Frugivory and seed dispersal by vertebrates in the Oriental (Indomalayan) Region

Current knowledge of frugivory and seed dispersal by vertebrates in the Oriental Region is summarized. Some degree of frugivory has been reported for many fish and reptile species, almost half the genera of non-marine mammals and more than 40% of bird genera in the region. Highly frugivorous species, for which fruit dominates the diet for at least part of the year, occur in at least two families of reptiles, 12 families of mammals and 17 families of birds. Predation on seeds in fleshy fruits is much less widespread taxonomically: the major seed predators are colobine monkeys and rodents among the mammals, and parrots, some pigeons, and finches among the birds. Most seeds in the Oriental Region, except near its northern margins, are dispersed by vertebrate families which are endemic to the region or to the Old World. Small fruits and large, soft fruits with many small seeds are consumed by a wide range of potential seed dispersal agents, including species which thrive in small forest fragments and degraded landscapes. Larger, bigger-seeded fruits are consumed by progressively fewer dispersers, and the largest depend on a few species of mammals and birds which are highly vulnerable to hunting, fragmentation and habitat loss.     

Primate seed dispersal: Coevolution and conservation implications

Early studies of primates have demonstrated that many species rely heavily on fruit, and that primates constitute a large component of the frugivore biomass in tropical forests. Consequently, primates have long been thought to be important seed dispersers. It is only recently that studies have been conducted that have illustrated the complex nature of the interactions between fruit-eating primates and their food trees. Such studies have raised questions as to the causes and conse-quences of the intriguing differences between primate communities, the importance of other animals in the interactions (such as dung beetles and rodents that secon-darily disperse seeds), how primate-plant interactions evolve, and the significance of primates in forest regeneration and conservation. Since subsistence and com-mercial hunting of primates has heavily impacted frugivore communities, but left the physical structure of the forest relatively unaltered, studies of primate seed dispersal have important implications for the future of forests where seed dispersers have declined or disappeared.     

Aerial seed bank in a cold desert annual-ephemeral species: Role of anatomical structure of stem and delayed fruit dehiscence in timing of seed dispersal

Why the fruits are retained on dead upright herbaceous plants and how this relates to seed dispersal and timing of germination remain unclear. Stems of the annual Euclidium syriacum (Brassicaceae) with infructescences bearing indehiscent silicles remain upright after plants die in the spring. We investigated the effect of anatomical structures of stem and pedicle and delayed silicle dehiscence on seed dispersal phenology of this species. For comparison, sections were made of the stem of the annual Goldbachia laevigata (Brassicaceae), which has stems that fall over when plants die. Compared to G. laevigata, the stem of E. syriacum has vascular bundles that are closer together, a thicker xylem and phloem, more fibers, a thicker perimedullary zone and a smaller pith diameter:stem diameter ratio. The thickened pedicle did not form an abcission layer. By late October, 5–20% of seeds were dispersed, depending on the position of infructescences on the plant. Snow covered the plants in late autumn and when it melted in mid-April many of the plants had fallen over, with a high number of seeds germinating in attached silicles; seedlings became rooted in soil. After snowmelt, 14–15% of the silicles on the remaining upright plants contained seeds; all seeds were dispersed by early July. The anatomical structures of the stem and pedicle plus the delayed dehiscence of silicles explain the presence of an aerial seed bank in E. syriacum and delay of germination of many of seeds until spring. Further, pieces of upright plants are broken off and dispersed by wind, which helps to explain the wide distribution of E. syriacum in the cold desert.     

Estimating seed vs. pollen dispersal from spatial genetic structure in the common ash

Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, sigmas pound 14 m, and moderate pollen flow, 70 m pound sigmap pound 140 m.     

种子特征和结实量对啮齿动物取食和扩散种子行为的影响

为了深入了解啮齿动物在不同种子丰富度条件下对不同大小和单宁含量种子的觅食行为策略及其与植物种群更新的关系,在宁夏六盘山区的华北落叶松人工林,研究了不同大小和单宁含量[0%Tannin(T)、2%T、8%T和15%T]的人工种子在模拟结实小年和结实大年对啮齿动物取食和扩散行为的影响.结果表明: 啮齿动物消耗种子速度在结实小年更快,结实大年的种子消耗速度相对缓慢. 种子就地取食率(ISPR)在不同结实年份间无显著差异,扩散后取食率(PRAD)在结实小年显著高于结实大年,但前者的扩散后贮藏率(HRAD)显著低于后者;种子扩散后的取食距离(PDAD)和贮藏距离(HDAD)在结实小年均显著大于结实大年.在结实小年,大种子的PDAD和HDAD均大于小种子,前者在不同大小种子间均差异显著,而后者仅在2%T和15%T的不同大小种子间差异显著;在结实大年,除0%T外的其他单宁含量种子的PDAD和HDAD在不同大小种子间均差异显著.ISPR在中等单宁含量种子最大,高单宁含量种子最小;PRAD分别在结实小年的高单宁含量种子和结实大年的无单宁种子最大;不论在结实大年还是结实小年,HRAD均在高单宁含量种子最大,中等单宁含量种子最小.这说明结实大年可延缓啮齿动物对种子的消耗速率,提高种子的HRAD,但种子扩散距离减小;啮齿动物在结实大年和小年均表现出对大种子的扩散偏好,且大种子被扩散的距离更远;啮齿动物在不同结实年份均偏好于就地取食中等单宁含量种子,而扩散高单宁含量种子.     

The role of the brown-eared bulbulHypsypetes amaurotis as a seed dispersal agent

The role of the brown-eared bulbul,Hypsypetes amaurotis, as a dispersal agent for seeds of fruiting plants was studied by field observations for two years, in parallel with laboratory experiments on seed germination. Bulbuls consumed fruits of 53 species from 24 plant families. The fruits of these plants had similar color and size, and these characteristics were likely to enhance the feeding efficiency of the frugivore. Laboratory experiments on 20 food plant species demonstrated that: (1) no seeds were injured by passing through the bulbul's gut; (2) seeds that had passed through the bulbul's gut were still able to germinate and (3) fruit pulp reduced germination ability. When pulp was removed by passing through bulbul's gut, or by hand, germination was improved. An estimate of the home range of six bulbuls suggested that they may transport seeds for at least 300 m.     

杂草种子传播研究进展

种子传播将母株生殖周期的末端与它们后代种群的建立连结了起来,广泛认为,其对植被结构具有深刻的影响。种子传播的整个过程称为种子传播循环。研究表明,杂草种子传播的因子多种多样,包括仅依赖自身来完成的主动传播,以及依赖风、水、动物、人类等外界媒介的被动传播。其中,人类传播杂草种子是影响最广泛的一种,对现代植物的分布格局产生了深刻的影响。杂草种子的传播,对杂草种子库的数量和空间动态影响很大。研究种子传播的主要方法有荧光染料标记法、放射性同位素标记法、稳定同位素分析、分子遗传标记等。结合近几年国内外的研究进展,作者就杂草种子传播对种子库数量和空间动态影响的精确直接研究、杂草种子传播的过程及传播后的命运、杂草种子适应传播的机理、生态控草措施研究、外来杂草入侵蔓延与其种子传播的关系等方面提出了展望。     

Analysis of a hyper-diverse seed dispersal network: modularity and underlying mechanisms

Mutualistic interactions involving pollination and ant-plant mutualistic networks typically feature tightly linked species grouped in modules. However, such modularity is infrequent in seed dispersal networks, presumably because research on those networks predominantly includes a single taxonomic animal group (e.g. birds). Herein, for the first time, we examine the pattern of interaction in a network that includes multiple taxonomic groups of seed dispersers, and the mechanisms underlying modularity. We found that the network was nested and modular, with five distinguishable modules. Our examination of the mechanisms underlying such modularity showed that plant and animal trait values were associated with specific modules but phylogenetic effect was limited. Thus, the pattern of interaction in this network is only partially explained by shared evolutionary history. We conclude that the observed modularity emerged by a combination of phylogenetic history and trait convergence of phylogenetically unrelated species, shaped by interactions with particular types of dispersal agents.     

动物对松属植物种子的传播作用研究进展

松属植物约110种,根据种子传播方式可分为风传播松和动物传播松。风传播松占绝大多数,种子多具有适应风力的翅。动物传播松大约23种,都具有大、可食用、无翅或短翅的种子,无法借助风力传播。动物传播松的分布生境多为贫瘠的山地,而且多位于高海拔地区。目前已知9种松树的动物传播种类,其余14种可推测为动物传播。动物传播者包括鸦科鸟类和啮齿类动物,动物将获得的种子分散贮藏,未被重取的种子可能萌发,完成传播。动物传播是定向传播,微生境多适合种子萌发。啮齿类的传播距离可达数10 m,而鸦科鸟类的传播距离可达数公里。动物传播的松树会出现树丛和多树干现象,一般由同一贮点内贮藏的多粒种子萌发造成的。动物贮藏的种子大部分被重取,称传播后取食。一些具有大种子的风传播松在种子落地后,啮齿类和鸟类会再次埋藏而形成二次传播,可看做是一个单独的传播类型,即风-动物传播松。动物传播者与依赖传播松树之间可看作是互利共生关系。     

Effects of seed size on dispersal distance in five rodent-dispersed fagaceous species

We studied the effect of seed size on dispersal by comparing dispersal distances in five rodent-dispersed fagaceous species (Lithocarpus harlandii, Quercus variabilis, Q. serrata, Cyclobalanopsis glauca, Castanopsis fargesii) with different seed size. We tracked individual seeds with coded tin-tags in two stands over 3 years in a subtropical evergreen broadleaved forest in the Dujiangyan Region of Sichuan Province, Southwest China. Our seed tracking data indicate that dispersal distances (including mean, maximum and distribution range) of seeds in primary caches and of seeds eaten after dispersal significantly increased with seed size, for both stands and all years. In addition, larger seeds (L. harlandii and Q. variabilis) were re-cached more often than smaller ones, which further reduced the relative density among caches and extended dispersal distances. Our findings indicate that greater dispersal distances for larger seeds might benefit the evolution of differences in seed size, and that scatter-hoarding might be advantageous for rodent-dispersed tree species.     

Selective interactions between short-distance pollen and seed dispersal in self-compatible species

In plants, genes may disperse through both pollen and seeds. Here we provide a first theoretical study of the mechanisms and consequences of the joint evolution of pollen and seed dispersal. We focus on hermaphroditic self-compatible species distributed in structured populations, assuming island dispersal of pollen and seeds among small patches of plants within large populations. Three traits are studied: the rate of among-patch seed dispersal, the rate of among-patch pollen dispersal, and the rate of within-patch pollen movement. We first analytically derive the evolutionary equilibrium state of each trait, dissect the pairwise selective interactions, and describe the joint three-trait evolutionary equilibrium under the cost of dispersal and kin competition. These results are then analytically and numerically extended to the case when selfed seeds suffer from depressed competitiveness (inbreeding depression, no heterosis). Finally individual-based simulations are used to account for a more realistic model of inbreeding load. Pollen movement is shown to generate opposite selection pressures on seed dispersal depending on spatial scale: within-patch pollen movement favors seed dispersal, whereas among-patch pollen dispersal inhibits seed dispersal. Seed dispersal selects for short-distance movements of pollen and it selects against long-distance dispersal. These interactions shape the joint evolution of these traits. Kin competition favors among-patch seed dispersal over among-patch pollen dispersal for low costs of within-patch pollen movement (and vice versa for significant costs of within-patch pollen movement). Inbreeding depression favors allogamy through high rates of within- and among-patch pollen movement. Surprisingly, it may select either for or against seed dispersal depending on the cost of among-patch pollen dispersal. Heterosis favors increased among-patch dispersal through pollen and seeds. But because these two stages inhibit each other, their joint evolution might lead to decreased seed dispersal in the presence of heterosis. Of crucial importance are the costs of dispersal.     

Contemporary pollen and seed dispersal in a Prunus mahaleb population: patterns in distance and direction

Pollination and seed dispersal determine the spatial pattern of gene flow in plant populations and, for those species relying on pollinators and frugivores as dispersal vectors, animal activity plays a key role in determining this spatial pattern. For these plant species, reported dispersal patterns are dominated by short-distance movements with a significant amount of immigration. However, the contribution of seed and pollen to the overall contemporary gene immigration is still poorly documented for most plant populations. In this study we investigated pollination and seed dispersal at two spatial scales in a local population of Prunus mahaleb (L.), a species pollinated by insects and dispersed by frugivorous vertebrates. First, we dissected the relative contribution of pollen and seed dispersal to gene immigration from other parts of the metapopulation. We found high levels of gene immigration (18.50%), due to frequent long distance seed dispersal events. Second, we assessed the distance and directionality for pollen and seed dispersal events within the local population. Pollen and seed movement patterns were non-random, with skewed distance distributions: pollen tended moved up to 548 m along an axis approaching the N-S direction, and seeds were dispersed up to 990 m, frequently along the SW and SE axes. Animal-mediated dispersal contributed significantly towards gene immigration into the local population and had a markedly nonrandom pattern within the local population. Our data suggest that animals can impose distinct spatial signatures in contemporary gene flow, with the potential to induce significant genetic structure at a local level.     

果实类型和种子传播的进化:系统发育和生态学简论

Success of flowering plants is greatly dependent on effective seed dispersal. Specific fruit types aid different mechanisms of seed dispersal. However, little is known about what evolutionary forces have driven the diversification of fruit types and whether there were phylogenetic constraints on fruit evolution among angiosperm lineages. To address these questions, we first surveyed the orders and families of angiosperms for fruit types and found no clear association between fruit types and major angiosperm lineages, suggesting there was little phylogenetic constraint on fruit evolution at this level. We then surveyed fruit types found in two contrasting habitats an open habitat including the Indian desert and North American plains and prairies, and a closed forest habitat of Australian tropical forest. The majority of genera in the survey of tropical forests in Australia were fleshy fruit trees, whereas the majority of genera in the survey of prairies and plains in central North America were herbs with capsules and achenes. Both capsules and achenes are frequently dispersed by wind in the open, arid habitat, whereas fleshy fruits are generally dispersed by animals. Since desert and plains tend to provide continuous wind to aid dispersal and there are more abundant mammal and bird dispersers in the closed forest, this survey suggests that fruit evolution was driven at least in part by dispersal agents abundant in particular habitats.