小果野芭蕉种子散布和不同时空尺度上种子被捕食格局

 以分布在云南西双版纳地区的大型先锋草本植物小果野芭蕉(Musa acuminata)为研究材料,研究其种子初次散布过程和不同时空尺度上种子被 捕食格局。小果野芭蕉的成熟果实有75%在夜间被取食和传播,在白天消失的果实则占25%。蝙蝠是其最主要的种子传播者,鸟类在其种子传播 过程中也起到一定的作用。人工摆放种子试验结果显示小果野芭蕉种子的主要转移者是小型啮齿类(鼠类)和蚁类：在开放处理下3 d后转移率为 86%,排除蚁类(鼠类可进入)处理下种子转移率为69%以及排除鼠类(蚂蚁可进入)处理下种子被转移率为56%。季节、地点和生境均显著影响人工 摆放种子被转移强度：雨季显著高于旱季(p<0.001), 野芭蕉生境显著高于与其相连的自然森林和荒地(p<0.001),在人为干扰较少的补蚌自然 保护区显著低于西双版纳热带植物园和新山,而后两者之间并无显著差异(p>0.05)。同时,地点和生境以及季节、地点和生境都有显著的交互 作用。与相邻的森林和荒地相比,野芭蕉群落中种子被鼠类捕食的强度最大且受蚁类二次转移的比例最少,森林和荒地中种子被鼠类捕食的强 度相对较小且蚁类对种子的二次转移比例较高,从而更好地帮助种子逃避鼠类捕食。因此,依赖于食果动物(主要是蝙蝠, 也包括鸟类)的初次 散布是小果野芭蕉种子逃避捕食的关键。     

Trophic and non-trophic pathways mediate apparent competition through post-dispersal seed predation in a Patagonian mixed forest

Post‐dispersal predation can be a major source of seed loss in temperate forests. Little is known, however, about how predator‐mediated indirect interactions such as apparent competition alter survival patterns of canopy tree seeds. Understorey plants may enhance tree seed predation by providing sheltered habitat to granivores (non‐trophic pathway). In addition, occurrence of different tree seeds in mixed patches may lead to short‐term apparent competition between seed types, because of the granivores’ foraging response to changes in food patch quality (trophic pathway). We hypothesised that understorey bamboo cover and mixing of seed species in food patches would both increase tree seed predation in a Nothofagus dombeyi?Austrocedrus chilensis forest in northern Patagonia, Argentina. Seed removal experiments were conducted for three consecutive years (2000–2002) differing in overall granivory rates. Seed patch encounter and seed removal rates were consistently higher for the larger and more nutritious Austrocedrus seeds than for the smaller Nothofagus seeds. Seed removal was greater beneath bamboo than in open areas. This apparent competition pathway was stronger in a low‐predation year (2000) than in high‐predation years (2001–2002), suggesting a shift in microhabitat use by rodents. Patch composition had a significant, though weaker, impact on seed survival across study years, whereas seed density per patch enhanced encounter rates but did not influence seed removal. Removal of the less‐preferred Nothofagus seeds increased in the presence of Austrocedrus seeds, but the reciprocal indirect effect was not observed. However, this non‐reciprocal apparent competition between seed species was only significant in the high‐predation years. Our study shows that granivore‐mediated indirect effects can arise through different interaction pathways, affecting seed survival patterns according to the predator's preference for alternative seed types. Moreover, results indicate that the occurrence and relative strength of trophic vs non‐trophic pathways of apparent competition may change under contrasting predation scenarios.     

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。     

The intermediate dispersal hypothesis: seed dispersal is maximized in areas with intermediate usage by hoarders

Seed dispersal and predation are paramount for tropical plant diversity. When encountered by scatter-hoarding frugivores, seeds can be either eaten, dispersed or ignored. But even after dispersal, seed caches are still subjected to predation. Many factors are known to influence these dynamics; however, how frequently hoarders use certain patches has seldom been related to cache predation rates. We used the interaction between agoutis (Dasyprocta leporina), a scatter-hoarding rodent, and Joannesia princeps, a tropical tree, as a model to investigate how the number of visits by hoarders in certain areas influences cache predation and seed fate. Camera-traps were used for 30 days in twenty different locations in Tijuca National Park to assess number of visits by agoutis. Thereafter, we placed seed piles on the same areas and determined their fate using the spool-and-line method to track seeds for over one hundred days. We found a non-linear relationship between how often an area is used by hoarders and the final proportion of dispersed seeds. At areas with a low number of visits, proportion of dispersed seeds was low due to low removal. As frequency of visits by hoarders increased, seed removal and the number of dispersal events increased but so did cache predation. Thus, in areas intensively used by hoarders, high cache predation resulted in a low number of dispersed seeds that remained alive in caches. As a result, dispersal was maximized in areas with intermediate use by scatter-hoarders, where there was a balance between primary seed dispersal and cache predation.

     

Mixed effects of landscape complexity and farming practice on weed seed removal

Agricultural intensification negatively affects farmland biodiversity, and thereby, ecosystem services such as predation of weed seeds. Landscape complexity (large and diverse areas of semi-natural habitats) and organic farming (without pesticides and mineral fertilizers) can counteract this negative trend, but little is known about their relative importance. We experimentally studied seed removal of four economically relevant weed species by excluding (i) vertebrates, (ii) vertebrates plus large invertebrates and (iii) neither vertebrates nor invertebrates (control) at the field edge and in the interior of 22 organically or conventionally managed winter wheat fields, located across a gradient of landscape complexity (41–94% arable land). Arable land (%) was used as a simple predictor of landscape complexity, as it is closely related to landscape parameters such as habitat type diversity. Seed predation and removal were mainly influenced by large invertebrates, seed species identity, with Cirsium arvense being more affected than Poa trivialis, Apera spica-venti and Galium aparine and landscape complexity in interaction with farming practice, as it increased in conventional fields, but decreased in organic fields as landscape complexity decreased. Seed predation and removal did not consistently correspond to seed predator densities, as small mammal abundances decreased in conventional fields, but increased in organic fields as landscape complexity decreased and carabid activity densities were higher in organic compared to conventional fields. Slug activity density showed same response to landscape complexity and farming practice like seed removal and appeared to additionally influence the movement of seeds. In conclusion, our assessment of interacting local and landscape effect adds to the current knowledge of seed predation and removal. Farming practice and landscape complexity affect seed predator species differentially, thereby resulting in complex pattern of seed predation and removal. The service of weed seed predation is provided by small mammals and invertebrates and the disservice of seed dispersal and movement is provided by slugs.     

Poachers and Forest Fragmentation Alter Seed Dispersal,Seed Survival,and Seedling Recruitment in the Palm Attalea butyraceae,with Implications for Tropical Tree Diversity1

We examined the interaction between a palm and two bruchid beetles along with several mammal species to explore how poachers and habitat fragmentation may indirectly alter the spatial pattern of seed dispersal, seed predation, and seedling recruitment in central Panama. The large, stony endocarps of Attalea butyraceae decay slowly and bear distinctive scars when opened by rodents or beetles. We determined the final distance between endocarps and reproductive trees (which we call an ecologically effective dispersal distance), the predation status of each endocarp, and the distance between seedlings and reproductive trees. The 68 focal trees were divided among 14 sites and four levels of anthropogenic disturbance. Levels of disturbance included full protection from poachers, light and heavy pressure from poachers, and small island habitat fragments. Ecologically effective seed dispersal distances were greatest for protected sites, intermediate for lightly poached sites, and shortest for heavily poached sites and habitat fragments. Seed predation by rodents increased with distance to the nearest reproductive Attalea and was greatest for fully protected sites, intermediate for lightly poached sites, and least for heavily poached sites and habitat fragments. Seed predation by beetles reversed the patterns described for seed predation by rodents. Total seed predation by beetles and rodents combined was independent of distance, greatest for fully protected sites, and lower for poached sites and habitat fragments. Seedling densities were always greatest close to reproductive trees; however, the increase in seedling densities close to reproductive trees was minimal for fully protected sites, clearly evident for poached sites, and pronounced for habitat fragments. Increased seedling recruitment near conspecific trees may in time reduce tree diversity where humans disrupt mammal communities.     

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.     

Temporal consistency in the spatial pattern of seed predation across a forest – old field edge

Seed predation is an important factor in determining the rate of tree establishment in abandoned agricultural land. Edges, through altered habitat use by small mammals, may influence the spatial pattern of forest regeneration in these successional sites. To determine the spatial pattern of seed predation across a forest-old field edge, we used a grid that began 30 m inside the forest and extended 60 m into the old field. Seed stations were placed at regular 10-m intervals and were monitored for removal of Acer rubrum seed for 50 d. This design was repeated over four years (1995–1998). Small mammal trapping was conducted in the final year of the study to determine the spatial pattern of seed predators within the site. Removal rates varied among the four years of the study with years of high and low removal rates. However, the spatial pattern of seed removal rate was similar in all years. Final survival ranged from 0.7–15.5% of seeds, with lower final survival in years with faster rates of seed removal (1996 and 1998). Seed removal rates and rates of discovery were greatest at the forest edge and decreased with distance into the old field. The number of seeds surviving to the end of the experiment also varied across the edge gradient, with highest survival at greater distances into the old field in low predation years. Seed removal rate covaried with spatial pattern of Peromyscus leucopus captures within the site. Seed removal and discovery was also higher under the exotic shrub Rosa multiflora, which may have provided cover for foraging seed predators. These indirect effects of edges on plant communities can potentially alter the rate and spatial pattern of tree invasion into disturbed lands and illustrate the importance of understanding plant-animal interactions in the context of habitat fragmentation.     

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.     

Post-dispersal seed predation of three grassland species in a plant diversity experiment

Aims Post-dispersal seed predation is an important ecosystem process because it can influence the seed's fate after the initial dispersal from the mother plant and subsequently transform communities. Even at small scales, post-dispersal seed predation can vary greatly depending on seed identity, granivorous taxa or microhabitat structure. However, little is known about the role of plant species richness and functional group richness in post-dispersal seed predation. The overall aim of this study was to test whether increasing plant species richness or plant functional group richness affects the rate and variability of post-dispersal seed predation. We additionally investigated the influence of vegetation structure and seed species identity on the rate and variability of post-dispersal seed predation and whether the influence of different granivorous taxa changed with increasing plant species richness.Methods We conducted seed removal experiments along a long-term experimental plant diversity gradient, comprising plots with monocultures to 60 species mixtures of common grassland species in Jena, Germany, in August 2011. We studied seeds of Onobrychis viciifolia, Pastinaca sativa and Trifolium pratense in exclusion experiments (seed cafeterias), an experimental setup that allowed access either for arthropods or slugs or for all granivorous taxa. Traditionally, seeds removed from seed cafeterias were classified as consumed but we used traceable fluorescent-coloured seeds to obtain more accurate predation rates by subtracting recovered seeds from overall removed seeds. The effect of multiple vegetation variables on mean and variability of seed predation rates was analysed using generalized mixed-effect models and linear regressions, respectively.Important findings Rates of recovered seeds were low but contributed to significant differences between seed predation rates and removal rates of seeds in some treatments. Seed predation rates were not directly correlated with increasing plant species richness or plant functional group richness but were influenced byseed species identity and granivorous taxa. Vegetation variables such as vegetation height and cover were significantly associated with seed predation rates. Depending on the seed species and/or the granivorous taxa, different vegetation variables correlated with seed predation rates. Our results indicate that effects of plant functional group richness and multiple vegetation variables on the magnitude of post-dispersal seed predation varied with seed identity and seed predator taxa. A direct effect of plant species and plant functional group richness could be shown on the variability of post-dispersal seed predation for some seed species and their respective predators. Thus, the changes in magnitude of post-dispersal seed predation with increasing plant species richness could potentially impact the fitness of some plant species and thereby influence plant community structure.     

Geographical variation in the potential of mice to constrain an ant-seed dispersal mutualism

Pre‐ and post‐dispersal Helleborus foetidus (Ranunculaceae) seed predation by mice Apodemus sylvaticus as well as post‐dispersal seed removal by ants was studied, during two years, in six plant populations within three geographical regions (Caurel, Cazorla and Mágina) of the Iberian Peninsula. An observational approach revealed strong interregional differences in seed predation by mice during the pre‐dispersal phase, with high and similar rates of predation in Cazorla and Mágina and much lower rates in Caurel. There were also significant inter‐annual variations on pre‐dispersal seed predation by mice, while the existing habitat‐related differences (of lower magnitude) were not consistent across regions. Field experiments based on seed‐offering exclosures, showed that, despite some interregional variation, post‐dispersal seed removal by ants was consistently high through all spatial and temporal scales considered, with most seeds being removed within 48 h. Conversely, post‐dispersal seed predation by mice was highly variable among regions, being very high in Cazorla and minimal or absent in Caurel and Mágina. Interestingly, in Cazorla, in presence of mice, the number of seeds removed was rather independent of the presence/absence of ants, while under mice exclusion, it was determined by the presence/absence of ants. Conversely, in Caurel, the number of seeds removed by each remover agent (ants or mice) was independent of the presence/absence of the other agent. Thus, though uniquely in Cazorla, mice limited the number of seeds available to ants and, therefore, in this region could potentially have interfered on the development of seed traits that enable ants to efficiently harvest them. Our results support the notion that geographical variation over the Iberian Peninsula of mice seed predation may have promoted a mosaic of well‐matching and mismatching situations between H. foetidus diaspore traits and the characteristics of ant communities, which is consistent with some recent theories on the geographical structure of interactions.     

A new hypothesis for the importance of seed dispersal in time

Most studies on seed dispersal in time have focused on seed dormancy and the physiological triggers for germination. However, seed dispersed by animals with low metabolic and moving rates, and long gut-passage times such as terrestrial turtles, could be considered another type of dispersal in time. This study tests the hypothesis that seeds dispersed in time may lower predation rates. We predicted that seeds deposited below parent trees after fruiting fall has finished is advantageous to minimize seed predators and should show higher survival rates. Four Amazonian plant species, Dicranostyles ampla, Oenocarpus bataua, Guatteria atabapensis and Ocotea floribunda, were tested for seed survival probabilities in two periods: during fruiting and 10-21 days after fruiting. Experiments were carried out in two biological stations located in the Colombian Amazon (Caparú and Zafire Biological Stations). Seed predation was high and mainly caused by non-vertebrates. Out of the four plant species tested, only Guatteria atabapensis supported the time escape hypothesis. For this species, seed predation by vertebrates after the fruiting period increased (from 4.1% to 9.2%) while seed predation by non-vertebrates decreased (from 54.0% to 40.2%). In contrast, seed predation by vertebrates and by non-vertebrates after the fruiting period in D. ampla increased (from 7.9% to 22.8% and from 40.4% to 50.6%, respectively), suggesting predator satiation. Results suggest that for some species dispersal in time could be advantageous to avoid some type of seed predators. Escape in time could be an additional dimension in which seeds may reach adequate sites for recruitment. Thus, future studies should be address to better understand the survival advantages given by an endozoochory time-dispersal process.     

小叶藤黄(Garcinia cowa)种子传播、种子被捕食及幼苗空间分布

 1999年8月至2001年2月,对热带雨林树种小叶藤黄(Garcinia cowa)种子的初级传播、二次传播、种子被取食及幼苗空间分布进行了研究。结果表明：林上拜访动物主要有猕猴(Macaca mulatta)、花面狸(Paguma larvata)、赤腹松鼠(Callosciu ruserythraeus)、蓝腹松鼠(C. pygertthrus)、小花鼠(Tamiops macclellandi)等5种。有86.5%±4.9%(1999年)和91.4%±8.2%(2000年)的成熟果实被林上动物所取食     

Seed removal,seed dispersers,and the allocation of tissues in Myrtaceae seeds

To avoid seed predation, plants may invest in protective seed tissues. Often related to seed size, allocation in seeds' physical defenses can also be influenced by dispersers. We explore the relationships between seed traits (seed mass and hardness) and seed removal in 22 Myrtaceae species of the Brazilian Atlantic Forest, a dominant and diverse fleshy-fruited taxon dispersed by birds, rodents, and other mammals. Our goal is to understand how seed traits influence seed removal rates, and whether dispersers can affect tissue allocation in the seed coat. Seeds were exposed to field removal experiments. In the laboratory, total seed mass and seed coat mass were obtained. To evaluate the influence of seed traits on removal, we performed Kruskal–Wallis and Simple Linear Regression tests. We assessed seed coat and seed mass covariation through standardized major-axis allometric regressions. Harder seeds were larger than softer ones. Seed traits affect removal rates, as tougher and heavier seeds had lower removal. Seed mass significantly predicts seed coat proportion in seven of the 14 species tested. Bird-dispersed species tend to exhibit lower proportions of seed coat as seed mass increases, whereas rodent-dispersed species apparently present the opposite trend, with seed coat proportion increasing with seed mass. Such difference may be caused by the contrasting seed predation pressure represented by birds and rodents. Energy allocation for defense, expressed in seed coat proportion, is greater in large seeds, as these are mostly dispersed by rodents whose propensity to cache and disperse seeds is greater for large and well-protected seeds.     

Response of ants to human‐altered habitats with reference to seed dispersal of the myrmecochore Corydalis giraldii Fedde (Papaveraceae)

Anthropogenic habitat disturbance has potential consequences for ant communities. However, there is limited information on the effects of ant responses on associated ecological processes such as seed dispersal. We investigated the effect of disturbance on the abundance, richness, and composition of ant communities and the resulting seed‐dispersal services for a herbaceous myrmecochore, Corydalis giraldii (Papaveraceae), in an undisturbed habitat (forest understory), moderately disturbed habitat (abandoned arable field), and highly disturbed habitat (road verge) on Qinling Mountains, China. In total, we recorded 13 ant species, and five out of these were observed to transport seeds. The community composition of dispersers was significantly different amongst habitats. The richness of the dispersers did not differ among the habitats, but their total abundance varied significantly across habitats and was 21% lower in the road verge than in the abandoned arable fields. The major seed‐dispersing ant species in both the forest understory and the abandoned arable field were large‐bodied (Myrmica sp. and Formica fusca, respectively), whereas the major seed‐dispersing ants found in the road verge were the small‐bodied Lasius alienus. This difference resulted in lower seed removal rates and dispersal distances in the road verge than in the other two habitats. The different dispersal patterns were attributed primarily to differences in dispersing ant abundance and identity, most likely in response to habitats with different degree of anthropogenic disturbance. The possible influence of disturbance on the ecological specialization of ant‐seed dispersal interaction is also discussed.     

Seed preferences by rodents in the agri‐environment and implications for biological weed control

Post‐dispersal seed predation and endozoochorous seed dispersal are two antagonistic processes in relation to plant recruitment, but rely on similar preconditions such as feeding behavior of seed consumers and seed traits. In agricultural landscapes, rodents are considered important seed predators, thereby potentially providing regulating ecosystem services in terms of biological weed control. However, their potential to disperse seeds endozoochorously is largely unknown. We exposed seeds of arable plant species with different seed traits (seed weight, nutrient content) and different Red List status in an experimental rye field and assessed seed removal by rodents. In a complementary laboratory experiment, consumption rates, feeding preferences, and potential endozoochory by two vole species (Microtus arvalis and Myodes glareolus) were tested. Seed consumption by rodents after 24 h was 35% in the field and 90% in the laboratory. Both vole species preferred nutrient‐rich over nutrient‐poor seeds and M. glareolus further preferred light over heavy seeds and seeds of common over those of endangered plants. Endozoochory by voles could be neglected for all tested plant species as no seeds germinated, and only few intact seeds could be retrieved from feces. Synthesis and applications. Our results suggest that voles can provide regulating services in agricultural landscapes by depleting the seed shadow of weeds, rather than facilitating plant recruitment by endozoochory. In the laboratory, endangered arable plants were less preferred by voles than noxious weeds, and thus, our results provide implications for seed choice in restoration approaches. However, other factors such as seed and predator densities need to be taken into account to reliably predict the impact of rodents on the seed fate of arable plants.     

Experimental Seed Predator Removal Reveals Shifting Importance of Predation and Dispersal Limitation in Early Life History Stages of Tropical Forest Trees

Recruitment limitation of trees in tropical forests can occur because of high rates of seed predation or low rates of seed dispersal, but the degree to which limitation is influenced by variation in seed predator abundance, and hence variation in seed predation and dispersal, is not well understood. We experimentally reduced the density of a granivorous small mammal (Heteromys desmarestianus) by 90 % to assess the degree to which its rates of seed predation and dispersal limit seed to seedling survival of nine species of trees in a Neotropical lowland forest. Overall, the proportion of seeds that germinated was influenced more by high rates of predation than by limited dispersal. Reduction in density of H. desmarestianus resulted in an order of magnitude decrease in fruit removal rates and an order of magnitude increase in both the absolute and relative numbers of seeds that germinated. However, the proportion of seeds that were cached remained relatively constant across all periods and between control grids and removal plots. In removal plots, H. desmarestianus dispersed and cached about 10 % of the fruits they handled, of which approximately 25 % germinated. This was 2 to 3 times greater than the germination rates of undispersed seeds, and for two species dispersed seeds were the only ones that germinated. The results suggest the simultaneous occurrence of both seed predation and dispersal limitation for trees with animal-dispersed seeds, but there may also be a hierarchy of importance in the relative strength of these two mechanisms that is determined by the dynamics of seed predator populations.     

Seed dispersal by lizards on a continental‐shelf island: predicting interspecific variation in seed rain based on plant distribution and lizard movement patterns

Aim We estimated the patterns of seed deposition provided by the eyed lizard, Timon lepidus, and evaluated whether these patterns can be generalized across plant species with different traits (fruit and seed size) and spatial distributions. Location Monteagudo Island, Atlantic Islands National Park (north‐western Spain). Methods We radio‐tracked seven lizards for 14 days and estimated their home ranges using fixed kernels. We also geo‐referenced all fruit‐bearing individuals of four plant species dispersed by eyed lizards in the study area (Corema album, Osyris alba, Rubus ulmifolius and Tamus communis), measured the passage time of their seeds through the lizard gut, and estimated seed predation in four habitats (bare sand, grassland, shrub and gorse). Seed dispersal kernels were estimated using a combination of these data and were combined with seed predation probability maps to incorporate post‐dispersal seed fate (‘seed survival kernels’). Results Median seed gut‐passage times were around 52–98 h, with maximum values up to 250 h. Lizards achieved maximum displacement in their home ranges within 24–48 h. Seed predation was high (80–100% of seeds in 2 months), particularly under Corema shrub and gorse. Seed dispersal kernels showed a common pattern, with two areas of preferential seed deposition, but the importance of these varied among plant species. Interspecific differences among dispersal kernels were strongly reduced by post‐dispersal seed predation; hence, seed survival kernels of the different plant species showed high auto‐ and pairwise‐correlations at small distances (< 50 m). As a result, survival to post‐dispersal seed predation increased with dispersal distance for O. alba and T. communis, but not for C. album. Main conclusions Seed dispersal by lizards was determined primarily by the interaction between the dispersers’ home ranges and the position of the fruit‐bearing plants. As a result, seed rain shared a common template, but showed considerable variation among species, determined by their specific spatial context. Seed predation increased the spatial coherence of the seed rain of the different species, but also resulted in contrasting relationships between seed survival and dispersal distance, which may be of importance for the demographic and evolutionary processes of the plants.     

大耳姬鼠对滇西北18种植物种子的捕食

2004年9月至10月在滇西北高海拔地区对18种植物种子进行了野外被捕食研究。选取高、低两种人为干扰程度的生境;高、低两种种子密度:3粒种子/塑料盘和15粒种子/塑料盘;3种试验设置:排除啮齿动物等大型捕食者、排除蚂蚁等小型捕食者,不作任何处理作为对照。其结果表明,种子捕食者主要为夜间活动的大耳姬鼠(Apodemus latronum)。种子在高人为干扰的生境中被捕食率要显著低于低人为干扰的生境(F1,430=7.78,P<0.01);种子在高密度状况下的被捕食率要显著高于低密度状况(F1,430=13.16,P<0.001)。大耳姬鼠对于不同种类植物种子也有很强的选择性(F17,414=106.69,P<0.001),如喜好取食华山松(Pinus armandi)、中甸乌头(Aconitum chungdianensis)、豆科一种(Leguminosae sp.)和大头续断(Dipsacusasper)的种子,而不喜好取食高山柏(Sabina squamata)、黄花木(Piptanthus concolor)、子(Cotoneaster sp.)和西南鸢尾(Iris bulleyana)的种子。18种植物中,种子大小与其被捕食率高低之间无显著相关性,不同硬度等级的种子与被捕食率也无显著差异(P>0.05)。     

Evidence for secondary seed dispersal by rodents in Panama

Summary The data presented show thatVirola nobilis (Myristicaceae), a bird/mammal-dispersed tree species in Panama, may also be dispersed by a terrestrial rodent, the agouti (Dasyprocta punctata). Using a thread-marking method, we observed that agoutis scatterhoardedV. nobilis seeds that they found both singly or in clumps. Seed removal and seed burial rates were strongly affected by features of forest habitats, such asV. nobilis tree richness (rich vs poor) and/or forest age (old vs young), but not by seed dispersal treatment (scattered vs clumped). Predation (mostly post-dispersal) of unburied seeds by weevils was independent of habitat and dispersal treatment. Seeds artificially buried in aVirola-rich area were more likely to escape predation and become established than unburied seeds under natural conditions. The food reward for agoutis is in the germinating seedlings. The seed dispersal syndrome ofV. nobilis involves long- and short-distance dispersers which both appear important for tree recruitment.