Quantity,quality and the effectiveness of seed dispersal by animals

Disperser effectiveness is the contribution a disperser makes to the future reproduction of a plant. Although it is a key notion in studies of seed dispersal by animals, we know little about what determines the effectiveness of a disperser. The role of the present paper is to review the available information and construct a hierarchical framework for viewing the components of disperser effectiveness.Effectiveness has both quantitative and qualitative components. The quantity of seed dispersal depends on (A) the number of visits made to the plant by a disperser and (B) the number of seeds dispersed per visit. The quality of seed dispersal depends on (A) the quality of treatment given a seed in the mouth and in the gut and (B) the quality of seed deposition as determined by the probability that a deposited seed will survive and become an adult. In this paper I review the ways disperser behavior, morphology and physiology can influence these major components of disperser effectiveness, and when data permit present preliminary analyses of relationships among components.     

Seed dispersal by ungulates in the point calimere wildlife sanctuary: A scientific and perspective analysis

Exotic woody weed plants are a very serious threat to seed dispersed by ungulate in the tropical forest of Asia. The ungulates in Point Calimere Wildlife Sanctuary (PCWS) are a significant role in native indigenous seed dispersal. The exotic woody weed tree Prosopis juliflora prevalence distributed in the PCWS and they might potentially alter the native medicinal plant species. In the present investigation, we have assessed the seed dispersal by ungulates in PCWS from January to March 2017. Four different ungulate species were selected to understand their seed dispersal rate of different plant species in selected sanctuary. This investigation was planned to confirm the seed dispersal by ungulates of blackbuck, spotted deer, wild boar and feral horse. Among the four different ungulates tested, the maximum numbers of pellets collected from blackbuck and no seed found in their pellets. The low quantities of pellets were collected from wild boar and this study has recorded medium-sized ungulates which dispersed variety of plant. However, the dispersal of the seed of medicinal plants were not considerably high and relatively moderate percentage of seeds dispersal occurred in medium-sized ungulates like wild boar and spotted deer. P. juliflora had 100% seed germination rate were observed from the faecal samples of wild boar and feral horse. The control seed achieved maximum seedling rate than the ungulates seeds.     

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     

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.     

Long-distance dispersal of tree seeds by wind

Some mechanisms that promote long-distance dispersal of tree seeds by wind are explored. Winged seeds must be lifted above the canopy by updrafts to have a chance of further dispersal in high velocity horizontal winds aloft or in landscape-scale convection cells. Shear-induced turbulent eddies of a scale up to one-third of canopy height provide a lifting mechanism. Preliminary data suggest that all seeds of a given species may be viable candidates for uplift and long-distance dispersal, despite the evidence that slow-falling seeds are dispersed farther under any given wind conditions. Turbulence is argued more often and more extensively to advance long-distance dispersal than to retard it. Seeds may take advantage of Bernoulli sailing to move with faster than average winds. Elasticity of branches and trees may play a role in regulating the release of seeds into unusually favorable winds. Dispersal is at least biphasic, and the study of long-distance dispersal calls for mixed models and mixed methods of gathering data.     

Plant colonization: are wind dispersed seeds really dispersed by birds at larger spatial and temporal scales?

ABSTRACT. It is suggested that many plant species often thought of as wind dispersed may in fact be largely dispersed by animals, mostly birds, at larger spatial and temporal scales. This possibility is illustrated by using data on Holocene tree migrations in Europe. It is suggested that exploratory movements, often by young birds, may play an important role in such dispersal rather than the classic return migrations of birds. In the case of European trees there could have been active selection for rapid migrations occurring even in the glacial refugia sites in the mountains of southern Europe. Plant migration rates, and hence the ability to deal with climatic change, may have been lower before the evolution of a diverse avifanua. It is suggested that for many 'wind dispersed' seeds the wind dispersal mechanism is adapted to local dispersal (over distances of a few canopy diameters) and larger scale dispersion is due to birds.     

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.     

Larger seeds in tropical floras: consistent patterns independent of growth form and dispersal mode

Many species of tropical moist forests have large seeds compared to those found in temperate floras. This could be attributed to a prevalence of woody growth forms, or adaptation to dispersal by vertebrates, or the dense shade of a closed canopy, rather than to an intrinsic tropical v. temperate difference. We compared tropical v. temperate seed mass data at two geographic scales; firstly within Australia between tropical, subtropical and temperate open woodlands, then between six tropical and temperate datasets from five continents. Within Australia we found that seed mass increased with decreasing latitude in ten out of eleven growth form-dispersal mode combinations: only wind-dispersed graminoids showed no significant effect. While the pattern of generally larger seeds in the tropical flora was associated with tropical families tending to have larger seeds than temperate families, we also found that tropical species had larger seeds than temperate cofamilials. As a preliminary test of the generality of these findings we included a further four tropical and temperate data sets in a second analysis. Average tropical seed masses were larger than temperate seed masses in all testable growth form-dispersal mode combinations, and statistically larger in five out of seven cases: unassisted, vertebrate- and wind-dispersed woody species, and unassisted and vertebrate-dispersed forbs. No difference was found for wind-dispersed forbs or for graminoids lacking dispersal structures. That an effect was found in these combinations rules out explanations based solely on characteristics of tropical v. temperate dispersers, although this may be a contributing factor. Instead we suggest that some aspect of tropical systems, for example higher metabolic costs of seedling production, has selected for a general increase in seed mass among tropical taxa.     

Plant-defense mimicry facilitates rapid dispersal of short-lived seeds by hornets

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Cheek-pouch dispersal of seeds by Japanese monkeys (Macaca fuscata yakui) on Yakushima Island, Japan

Seed dispersal by Japanese monkeys (Macaca fuscata yakui) via cheek-pouch was studied in a warm temperate evergreen forest on Yakushima Island. Plant list was compiled based on a study during 1986–1995, of which troops of monkeys have been habituated without artificial feeding. We followed the well-habituated monkeys in 1993 and 1994 to observe the feeding behavior and their treatments of fruits and seeds, and collected seeds dispersed by monkeys to record the distance carried from the mother trees. We checked the difference of germination ratio between seeds dispersed via cheek-pouch and seeds taken from mother trees by sowing experiments. Seeds and acorns of 22 species were observed to be dispersed via cheek-pouch of monkeys. Among them, three species with acorns were never dispersed via feces, and 15 species with drupes were seldom dispersed via feces. Plant species of which seeds are dispersed only via cheek-pouch had larger seeds than those of dispersed both via cheek-pouch and via feces, and typically had only one or two seeds in a fruit. As for one of cheek-pouch dispersal species,Persea thunbergii, the mean distance when seeds were carried from the mother trees via cheek-pouch was 19.7 m, and the maximum distance was as long as 105 m although more than 80% of seeds were dispersed within 30 m from mother trees. And 82% of seeds dispersed via cheek-pouch germinated. The easy separation of seeds from other parts of the fruit seems to facilitate cheek-pouch dispersal more than dispersal via feces. Cheek-pouch dispersal by monkeys has possibly enhanced the natural selection for larger seeds which bring forth larger seedlings with high shade-tolerance. In conclusion, cheek-pouch dispersal by monkeys is quite an important mode for trees in the mature stand in a warm temperate evergreen forest on Yakushima Island.     

A herbivory-induced increase in the proportion of floating seeds in an invasive plant

It is important to determine the factors prompting seed dispersal because for plant species seed dispersal is the only opportunity to disperse into a new habitat. Previous studies showed that the maternal stress, such as high density and low nutrient levels, induces the adaptive plastic increase of the dispersal ability in seed heteromorphic plants. In this study, we examined whether herbivory can change the relative proportion of dispersal-related seed heteromorphism (floating or non floating seeds) in an invasive weed Ambrosia artemisiifolia. Because A. artemisiifolia often distributes in the riparian habitat, floating seeds might contribute to the long distance dispersal by hydrochory. Floating ability and seed weight were compared between plants damaged by a specialist herbivore Ophraella communa and undamaged plants. The damaged plants produced lighter and more likely floating seeds than the undamaged plants. However, multi-regression analysis revealed that the probability of floating was affected by seed weight but was not affected by herbivore treatment (damaged vs. undamaged plants). These results suggest that the increased proportion of floating seeds was not a direct response to the herbivore signal but an indirect response through the herbivore's effect on the reduction of seed weight. Plants damaged by herbivores might not only decrease seed production and quality but also increase the dispersal ability. These responses in dispersal ability against the herbivores might contribute to the spread of invasive plants.     

以种子为繁殖体的植物更新模型研揪

种子植物的自然更新过程是20世纪70年代以来生态学领域研究的热点问题之一。对影响种子植物更新过程因子的研究主要涉及3个阶段,即种子生产、种子运动(主要为种子扩散的过程)和种子萌发、幼苗建成以及幼树生长到成树。一些完整的理论和实验模型被提出。反过来模型的研究促进了野外研究的进一步发展。关于种子植物更新的定性模型和定量模型陆续被提出,定量研究种子植物的更新过程将成为主要的发展方向。本文综述了近年来关于种子植物更新过程的3个较为完整的定性模型,即Chambers等的种子命运模型、Clark等的补充限制模型和Nathan等的时空模型,以及2个定量模型,即Vander和Boehning等的种子扩散模型。     

济源太行山区鼠类对三种林木种子的扩散和贮藏

对取食种子的动物而言,种子的选择、扩散以及随后的处理是一个复杂的过程。为了解济源太行山区鼠类对不同种林木种子的选择和扩散策略的差异,于2011 年9 月10 日至11 月8 日,选取山杏、桃和栓皮栎3 种林木种子,将种子标记后,释放于次生林中,以5 d 间隔,调查并记录种子命运。结果表明: (1)大林姬鼠和岩松鼠是该地区主要的种子取食者和扩散者; (2)3 种种子的扩散速率明显不同,栓皮栎种子扩散速率最快(中位存留时间8. 6 d),其次为山杏种子(中位存留时间20. 9 d),桃种子扩散速率最慢(中位存留时间37. 5 d); (3)鼠类倾向于取食栓皮栎种子(55.0%) , 埋藏山杏种子(62. 0% ),但忽略桃种子(原地存留率99. 0% );(4)88. 6%的山杏和78. 8% 的栓皮栎种子被贮藏在灌丛下方、树干基部周围和石块旁边等生境中,而仅有4 3% 的山杏和9.1% 的栓皮栎种子被贮藏于裸地中;(5)鼠类将山杏种子搬运到更远(3. 4 ± 2. 1 m,mean± SE,n =63)处贮藏;而栓皮栎种子的搬运距离则相对较近(2. 5 ± 2. 4 m,n = 57)。结果显示:鼠类对不同种植物种子具有明显的取食、贮藏偏好和不同的贮藏策略。     

Introducing cultivated trees into the wild: Wood pigeons as dispersers of domestic olive seeds

Animals may disperse cultivated trees outside the agricultural land, favoring the naturalization or, even, the invasiveness of domestic plants. However, the ecological and conservation implications of new or unexplored mutualisms between cultivated trees and wild animals are still far from clear. Here, we examine the possible role of an expanding and, locally, overabundant pigeon species (Columba palumbus) as an effective disperser of domestic olive trees (Olea europaea), a widespread cultivated tree, considered a naturalized and invasive species in many areas of the world. By analyzing crop and gizzard content we found that olive fruits were an important food item for pigeons in late winter and spring. A proportion of 40.3% pigeons consumed olive seeds, with an average consumption of 7.8 seeds per pigeon and day. Additionally, most seed sizes (up to 0.7 g) passed undamaged through the gut and were dispersed from cultivated olive orchards to areas covered by protected Mediterranean vegetation, recording minimal dispersal distances of 1.8–7.4 km. Greenhouse experiments showed that seeds dispersed by pigeons significantly favored the germination and establishment in comparison to non-ingested seeds. The ability of pigeons to effectively disperse domestic olive seeds may facilitate the introduction of cultivated olive trees into natural systems, including highly-protected wild olive woodlands. We recommend harvesting ornamental olive trees to reduce both pigeon overpopulation and the spread of artificially selected trees into the natural environment.     

Seed dispersal spectra of plant communities in the Iberian Peninsula

We studied the seed dispersal spectra of 46 Iberian plant communities of five types: potential woodland, forest fringe, substitutional scrubland, nitrophile communities and montane communities. There were no significant differences between the spectra of communities of the same type from Mediterranean and Eurosiberian regions. Biotic dispersal is most common at mature stages of succession, and abiotic dispersal at immature stages.     

Savanna fires increase rates and distances of seed dispersal by ants

Myrmecochory (seed dispersal by ants) is a prominent dispersal mechanism in many environments, and can play a key role in local vegetation dynamics. Here we investigate its interaction with another key process in vegetation dynamics—fire. We examine ant dispersal of seeds immediately before and after experimental burning in an Australian tropical savanna, one of the world’s most fire-prone ecosystems. Specifically, our study addressed the effects of burning on: (1) the composition of ants removing seeds, (2) number of seed removals, and (3) distance of seed dispersal. Fire led to higher rates of seed removal post-fire when compared with unburnt habitat, and markedly altered dispersal distance, with mean dispersal distance increasing more than twofold (from 1.6 to 3.8 m), and many distance dispersal events greater than the pre-fire maximum (7.55 m) being recorded. These changes were due primarily to longer foraging ranges of species of Iridomyrmex, most likely in response to the simplification of their foraging landscape. The significance of enhanced seed-removal rates and distance dispersal for seedling establishment is unclear because the benefits to plants in having their seeds dispersed by ants in northern Australia are poorly known. However, an enhanced removal rate would enhance any benefit of reduced predation by rodents. Similarly, the broader range of dispersal distances would appear to benefit plants in terms of reduced parent–offspring conflict and sibling competition, and the location of favourable seedling microsites. Given the high frequency of fire in Australian tropical savannas, enhanced benefits of seed dispersal by ants would apply for much of the year.     

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。