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.     

A novel trap for quantifying the dispersal of seeds by wind

Question: Understanding the aerial movement of seed is of great significance to the management of native and invasive plant species, but has proven difficult to measure. Here we examine how a more quantitative approach to measuring the aerial movement of seed can be achieved. Location: SE Australia. Methods: We describe a novel seed trap (the ‘Melbourne trap’), for which the proportion of free‐stream airflow through the trap can be measured, allowing a more quantitative approach to measuring aerial seed movement. We assessed airflow through the Melbourne trap in a wind tunnel and describe how this information, along with measurements of wind speed and direction, can now be used to derive seed density per volume of airflow. We compare the seed capture and retention efficiency of the Melbourne trap with two simpler and cheaper trap designs, bucket traps and sticky traps. Results: Melbourne and bucket traps captured significantly more species than sticky traps. Seed catch was dominated numerically by Lachnagrostis filiformis (G. Forst.) Trin. Melbourne traps proved more effective than sticky traps, but not bucket traps, in capturing L. filiformis, based on intake area. For all other seeds, Melbourne traps were more effective than both bucket and sticky traps. Conclusion: The Melbourne trap design is a significant advance in quantifying seed dispersal by wind. Melbourne traps will improve the capacity and accuracy of studies that seek to: (i) quantify seed fluxes across landscapes boundaries; (ii) assess directionality of dispersal; (iii) understand processes controlling seed release; and (iv) compare dispersal in wind and water.     

First evidence for multimodal animal seed dispersal in orchids

1. Download : Download high-res image (208KB)
2. Download : Download full-size image

     

季节变化对锐齿栎种子扩散的影响

季节变化是影响鼠类扩散植物种子的一个主要环境因素.2008年9-11月(秋季)和2009年3-4月(春季)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锐齿栎种子的扩散,并与种子大小年假说的预测进行了比较分析.结果表明:春季锐齿栎种子的扩散速度比秋季快,平均扩散距离(取食距离和贮藏距离)也比秋季远,该结果与种子...     

Estimating human-mediated dispersal of seeds within an Australian protected area

Dispersal is critical step in plant invasions but there is limited information about human-mediated long distance seed dispersal, including in protected areas. Seed dispersal by hikers was quantified for five invasive species (the native Acaena novae-zelandiae, and the non-native weeds Rumex acetosella Anthoxanthum odoratum, Dactylis glomerata and Festuca rubra) in part of Australia’s Kosciuszko National Park. The proportion of seeds remaining attached to trousers and socks was quantified for replicated short (150 m) and long (5,000 m) distance walks. Functions were fitted for each dataset, and parameters compared among species and between trousers and socks. Dispersal data were combined with attachment rates and the number of people undertaking walks to estimate the total number of weed seeds that might be dispersed. The power exponential function gave the best fit for the majority of datasets, indicating that detachment probability decreased with distance. Seeds of all five species were more tightly attached to socks than trousers, with some seeds still present on socks at 5,000 m. Anthoxanthum and Acaena seeds were more tightly attached to clothing than the other species. Theoretically 1.9 million seeds could be dispersed on socks or 2.4 million seeds on trousers through a season but the actual numbers are likely to be much lower because of limited weed seed at the start of the walks. Because of differences in attachment and detachment rates, seeds from Acaena were more likely to be dispersed longer distances. Long distance human-mediated seed dispersal is potentially a major cause of spread of invasive weeds into protected areas that favours some invasive species over others.     

Retention time variability as a mechanism for animal mediated long-distance dispersal

Long-distance dispersal (LDD) events, although rare for most plant species, can strongly influence population and community dynamics. Animals function as a key biotic vector of seeds and thus, a mechanistic and quantitative understanding of how individual animal behaviors scale to dispersal patterns at different spatial scales is a question of critical importance from both basic and applied perspectives. Using a diffusion-theory based analytical approach for a wide range of animal movement and seed transportation patterns, we show that the scale (a measure of local dispersal) of the seed dispersal kernel increases with the organisms' rate of movement and mean seed retention time. We reveal that variations in seed retention time is a key determinant of various measures of LDD such as kurtosis (or shape) of the kernel, thinkness of tails and the absolute number of seeds falling beyond a threshold distance. Using empirical data sets of frugivores, we illustrate the importance of variability in retention times for predicting the key disperser species that influence LDD. Our study makes testable predictions linking animal movement behaviors and gut retention times to dispersal patterns and, more generally, highlights the potential importance of animal behavioral variability for the LDD of seeds.     

Long-distance dispersal of seeds in the fire-tolerant shrub Banksia attenuata

Long-distance dispersal (LDD) of seeds enables alleles, individuals and species of plants to (re)colonize suitable but remote habitats. Banksia attenuata is a long-lived resprouting shrub restricted to dune crests in fire-prone sclerophyll shrublands of the Eneabba sandplain, southwestern Australia. Highly polymorphic microsatellite DNA genetic markers and population assignment tests were employed to identify LDD immigrants among 788 individuals from 27 stands of B. attenuata comprising a metapopulation. Of the 487 (61.8% of the total) individuals unambiguously assigned to a unique source population, 27 (5.5%) were identified as immigrants by assignment to a known population other than that from which they were sampled, while the remaining 460 were assigned to the population from which they were sampled. The distance between source and sink populations for these immigrants ranged from 0.2 to 2.6  km, averaging 1.4  km, and broadly trending in the direction of seasonal winds. These results suggest that B. attenuata has similar long-distance seed dispersal properties as its co-occurring shorter-lived and fire-sensitive congener, B. hookeriana , despite fewer, larger and less mobile seeds. The frequency and distance of LDD for seeds observed in both species (5.5–6.8%) helps explain the persistence of populations on these geographically isolated dunes, where they are subject to local extinction from recurrent fire and severe summer drought, and will remain important under predicted climate change conditions. Analysis also revealed that species richness of the functional group to which B. attenuata belongs was positively correlated with the number of immigrants identified per dune, and such correlation was likely driven by environmental properties of the dunes, particularly water availability.     

Integration of exotic seeds into an Azorean seed dispersal network

Seed dispersal plays a central role in plant ecology. Among animals, birds are particularly important seed dispersers, often incorporating exotic plants into their diets and facilitating their integration in the communities. Network theory offers a highly informative framework to study the structural and functional attributes of complex interactions networks. We used information from bird fecal samples to build a quantitative seed dispersal network for the last fragment of native laurel forest in the island of São Miguel—Azores with three specific objectives: (1) to assess the integration of exotic seeds into seed dispersal; (2) to evaluate the impact of exotic plants in network structure; (3) to test the potential of an exotic species to reduce the seed dispersal of a co-occurring native, via competition for seed dispersers. The seed dispersal network was based on the analysis of 1,121 droppings and described 74 unique interactions between 41 plant species and 7 bird species. Exotic seeds deeply infiltrated into the seed dispersal network forming the majority (59 %) of seeds in the droppings and including those of three globally invasive plants. Overall, birds depended equally on native and exotic fruits despite the lower abundance of the latter in the study area. In an experiment, birds did not show a preference for fruits of the exotic Leycesteria formosa over the native Vaccinium cylindraceum consuming them equally. However, the presence of the exotic plant negatively affected the number of native seeds dispersed, by diverting some of the consumers of the native fruits. Taken altogether the results reveal an alarming invasion level of seed dispersal systems in one of the last remnant native forests of the Azores.     

Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations

There is accumulating evidence that individuals leave their natal area and select a breeding habitat non-randomly by relying upon information about their natal and future breeding environments. This variation in dispersal is not only based on external information (condition dependence) but also depends upon the internal state of individuals (phenotype dependence). As a consequence, not all dispersers are of the same quality or search for the same habitats. In addition, the individual's state is characterized by morphological, physiological or behavioural attributes that might themselves serve as a cue altering the habitat choice of conspecifics. These combined effects of internal and external information have the potential to generate complex movement patterns and could influence population dynamics and colonization processes. Here, we highlight three particular processes that link condition-dependent dispersal, phenotype-dependent dispersal and habitat choice strategies: (1) the relationship between the cause of departure and the dispersers' phenotype; (2) the relationship between the cause of departure and the settlement behaviour and (3) the concept of informed dispersal, where individuals gather and transfer information before and during their movements through the landscape. We review the empirical evidence for these processes with a special emphasis on vertebrate and arthropod model systems, and present case studies that have quantified the impacts of these processes on spatially structured population dynamics. We also discuss recent literature providing strong evidence that individual variation in dispersal has an important impact on both reinforcement and colonization success and therefore must be taken into account when predicting ecological responses to global warming and habitat fragmentation.     

Comparison of survey methods for monitoring Clark's Nutcrackers and predicting dispersal of whitebark pine seeds

ABSTRACT Clark's Nutcrackers (Nucifraga columbiana) disperse seeds of whitebark pines (Pinus albicaulis) in western North America by their scatter‐hoarding behavior. Because of declines in whitebark pine, resource managers are seeking an effective means of monitoring nutcracker population trends and the probability of seed dispersal by nutcrackers. We tested the reliability of four survey techniques (standard point counts, playback point counts, line transects, and Breeding Bird Survey routes) for estimating population size by conducting surveys at sites where a portion of the nutcracker population was marked with radio transmitters. The efficacy of distance sampling, based on detection rates from our unadjusted surveys, was also assessed. We conducted counts of whitebark pine cones within stands and related the probability of seed dispersal within stands to cone production and nutcracker abundance. We conducted 70 h of surveys for Clark's Nutcrackers at eight sites from July through November in 2007 and 2009 and estimated cone densities at six of these sites. Detection rates for all survey techniques were low and variable and we detected an average of 5.6 nutcrackers per 30 min of survey time. We also found no difference in detection rates among survey types, although significantly more nutcrackers were detected during surveys conducted during the peak of whitebark pine cone harvest (P < 0.0001). Nutcracker abundance was not correlated with cone density (P= 0.29) and we observed nutcrackers pouching seeds at all sites. Thus, cone density did not provide reliable information on whether seed dispersal was likely to occur. We suggest that alternate methods be considered for monitoring populations and assessing seed dispersal probability because we did not reliably detect nutcrackers using conventional survey techniques and because nutcracker abundance was not correlated with cone density.     

Dormancy as exaptation to protect mimetic seeds against deterioration before dispersal

Background and Aims

Mimetic seeds simulate the appearance of fleshy fruits and arilled seeds without producing nutritive tissues as a reward for seed dispersers. In this strategy of seed dispersal, seeds may remain attached to the mother plant for long periods after maturity, increasing their availability to naïve seed dispersers. The hypothesis that seed coat impermeability in many tropical Fabaceae with mimetic seeds serves as an exaptation to protect the seeds from deterioration and rotting while awaiting dispersal was investigated.

Methods

Seed coat impermeability was evaluated in five mimetic-seeded species of tropical Fabaceae in south-eastern Brazil (Abarema langsdorffii, Abrus precatorius, Adenanthera pavonina, Erythrina velutina and Ormosia arborea) and in Erythrina speciosa, a ‘basal’ species in its genus, which has monochromatic brown seeds and no mimetic displays. Seed hardness was evaluated as a defence against accelerated ageing (humid chamber at 41 °C for 144 h). Seed development and physiological potential of O. arborea was evaluated and the effect of holding mature seeds in pods on the mother plant in the field for a period of 1 year under humid tropical conditions was compared with seeds stored under controlled conditions (15 °C and 40 % relative air humidity).

Key Results

All five mimetic-seeded species, and E. speciosa, showed strong coat impermeability, which protected the seeds against deterioration in accelerated ageing. Most O. arborea seeds only became dormant 2 months after pod dehiscence. Germination of seeds after 1 year on the plant in a humid tropical climate was 56 %, compared with 80 % for seeds stored in controlled conditions (15 °C, 45 % relative humidity). Seedling shoot length after 1 year did not differ between seed sources.

Conclusions

Dormancy acts in mimetic-seeded species as an exaptation to reduce seed deterioration, allowing an increase in their effective dispersal period and mitigating the losses incurred by low removal rates by naïve avian frugivores.     

Differential dispersal of Chamaesyce maculata seeds by two ant species in Japan

Seed dispersal by ants (myrmecochory) is a widely distributed plant–animal interaction in many ecosystems, and it has been regarded as a generalized (multiple species) interaction in which specialization on specific ant partners is uncommon. In this paper, we demonstrate species-specific seed dispersal of spotted spurge (Chamaesyce maculata) by ants in Japan. C. maculata produces seeds from summer to autumn in Japan. The seeds produced in autumn are carried by two ant species, Tetramorium tsushimae and Pheidole noda. We performed laboratory experiments to investigate the fate of C. maculata seeds in the nests of T. tsushimae and P. noda. P. noda consumed the seeds in the nest and rarely carried seeds out of the nest, while T. tsushimae consumed only the seed coat, and subsequently carried the seeds out of the nest. Removal of the seed coat by T. tsushimae may increase seed survival by reducing their susceptibility to infection by fungi. We also observed ant responses to filter paper soaked with an aqueous extract of the seed coat. P. noda did not react to the filter paper, but T. tsushimae carried the filter paper into their nest. Analysis by high-pressure liquid chromatography revealed that the aqueous extract contained at least four sugars and one unknown substance. Myrmecochory has been regarded as a generalized interaction with specialization for specific ant partners uncommon. However, our study suggests there is a species-specific interaction in seed dispersal by ants in autumn-flowering individuals of C. maculata in Japan.     

Germination and water dispersal of seeds from a threatened plant species Penthorum chinense

To conserve a threatened plant species (Penthorum chinense Pursh) in Japan, seed germination responses to pretreatment (imbibition and/or chilled), temperature and light, and seed dispersal by water were examined. The seeds collected from abandoned paddy fields in a warm temperate region, central Japan, germinated in light (14 h photoperiod; light 22°C, dark 21°C) after a moist-chilled treatment. After this pretreatment, the seeds germinated well at 10–25°C (optimum temperature 15°C), but did not germinate in darkness even at the optimum temperature. Most of the seeds floated on distilled water, but 20–60% of the seeds that were collected from several populations sank in distilled water, indicating dimorphism in seed dispersal by water. The floating and sunken seeds did not show significant differences in weight and germination rate within a population. The addition of a surface-active agent in distilled water submerged the seeds, indicating that the buoyancy of the seeds is attributable to an oil coating on the seed surface that enhances the interfacial tension on the seeds. Three times the number of seeds sank in river water collected from a rural area than in distilled water. A greater number of seeds also sank in water that had increasing concentrations of linear alkylbenzenesulfonate, which is a major component of synthetic detergents. This suggests that the water dispersal of this species is suppressed by surface-active agents, including detergents, in river water.     

Chemical composition of pods and seeds of Dichrostachys cinerea as a basis of seed dispersal

The occurrence of very few seeds of Dichrostachys cinerea in the soil seed bank prompted the present study as to why animal browsers and seed predators should select the infructescence of this plant. The preferential and extensive browsing of this indehiscent legume is apparently not due to any exceptional nutritive value of the pods and seeds. However, it is probably the strong rich aroma of the infructescence which initially attracts animals to this food source. The structure of the infructescence, ensures that upon location a large number of pods and seeds are consumed. Ingestion of the pods will provide fibre, lipid, fatty acids, carbohydrates, amino acids, nitrogen and protein.     

A Suite of Adaptations for Intertidal Spawning

Salt marshes and similar tide-dominated habitats present anunusual challenge for reproduction of resident aquatic organisms.Strong currents, siltation and hypoxia can potentially contributeto reproductive failure through mortality of the eggs or flushingof the eggs and larvae from the habitat. Fundulus heteroclitus,a small brackish water killifish, is a common resident of tidalmarshes along the east coast of North America from Newfoundlandto Florida. The reproductive strategy of this and related speciesis based on aerial incubation of eggs in the high intertidalzone. The eggs are resistant to desiccation and, when fullydeveloped, hatch on immersion. Copulatory behavior and anatomyof accessory reproductive structures are adapted to placementof eggs in protected incubation sites. The gonads of both malesand females mature rhythmically with an endogenous circasemilunarperiod, which is synchronized with the "spring" tides of newand full moons. Spawning occurs on high tides. Embryos developin 9–15 days, and usually hatch on the succeeding springtide series. Reproductive cyclicity in F. heteroclitus and relatedfishes ensures that spawning fish will have access to the highintertidal zone, thereby permitting aerial incubation of eggs.     

Experimental studies of diaspore attachment to animal coats: predicting epizoochorous dispersal potential

The transport of diaspores on animal hairs depends on the ability of a diaspore to attach to the hair and to be retained in it over longer periods of time. Whereas several studies of diaspore retention on animal hairs have been conducted recently, the process of diaspore attachment to the hair has not yet been studied systematically. We describe a new method to quantify the attachment potential (AtP) of plant diaspores. Attachment potential was measured as the proportion of diaspores of a given species that attached to pieces of an animal coat in a standardised experiment. The experiment was conducted for 58 plant species (herbs and grasses) and three different coat types: sheep wool, cattle and roe deer hair. Attachment potentials differed widely between the three coat types, but also between plant species. We found diaspore surface structure (a quantitative measure of diaspore morphology) and diaspore exposition (describing the morphology of the infructescence) to be the most important plant traits regulating AtP. An influence of seed mass on attachment potential could not be detected. For sheep wool, a general linear model (with diaspore exposure as a factor and diaspore surface structure as covariate) explained 77% of the variation in AtPs. To validate this model, we predicted AtPs for 27 additional species and compared these to the measured Atps; the predicted and measured AtPscorrelated significantly with r _s = 0.68. A comparison of attachment and retention potentials to sheep wool for 127 randomly selected plant species showed that attachment and retention are only very weakly correlated, indicating that both processes act rather independently of each other. Since many diaspores seem to perform well in only one of these processes, attachment can be considered to be as equally as decisive as retention in terms of epizoochorous dispersal. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.