扰,其自然种群分布范围不断缩小。种子扩散作为植物生活史过程中的重要阶段,不仅对物种生存及其多样性至关重要,还影响物种分布范围和局部丰度。2015年和2016年分别在新疆哈密地区,采用布设种子收集器的方法,对其自然种群种子扩散的时空动态进行了定点连续观测。结果表明:该物种于当年6月上旬开始扩散,2015年略早于2016年。每年种子扩散持续时间约两个月,扩散趋势为单峰曲线,且呈集中大量扩散的模式,扩散高峰期与当年初次月降水高峰期吻合;在顺风的正南和东南方向上,种子扩散密度大且距离远;种子扩散主要集中在母株冠幅下,随着距母株距离的增加,种子扩散密度减少,二者间存在极显著的负相关性(P0.01),由于裸果木枝条繁多,对风力强度起到了一定的阻碍作用,可能是造成种子集中扩散在母株下的原因。裸果木种子扩散受外界环境(降水、风向)和自身因素等方面的影响,当种子在大量降水前完成扩散,将有利于种子在适宜的微生境萌发,是对多风、干旱的恶劣生境的一种长期适应。     

The seed dimorphism of Spergularia marina in relation to dispersal by wind and water

Summary The seeds of the halophyte Spergularia marina differ both within and between individuals in that they either possess or lack a membranaceous border. This paper presents a morphological study of the length, weight and area of the seed types, and their dispersal characteristics under experimental conditions of wind and water dispersal. The winged seeds are shown to be larger both by length and by weight. Their rate of descent increases with wing loading. If the wing is lacking, however, the rate of descent increases with weight only. The distance of dispersal is equal for both seed types except at low wind speeds, when the winged seeds disperse farther. If the seed wing is removed, the excised seeds have shorter dispersal distances. When dispersed by water, a difference in the distance seeds are dispersed can only be detected in the presence of vegetation. The winged seeds are more frequently trapped in the vegetation as compared to the unwinged seeds. The hypothesis that the seed dimorphism is an adaptation for differential dispersal distances is discussed.     

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     

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.     

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.     

Geographic variation in walnut seed size correlates with hoarding behaviour of two rodent 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.     

云南拉沙山黑白仰鼻猴对种子传播潜力的评估

灵长类是森林生态系统中植物种子的主要传播者,有助于森林植被的更新,然而受研究方法的限制,灵长类种子传播潜力常被低估。为全面评估温带灵长类动物的种子传播潜力,采用直接观察法和粪便分析法评估珍稀濒危灵长类动物黑白仰鼻猴的种子传播潜力。于2018年11月—2019年10月采用直接观察法(瞬时扫描取样法)收集云岭省级自然保护区拉沙山黑白仰鼻猴的活动时间分配数据,获取每月取食果实的比例;同时每月收集黑白仰鼻猴的粪便,采用粪便分析法分拣猴粪中残留的植物种子,统计有完整种子残留的月份和粪便比例,应用这两种方法评估黑白仰鼻猴种子传播潜力及其差异。结果表明：直接观察法收集到黑白仰鼻猴取食果实的月份数为6个月(7—12月),月均取食果实的比例为(15.31±20.15)%,共取食13种果实;而粪便分析法发现黑白仰鼻猴粪粒内全年都有完整种子残留,粪便中月均完整种子残留比例(35.19±35.43)%,其中9月至第二年1月粪便中种子残留比例都大于50%,共取食18种果实;综合两种方法发现云南拉沙山黑白仰鼻猴共取食20种植物果实,具有较高的种子传播潜力。直接观察法可确定黑白仰鼻猴取食果实的物种数,而粪便分析法能...     

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.     

Individual-based modeling of the spread of pine wilt disease: vector beetle dispersal and the Allee effect

Pine wilt disease is caused by the pinewood nematode Bursaphelenchus xylophilus, which is vectored by the Japanese pine sawyer beetle Monochamus alternatus. Due to their mutualistic relationship, according to which the nematode weakens and makes trees available for beetle reproduction and the beetle in turn carries and transmits the nematode to healthy pine trees, this disease has resulted in severe damage to pine trees in Japan in recent decades. Previous studies have worked on modeling of population dynamics of the vector beetle and the pine tree to explore spatial expansion of the disease using an integro-difference equation with a dispersal kernel that describes beetle mobility over space. In this paper, I revisit these previous models but retaining individuality: by considering mechanistic interactions at the individual level it is shown that the Allee effect, an increasing per-capita growth rate as population abundance increases, can arise in the beetle dynamics because of the necessity for beetles to contact pine trees at least twice to reproduce successfully. The incubation period after which a tree contacted by a first beetle becomes ready for beetle oviposition by later beetles is crucial for the emergence of this Allee effect. It is also shown, however, that the strength of this Allee effect depends strongly on biological mechanistic properties, especially on beetle mobility. Realistic individual-based modeling highlights the importance of how spatial scales are dealt with in mathematical models. The link between mechanistic individual-based modeling and conventional analytical approaches is also discussed.     

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.     

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.     

Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

An evergreen oak species, Cyclobalanopsis multinervis, and a deciduous oak species, Quercus aliena var. acuteserrata were grown from acorns under two light levels (full sunlight and shade at about 18 % of full sunlight, simulating the light intensities in forest clearings and gaps, respectively) for one growing season. Three hypotheses were tested: (i) the deciduous species grows faster than the evergreen species in forest gaps and clearings; (ii) the deciduous species responds more strongly in terms of growth and morphology to variation in light climate than the evergreen species; and (iii) seedling size is positively correlated to acorn size. The results showed: (i) at both light levels, the deciduous seedlings gained significantly more growth in biomass and height than the evergreen seedlings; (ii) both species produced significantly more biomass in full sunlight than in shade, without showing any significant difference in height between treatments. Increase in light intensity improved the growth of the deciduous seedlings more strongly; (iii) at a similar age, the deciduous seedlings showed a greater response in leaf morphology and biomass allocation to variation in light levels, but when compared at a similar size, biomass allocation patterns did not differ significantly between species; (iv) bigger acorns tended to produce larger seedlings, larger leaf sizes and more leaf area, between and within species. These differences demonstrate that the deciduous species is gap-dependent and has the advantage over the evergreen species in forest gaps and clearings.