种子重量的生态学研究进展

作为植物生活史中的一个关键性特征,种子重量与其它许多植物性状和生态因子有关,种子重量的分异与其它一些植物性状及环境的变化关系在进化生物学上已经成为一个非常有意义的研究内容,且具有一定的实践意义。种子重量被发现与下列的一些植物学和群落学性状有关:植物的生活型、种子的散布能力、种子的散布方式、植物的高度、植物的冠幅、植物的比叶面积、植物的寿命、动物的捕食、植被中植物的数量或多度、土壤中种子的数量或多度、种子的休眠、种子在土壤中的持久性和植物的净初级生产力等,另外生态因子如降雨、温度、坡向、海拔、经度、纬度、光强和干扰等都影响种子的重量。种子的重量被认为是在大量小种子和少量大种子之间的进化折衷,在一定的能量限度内,较大重量的种子一般具有较少的数量,而较小重量的种子一般数量较多,这是种子重量和数量方面具有的一种反向关系。与其它性状相比,很多研究都表明种子重量和植物的生活型的关系密切。没有散布结构或风散布的种子比以动物和水作为散布媒介的种子重量要小。种子重量与捕食的关系现发现有3种格局。种子重量和形状与种子在土壤中的持久性的关系有4种格局。在干旱和阴暗的环境条件下,种子有变大的趋势。大重量种子比小种子赋予幼苗较优势的竞争地位,其原理尚有争论,尚不清楚是否是幼苗阶段的竞争决定了世界上大部分植被类型的物种组成。未来的研究方向主要有以下几个方面:1) 种子重量与植物系统学相结合,探索种子重量的变化规律;2)调查群落三向(纬度、经度和海拔)性的种子重量谱变化规律;3) 群落演替与群落种子重量谱的变化;4) 种子重量与群落中植物个体和种子的数量的关系及机理研究;5) 微生境、微地形如坡向、坡位和林间隙等对种子重量的影响;6) 全球气候变化和种子重量变化的关系。     

片段化景观中壳斗科植物种子捕食和扩散模式

生境片段化伴随的面积效应和边缘效应, 可改变分散贮食动物的竞争强度、觅食行为以及隐蔽条件, 影响种子捕食和扩散模式。阐明生境片段化对多物种种子捕食和扩散的影响, 对理解片段化生境中的植物更新和生物多样性维持十分重要。该研究在浙江省千岛湖地区的岛屿和大陆上开展了针对6种壳斗科植物的种子捕食和扩散实验, 分析了物种、分散贮食动物相对多度、种子产量、岛屿大小和边缘效应如何共同影响种子命运和种子扩散距离。主要结果: (1)种子命运和扩散距离在物种间存在显著差异; (2)大陆比岛屿有更长的种子留存时间, 小岛种子留存时间最短, 岛屿内部比岛屿边缘有更长的种子留存时间; (3)物种和岛屿大小对种子原地取食率存在交互作用, 白栎(Quercus fabri)种子在大岛上有更高的原地取食率; (4)种子在小岛上有最高的扩散率, 分散贮食动物相对多度对种子扩散后贮藏率有负效应。表明在千岛湖地区, 生境片段化改变了种子捕食和扩散模式, 且面积效应对不同物种的种子捕食和扩散模式产生了不同作用, 从而影响森林群落更新和生物多样性维持。     

Evolutionary size changes in plants of the south‐west Pacific

Aim To investigate evolutionary changes in the size of leaves, stems and seeds of plants inhabiting isolated islands surrounding New Zealand. Location Antipodes, Auckland, Campbell, Chatham, Kermadec, Three Kings and Poor Knights Islands. Methods First, we compared the size of leaves and stems produced by 14 pairs of plant taxa between offshore islands and the New Zealand mainland, which were grown in a common garden to control for environmental effects. Similar comparisons of seed sizes were made between eight additional pairs of taxa. Second, we used herbarium specimens from 13 species pairs to investigate scaling relationships between leaf and stem sizes in an attempt to pinpoint which trait might be under selection. Third, we used herbarium specimens from 20 species to test whether changes in leaf size vary among islands located at different latitudes. Lastly, we compiled published records of plant heights to test whether insular species in the genus Hebe differed in size from their respective subgenera on the mainland. Results Although some evidence of dwarfism was observed, most insular taxa were larger than their mainland relatives. Leaf sizes scaled positively with stem diameters, with island taxa consistently producing larger leaves for any given stem size than mainland species. Leaf sizes also increased similarly among islands located at different latitudes. Size changes in insular Hebe species were unrelated to the average size of the respective subgenera on the mainland. Main conclusions Consistent evidence of gigantism was observed, suggesting that plants do not obey the island rule. Because our analyses were restricted to woody plants, results are also inconsistent with the ‘weeds‐to‐trees’ hypothesis. Disproportionate increases in leaf size relative to other plant traits suggest that selection may favour the evolution of larger leaves on islands, perhaps due to release from predation or increased intra‐specific competition.     

A multi-scale test for dispersal filters in an island plant community

Constraints on plant distributions resulting from seed limitation (i.e. dispersal filters) were evaluated on two scales of ecological organization on islands off the coast of British Columbia, Canada. First, island plant communities were separated into groups based on fruit morphology, and patterns in species diversity were compared between fruit‐type groups. Second, abundance patterns in several common fleshy‐fruited, woody angiosperm species were compared to species‐specific patterns in seed dispersal by birds. Results from community‐level analyses showed evidence for dispersal filters. Dry‐fruited species were rare on islands, despite being common on the mainland. Island plant communities were instead dominated by fleshy‐fruited species. Patterns in seed dispersal were consistent with differences in diversity, as birds dispersed thousands of fleshy‐fruited seeds out to islands, while dry fruited species showed no evidence of mainland‐island dispersal. Results from population‐level analyses showed no evidence for dispersal filters. Population sizes of common fleshy‐fruited species were unrelated to island isolation, as were rates of seed dispersal. Therefore, island isolation distances were not large enough to impose constraints on species’ distributions resulting from seed limitation. Rates of seed dispersal were also unrelated to island area. However, several species increased in abundance with island area, indicating post‐dispersal processes also help to shape species distributions. Overall results suggest that seed dispersal processes play an important role in determining the diversity and distribution of plants on islands. At the community‐level, dry‐fruited species were seed limited and island communities were instead dominated by fleshy‐fruited species. At the population‐level, common fleshy‐fruited species were not seed limited and showed few differences in distribution among islands. Therefore, although evidence for dispersal filters was observed, their effects on plant distributions were scale‐dependent.     

Geographic variation in seed traits within and among forty‐two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude,habitat, plant height,and phylogeny

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra‐ and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long‐term adaptation and constraints of the taxonomic group over their long evolutionary history.     

Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

Influence of selfing and maternal effects on life-cycle traits and dispersal ability in the herb Hypochaeris radicata (Asteraceae)

The ecological and evolutionary implications of dispersal are many. Pollination type and maternal effects may affect plant fitness traits, including life-cycle traits as well as dispersal ability. This study investigated the joint influence of pollination type and maternal effects on both life-cycle traits and dispersal ability in the herb Hypochaeris radicata . We conducted experimental crosses to obtain selfed and outcrossed progeny. Individual seeds and their pappuses were measured to determine seed terminal velocity. Seed size was also used to assess maternal effects. Selfing dramatically decreased seed set, indicating that H. radicata is self-incompatible. However, the few selfed seeds produced outperformed outcrossed seeds in seed size and flowering probability, surely as a result of an effective reallocation of resources among selfed seeds. None of the life-cycle traits was affected by seed size, the estimate of maternal effects. Selfed seeds were larger and bore a smaller pappus than outcrossed seeds. As a result, dispersal ability was lower for selfed than outcrossed seeds. Several factors, such as the low proportion of plants that produced selfed seeds, the low number of selfed seeds produced per plant, and the lack of self-fertility mechanisms might act in concert to prevent the evolution of selfing in H. radicata .  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 163–170.     

D3: The Dispersal and Diaspore Database – Baseline data and statistics on seed dispersal

Seed dispersal is hard to measure, and there is still a lack of knowledge about dispersal-related traits of plant species. Therefore, we developed D³, the Dispersal and Diaspore Database (available at www.seed-dispersal.info), which aims at simplifying ecological and evolutionary analyses by providing and integrating various items related to seed dispersal: empirical studies, functional traits, image analyses and ranking indices (quantifying the adaptation to dispersal modes).Currently, the database includes data for more than 5000 taxa and 33 items as well as digital images of diaspores (i.e. the dispersal units), seeds, fruits and infructescences. The included items cover common traits like diaspore mass, size, shape, terminal velocity and seed number per diaspore. Furthermore, we present newly or further developed items like ecomorphological categorizations of the diaspore and fruit as well as information from literature on prevailing dispersal modes. Finally, we introduce several items which are not covered in other databases yet: surface structure and form of the diaspore, the exposure of the diaspores in the infructescence and dispersal rankings. Dispersal rankings allow estimations of how well certain species are adapted to a specific dispersal mode in comparison to a larger species set. They are calculated as the percentile rank of an indicator of species’ dispersal potential in relation to a larger species set.Especially for the new and further developed items we outline the basic concepts in detail, describe the measurement and categorization methods and show how to interpret and integrate these data for single species as well as for larger species sets. Thereby, we calculate baseline statistics of seed dispersal of the Central European flora. We found that diaspores of 72% of the taxa show specializations related to long-distance dispersal, i.e. most often elongated appendages or nutrient-rich tissues. Diaspore masses, sizes and terminal velocities vary over several orders of magnitude and can be approximated by lognormal distributions.     

Seed size predicts global effects of small mammal seed predation on plant recruitment

Recent studies demonstrate that by focusing on traits linked to fundamental plant life‐history trade‐offs, ecologists can begin to predict plant community structure at global scales. Yet, consumers can strongly affect plant communities, and means for linking consumer effects to key plant traits and community assembly processes are lacking. We conducted a global literature review and meta‐analysis to evaluate whether seed size, a trait representing fundamental life‐history trade‐offs in plant offspring investment, could predict post‐dispersal seed predator effects on seed removal and plant recruitment. Seed size predicted small mammal seed removal rates and their impacts on plant recruitment consistent with optimal foraging theory, with intermediate seed sizes most strongly impacted globally – for both native and exotic plants. However, differences in seed size distributions among ecosystems conditioned seed predation patterns, with relatively large‐seeded species most strongly affected in grasslands (smallest seeds), and relatively small‐seeded species most strongly affected in tropical forests (largest seeds). Such size‐dependent seed predation has profound implications for coexistence among plants because it may enhance or weaken opposing life‐history trade‐offs in an ecosystem‐specific manner. Our results suggest that seed size may serve as a key life‐history trait that can integrate consumer effects to improve understandings of plant coexistence.     

Seeds photoblastism and its relationship with some plant traits in 136 cacti taxa

Seed germination triggered by light exposure (positive photoblastism) has been determined in quantitative studies for numerous plant families and species. For Cactaceae, positive photoblastism is thought to be associated with life form and seed mass, but this association has never been evaluated. To explore hypotheses on associations between seed mass, seed dispersal, seed dormancy, life form, taxa and plant height with Relative Light Germination (RLG) in Cactaceae, we evaluated the effect of light on seed germination of 136 taxa. The taxa studied are native to several countries: México, Chile, Argentina, Brazil, Perú, USA, and Venezuela. Seed traits contrasted with RLG were life form, seed mass, seed dispersal, seed dormancy, adult plant height and taxon. We found some differences between RLG among taxa; Cacteae, Pachycereeae and Trichocereeae had higher RLG than Notocacteae. RLG was lower for seeds from taller than for shorter taxa, and lower for taxa with heavier seeds than for taxa with lighter seeds. Dispersal syndrome groups varied with RLG. RLG did not differ between cylindrical and globose taxa. Trends found here were in agreement with expectations for small-seeded species to have a light requirement to germinate more often than large-seeded species. This is the first time that cactus height is related to photoblastism. It is possible that seeds from tall plants are larger and thus have the capacity to produce taller seedlings than those from small plants, and that seedlings from large seeds with more resources have the ability to emerge from greater soil depths than those from small seeds.     

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.     

Convergent evolution of gigantism in the flora of an isolated archipelago

Animals often evolve conspicuous differences in body size after colonising isolated islands. However, far less is known about repeated patterns in the evolution of plant size on islands. We tested for convergent evolution of leaf area, seed size and plant stature in the flora of the Chatham Islands (i.e. Rēkohu), which are located 700 km off the east coast of New Zealand. First, we measured leaf area, seed size and plant stature from populations of 22 plant taxa on the Chatham Islands. These data were then compared to analogous measurements from their sister taxa on the mainland to test for evidence of island gigantism, and whether size changes differ between leaves, seeds and stature. Second, we collated data from the literature to test whether size changes in endemic taxa differed among plant growth forms or were correlated with divergence times. Results showed that all three plant traits tended to increase in size on the Chatham Islands. However, field data showed that size increases tended to be more consistent in seeds and leaves than in stature. Data from the literature indicated that size increases also differed among growth forms. Herbaceous species showed the strongest evidence of gigantism, followed by woody plants, while graminoids showed a weak trend towards dwarfism. Insular size increases in seeds and leaves were also positively related to divergence times, indicating that taxa which have resided on the Chatham Islands for longer periods show stronger evidence of gigantism than taxa which arrived more recently. Overall results illustrate that gigantism is a hallmark of the Chatham Island flora, providing a remarkable example of convergent evolution.     

Influence of seed size on dispersal patterns of woolly monkeys (Lagothrix lagothricha) at Tinigua Park, Colombia

Seed size in tropical forests is expected to vary in relation to dispersal mode, recruitment requirements and the nature of seed enemies in each community. Some studies have emphasized an advantage of large-seeded species in environments subject to low rates of disturbance, but at the same time the number of dispersers tends to decrease as seed size increases. In this paper we describe how seed size affects the probabilities of seed dispersal by woolly monkeys at Tinigua National Park and we compare dispersal patterns among age/sex classes. The results are based on 1236 fecal samples recovered from focal individuals during two years. Woolly monkeys are able to swallow wide seeds; however, there seems to be a limit imposed by anatomical constraints that does not allow them to swallow seeds wider than 18 mm. Most of the seed mass dispersed by the monkeys falls in the categories between 6 and 12 mm wide. Seed selection in terms of mass was not observed for small-seeded species, but it was observed for some of the medium sized species (without any clear size preference) and there was a clear tendency to swallow relatively small seeds from the large-seeded species. Although we did not observe a difference in the number of seeds dispersed by deposition among age/sex classes, juveniles disperse a lower seed mass than adult animals. These differences highlight that different age/sex categories play distinct ecological roles in terms of seed dispersal processes. Seed selection by primates might impose selection pressures in seed size traits, but more studies are necessary to ascertain their potential evolutionary role.     

Functional traits but not environmental gradients explain seed weight in Mongolian plant species

• Seed weight varies by several orders of magnitude among vascular plant species. However, the importance of potential drivers such as environmental conditions and plant functional traits have rarely been assessed for a larger taxonomic sample.
• We collected seeds of 148 species from 237 sites spread across Mongolia and compared their weight among the major zonal vegetation types, taxonomic groups and a set of functional traits (growth form, dispersal mode, fruit type, storage organs and palatability).
• Seed weight strongly varied among all functional traits and taxonomic groups, but no differences among vegetation zones were detected.
• These results suggest a low impact of environmental conditions on the evolution of seed weight, contrasting the strong phylogenetic signal.

     

Why are small seeds dispersed through animal guts: large numbers or seed size per se?

Long-distance dispersal of seeds is an important process in metapopulation dynamics and in plant migrations, but at the same time extremely difficult to observe or quantify directly. If seed dispersal ability were related to attributes of seeds or motherplants, long-distance seed dispersal would be predictable by indirect approximation using easy-to-measure traits. Seed size has been suggested to be such a key trait in seed dispersal ability. However, having smaller seeds also implies having more numerous seeds per plant individual (given equal reproductive effort), and consequently increases the probability of seeds being ingested accidentally. The question is whether small-seeded species are more abundant in herbivore dung because smaller seed size increases survival rate during gut passage or because they are produced (and ingested) in greater numbers than larger seeds. We investigated endozoochorous seed dispersal via cattle grazing a meadow, and related seed abundance in dung samples to seed attributes. We found that seeds were ingested and passed through the bovine intestinal tract in proportion to the numbers produced per unit area in the grazed vegetation. In contrast, no relationship could be found between endozoochorous dispersal potential (measured as abundance of seeds in dung samples corrected for seed output in the grazed vegetation) and seed attributes such as seed mass, seed shape (roundness), and thickness of the seed coat. This finding underlines the importance of seed number in plant dispersal ability. In addition, it shows that grazing mammals may constitute an important dispersal vector for many plant species conventionally classified as 'unspecialised'.     

Comparative evolutionary ecology of seed size

A seedling's chances of establishing successfully are likely to be affected by the quantity of metabolic reserves in the seed. Seed size is thought to evolve as a compromise between producing numerous smaller seeds, each with few resources, and fewer larger seeds, each with more resources. Seed size varies 10(11)-fold across plant species, so the compromise has been struck at very different levels. These basic ideas have been accepted for 50 years, and many studies have interpreted seed size differences between species by reference to larger seed size being adaptive under a variety of hazards. However, experimental tests of the benefits of large seed size in relation to particular hazards have been rare. More experiments are now being reported, but a consistent picture has yet to emerge. There is typically at least a 10(5)-fold range of seed mass between species even within a single area, suggesting that much seed size variation is evolutionarily associated with other plant attributes.     

Reserve mass and dispersal investment in relation to geographic range of plant species: phylogenetically independent contrasts

Recent studies have reported conflicting evidence about correlations between seed size and plant species geographic range sizes. Using phylogenetically independent contrasts (PICs) within genera, we found no consistent differences in reserve mass between species with similar dispersal morphology and «wide>> versus «narrow>> geographic ranges. There was also no tendency within genera for broad ranged species to be those that allocate a larger percentage of the resources invested in each diaspora to dispersal structures. PICs were also constructed between species having a tenfold difference in seed size. In these PICs, the larger seeded species often occupied a greater number of regions than species with smaller seed sizes. This result was generated primarily through the comparison of species from different genera, families or higher level taxa which differed not only in seed mass but also in dispersal modes and growth forms. Finally, comparing species within Acacia and Eucalyptus having similar seed size but different dispersal modes, we found that bird dispersal (in Acacia ) and possession of a wing for wind dispersal (in Eucalyptus ) was associated with wider geographic range compared to lower-investment dispersal modes. Taken together, these comparisons indicate that seed size is not itself important as a factor influencing breadth of geographic range. Dispersal mode and growth form may have an influence, however, and seed size differences may be associated with contrasts in dispersal mode or growth form.     

Seed Size,Fecundity and Postfire Regeneration Strategy Are Interdependent in Hakea

Seed size is a key functional trait that affects plant fitness at the seedling stage and may vary greatly with species fruit size, growth form and fecundity. Using structural equation modelling (SEM) and correlated trait evolution analysis, we investigated the interaction network between seed size and fecundity, postfire regeneration strategy, fruit size, plant height and serotiny (on-plant seed storage) among 82 species of the woody shrub genus, Hakea, with a wide spectrum of seed sizes (2–500 mg). Seed size is negatively correlated with fecundity, while fire-killed species (nonsprouters) produce more seeds than resprouters though they are of similar size. Seed size is unrelated to plant height and level of serotiny while it scales allometrically with fruit size. A strong phylogenetic signal in seed size revealed phylogenetic constraints on seed size variation in Hakea. Our analyses suggest a causal relationship between seed size, fecundity and postfire regeneration strategy in Hakea. These results demonstrate that fruit size, fecundity and evolutionary history have had most control over seed size variation among Hakea species.     

Reproductive output of invasive versus native plants

Aim Propagule size and output are critical for the ability of a plant species to colonize new environments. If invasive species have a greater reproductive output than native species (via more and/or larger seeds), then they will have a greater dispersal and establishment ability. Previous comparisons within plant genera, families or environments have conflicted over the differences in reproductive traits between native and invasive species. We went beyond a genus‐, family‐ or habitat‐specific approach and analysed data for plant reproductive traits from the global literature, to investigate whether: (1) seed mass and production differ between the original and introduced ranges of invasive species; (2) seed mass and production differ between invasives and natives; and (3) invasives produce more seeds per unit seed mass than natives. Location Global. Methods We combined an existing data set of native plant reproductive data with a new data compilation for invasive species. We used t‐tests to compare original and introduced range populations, two‐way ANOVAs to compare natives and invasives, and an ANCOVA to examine the relationship between seed mass and production for natives and invasives. The ANCOVA was performed again incorporating phylogenetically independent contrasts to overcome any phylogenetic bias in the data sets. Results Neither seed mass nor seed production of invasive species differed between their introduced and original ranges. We found no significant difference in seed mass between invasives and natives after growth form had been accounted for. Seed production was greater for invasive species overall and within herb and woody growth forms. For a given seed mass, invasive species produced 6.7‐fold (all species), 6.9‐fold (herbs only) and 26.1‐fold (woody species only) more seeds per individual per year than native species. The phylogenetic ANCOVA verified that this trend did not appear to be influenced by phylogenetic bias within either data set. Main conclusions This study provides the first global examination of both seed mass and production traits in native and invasive species. Invasive species express a strategy of greater seed production both overall and per unit seed mass compared with natives. The consequent increased likelihood of establishment from long‐distance seed dispersal may significantly contribute to the invasiveness of many exotic species.     

A reassessment of the role of simple seed traits in mortality following herbivore ingestion

Grazing mammals are regarded as major vectors in seed dispersal of grassland plants, through seed ingestion and subsequent excretion (endozoochory). The (evolutionary) ecology underlying this dispersal mode is relatively poorly understood because there are limited data, among others, on how seed attributes perform in this process (and could thus be selected for). For seed mortality following ingestion, contrasting patterns described for the role of simple seed traits seem partly due to inadequate comparative analytical methods. We conducted a feeding experiment in which controlled seed quantities from 48 grassland herb and grass species were fed to cattle. Seed mass, length and shape measurements were related to seed mortality rate using phylogenetically independent contrasts, which account for taxonomic interdependence. The proportion of seeds surviving the digestive tract was generally low, but it reached 100%, with increased germination for some species. Neither seed size nor shape correlated significantly with mortality. Structural traits are likely to overrule these simple seed traits, as illustrated by high survival of species having water-impermeable seeds. As this trait has interesting properties with respect to intraspecific variation and genetics, it could provide opportunities for inference on evolutionary consequences for this type of dispersal.