Avian seed dispersal and seedling distribution of the endangered tree species,Taxus chinensis,in patchy habitats

Background: There is limited understanding about bird dispersal behaviour and seedling distribution of endangered tree species in patchy environments, although these processes are important for plant species persistence.

Aims: We tested how patch features affected bird behaviour and seed dispersal, and thus seedling distribution of the endangered Chinese yew tree (Taxus chinensis).

Methods: In the present study, we combined field data of bird dispersal behaviour and GIS-based information to elucidate the influence of spatial features of habitat patches on bird dispersal behaviour, and the resulting effects on the seedling distribution of the endangered Chinese yew in two patchy habitats.

Results: Our results showed that the only seed source patch could attract eight bird species for dispersal at the two sites. Post-foraging movements of bird dispersers was strongly related to both topography and the relative locations of habitat patches. Yew seedlings aggregated only at the seed source and bamboo recruitment patches, which was affect by both the spatial distribution of recruitment patches and patch use by dispersers.

Conclusions: Our results emphasise that bamboo patches in both patchy environments provide the necessary conditions for germination of yew seeds, and the post-foraging behaviour of dispersers determines seed deposited in these patches. Our study highlights the importance of the dispersal behaviour of frugivorous birds in the successful regeneration and colonisation of yew populations in patchy habitats.     

Patch configuration affects alpine plant distribution

The relative importance of niche requirements and dispersal limitation in controlling the landscape‐scale distribution of plants is still contentious. Local occurrence and abundance of alpine plants are commonly thought to be driven by abiotic site conditions due to pronounced environmental gradients over short distances. However, explicit tests of the additional role of dispersal‐related processes for alpine plant distribution patterns are lacking. Here, we combine niche‐based species distribution models with variables describing patch size and connectivity to evaluate if, besides abiotic limitations, spatial habitat configuration affects the occurrence and abundance of six plant species inhabiting patchy snowbed mosaics of the northeastern Calcareous Alps in Austria. Moreover, we assess if eventual effects of spatial patch configuration are more clearly detectable when calculating connectivity based on parameterized mechanistic dispersal kernels for both wind and animal vectors instead of using nearest neighbour metrics. We show that patch size and connectivity are significantly correlated to the occurrence of all and to the abundance of four out of six study species, although the relative importance of these variables, as compared to niche constraints, varies among species. In addition, connectivity measures derived from parameterized dispersal kernels were more closely related to occupancy, and in particular to abundance patterns than a simple nearest neighbour metric. The fitted kernels also suggest that dispersal by alpine chamois plays an important role for inter‐patch seed exchange. We conclude that, despite evident abiotic limitations, recurrent local extinctions and delayed re‐colonizations indeed play a role for the distribution of our study species, and that alpine plants may hence be less in equilibrium with their abiotic environment than commonly thought. Moreover, the relatively high long‐distance dispersal probabilities of animal kernels indicate that the ability of alpine plants to adapt their ranges to a rapidly warming climate may, among other factors, depend on the availability of dispersal services by large mammals.     

Seed-deposition and recruitment patterns of Clusia species in a disturbed tropical montane forest in Bolivia

Spatial patterns of seed dispersal and recruitment of fleshy-fruited plants in tropical forests are supposed to be driven by the activity of animal seed dispersers, but the spatial patterns of seed dispersal, seedlings and saplings have rarely been analyzed simultaneously. We studied seed deposition and recruitment patterns of three Clusia species in a tropical montane forest of the Bolivian Andes and tested whether these patterns changed between habitat types (forest edge vs. forest interior), distance to the fruiting tree and consecutive recruitment stages of the seedlings. We recorded the number of seeds deposited in seed traps to assess the local seed-deposition pattern and the abundance and distribution of seedlings and saplings to evaluate the spatial pattern of recruitment. More seeds were removed and deposited at the forest edge than in the interior. The number of deposited seeds decreased with distance from the fruiting tree and was spatially clustered in both habitat types. The density of 1-yr-old seedlings and saplings was higher at forest edges, whereas the density of 2-yr-old seedlings was similar in both habitat types. While seedlings were almost randomly distributed, seeds and saplings were spatially clustered in both habitat types. Our findings demonstrate systematic changes in spatial patterns of recruits across the plant regeneration cycle and suggest that the differential effects of biotic and abiotic factors determine plant recruitment at the edges and in the interior of tropical montane forests. These differences in the spatial distribution of individuals across recruitment stages may have strong effects on plant community dynamics and influence plant species coexistence in disturbed tropical forests.     

辽东山区次生林木本植物空间分布

森林木本植物的空间格局有助于揭示群落结构的形成机制与潜在的生态学过程,且对林分经营具有一定指导意义。在0—50 m尺度范围内综合分析了辽东山区4 hm2温带次生林样地多度10的树种空间格局。研究发现:(1)在完全随机零模型下,大部分树种呈现聚集格局,聚集格局树种的比例随尺度增加而降低;在32 m的较大尺度下,随尺度增加,随机和规则格局成为树种分布的主要形式;(2)在异质性泊松过程零模型下,55.9%的树种呈现随机格局,其余大部分树种在10 m的尺度下呈现聚集格局,且随尺度增加,规则格局成为主要形式;(3)在完全随机零模型下,树种属性(林层、径级和多度)显著地影响种群聚集度,而在异质性泊松过程零模型下,树种属性对种群聚集度不存在显著影响。综上,生境异质性、扩散限制和树种属性部分解释了辽东山区次生林木本植物空间分布格局,相对而言,生境异质性的效应更为突出。研究结果有助于揭示次生林群落生物多样性的维持机制。     

Dispersal strategies and spatial organization of vegetation in arid ecosystems

Seed dispersal and establishment are critical stages for plants in arid environments, where vegetation is spatially organized in patches with suitable and unsuitable sites for establishment. Theoretical studies suggest that the ability of vegetation to self‐organize in patchy spatial patterns is a critical property for plant survival in arid environments, and is a consequence of a scale‐dependent feedback between plants and resource availability. Field observations show that plants of arid environments evolved towards short dispersal distance (proxichory) and that the investment in reproduction increases along an aridity gradient. Here, we investigated how plant dispersal strategies affect spatial organization and associated scale‐dependent feedback in arid ecosystems. We addressed this research question using a model where the spatio‐temporal vegetation patterns were driven by scale‐dependent feedbacks between plants and soil water availability. In the model, water availability limited vegetation growth, seed production and establishment ability. Seed dispersal was modelled with an integrodifferential equation that mimicked important plant dispersal characteristics (i.e. fecundity, mean dispersal distance and establishment ability). Results showed that, when the investment in fecundity was relatively high, short seed dispersal helped maintaining higher mean biomass in the system, improving the vegetation efficiency in water use. However, higher fecundity induced a large cost, and high mean biomass could be sustained only with high establishment ability. Considering low establishment ability, intermediate fecundity was more efficient than low fecundity in maintaining high plant biomass under the most arid conditions. Consistently, plant dispersal strategies that maintained more biomass were related to a vegetation spatial organization that allowed the most efficient soil water redistribution, through the strengthening of the scale‐dependent feedback. The efficient dispersal strategies and spatial patterns in the model are commonly observed in plants of arid environments. Thus, dispersal strategies in arid environments might contribute to a favourable spatial organization and associated scale‐dependent feedback.     

植物种群更新限制——从种子生产到幼树建成

更新限制是指种子由于各种原因,不能够萌发并生长成幼树。它作为解释生物多样性的理论,一直受到国内外群落生态学家关注。从种源限制、传播限制和建成限制3个角度,对更新限制机制研究进展进行了综述。从种源限制而言,时空因素是影响植物种群更新限制的重要因素,因为植物结实量存在明显时空变化,造成植物更新个体出现明显的时空规律。从传播限制而言,传播数量、距离和食果动物行为均限制植物种群更新。数量上,缺乏有限传播者势必减少传播数量,但如果种子拥有较高质量,则能逃脱数量限制;距离上,植物更新个体显示出明显的Janzen-Connell格局,但传播距离趋向稳定,形成植物种群的进化稳定对策;食果动物行为上,不同传播者对更新贡献存在差异,捕食者直接降低更新,融入两类动物行为的模型更能反映食果动物对更新的限制。从建成限制而言,环境因子制约植物生长。小尺度下,微生境的好坏对于植物幼苗建成至关重要;大尺度下,植物提供较好的广告效应则能摆脱生境限制。将传播者行为、捕食者行为与幼苗的空间分布格局、种子传播机理模型等结合,建立植物更新限制机理模型应是更新限制未来的研究热点。选择稀有种和古老种为主题的长期更新限制研究,为种群恢复提供指导,也是未来重要研究方向。     

Is the population turnover of patchy‐distributed annuals determined by dormancy dynamics or dispersal processes?

In species with fragmented distribution, regional turnover dynamics is given by the processes of local population extinction and patch (re)colonization by migrants spreading from neighboring occupied patches. In plants with dormant stages (e.g. seeds) and limited dispersal capacity, regional dynamics based on dispersal processes can be overridden by pseudo-turnover determined by signals inducing or breaking dormancy (e.g. due to changes in habitat quality) resulting in a low importance of habitat configuration and size.
In this study, I investigated the turnover dynamics of 5 annual plant species growing on ant mounds of Lasius flavus over three years. I analyzed whether the grassland-scale dynamics of these annuals is influenced by dispersal processes, or alternatively, by pseudo-turnover of soil seed populations. For that purpose I 1) searched for populations formed from soil seeds only, 2) compared the relative contribution of the soil seed bank and seed rain for population restoration after disappearance from the vegetation and 3) investigated whether colonization and extinction events are affected by patch isolation. I assumed if population turnover was rather a result of the soil seed bank dynamics then spatial effects would be hard to detect.
In spite of the presence of populations formed from soil seed and the relatively more important soil seed bank for potential population reestablishment, turnover dynamics followed the predictions of metapopulation theory. Population appearance was more probable in larger and less isolated patches. Probability of disappearance increased with decrease of population size that was negatively influenced by the patch size and its isolation. These findings indicate dispersal processes to be important in the turnover dynamics and only limited contribution of soil seed populations. Their small effectiveness is probably related to the low chance of recurrent disturbance on the mound surface.     

Effects of grazing on patch structure in a semi‐arid two‐phase vegetation mosaic

Abstract. Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two‐phase vegetation mosaic? Location: Patagonian steppe, Argentina. Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions. Results: The vegetation was spatially organized in a two‐phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions. Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.     

Optimum reproduction and dispersal strategies of a clonal plant in a metapopulation: a simulation study with Hieracium pilosella

Clonal spread is favoured in many plants at the expense of seed production in order to expand rapidly into open habitats or to occupy space by forming dense patches. However, for the dynamics of a population in a patchy landscape seed dispersal remains important even for clonal plants. We used a spatially explicit individual-based metapopulation model to examine the consequences of two trade-offs in Hieracium pilosella L: first, between vegetative and sexual reproduction, and second, between short and far-distance dispersal of seeds. Our main question was, what are the environmental conditions that cause a mixed strategy of vegetative and sexual reproduction to be optimal. The model was parameterised with field data on local population dynamics of H. pilosella. Patch dynamics were given firstly by disturbance events that opened patches in a matrix of a clonal grass that were colonisable for H. pilosella, and secondly by the gradual disappearance of H. pilosella patches due to the expanding grass. Simulations revealed opposing selection pressures on traits determined by the two trade-offs. Vegetative reproduction is favoured by local dynamics, i.e. the need for maintenance and expansion of established populations, whereas seed production is favoured by the necessity to colonise empty habitats. Similar pressures act on the proportion of seeds dispersed over short and far distances. Optimum reproductive and dispersal strategies depended on habitat quality (determined by seedling establishment probability), the fraction of dispersed seeds, and the fraction of seeds lost on unsuitable ground. Under habitat conditions supporting moderate to low seedling establishment, between 20% and 40% of reproductive effort in H. pilosella should be devoted to sexual reproduction with at least 10% of the seeds dispersed over distances suitable to attain empty patches. We conclude that in a spatially heterogeneous landscape sexual seed production in a clonal plant is advantageous even at the expense of local vegetative growth.     

Influence of environmental and spatial variables on regional distribution of forest plant species in a fragmented and changing landscape

During the past several centuries, forests in Europe and large parts of North America have been subject to extensive forest clearance. The last several decades, however, numerous new forest patches have been established onto former agricultural land. As a result, the present forest area often consists of a mixture of small forest patches of different age, area, habitat quality and connectivity embedded within a hostile agricultural landscape. In these patchy landscapes, distribution patterns of plant species may be affected by both regional and local factors, although the relative importance of both is still poorly understood. In this study, we investigated distribution patterns of 113 forest plant species in a fragmented landscape. Species abundances at the regional scale conformed to a clearly unimodal abundance distribution which we believe to be related to 1) environmental heterogeneity due to succession and 2) inequality in migration rates. Patch incidence was significantly related to life form, which in turn was correlated to seed mass and dispersal mechanism. Multiple logistic regressions showed that presence/absence of 59 species studied was significantly affected by patch connectivity, patch area and age for 35, 30 and 34 species, respectively. The results of this study indicate that distribution patterns of forest plant species are influenced by both local and regional factors. Moreover, they also demonstrate that next to spatial aspects of fragmentation, temporal patterns of landscape change may have far-reaching effects on presence/absence patterns of plant species and therefore should be incorporated in studies dealing with regional population structures of plants.     

The influence of spatial heterogeneity on regeneration by seed in a limestone grassland

Abstract. The spatial distribution of seedlings in fertilized and non-fertilized grassland patches (1 m x 2 m) was examined in alvar vegetation on the island of Öland, Sweden. We established whether variation in seedling distribution in grassland patches reflects the distribution of conspecific adults. We also established the significance of microsite turf attributes for prediction of seedling distribution at a small scale (10 cm x 10 cm), and the significance of conspecific adults abundance, assemblage of adult species and cover of lichens, mosses, litter and bare ground. Our results indicate that fertilization reduces the importance of regeneration by seed of perennial species and enhances seedling recruitment of winter annuals and biennials. At the patch scale, enrichment does not affect species richness. Community patchiness contributes to the maintenance of diversity by providing a variety of environments with differential regeneration of the component species. Cover of lichens, mosses, litter and bare ground, accounts, in part, for the spatial variation in seedling numbers of certain species. The strong association of seedlings of some species with conspecific adults indicates that limitations in dispersal and/or the occurrence of a more suitable environment for emergence and/or establishment close to conspecific adult plants are likely to constrain the spatial distribution of new individuals in many cases. For other species, the lack of association of seedling densities with the cover of their conspecific adults, suggests that long-distance dispersal or a long-lived seed bank can play a role in counteracting the effect of short-distance dispersal.     

Frugivore behaviour determines plant distribution: a spatially‐explicit analysis of a plant‐disperser interaction

The spatial distribution of plants (and other primarily sessile organisms) depends on the interplay between their ecological requirements and the spatial template set before, during, and after the dispersal process. In the case of animal‐dispersed plants, the spatial characteristics of animal behaviour during the seed dispersal process are likely to leave a lasting imprint on plant distribution. Here, we hypothesize that the activity patterns of the frugivorous lizard Podarcis lilfordi directly influence the spatial distribution of the fleshy‐fruited shrub Daphne rodriguezii. To evaluate this hypothesis, we first analysed lizard activity, following radio‐tracked lizards during the plant's fruiting period, and identified its main determinants at several spatial scales of habitat aggregation (from 12.5 to 150 m). We hypothesised that lizard activity depends on differential habitat features explaining its territory use plus habitat preferences associated with each movement bout. In a second step, the most important determinants of lizard activity plus the variables describing habitat structure were used to predict the presence of adult and juvenile plants. Predictability of lizard activity (based on AUC and Pearson regression coefficients) was higher at broad spatial‐scales of habitat aggregation (75 m). The two best predictors of lizard activity were the habitat features of and the distance to the core area (defined as the area enclosing the 0.50 cumulative probability of lizard locations). Plant presence was best predicted by models based on a combination of lizard activity and habitat features at local spatial scales (1.5 m). Best models included habitat features and lizard activity for adult plants, and local‐scale habitat features, the proximity of adult plants and lizard activity for juveniles. In both cases, most plants (50–60%) were located at ‘optimal sites’ (both favourable for lizards and with adequate habitat features), whereas a small fraction of them (3–10%) were located at dispersal‐limited sites (i.e. with adequate habitat features but suboptimal for lizards). Our results thus suggest that the interplay between lizard activity and local habitat features determines the spatial patterns of juvenile‐plant presence and leaves a lasting signature on adult‐plant distribution.     

Seed dispersal in heterogeneous landscapes: linking field observations with spatially explicit models

Seed dispersal by animals drives persistence and colonization of the majority of fleshy‐fruited plants. Different factors have been identified as important in shaping patterns of seed deposition. These factors include habitat heterogeneity, movement patterns of frugivore species, and their feeding behavior. Most studies, however, have analysed the effect of one factor at the time, either with a modelling approach or from field observations. Here, we combine empirical data with spatially‐explicit models to explore the contribution of habitat availability and patterns of frugivore post‐feeding flight distances to the spatial patterns of seed dispersal. We found that both factors, distance from the mother tree and microhabitat identity, were shaping those patterns. Our results show that seed dispersal is tremendously heterogeneous and complex in space. The observed seed shadow is not the result of a single process but instead an intricate combination of distance and habitat selection. We suggest that the apparent combination of processes results from the simultaneous effects of distinct functional groups of frugivores.     

Disentangling facilitation and seed dispersal from environmental heterogeneity as mechanisms generating associations between savanna plants

Question: How can we disentangle facilitation and seed dispersal from environmental heterogeneity as mechanisms causing spatial associations of plant species? Location: Semi‐arid savanna in the Kimberley Thorn Bushveld, South Africa. Methods: We developed a two‐step protocol for the statistical differentiation of association‐promoting mechanisms in plants based on the Acacia erioloba–Grewia flava association. Individuals of the savanna shrub G. flava and the tree A. erioloba were mapped on four study plots. Disentangling the mechanism causing the association of G. flava and A. erioloba involved tests of three spatial and one non‐spatial null model. The spatial null models include homogeneous and heterogeneous Poisson processes for spatial randomness based on the bivariate spatial point patterns of the four plots. With the non‐spatial analysis, we determined the relationship between the canopy diameter of A. erioloba trees and presence or absence of G. flava shrubs in the tree understorey to find whether shrub presence requires a minimum tree canopy diameter. Results: We first showed a significant positive spatial association of the two species. Thereafter, the non‐spatial analysis supported an exclusion of environmental heterogeneity as the sole cause of this positive association. We found a minimum tree size under which no G. flava shrubs occurred. Conclusions: Our two‐step analysis showed that it is unlikely that heterogeneous environmental conditions caused the spatial association of A. erioloba and G. flava. Instead, this association may have been caused by seed dispersal and/or facilitation (e.g. caused by hydraulic lift and/or nitrogen fixation by the host tree).     

Frugivory and spatial patterns of seed deposition by carnivorous mammals in anthropogenic landscapes: a multi-scale approach

Background

Knowledge about how frugivory and seed deposition are spatially distributed is valuable to understand the role of dispersers on the structure and dynamics of plant populations. This may be particularly important within anthropogenic areas, where either the patchy distribution of wild plants or the presence of cultivated fleshy-fruits may influence plant-disperser interactions.

Methodology/Principal Findings

We investigated frugivory and spatial patterns of seed deposition by carnivorous mammals in anthropogenic landscapes considering two spatial scales: ‘landscape’ (∼10 km²) and ‘habitat type’ (∼1–2 km²). We sampled carnivore faeces and plant abundance at three contrasting habitats (chestnut woods, mosaics and scrublands), each replicated within three different landscapes. Sixty-five percent of faeces collected (n = 1077) contained seeds, among which wild and cultivated seeds appeared in similar proportions (58% and 53%) despite that cultivated fruiting plants were much less abundant. Seed deposition was spatially structured among both spatial scales being different between fruit types. Whereas the most important source of spatial variation in deposition of wild seeds was the landscape scale, it was the habitat scale for cultivated seeds. At the habitat scale, seeds of wild species were mostly deposited within mosaics while seeds of cultivated species were within chestnut woods and scrublands. Spatial concordance between seed deposition and plant abundance was found only for wild species.

Conclusions/Significance

Spatial patterns of seed deposition by carnivores differed between fruit types and seemed to be modulated by the fleshy-fruited plant assemblages and the behaviour of dispersers. Our results suggest that a strong preference for cultivated fruits by carnivores may influence their spatial foraging behaviour and lower their dispersal services to wild species. However, the high amount of seeds removed within and between habitats suggests that carnivores must play an important role – often overlooked – as ‘restorers’ and ‘habitat shapers’ in anthropogenic areas.     

Habitat-specific dispersal: environmental effects on the mechanisms and patterns of seed movement in a grassland herb Rhinanthus minor

Little is known about how patterns and mechanisms of seed dispersal vary among different habitats. To address this we studied Rhinanthus minor , a grassland annual herb, in four environments: early or late hay cutting, grazing by sheep, and no management. Comprehensive measures were made of dispersal, by intensive seed trapping up to 25 m from source plants and in four directions. We found large differences in dispersal among the environments in terms of curve shape, maximum distance and directionality. Dispersal was shortest under grazing (maximum distance 0.9 m) and furthest under the early cut (19.1 m). Dispersal differences reflect the mechanisms of dispersal in each environment. Dispersal was by wind under no management, and by the mowing machinery under an early cut, whereas a late cut produced a combination of dispersal by wind and the machinery. Grazing hindered dispersal, through trampling of plants. Additional measures of seed mass supported the hypothesis of a negative seed size vs dispersal distance relationship and suggested its generality across a range of environments. Understanding the variation in dispersal patterns among environments may allow increased realism of spatial models.     

Neighborhood models of plant population dynamics 3. Models with spatial heterogeneity in the physical environment

Population dynamic models are developed for communities of annual plants in spatially heterogeneous environments. These models are constructed from submodels of the survivorship, fecundity, germination, and dispersal of individual plants. The submodels include the effects of spatially local interactions on plant performance and the spatial variation in performance caused by spatial heterogeneity in the physical environment. It is possible to estimate the submodels from data on experimental communities in either the field or greenhouse and so it is possible to empirically calibrate the population dynamic models developed. Each population dynamic model explicitly includes the spatial distribution of individuals in a plant community.Several two-species models for plants in patchy environments are studied to examine the community-level consequences of spatial heterogeneity in the physical environment. The results fall into two classes. First, community structure is in part determined by a relation between patch size and mean seed dispersal distance. Specifically, coexistence is, in some cases, possible only if patches are sufficiently larger than the mean dispersal distance. Second, community structure is also affected by relations between patch size and the maximum distance over which two plants interact (termed the neighborhood radius). In some cases, coexistence is possible only if patch size is sufficiently larger than the neighborhood radius. In others, the species coexist only if patch size is sufficiently smaller than the neighborhood radius. In still other cases, coexistence is possible only if patch sizes are within critical bounds, where the sizes of the critical bounds are in units of the neighborhood radius. All results involving relations between the neighborhood radius and patch size are direct consequences of the sedentary nature of plants and the fact that individual plants interact primarily with nearby plants.     

Patch dynamics and temporal dispersal partly shape annual plant communities in ephemeral habitat patches

Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.     

Anthropogenic modification disrupts species co‐occurrence in stream invertebrates

The question of whether species co‐occurrence is random or deterministic has received considerable attention, but little is known about how anthropogenic disturbance mediates the outcomes. By combining experiments, field surveys and analysis against null models, we tested the hypothesis that anthropogenic habitat modification disrupts species co‐occurrence in stream invertebrates across spatial scales. Whereas communities in unmodified conditions were structured deterministically with significant species segregation, catchment‐scale conversion to agriculture and sediment deposition at the patch‐ or micro‐habitat scale apparently randomized species co‐occurrences. This shift from non‐random to random was mostly independent of species richness, abundance and spatial scale. Data on community‐wide life‐history traits (body size, dispersal ability and predatory habits) and beta‐diversity indicated that anthropogenic modification disrupted community assembly by affecting biotic interactions and, to a lesser extent, altering habitat heterogeneity. These data illustrate that the balance between predictable and stochastic patterns in communities can reflect anthropogenic modifications that not only transcend scales but also change the relative forces that determine species coexistence. Research into the effects of habitat modification as a key to understanding global change should extend beyond species richness and composition to include species co‐occurrence, species interactions and any functional consequences.     

Seed dispersal by ungulates as an ecological filter: a trait‐based meta‐analysis

Plant communities are often dispersal‐limited and zoochory can be an efficient mechanism for plants to colonize new patches of potentially suitable habitat. We predicted that seed dispersal by ungulates acts as an ecological filter – which differentially affects individuals according to their characteristics and shapes species assemblages – and that the filter varies according to the dispersal mechanism (endozoochory, fur‐epizoochory and hoof‐epizoochory). We conducted two‐step individual participant data meta‐analyses of 52 studies on plant dispersal by ungulates in fragmented landscapes, comparing eight plant traits and two habitat indicators between dispersed and non‐dispersed plants. We found that ungulates dispersed at least 44% of the available plant species. Moreover, some plant traits and habitat indicators increased the likelihood for plant of being dispersed. Persistent or nitrophilous plant species from open habitats or bearing dry or elongated diaspores were more likely to be dispersed by ungulates, whatever the dispersal mechanism. In addition, endozoochory was more likely for diaspores bearing elongated appendages whereas epizoochory was more likely for diaspores released relatively high in vegetation. Hoof‐epizoochory was more likely for light diaspores without hooked appendages. Fur‐epizoochory was more likely for diaspores with appendages, particularly elongated or hooked ones. We thus observed a gradient of filtering effect among the three dispersal mechanisms. Endozoochory had an effect of rather weak intensity (impacting six plant characteristics with variations between ungulate‐dispersed and non‐dispersed plant species mostly below 25%), whereas hoof‐epizoochory had a stronger effect (eight characteristics included five ones with above 75% variation), and fur‐epizoochory an even stronger one (nine characteristics included six ones with above 75% variation). Our results demonstrate that seed dispersal by ungulates is an ecological filter whose intensity varies according to the dispersal mechanism considered. Ungulates can thus play a key role in plant community dynamics and have implications for plant spatial distribution patterns at multiple scales. Synthesis Plant communities are often dispersal‐limited and zoochory can be an efficient mechanism for plants to colonize new patches of potentially suitable habitat. Our analysis is the first synthesis of ungulate seed dispersal that compares characteristics from both non‐dispersed and dispersed diaspores, distinguishing the three zoochory mechanisms ungulates are involved in: endozoochory, hoof‐epizoochory and fur‐epizoochory. We confirmed that seed dispersal by ungulates is an ecological filter whose intensity increases from endozoochory, then hoof‐epizoochory to finally fur‐epizoochory. By filtering seed traits through dispersal, ungulates can thus play a key role in plant community dynamics and have implications for plant spatial distribution patterns at multiple scales.