Spatial and temporal variation in dispersal pattern of an invasive pine

Understanding dispersal ability of an invasive species is crucial for describing its potential spread. Despite this, we still know little about the dispersal potential of many invasive species. We explored dispersal spectra in Pinus strobus, an invasive tree in sandstone areas in Central Europe. We studied dispersal of the species using distribution of self-sown trees in the field. We compared these observed data with theoretical dispersal curves derived using information on wind speed, seed terminal velocity and tree height. Finally, we fitted various empirical dispersal curves to the observed data. All the analyses based on the observed field data were done for the whole dataset, and for the dataset divided by habitat types and age categories of the self-sown trees. P. strobus seeds can disperse up to 757.5 m from the source. The observed data fall within the confidence intervals of the predictions based on a negative exponential model. When comparing different dispersal functions fitted to the data, it was not easy to decide which of the dispersal curves provides the overall best fit. This was because different functions were the best predictors of different parts of the dispersal curve. We suggest that future studies should provide not only empirical fitted dispersal curves but also observed data and provide estimates of confidence intervals. Such information will provide insights into the reliability of the dispersal estimates in general and help to evaluate the predictive power of the different models.     

Experimental assessment of plant seed retention times in fur of cattle and horse

Epizoochorous dispersal of plant seeds is an important long-distance dispersal mechanism. Yet little is known about retention times of seeds in animal furs and hence about potential dispersal distances of the seeds. Here, we used marked seeds of 12 plant species to determine seed depletion curves on Galloway cattle and Haflinger horse in three vegetation types (forest, tall herbage vegetation and meadow), in both dry and rainy weather conditions. In the long fur of Galloway cattle, seeds were retained significantly longer than in the short fur of Haflinger horse. In general, seed retention times were not considerably affected by the structure of the surrounding vegetation. The impact of the weather was negligible, only affecting the retention of some plant species. Negative exponential functions were fitted to the seed depletion curves. Using the parameters of curve estimations in the different conditions of animal species and vegetation structure, half-life seed retention times of up to 13 h for Galloway cattle and up to more than 4 h for Haflinger horse could be calculated, with corresponding potential half-life dispersal distances in the order of magnitude of tens of metres to a few kilometres. Different seed traits correlated with seed retention times in the long cattle fur and in the short horse fur, respectively.     

Dropping rates of elaiosome-bearing seeds during transport by ants (Formica polyctena Foerst.): Implications for distance dispersal

In a deciduous forest, foraging ants collect elaiosome-bearing seeds and carry them to their nests. Some of the seeds reach the nest and are concentrated there. Others may be dropped by ants during transport. The dropped seeds enter the soil seed pool. However, they might be repeatedly removed by other ant individuals and carried again in the direction of the nest. Rates of seed dropping and repeated removals must be known to evaluate the effect of ant workers on dispersal distance of seeds. The rate of seed dropping is predicted to depend on size of seeds and of elaiosomes, both of which vary among plant species, and on the size of the ant workers. Mark-recapture experiments were used to evaluate dropping rates of seeds of five myrmecochorous and diplochorous plants (Chelidonium majus L., Asarum europaeum L., Viola matutina Klok., V. mirabilis L., V. hirta L.) during their transport by the ant Formica polyctena Foerst. In the series of species A. europaeum – V. hirta – V. mirabilis – Ch. majus – V. matutina, the dropping rate increased. Small workers dropped seeds of A. europaeum more often than did large ones, while seeds of V. hirta were dropped by ants of different size classes with the same frequency. Across species, dropping rates of seeds were negatively correlated with the rate at which ants removed them from the depot. The number of seeds which reach the nests is the other important parameter of seed dispersal. This parameter depends on dropping rates: seeds with lower dropping rates have higher chances of being deposited in nests. Diplochores usually produce many small seeds, which are characterised by low removal rates and high dropping rates during transport by ants. Obligate myrmecochores produce rather few large seeds, which have high removal rates and low dropping rates. To analyse the significance of seed dropping in the dispersal distance of seeds, a computer simulation based on two factors [(i) seed number produced by a plant; (ii) dropping rate of seeds] is proposed.     

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 Black Spear Grass (Heteropogon contortus) seed on socks and trouser legs by walkers in Kakadu National Park

Humans can contribute to the long‐distance dispersal of many plants, including weeds. We assessed the distance for which seed remained attached to the socks and trouser legs of walkers. The experiment in Kakadu National Park, Australia used seed of the Australian native Black Spear Grass (Heteropogon contortus) as a surrogate for the potential dispersal of weed seed. Two models were fitted to the data, with a double exponential model fitting the data slightly better than a power exponential model. Although 19% of seed were dispersed within the first 5 m of walking, most (55%) seed remained attached to socks and trousers at 5 km. Humans may, therefore, unintentionally carry and eventually disperse this grass and other invasive grasses with similar long awns and pointed seeds over long distances. Implementing strategies to reduce the potential for seed to attach to walkers (gaiters) and reduce potential dispersal (removal and careful disposal of seed) would reduce the risks posed by this type of human‐mediated seed dispersal.     

Pleistocene megafaunal extinctions and the functional loss of long‐distance seed‐dispersal services

Pleistocene extinctions affected mainly large‐bodied animals, determining the loss or changes in numerous ecological functions. Evidence points to a central role of many extinct megafauna herbivores as seed dispersers. An important step in understanding the legacy of extinct mutualistic interactions is to evaluate the roles and effectiveness of megafauna herbivores in seed dispersal. Here we use morphological and ecophysiological allometries to estimate both quantitative and qualitative aspects of seed‐dispersal services likely provided by extinct megafauna. We developed a mechanistic model that encompasses four stages of seed dispersal – seed ingestion, gut retention, animal movement, and seed deposition. We estimate seed‐dispersal kernels through simulations to infer the role of Pleistocene megafauna in promoting long‐distance dispersal and examine how seed dispersal was affected by extinctions. Simulations suggest extinct large‐bodied frugivores would frequently disperse large seeds over a thousand meters, whereas smaller‐bodied frugivores are more likely to deposit the seeds over a few hundred meters. Moreover, events of long‐distance seed dispersal by the extinct megafauna would be up to ten times longer than long‐distance dispersal by smaller‐sized extant mammals. By estimating the combined distribution of seed dispersal distances considering all large‐bodied mammalian frugivores in specific South American Pleistocene assemblages we found that long‐distance dispersal contracted by at least two thirds after the megafauna died out. The disruption of long‐distance dispersal is expected to have consequences for recruitment, spatial and genetic structure of plant populations, population persistence and community composition. Promoting long‐distance seed dispersal was one among other salient features of extinct Pleistocene megafauna that reveal their influence on natural ecosystems. Modeling the consequences of megafaunal extinctions can offer quantitative predictions on the consequences of ongoing defaunation to plant populations and ecological communities.     

Bird‐mediated seed dispersal: reduced digestive efficiency in active birds modulates the dispersal capacity of plant seeds

Plant populations in fragmented ecosystems rely largely on internal dispersal by animals. To unravel the mechanisms underlying this mode of dispersal, an increasing number of experimental feeding studies is carried out. However, while physical activity is known to affect vertebrate digestive processes, almost all current knowledge on mechanisms of internal seed dispersal has been obtained from experiments with resting animals. We investigated how physical activity of the mallard Anas platyrhynchos, probably the quantitatively most important biotic dispersal agent in aquatic habitats in the entire Northern Hemisphere, affects gut passage survival and retention time of ingested plant seeds. We fed seeds of nine common wetland plants to mallards trained to subsequently swim for six hours in a flume tank at different swimming speeds (activity levels). We compared gut passage survival and retention times of seeds against a control treatment with mallards resting in a conventional dry cage. Intact gut passage of seeds increased significantly with mallard activity (up to 80% in the fastest swimming treatment compared to the control), identifying reduced digestive efficiency due to increased metabolic rates as a mechanism enhancing the dispersal potential of ingested seeds. Gut passage speed was modestly accelerated (13% on average) by increased mallard activity, an effect partly obscured by the interaction between seed retention time and probability of digestion. Gut passage acceleration will be more pronounced in digestion‐resilient seed species, thereby modulating their dispersal distances. Our findings imply that seed dispersal potential by mallards calculated from previous experiments with resting birds is highly underestimated, while dispersal distances may be overestimated for some plant species. Similar effects of physical activity on digestive efficiency of mammals suggests that endozoochorous dispersal of plant seeds by vertebrates is more effective and plays a quantitatively more important ecological role in both terrestrial and aquatic ecosystems than previously thought.     

Seed traits and bird species influence the dispersal parameters of wetland plants

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Frugivore Behavioural Details Matter for Seed Dispersal: A Multi-Species Model for Cantabrian Thrushes and Trees

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.     

Dispersal kernels of butterflies: Power-law functions are invariant to marking frequency

Despite recent developments of sophisticated dispersal modelling, simple regression-based models remain useful for estimating frequencies of long-distance movements of animals. Since the inverse power function, IPF (ln I=ln C−m ln D), but not the negative exponential function, NEF (ln I=ln a−k D), exhibits the property of self-similarity, it should be robust against variation in effort invested into mark-recapture studies. We illustrate this using three data sets on movements of butterflies (Lepidoptera): Euphydryas aurinia, year 2002 (better fitted by IPF), E. aurinia, year 2003 (better fitted by NEF) and Parnassius mnemosyne (better fitted by NEF). By simulated reductions of numbers of animals, numbers of marking days, and marking effort, we show that IPF withstands severe decline in marking frequency without a change of parameters of regressions based on reduced data. In contrast, parameters of NEFs fitted to the reduced data widely varied and differed from functions based on unreduced data. Owing to the robust performance of IPF, reliable dispersal estimates may be obtained at relatively small field effort, which may facilitate quick and efficient comparisons of movement patterns among species, locations and populations.     

Predicting the time to colonization of the parasitoid Diadegma semiclausum: The importance of the shape of spatial dispersal kernels for biological control

The time at which natural enemies colonize crop fields is an important determinant of their ability to suppress pest populations. This timing depends on the distance between source and sink habitats in the landscape. Here we estimate the time to colonization of sink habitats from a distant source habitat, using empirical mark-capture data of Diadegma semiclausum in Broccoli. The data originated from experiments conducted at two locations and dispersal was quantified by suction sampling before and after a major disturbance. Three dispersal kernels were fitted to the dispersal data: a normal, a negative exponential, and a square root negative exponential kernel. These kernels are characterized by a thin, intermediate and a fat tail, respectively. The dispersal kernels were included in an integro-difference equation model for parasitoid population redistribution to generate estimates of time to colonization of D. semiclausum in sink habitats at distances between 100 and 2000 m from a source. We show that the three dispersal kernels receive similar support from the data, but can produce a wide range of outcomes. The estimated arrival time of 1% of the D. semiclausum population at a distance 2000 m from the source ranges from 12 days to a length of time greatly exceeding the life span of the parasitoid. The square root negative exponential function, having the thickest tail among the tested functions, gave the fastest spread and colonization in three of the four data sets, but it gave the slowest redistribution in the fourth. In all four data sets, the rate of accumulation at the target increased with the mean dispersal distance of the fitted kernel model, irrespective of the fatness of the tail. This study underscores the importance of selecting a proper dispersal kernel for modelling spread and colonization time of organisms, and of the collection of pertinent data that enable kernel estimation and that can discriminate between different kernel shapes.     

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.     

Does seed retention potential affect the distribution of plant species in highly fragmented calcareous grasslands?

Long-distance dispersal is a crucial factor in the life-cycle of plants, especially in our modern, highly fragmented landscapes. Because natural herds of large animals have disappeared and grazing practices have been abandoned, important potential vectors for seed dispersal over large distances may have been lost. In the context of the re-establishment of grazing management for nature conservation purposes, it is therefore important to gain insight in the ability of grazing animals to act as seed dispersal vectors. Whereas local dispersal mainly occurs through standard vectors typically described based on morphological adaptations of the diaspore, large herbivores act as non-standard seed dispersers. Therefore, traditional dispersal classes are loosing scientific relevance and continuous predictors of dispersal potential have been proposed. Here, we explored whether dispersal related plant traits, including the "seed retention potential", could explain the distribution patterns of 180 plant species over 64 fragmented semi-natural calcareous grasslands in Belgium. The distribution of habitat specialist plant species was strongly determined by the degree of isolation of the grasslands. Interestingly, species distribution patterns were clearly linked with a species' potential to migrate through large grazers, as quantified by its retention potential: species producing seeds with high retention capacity were less affected by habitat isolation. Categorical dispersal classes based on seed morphology did not explain a species' response to fragment isolation. Although seed retention potential outperformed simple seed dimensional traits, plant height, which is an indicator of epizoochorous attachment potential, was even more important. Therefore we suggest further extension of the epizoochorous retention potential model by incorporating basic ecological mechanisms that effectively contribute to successful dispersal events.     

Seed dispersal by woolly monkeys (Lagothrix lagothricha) at Tinigua National Park, Colombia: dispersal distance, germination rates, and dispersal quantity

The purpose of this study was to describe seed dispersal patterns of woolly monkeys (Lagothrix lagothricha) in terms of dispersal quantity and two factors related to dispersal quality: germination rates of dispersed seeds and the distance of dispersal to parental trees. The possible influence of retention time, travel distance, seed size, activity patterns, and fruit abundance on dispersal distance was also analyzed. Observations on activity, diet, daily movements, and seed dispersal were made on focal individuals of a group of woolly monkeys at a tropical rain forest in Tinigua National Park (Colombia). Sixty hours of focal samples per month were completed during 1 year. A total of 753 depositions were collected during the study. Each dropping contained seeds from an average of 2.68 different species (range 0 to 9). Collected depositions contained an underestimated total of 50,168 seeds (>1 mm). Given a population density of 30 individuals/km2, the woolly monkeys in the study area disperse more than 25,000 seeds/km2/day. These seeds belong to 112 different plant species. Germination rates of dispersed seeds are usually similar or higher than those of non-swallowed seeds. It was possible to determine dispersal distance in 264 cases when the focal animal was continuously followed from ingestion at the parental tree to deposition. Only 1% of these depositions landed in close proximity (<15 m) of the parental tree. It was very common that the droppings were deposited between 100 and 500 m from the parent tree, and up to 1.5 km. Higher retention times and longer travel distances were not correlated with increased dispersal distance. Two main reasons for this result were the prolonged and variable passage rates (avg=11.2 hr+/-6.5 SD.) and the circuitous routes of monkeys in this forest.     

Seed dispersal in a cycad,Macrozamia riedlei

The influence of animals on patterns of seed dispersal has not been well explored, despite the importance of seed dispersal in plant population biology. Furthermore, the exploitation of animals as dispersal agents has been considered one reason for the replacement of gymnosperms by angiosperms in the Cretaceous. We studied seed dispersal in a cycad, Macrozamia riedlei, and showed that in the absence of animals, ripe seeds drop directly beneath the parent not more than 40 cm from the base. Several animals eat the fleshy outer integument of the seeds, and possums (Trichosurus vulpecula), transport seeds up to 24 m from the parent. The postdispersal positioning of seeds gave a log density-log distance relationship of y = 7.20 – 2.85x (r²= 0.96, N = 17). Effective local dispersal may have contributed to the persistence of cycads in the world flora for the last 200 million years.     

Digesta retention time in the Galápagos tortoise (Chelonoidis nigra)

The retention time of food in the digestive tract of animals has important implications for digestive physiology. Retention time impacts digestive efficiency and among herbivores affects plant–animal interactions including herbivory and seed dispersal. Poorly studied yet iconic Galápagos tortoises are large-bodied generalist herbivores and ecosystem engineers which migrate seasonally. Potentially variable digesta retention times due to strong seasonal and altitudinal temperature gradients may influence tortoise seed dispersal abilities and rates of herbivory. We fed captive adult tortoises living in semi-natural conditions on Galápagos with inert particles and seeds from locally available fruits to determine whether seed size and ambient temperature influenced retention time. Median retention time varied from 6 to 28 days, with a mode of 12 days. Seed size had no effect on any of our measures of retention time, but ambient temperature was inversely correlated with retention times. Long retention time facilitates long distance seed dispersal by Galápagos tortoises, which may improve effectiveness. The effect of temperature, which may double from hot lowlands to cold highlands through the seasonal cycle, on tortoise digesta retention time will strongly influence seed dispersal efficiency and may influence patterns of food selection and migration in this species.     

Allometric scaling of seed retention time in seed dispersers and its application to estimation of seed dispersal potentials of theropod dinosaurs

Seed retention time (SRT), the time interval between seed ingestion and defaecation, is a critical parameter that determines the spatial pattern of seed dispersal created by an animal, and is therefore, an essential component of trait‐based modelling of seed dispersal functions. However, no simple predictive model of SRT for any given animal exists. We explored the linkage between animal traits and SRT. We collected previously published data on mean SRT for 112 species of birds, mammals, reptiles and fishes and investigated the general allometric scaling of mean SRT with body mass for each taxon. Moreover, we analysed the effects of food habit and digestive strategy on mean SRT for birds and mammals. In general, mean SRT increased with body mass in all four taxa, whereas the pattern of allometric scaling varied greatly among the taxa. Birds had a smaller intercept and larger slope than those of mammals, whereas reptiles had a much larger intercept and smaller slope than those of either birds or mammals. For birds, food habit was also detected as an important factor affecting SRT. We applied the allometric scaling that was obtained for birds to estimate mean SRT of extinct Mesozoic dinosaurs (Theropoda) – few of which are assumed to have acted as seed dispersers. SRT for large carnivorous theropods was estimated to be 4–5 days, when considering only body mass. The present study provides allometric scaling parameters of mean SRT for a variety of seed‐dispersing animals, and highlights large variations in scaling among taxa. The allometric scaling obtained could be a critical component of further trait‐based modelling of seed dispersal functions. Further, the potential and limitations of the scaling of animal SRT with body mass and a future pathway to the development of trait‐based modelling are discussed.     

Defaunation impacts on seed survival and its effect on the biomass of future tropical forests

Large animal species, which provide important ecological functions such as dispersal of seeds or top–down control of seed predators, are very vulnerable in fragmented forests, being unable to survive in small fragments, and facing increasing hunting pressure. The loss of large animals affects two main ecological processes crucial for the tree reproductive cycle: seed dispersal of large seeds (e.g. provided by tapirs) and control of seed predator population (e.g. provided by large cats). The changes in both processes are expected to increase seed mortality since seeds are not dispersed away from conspecifics (causing increased pre‐dispersal mortality due to negative density dependent effects) and/or face increased predation after a dispersal event (post‐dispersal mortality). Although an extensive body of empirical knowledge exists on seed predation, the link between seed loss and adult tree community composition and structure is not well established, as well as the temporal scale seed changes affect adults. Using an individual‐based forest model (FORMIND), we evaluate the long‐term consequences of increased pre and post‐dispersal seed mortality on the future forest biomass retention of a Brazilian northeastern Atlantic forest. Our results show that forest biomass is significantly affected after 80–93% pre‐dispersal loss of large seeds, or post‐dispersal predation densities of 20–25 predators per parent tree. Large‐seeded tree species are at increased risk of local extinction causing up to 26.2% loss of forest biomass when both pre and post‐dispersal processes are combined. However, these changes can last up to 100 years after the occurrence of defaunation. In summary we conclude that large animal loss has the potential to reduce future forest biomass and tree species‐richness by impacting seed survival, and should be considered in the planning of biodiversity friendly landscapes as well as in calculations of the global carbon budget.     

动物与植物种子更新的关系Ⅱ．动物对种子的捕食、扩散、贮藏及与幼苗建成的关系

植物的繁殖体总是面临来自各类生物（如昆虫、脊椎动物、真菌）的捕食风险。因动物捕食引起的种子死亡率影响植物的适合度、种群动态、群落结构和物种多样性的保持。种子被捕食的时间和强度成为植物生活史中发芽速度、地下种子库等特征的主要选择压力,而种子大小、生境类型等因素也影响动物对植物种子的捕食。捕食者饱和现象被认为是植物和种子捕食者之间的高度协同进化作用的结果,是限制动物破坏种子、提高被扩散种子存活率的一种选择压力。大部分群落中的大多数植物种子被动物扩散。种子扩散影响种子密度、种子被捕食率、病原体攻击率、种子与母树的距离、种子到达的生境类型以及建成的植株将与何种植物竞争,从而影响种子和幼苗的存活,最终影响母树及后代植物的适合度。种子被动物扩散后的分布一般遵循负指数分布曲线,大多数种子并没有扩散到离母树很远的地方。捕食风险、生境类型、植被盖度均影响动物对种子的扩散。植物结实的季节和果实损耗的过程也体现了其对扩散机会的适应。许多动物有贮藏植物种子的行为。动物贮藏植物繁殖体的行为,一方面调节食物的时空分布,提高了贮食动物在食物缺乏期的生存概率;另一方面也为种子萌发提供了适宜条件,促进了植物的扩散。于是,植物与贮食动物形成了一种协同进化关系,这种关系可能是自然界互惠关系（mutualism)的一种。影响幼苗存活和建成的因子包括种子贮蒇点的微生境、湿度、坡向、坡度、林冠盖度等。许多果食性动物吃掉果肉后,再将完好的种子反刍或排泄出来。种子经动物消化道处理后,发芽率常有所提高。