Aerial seed bank and dispersal traits in Anthemis chrysantha (Asteraceae), a critically endangered species

Mature plant density and fruit production were monitored in the main population of four successive cohorts of the endangered winter annual Anthemis chrysantha (Asteraceae) in southeastern Spain. Experiments were conducted with artificial rainfall and a wind tunnel to determine the temporal and spatial dispersal pattern of the species and the relationship with rain and wind.     

Epizoochorous seed dispersal in relation to seed availability – an experiment with a red fox dummy

Questions: Is the red fox a potential vector for epizoochorous seed dispersal? Can seed attachment and retention be predicted from plant and seed traits? Location: Grasslands in southern Norway. Methods: Epizoochorous seed attachment on the red fox was studied by walking a dummy fox through the vegetation and comparing seeds found on the dummy with the estimated seed availability in the vegetation. Seed retention, i.e. the ability of different seeds to stay on the fox, was estimated in a separate experiment. Seed attachment and retention were related to plant and seed traits using statistical models that account for heteroscedasticity and zero‐inflated data. Results: The majority of seeds attached to the fox originated from a few species, but also species without specific seed traits that are supposed to enhance epizoochory attached at least some seeds to the fox. The probability of seed attachment was positively related to plant height, bristle and hooked seed appendages, and negatively related to winged appendages, seed mass, and seed sphericity. Seed retention was positively related to the seed traits bristles, hooks and pappus. For several species, the results indicate a high potential for dispersal over long distances. Conclusions: In modern agricultural landscapes, large herbivores are often restricted in their mobility or are found at low densities, and other animal vectors may therefore be important for seed dispersal. In our study, a range of plant species were able to disperse by attaching seeds to, and having their seeds retained in, the fox fur some distance. We suggest that the red fox may be an important vector for epizoochorous seed dispersal in the agricultural landscape.     

Seed dispersal by water: a contribution to the interpretation of seed assemblages

The composition of a seed flora always differs from actual vegetation. For archaeobotanists, who try to reconstruct former communities on the basis of plant macrofossils extracted from soil samples, this is a serious handicap. This difference can be explained by dispersal processes and by differences in preservation. Seeds that are incorporated into the soil may originate from both local and regional vegetation. Once incorporated, differences in preservation may result in a seed flora from a mixture of communities. The comparison may be further confounded when seeds that are transported over long distances are also of subfossil or even fossil origin. Both wind and water are effective agencies for long-distance dispersal. This study deals with the dispersal of botanical macro-remains by water. Water may be considered an important dispersal agent, especially in sites situated in the vicinity of running water, or liable to contact with water during storm surges or river floods. Therefore, the interpretation of seed assemblages from sediments that may have been in contact with running water needs special attention. In order to obtain information about the dispersal potential of plant remains by water transport, litter which had been transported by the river Rhine, and litter which had been washed ashore on the North Sea coast of the Netherlands was examined.     

种子产量对鼠类扩散栓皮栎坚果的影响

为了解林木种子产量对鼠类种子扩散行为的影响,于2008 年和2009 年,在国有济源市愚公林场调查了栓皮栎的种子雨;在每年的种子雨结束后,选择次生林生境,研究了鼠类对人工释放栓皮栎坚果的扩散,旨在探讨种子产量与种子扩散间的关系。结果表明:1)取食栓皮栎坚果的鼠类主要有大林姬鼠、社鼠和岩松鼠,2008 年的鼠类捕获率(2% )低于2009 年(10%),其差异并未达到显著性水平;2)栓皮栎的种子雨构成和产量存在年际差异,2008 年以完好种子为主且产量高于2009 年,而2009 年以败育种子为主;3)2008 年人工释放栓皮栎坚果的中位存留时间显著高于2009 年;4)2008 年鼠类对栓皮栎坚果的平均扩散距离显著低于2009 年,且两年的搬运距离几乎都集中在9 m 以内;5)2008 年鼠类对栓皮栎坚果的埋藏比例显著高于2009 年。结果提示,在种子高产年份,可能有较多的种子逃脱动物的取食,从而增加种子萌发和幼苗建成的机会,最终促进植物的更新。     

Monitoring seed dispersal at isolated standing trees in tropical pastures: consequences for local species availability

The tropical rain forest landscape has been transformed to a mosaic composed of patches of crops, secondary vegetation and remnant forest fragments of different shapes and sizes. Isolation of patches and fragments is a critical issue in the maintenance of local species diversity. In this study we focus on the dispersal of propagules by birds to understant the movement of plants between landscape components. Seed deposition and the behavior of frugivorous birds were monitored at four isolated fig trees (Ficus yoponensis and F. aurea) in man-made pastures. Seed deposition was measured by trapping seeds under canopy trees for six months and by direct observation of bird visits to the four trees for one year. Seed deposition densities were 465, 614, 632 and 1097 seeds/m² accumulated over six months under each of the four trees. We recorded 8268 seeds of 107 species under the trees, among them, 6726 seeds (81%) were of 56 species dispersed by vertebrate frugivores. Seeds of tree species accounted for 26% of the total species. Seventy-three species of birds perched in the observed trees, and 3344 visits were made by 47 species of frugivores. Frugivorous birds occurred in two groups: resident species nesting in the pastures and resident species nesting elsewhere. Propagule exchange between landscape components is clearly influenced by the behavior of these two groups. Structure and dynamics of the landscape depend on plant species availability within the mosaic. This availability is high and suggests possibilities for the management of the local species diversity of tropical rain forests.     

Types of pollination and seed dispersal in Mediterranean plants

Abstract

Selected examples of pollen and seed dispersal in Mediterranean plants are described. The aspects of pollination considered are: comparison between cleistogamous and chasmogamous forms in the same species; differences in attractants and rewards; duration of pollen viability according to pollination syndrome. The aspects of seed dispersal considered are: presence or absence of specialized structures for dispersal; examples of active, passive and induced dispersal; animals involved in seed dispersal and their reward; type and functions of elaiosomes.     

Desert species adapted for dispersal and germination during floods: Experimental evidence in two Astrophytum species (Cactaceae)

Dispersal of organisms by water is known as hydrochory and is an important means of seed transportation. Here we present experimental evidence of possible dispersal and germination of seeds in water for arid land cacti. Seeds from Astrophytum spp. have unusual traits for plants from arid environments, traits that are typical of water dispersed seeds. Astrophytum capricorne and A. ornatum seeds disperse by floating in the Chihuahuan Desert. Seeds of other native species (Acacia farnesiana, Opuntia streptacantha and Prosopis laevigata (mesquite) were used as control, as well as commercial beans (Phaseolus vulgaris). Seed structures of A. capricorne and A. ornatum are consistent with water dispersal (hat shape, a funicular envelope covering a prominent hilum, and air chambers throughout the tegument). Seeds of A. capricorne showed the greatest water permeability, higher than those of A. ornatum which had similar permeability to common beans and mesquite. Acacia farnesiana and Opuntia streptacantha had the lowest permeability. Seeds of A. capricorne without a funicular layer floated more than those with a funicular layer. All seeds of A. ornatum floated initially, but 10% of those with funicular layer sank after a 30 days floating period. P. laevigata seeds floated also, but less than those of Astrophytum spp., and seeds of A. farnesiana and Phaseolus vulgaris did not float. Germination of A. capricorne was high under all treatments, both when immersed in a water layer or only moistened. Germination of A. ornatum was generally low (<30%), with <5% germination for seeds immersed in water and for those placed on a water film. Seeds of A. capricorne germinated slower in a water layer than in other treatments. No difference in germination rate was found across all treatments in A. ornatum.     

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.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

干扰对动物传播森林植物种子有效性影响的研究进展

干扰在森林生态系统中普遍存在,并影响森林的更新和演替.动物传播种子是种子更新的必经阶段,其对森林干扰的响应在一定程度上能够预测未来的森林群落组成和结构变化,对于明确森林演替方向具有重要意义.本文论述了森林干扰对动物传播种子有效性(包括动物传播种子的数量和质量)影响研究的生态学意义,全面揭示了自然干扰(火干扰、林窗干扰等)和人为干扰(生境破碎化、狩猎、采伐等)对动物传播种子数量、传播距离以及传播后幼苗更新影响的研究进展,指出干扰通过影响动物种群动态,进而造成动物传播种子数量发生了改变,动物传播种子的距离对干扰的响应基本表现出轻微负相关;干扰对传播后幼苗更新的影响结果因干扰类型的不同而复杂多变,干扰迹地环境因子的变化也影响着传播后的种子萌发和幼苗更新.干扰对动物传播种子有效性影响研究中存在的问题,主要表现为火干扰迹地恢复过程、增益性的干扰(如抚育、间伐、林窗)等对种子传播有效性影响研究的匮乏,以及忽略了温带森林内的干扰对动物传播种子的影响等.今后,应开展干扰对种子传播有效性的长期研究;对于干扰多发地带的森林,应高度重视增益性干扰影响动物传播植物种子的研究.     

Seed dispersal of the non-native invasive tree <Emphasis Type="Italic">Ailanthus altissima</Emphasis> into contrasting environments

Ailanthus altissima has a long history of invasion in urban areas and is currently spreading into suburban and rural areas in the eastern U.S. The objectives of our study were to (1) determine whether A. altissima seed dispersal distance differed between populations on the edges of open fields and intact deciduous forest, and (2) determine whether dispersal differed for north and south winds. We also assessed the relationship between seed characteristics and distance from source populations in fields and forests, and whether seeds disperse at different rates throughout the dispersal season. Using two fields, two intact forest stands, and one partially harvested stand, we sampled the seed rain at 10 m intervals 100 m into each site from October to April 2002–2003. We compared seed density in field and intact forests using a three-way ANOVA with distance from source, wind direction, and environmental structure as independent variables. To assess the accuracy of common empirical dispersal models, mean seed density data at each site were fitted with alternative regression models. We found that mean seed dispersal distance depended on environmental structure and wind direction, a result driven in large part by dispersal at a single site where seed density did not decline with distance. The two alternative regression models fit each site’s dispersal curve equally well. More seeds were dispersed early than in mid- or late-season. Large, heavy seeds traveled as far as small light seeds. Turbulent winds appear to be necessary for seed release, as indicated by a wind tunnel experiment. A. altissima is able to disperse long distances into fields and into mature forests, and can reach canopy gaps and other suitable habitats at least 100 m from the forest edge. It is an effective disperser and can spread rapidly in fragmented landscapes where edges and other high light environments occur. These conditions are increasingly common throughout the eastern U.S. and in other temperate regions worldwide.     

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.     

Long distance seed dispersal by wind: measuring and modelling the tail of the curve

The size and shape of the tail of the seed dispersal curve is important in determining the spatial dynamics of plants, but is difficult to quantify. We devised an experimental protocol to measure long-distance dispersal which involved measuring dispersal by wind from isolated individuals at a range of distances from the source, but maintaining a large and constant sampling intensity at each distance. Seeds were trapped up to 80 m from the plants, the furthest a dispersal curve for an individual plant has been measured for a non-tree species. Standard empirical negative exponential and inverse power models were fitted using likelihood methods. The latter always had a better fit than the former, but in most cases neither described the data well, and strongly under-estimated the tail of the dispersal curve. An alternative model formulation with two kernel components had a much better fit in most cases and described the tail data more accurately. Mechanistic models provide an alternative to direct measurement of dispersal. However, while a previous mechanistic model accurately predicted the modal dispersal distance, it always under-predicted the measured tail. Long-distance dispersal may be caused by rare extremes in horizontal wind speed or turbulence. Therefore, under-estimation of the tail by standard empirical models and mechanistic models may indicate a lack of flexibility to take account of such extremes. Future studies should examine carefully whether the widely used exponential and power models are, in fact, valid, and investigate alternative models. Received: 7 March 1999 / Accepted: 2 April 2000     

Timing and spatial patterning of seed dispersal and redistribution in a South American warm desert

We measured newly-produced seeds entering the soil (Potential Seed Bank) to assess the timing and spatial patterning of Phase I dispersal in the central Monte desert, Argentina. Rates of forb- (6.13 mg m^-2 d^-1) and shrub-seed input (48.9 mg m^-2 d^-1) were maximum in early summer. The rate of grass-seed input, instead, was similar in early and late summer (7 to 8 mg m^-2 d^-1). About 90% of forb- and shrub-seed mass entered the habitat through protected (i.e., under canopy) areas, whereas 70% of grass-seed mass did so through exposed areas. Adult plant location and the uneven impact of wind on shrub, forb and grass seeds may explain such patterns.We also compared the Potential Seed Bank with the soil seed bank in the following spring (Realized Seed Bank). Seeds that form transient banks in other ecosystems (e.g., shrub seeds of the genus Larrea, or perennial grass seeds like those of Pappophorum and Trichloris) prevailed in the Potential Seed Bank. Some annual forb seeds, instead, appeared to form a more persistent seed bank, and prevailed in the Realized Seed Bank (e.g., Chenopodium). Horizontal redistribution did not affect the spatial patterning of forb and shrub seeds, but produced a more homogeneous distribution of grass seeds in the habitat. The impact of wind could explain the redistribution pattern of grass seeds. Finally, we found almost 80% of total seeds in the top 2 cm of soil. The smallest grass and forb seeds (Sporobolus and Descurainia) as well as some medium-sized and large forb seeds (e.g., Glandularia, Sphaeralcea, Phacelia) were able to reach deeper soil layers in the central Monte desert.     

Potential for red spruce (Picea rubens Sarg.) establishment from natural seed dispersal in old fields adjacent to forest stands

Red spruce can establish on abandoned agricultural land only from seed, unlike in logged environments where red spruce forests can establish from seedlings that survived the harvest. In this study we collected seeds from the seed rain and from soil cores to examine the abundance and distribution of the red spruce seed rain and the seed bank along a gradient from the forest interior to adjacent old fields in Greenwich, Prince Edward Island National Park (PEINP), Canada. In addition, we examined the temporal abundance and distribution of the seed rain through the seed-fall season. We subsequently tested the germination potential of red spruce seeds from the forest portion of our sites. Because red spruce seeds are usually viable for only one year, we expected the seed bank to be either very small or non-existent. We found 39 red spruce seeds in the seed bank, distributed over 13.1% of the sampled area; 37 of these seeds were definitely nonviable. From the seed rain, we collected 224 red spruce seeds, distributed over 29.4% of the sampled area; 213 of these seeds were definitely nonviable. Nearly all of the red spruce seed rain fell within the forest; differences in abundance among collection dates were not statistically significant. Our seeds had a low germination rate of 0.004%, in part because red and black spruce commonly hybridise in our study area. Despite the low rates of red spruce seed dispersal and viability, the presence of red spruce saplings in our two longest-abandoned fields shows that the species is able to slowly colonise some old fields in PEINP.     

Migration load in plants: role of pollen and seed dispersal in heterogeneous landscapes

Evolution of local adaptation depends critically on the level of gene flow, which, in plants, can be due to either pollen or seed dispersal. Using analytical predictions and individual-centred simulations, we investigate the specific influence of seed and pollen dispersal on local adaptation in plant populations growing in patchy heterogeneous landscapes. We study the evolution of a polygenic trait subject to stabilizing selection within populations, but divergent selection between populations. Deviations from linkage equilibrium and Hardy-Weinberg equilibrium make different contributions to genotypic variance depending on the dispersal mode. Local genotypic variance, differentiation between populations and genetic load vary with the rate of gene flow but are similar for seed and pollen dispersal, unless the landscape is very heterogeneous. In this case, genetic load is higher in the case of pollen dispersal, which appears to be due to differences in the distribution of genotypic values before selection.     

油质体在5种蚁播植物种子散布中的作用

蚁播植物种子上常附着有蚂蚁喜食的油质体,该物体可吸引蚂蚁取食或为蚂蚁提供钳着位点从而影响种子散布。为进一步揭示油质体在种子散布中的作用,在野外研究了4属5种典型蚁播植物包括小花宽瓣黄堇(Corydalis giraldii Fedde)、假刻叶紫堇(C.pseudoincisa C.Y.Wu)、白屈菜(Chelidonium majus L.)、紫花堇菜(Viola grypoceras A.Gray)和柔毛淫羊藿(Epimedium pubescens Maxim.)其相应的搬运蚂蚁即玉米毛蚁(Lasius alienus(Foerster))和尼特纳大头蚁(Pheidole nietneri Emery)对植物完整种子(SE)、去除油质体的种子(S)和粘有人工模拟油质体的种子(S+H)的搬运行为和搬运效率。结果显示,蚂蚁对相同植物3类种子的触碰和检查次数均无显著差异。蚂蚁对种子的尝试搬运次数除玉米毛蚁对小花宽瓣黄堇、假刻叶紫堇和白屈菜去除油质体的种子(S)显著高于完整种子(SE)和粘有人工模拟油质体的种子(S+H)外,其它的均无显著差异。玉米毛蚁对小花宽瓣黄堇、假刻叶紫堇、白屈菜和紫花堇菜以及尼特纳大头蚁对小花宽瓣黄堇、假刻叶紫堇和紫花堇菜完整种子(SE)的搬运效率显著高于粘有人工模拟油质体的种子(S+H)和去除油质体的种子(S),此外,玉米毛蚁对小花宽瓣黄堇粘有人工模拟油质体的种子(S+H)的搬运效率显著高于去除油质体的种子(S)。这说明玉米毛蚁在搬运小花宽瓣黄堇种子过程中油质体不仅起到吸引作用,而且起到钳着位点作用;玉米毛蚁在搬运假刻叶紫堇、白屈菜和紫花堇菜以及尼特纳大头蚁搬运小花宽瓣黄堇、假刻叶紫堇和紫花堇菜种子过程中油质体仅起到吸引作用。研究表明油质体可通过对蚂蚁起吸引作用,或同时起吸引和钳着位点的双重作用等影响种子散布,油质体的影响作用不但取决于植物种类,也与搬运蚂蚁的种类有关。