昆虫寄生对辽东栎种子命运的影响

报道了昆虫寄生对辽东栎 Quercus liaotungensis 种子命运的影响。结果表明：（1）被昆虫寄生的种子发芽率明显低于正常成熟的种子,被昆虫寄生的种子或者不能发芽,或者能发芽但随后死亡;（2）从虫卵到老龄幼虫的发育在橡实内完成,当橡实落地后幼虫破壳而出,整个种子库的幼虫破壳时间延续2～50天,并非高度同步化;种子库的虫寄生率高达45.4%,以柞栎象Curculio dentipes为主,还有少量其它种类,如另一种象虫Curculio sp.、栗白小卷蛾 Cydia kurokoi 和螟蛾科（Pyralidae）的一未定名种;（3）昆虫寄生影响橡实成熟,测量种子大小分布表明,被昆虫寄生的种子的大小分布介于未成熟和成熟种子之间;（4）象虫寄生取食引起16.05% 的种子能量损失,显著低于对照组。结果证明昆虫寄生对辽东栎种子的命运有重要影响,是影响辽东栎种群更新的关键因素之一。     

Predicting forest management effects on oak–rodent mutualisms

Wood mice Apodemus sylvaticus are the main dispersers of acorns in highly managed Mediterranean holm‐oak woodlands. Mice mobilize and cache acorns to store them for winter consumption. They carry acorns away from potential competitors, face predation risks during mobilization, and cache acorns in areas where pilfering risks are low. However, mice can act either as net predators or as moderately efficient dispersers, depending on the way landscape management affects intraspecific competition for acorns and shelter availability. To assess the influence of landscape structure and mouse behavior on acorn dispersal, we developed an agent‐based model (ABM) that translates forest management into changes in key environmental factors driving mouse foraging decisions. The model was able to predict accurately acorn dispersal patterns in a wide range of forest management practices based on information on forest habitat availability, stem density and shrub cover. Sensitivity analysis revealed that caching rates emerged from the interplay between intraspecific competition for seeds and predation risk accepted during mobilization. It also showed that intraspecific competition for acorns decreased with increasing habitat loss (due to positive edge effects on acorn production) while landscape resistance to mouse movements increased. As a result, the net benefits of caching declined and acorn predation became the dominant strategy. Finally, we assessed the effects of shrub encroachment as a management practice to enhance dispersal services in savanna‐like landscapes (dehesas). The model predicted non‐linear responses with a 65% threshold of shrub cover needed to achieve relatively high levels of acorn dispersal. This value may not be compatible with the traditional exploitation of dehesas (livestock rearing). Our study shows that integrated approaches that combine environmental change driven by management with behavioral responses of dispersers improve our understanding of the causes of recruitment bottlenecks, and are useful tools for evaluating conservation strategies aimed at enhancing dispersal services.     

Oviposition preference and offspring performance in <Emphasis Type="Italic">Mechoris</Emphasis><Emphasis Type="Italic">ursulus</Emphasis> Roelofs (Coleoptera: Attelabidae)

Oak nut weevil (Mechoris ursulus Roelofs) females lay eggs in acorns and cut off the branch of oviposited acorns. We investigated the relationship between oviposition preference and offspring performance (growth and survival). M. ursulus appeared to estimate the size of an acorn by walking around it before and after oviposition. When we offered paired acorns of different sizes, females showed strong preference for larger acorns. In the field, egg-bearing acorns were larger than egg-free acorns in cut branches. A parallel series of experiments was conducted to assess the influence of acorn size on offspring performance. Larvae and newly emerged adults from larger acorns were heavier than those from smaller acorns. However, acorn size did not affect the survivorship of larvae. We also tested if M. ursulus avoided oviposited acorns, but there was no evidence that M. ursulus could assess the presence of eggs in acorns. Electronic Publication     

Acorn and aquatic invertebrate biomass in Mississippi Alluvial Valley hardwood bottomlands

The Mississippi Alluvial Valley (MAV) is an internationally important migration and wintering region for Nearctic waterfowl. Most of the MAV is a lowland forested floodplain that contains vast stands of red oaks (Quercus spp.). These trees produce acorns and, when forests flood, diverse communities of aquatic invertebrates emerge, providing diverse nutritious foods for wintering ducks. The MAV is within the Lower Mississippi Valley Joint Venture (LMV JV) region of the North American Waterfowl Management Plan, but no combined MAV-wide estimates of acorn and invertebrate biomass exist to determine foraging carrying capacity for conservation planning or actions by the LMV JV or other partners in regions containing southern red oaks. We sampled acorns that fell to the ground or were submersed under shallow water deemed accessible to foraging ducks and aquatic invertebrates in the MAV of Louisiana, Mississippi, Missouri, and Tennessee, USA, during fall-winter 2009–2011. In good and poor masting years, acorn abundance was non-linearly related to the percentage of the forest canopy made up of red oaks and peaked in late autumn or winter when most other waterfowl resources are depleted or decomposed. This finding is novel and represents a deviation from how the LMV JV has traditionally assumed food resources exist for waterfowl in hardwood bottomlands. We used a daily ration model to estimate energy use days (EUDs) from combined acorn and invertebrate biomasses relative to red oak canopy coverage. For good and poor acorn masting years at the mean MAV-wide red oak canopy coverage of 45%, EUD = 2,273.1 days/ha and 161.2 days/ha, respectively. The LMV JV currently uses EUD = 385–502 days/ha for forests with 40–50% red oak canopy coverage. Because acorns and aquatic macro-invertebrates are a food resource that persists through winter and reaches peak abundance later in winter, we contend conservation planners have undervalued the potential of bottomland hardwoods to provide energy for wintering ducks.     

Large acorns benefit seedling recruitment by satiating weevil larvae in <Emphasis Type="Italic">Quercus aliena</Emphasis>

Plants can enhance their seed viability and survival through reducing the fitness costs of herbivory by satiating seed predators at either plant or seed level, or both. The former satiates with production of large crops while the latter with large-sized seeds, enhancing the probability of seed survival. We analyzed both types of satiation in the interaction between the Quercus aliena and the weevil Curculio spp in 2 years with different crop size and acorn size. Larger crop size seemed to satiate less effectively weevils due to higher proportions of the seeds were attacked in oaks producing more crops of smaller acorns. However, prematurely abscission of infested acorns in large crop year might compensate this ineffectiveness. Larger acorns in lean year well satiated weevil larvae, as a larger acorn size increased the likelihood of embryo survival and seedling establishment. Although effective satiation by larger acorns would be negated by smaller seed crops, the proportion of attacked acorns that survived increased with large acorn size in lean year. These results highlighted the importance of annual variation in acorn size of Quercus aliena in satiating and defending weevil larval predations, consequently in successful seedling recruitment and establishment.     

包衣、埋藏的栓皮栎和枹栎种子在鼠类捕食下的存留

鼠类对壳斗科植物种子的捕食作用十分强烈,从而影响此类植物的更新.栓皮栎和枹栎是中国西南地区常绿阔叶林主要树种,不仅有重要的经济价值,而且还可用于植树造林.对栓皮栎和枹栎种子分别进行包衣地表、无包衣地表、包衣埋藏和无包衣埋藏等4种处理,并跟踪各种处理种子被鼠类捕食的情况.结果表明:各处理之间种子的中位存留时间显著不同,包衣埋藏后的种子存留时间显著长于未包衣且放置于地表的种子,埋藏显著地降低了鼠类对这2种种子的捕食;埋藏及包衣处理能够很好地保护栓皮栎和枹栎种子免于鼠类的捕食,有利于种子存留并萌发建成幼苗.该方法可用于人工播种造林以提高造林成活率.     

Factors limiting the recruitment of Quercus schottkyana,a dominant evergreen oak in SW China

Quercus schottkyana is a dominant species of oak in the Asian evergreen broad-leaved forests in southwestern China but seedlings are uncommon and recruitment is rare. Annual acorn production by Q. schottkyana is variable and the acorns are exposed to a series of mortality risks. Understanding the factors that limit recruitment of the oak requires knowledge of the oak's life cycle from acorn production to germination and seedling establishment. In this study, we first tested the effects of acorn density on establishment of seedlings by placing batches of acorns at different densities throughout the study area. Second, we tested the effects of herbivores on seedling survival by erecting fences around both natural and transplanted seedling populations. Our results show that even though the rate of seedling establishment increases as acorn density increases (for 32-8000 acorns·m^-2), survival rates of seedlings in the field were generally low (0-0.6%). We show that seedling recruitment of Q. schottkyana is mainly limited to the acorn stage where 88% of the acorns died from the combined effects of desiccation and predation by weevils (Curculio) and bark beetles (Coccotrypes sp.). Herbivory results in the death of some seedlings and consequently also affects the recruitment of seedlings of Q. schottkyana.     

槲栎种子雨进程中昆虫的捕食特征

为了了解昆虫捕食与槲栎Quercus aliena种子大小和产量的关系以及在栎林更新中的作用,于2008和2009年秋季,分别在暖温带伏牛山系天池山国家森林公园内研究了两个年度槲栎的种子雨过程及昆虫捕食特征。结果表明：（1）种子雨过程从8月中下旬到9月底约经历40 d,存在高峰期且时段较明显,高峰期下落种子量分别占全部种子雨量的78.13%（2008年）和75.91%（2009年）;（2）槲栎的种子雨强度年间存在较大差异,2008年明显小于2009年（两年分别为31.75±16.65粒/m²和51.92±29.26粒/m²）,但2009年的橡子明显比2008年小（两年分别为1.94±0.61 cm³和2.46±0.57 cm³）;（3）种子雨构成比例在两个年份间存在差异,完好种子的量分别为59.05%（2008年）和36.12%（2009年）,虫蛀率在大量结实的2009年显著提高;（4）虫蛀橡子（2.29±0.42 cm³）显著大于完整橡子（1.59±0.32 cm³）,且虫蛀种子中所含虫卵数与种子大小显著正相关,昆虫有选择大种子产卵寄生的偏好。本研究的结果说明,昆虫对槲栎大种子有寄生选择偏好;大部分槲栎种子遭遇象甲虫蛀而降低生命活力,这可能是影响槲栎林更新的主要因素之一。     

The Proximate Basis of the Oak Dispersal Syndrome: Detection of Seed Dormancy by Rodents

Previously we have shown how a range of physical and chemicalcharacteristics of acorns influences the behavioral decisionsof food-hoarding rodents which in turn affects the dispersal,establishment and spatial arrangement of oaks. One such behaviorinvolves the selective caching of acorns of red oaks (subgenus:Erythrobalanus) over those of white oaks (Quercus) because ofreduced perishability that results from delayed germinationof acorns in the red oak group. In this study, we sought toidentify the specific proximate cues (visual and olfactory)that eastern gray squirrels (Sciurus carolinensis) use whenmaking these decisions. In two series of field experiments,we presented individual, free-ranging animals with pairs ofexperimentally altered acorns (that differed with respect toa single chemical or visual characteristic) and recorded theirfeeding and caching responses. Squirrels cached artificial acornswith pericarps (shells) of red oak acorns and ate those withshells of white oak regardless of the internal chemical compositionof either type of acorn. Only when the shells of artificialacorns were first soaked in acetone (to remove potential chemicalodors) did animals eat artificial acorns made with the shellsof red oak acorns. Squirrels also ate one-year old red oak acornsthat had broken dormancy, even when they exhibited no signsof germination. We argue that a chemical cue in the shell ofacorns is important in the detection of seed dormancy and thedecision to cache acorns, and that such a cue might ultimatelycontribute to the differential dispersal of red and white oaksby rodents.     

Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis

By caching acorns, jays serve as important dispersal agents for oak (Quercus) species. Yet little is known about which acorn characteristics affect selection by jays. In the traditional model of jay/oak symbiosis, large, brown, ripe acorns free of invertebrate parasites (e.g., Curculio acorn weevils) are selected by jays. Recently, it has been suggested that a tri-trophic relationship between oaks, jays, and weevils may have evolved to counter the negative dietary effects of acorn tannins. Under the tri-trophic model, jays would preferentially select acorns containing weevil larvae. We tested the assumptions that (1) acorns containing curculionid larvae exist in sufficient quantities to support jay populations and (2) jays can detect, and preferentially select, acorns containing weevil larvae, and investigated the cues by which jays select acorns. Captive Mexican jays (Aphelocomaultramarina) were presented Emory oak (Quercusemoryi) acorns in aviary feeding trials. Large, dense, viable acorns free of curculionid larvae were preferentially selected. Contrary to results of previous research, color did not affect selection. Acorn viability increased and curculionid larval occupancy decreased in adjacent savannas and isolated stands relative to existing oak woodland, perhaps favoring oak recruitment into adjacent lower-elevation grasslands. Our results compel us to reject the tri-trophic model for this system, and are consistent with the traditional jay/oak symbiosis model. Relatively long-distance dispersal of viable acorns favors Emory oak replacement, and spatial patterns of acorn viability and curculionid parasitism suggest expansion of Emory oak into adjacent low-elevation semi-arid grasslands. Received: 29 February 1996 / Accepted: 26 September 1996     

Utilization of red oak acorns in non-bumper crop year

Utilization of acorns from individual red oaks Quercus rubra Fagaceae) was examined in the tree canopies during fall and from the ground beneath the canopies during winter in a Missouri oak-hickory forest. The goal of the study was to determine whether vertebrates show preference for acorns from individual trees on the basis of acorn or crop characteristics. Seed production, percentage of crop which was viable, maldeveloped, or infested by insects, average seed weight and tannin content of mature, viable acorns were measured for 11 red oak adults. Behavioral observations were conducted in September and October during the peak period of seed fall. Over winter removal was determined by counting the number of acorns removed from 3x3 m plots underneath the trees' canopies between December and mid-April. Canopy removal of acorns was surprisingly low-an estimated average of 52 acorns per tree compared with a mean estimated crop size of approximately 1,200 mature acorns. Over winter, approximately 50% of the acorns were removed from ground plots (range 7% to 93.1%). Number removed corresponded more to the density of nuts rather than to seed and crop characteristics. The low rate of acorn utilization by canopy visitors contrasts with other studies in the literature and may have been due to 1) the fact that this study was done in a relatively homogeneous forest where high density of conspecifics reduces the impact on any one individual or 2) perhaps an unusually low density of birds and mammals.     

Partial acorn consumption by small rodents: implication for regeneration of white oak, <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Partial consumption of acorns by rodents, birds, and insects has been widely reported in various oak species. However, to what extent these partially eaten acorns contribute to the regeneration of oak trees is poorly understood. To date, there is limited knowledge of the effects of seed availability on partial consumption of acorns. Herein, we released tagged Quercus mongolica acorns in two consecutive years with different seed crops, to explore the probability of partial acorn consumption. We also placed simulated partially consumed acorns in the field to investigate their contribution to regeneration of white oak. Our results showed that more acorns were partially eaten in a good crop year than in poor crop year, reflecting an effect of predator satiation on acorn partial consumption by rodents at the population level. Partially eaten acorns were more likely to be damaged at the basal end, suggesting consistent consumption preferences of small rodents. Although, partially consumed acorns were less likely to be scatter-hoarded by small rodents, they germinated more rapidly than the intact acorns in the field, offsetting the negative effects of the non-buried deposition. Despite lower germination rates, lightly damaged acorns exhibited greater growth of roots and shoots, suggesting a compensatory response to partial acorn consumption. Partial consumption may spread predation pressure on acorns and thus appears to be much better for the plant than total consumption by seed-eating animals. Therefore, partially consumed acorns as dispersal leftovers may play a potential role in natural regeneration of Quercus mongolica, especially in mast years. However, this role and the underlying mechanisms of partial acorn consumption by rodents, birds, and herbivore insects need further investigation.     

Not only size matters: Acorn selection by the European jay (Garrulus glandarius)

A strong selection for acorn characteristics is expected to have evolved in the mutualistic relationship between the European jay (Garrulus glandarius) and the oak (Quercus spp.). Bossema's pioneer work suggested that jays do not select acorns randomly, but rather they preferentially select some size and species. Preference for some seeds over others may have implications on plant community dynamics by conferring advantages (or disadvantages) on the selected (avoided) seed characteristics. In this paper we test to what extent jays select acorns by species and/or by size and the relation between these two traits in Mediterranean oak species. The experiments consist of a set of field tests in which acorns from four different coexisting Mediterranean oak species (Quercus ilex, Quercus faginea, Quercus suber, and Quercus coccifera) were placed in artificial feeders accessible to wild jays. The acorns were previously measured to control individual acorn characteristics. Using video-recording techniques, we followed jay activity and the fate of each acorn (sequence of acorn selection and method of transport). Q. ilex acorns were preferred over other acorns, and Q. coccifera acorns were avoided when other acorns were available. Preference for Q. faginea and Q. suber acorns was intermediate, that is, they were preferred over Q. coccifera acorns but not over Q. ilex acorns. Large acorns were also preferred although acorn species selection was stronger than size selection. Jays selected species and size both by visual means and by using acorn area as an indicator of size. Acorns wider than 17–19 mm were carried in the bill because of throat limitation. Our results confirm Bossema's study on temperate oaks and extend it to Mediterranean oak species, revealing implications on mixed oak forest dynamics.     

A Rapid Hard-Mast Index From Acorn Presence-Absence Tallies

Abstract: We used 21 years of acorn data from visual surveys of oak (Quercus spp.) trees (n = 20,113) conducted in western North Carolina, USA, to develop predictive equations for hard-mast indices (HMIs) based on the proportion of trees bearing acorns (PBA). We calculated PBA using visual estimates of the percentage of oak crown with acorns (PCA), assigning acorn presence if PCA ≥ 33.5%.The proportion of trees bearing acorns and average PCA were highly correlated, and PBA alone was a successful predictor of HMIs. Precise estimates of PBA (therefore HMIs) at a 95% confidence level required 139-385 sample trees for each oak subgroup or spatial scale of interest, and the sample size required varied with the true PBA. Substituting this faster, simpler visual survey method for others involving labor-intensive counts of twigs and acorns means that more trees can be sampled (if needed) with less time and effort for improved PBA (therefore HMI) precision. We offer a reliable method for predicting HMIs that are comparable to past HMI estimates for states using the Whitehead (1969) method, thus providing continuity in tracking long-term acorn production patterns. We also developed categories for subjectively ranking acorn crop sizes based on the range of PBA observed during 21 years. We recommend that PBA be adopted by resource management agencies as a standard, stand-alone index of acorn production to ensure comparable data among years and across the eastern United States. A standardized protocol for assigning acorn presence or absence must be used for consistent, comparable regional use of PBA in predicting HMIs or by itself as an index of acorn production.     

Rodent acorn selection in a Mediterranean oak landscape

Quercus suber, Quercus ilex and Quercus coccifera (Cork, Holm and Kermes oaks, respectively) are common evergreen oak species that coexist in the landscapes of the western part of the Mediterranean basin. Rodents are the main acorn predators and thus one of the main factors for understanding recruitment patterns in oaks. In this paper we analyse to what extent mice prefer acorns from one oak species over another in three oak species studied using acorn removal experiments and video tape recordings. Twenty labelled acorns from each of the three Quercus species (60 acorns) were placed in 40 cm×40 cm quadrats on each plot. Because selection might vary as a result of the vegetation context, we performed the trials in the five main vegetation types within the study area (four replicates in each vegetation type) in order to control for habitat influences on rodent acorn preferences (a total of 20 plots). The removal of 1,200 acorns occurred within 68 days. Mice removed 98.7% of the acorns. Q. ilex acorns were preferred over Q. suber and Q. coccifera in all vegetation types except in pine forest, where no acorn preferences were detected. Acorn removal rates differed with vegetation type, correlating positively with shrub cover. The distance at which acorns were displaced by rodents (mean =4.6 m±5.1 SD) did not differ between acorn species, but varied among vegetation types. Bigger acorns of Q. coccifera were selected only after Q. ilex and Q. suber acorns were depleted, while no size selection was detected for the latter two species. Thus, we conclude that rodents show preference for some oak acorns and that landscape context contributes significantly to rodent activities and decisions.     

Satiation of predispersal seed predators: the importance of considering both plant and seed levels

Plants can reduce the fitness costs of granivory by satiating seed predators. The most common satiation mechanism is the production of large crops, which ensures that a proportion of the seeds survive predation. Nevertheless, satiation of small granivores at the seed level may also exist. Larger seeds would satiate more efficiently, enhancing the probability of seed survival after having been attacked. However, a larger seed size could compromise the efficiency of satiation by means of large crops if there were a negative relationship between seed size and the number of seeds produced by an individual plant. We analyze both types of satiation in the interaction between the holm oak Quercus ilex and the chestnut weevil Curculio elephas. Both crop size and acorn size differed strongly in a sample of 32 trees. Larger crop sizes satiated weevils, and higher proportions of the seeds were not attacked as crop size increased. Larger seeds also satiated weevil larvae, as a larger acorn size increased the likelihood of embryo survival. Seedling size was strongly related to acorn size and was reduced by weevil attack, but seedlings coming from large weeviled acorns were still larger. The number and the size of the acorns produced by individual trees were negatively related. Larger proportions of the crop were infested in oaks producing less numerous crops of larger acorns. However, contrary to expectations, these trees did not satiate more effectively at the seed level either. Effective satiation by larger acorns was precluded by larger multi-infestation rates associated to smaller seed crops, in such a way that the proportion of attacked seeds that survived did not vary among trees with different acorn sizes. These results highlight the need of considering satiation by means of large crops and large seeds in studies of predispersal seed predation. Long-term monitoring on individual oaks will help to assess whether there is a trade-off between the number and the size of the acorns and, if it existed, how it could condition the fitness consequences of both types of satiation.     

The coexistence of acorns with different maturation patterns explains acorn production variability in cork oak

In dry areas such as Mediterranean ecosystems, fluctuations in seed production are typically explained by resource (water) availability. However, acorn production in cork oak (Quercus suber) populations shows a very low relationship to weather. Because cork oak trees produce acorns with different maturation patterns (annual and biennial), we hypothesized that acorn production in coexisting individuals with a different dominant acorn maturation type should respond differently to climatic factors and that disaggregating the trees according to their acorn-maturation pattern should provide a more proximal relation to weather factors. We assessed acorn production variability in fragmented cork oak populations of the eastern Iberian Peninsula by counting the total number of acorns in 155 trees during an 8-year period. An initial assessment of acorn production variability in relation to weather parameters yielded very low explained variance (7%). However, after the trees were grouped according to their dominant acorn maturation pattern, weather parameters were found to account for 44% of the variability in acorn crops, with trees with annual acorns exhibiting mast fruiting in years with reduced spring frost and shorter summer droughts and trees with biennial acorns showing the opposite pattern. Thus, conditions that negatively affect annual production could be beneficial for biennial production (and vice versa). The results highlight the importance of the resource-matching hypothesis for explaining acorn production in Quercus suber and suggest that different seed maturation types within a population may allow the species to deal with highly variable weather conditions. They also emphasize the importance of understanding acorn maturation patterns for interpreting masting cycles.     

北京东灵山落叶阔叶林中辽东栎种子雨

在北京东灵山地区的一个落叶阔叶林中调查了辽东栎（Ｑｕｅｒｃｕｓ ｌｉａｏｔｕｎｇｅｎｓｉｓ Ｋｏｉｄｚ．）的种子雨。对于选定的４棵辽东栎中的３棵,树冠下的种子雨分布格局符合二次分布,具有很高的决定系数。由设置在树冠下的种子捕捉器收集的坚果数量来估计整棵树的种子雨。４棵树的种子雨中有活力的种子很少,变化范围从２６到２５９个。每棵树的树冠下的种子雨密度变化范围从０．７６到７．２６个／ｍ＾２。林中平均种     

昆虫蛀蚀对鼠类介导下的锐齿槲栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散和自然更新有着非常重要的影响。然而,鼠类是否具有鉴别虫蛀种子的能力还存在一定的争议。此外,鼠类的鉴别能力是否受到食物丰富度变化的影响也未见相关报道。采用标签标记法,2011年秋季(9—11月,食物丰富季节)和2012年春季(4—6月,食物匮乏季节)分别在秦岭南坡的佛坪国家级自然保护区内,调查了森林鼠类对完好和虫蛀锐齿槲栎(Quercus aliena)种子的选择差异。结果显示:1)在秋季,尽管2种类型种子的存留动态没有显著差异,但是在后期虫蛀种子的存留时间相对更长;而在春季2种类型种子的存留动态则极为显著,几乎所有的完好种子(99%)在释放后的第3天就被鼠类全部扩散,虫蛀种子的存留时间则相对较长。2)在秋季,鼠类更喜好扩散后取食完好种子;而在春季,鼠类则喜好在原地取食绝大部分的种子,并且优先取食完好种子。3)在秋季,鼠类贮藏了更多的完好种子;而在春季,尽管完好种子在释放后第1天便达到贮藏高峰,然而由于后期的大量被捕食,2种类型种子在贮藏动态上没有显示出显著差异。研究结果表明秦岭地区森林鼠类可以准确区分完好与虫蛀种子,但是食物丰富度会影响鼠类对种子的选择策略。在食物丰富的秋季,鼠类更多地选择贮藏完好种子;而在食物相对匮乏的春季,鼠类更倾向于同时取食2种类型种子。森林鼠类通过对2种类型种子的鉴别和选择,影响不同种子的命运,从而可能对种子的扩散和自然更新产生重要影响。     

Fruit abortion,developmental selection and developmental stability in<Emphasis Type="Italic"> Quercus ilex</Emphasis>

Fruit abortion has been hypothesized to be a parental means of selective removal of propagules with low viability. In particular, aborted zygotes have been suggested to have developmentally deviant phenotypes, and surviving offspring may therefore give rise to adults with a developmentally stable phenotype. We tested predictions from this hypothesis using acorns of holm oaks Quercus ilex as a model system. Fecundity of oak trees was negatively related to mean fluctuating asymmetry of leaves, and abortion rates were positively related to leaf fluctuating asymmetry in at least one population. Aborted acorns were asymmetric in 83-99% of cases in three samples, while mature acorns were only asymmetric in 57-78% of cases. Acorn asymmetry was unrelated to germination probability and germination date, and had no significant effect on number of leaves, leaf mass, stem mass, seedling height or leaf area of seedlings. However, acorn asymmetry affected the trade-off between number and size of leaves in seedlings. Seedlings from asymmetric acorns showed a positive relationship between acorn size and number of leaves, but no relationships between acorn size and leaf area, while symmetric acorns showed the opposite. A positive relationship between acorn size and number of leaves in spring was found for naturally emerged seedlings that died during their first summer, whereas the number of leaves produced by surviving seedlings did not depend on acorn size. These findings are consistent with the hypothesis that stressed trees selectively abort propagules of low viability, and that developmental selection acts on a measure of developmental instability of fruits.