Genetic structure and reproduction dynamics of Salix reinii during primary succession on Mount Fuji,as revealed by nuclear and chloroplast microsatellite analysis

The early stage of volcanic desert succession is underway on the southeastern slope of Mount Fuji. We used markers of nuclear microsatellites (simple sequence repeats; SSR) and chloroplast microsatellites (cpSSR) to investigate the population genetic structure and reproduction dynamics of Salix reinii, one of the dominant pioneer shrubs in this area. The number of S. reinii genets in a patch and the area of the largest genet within the patch increased with patch area, suggesting that both clonal growth and seedling recruitment are involved in the reproduction dynamics of S. reinii. Five polymorphic cpSSR markers were developed for S. reinii by sequencing the noncoding regions between universal sequences in the chloroplast genome. Nineteen different cpSSR haplotypes were identified, indicating that S. reinii pioneer genets were created by the long-distance dispersal of seeds originating from different mother genets around the study site, where all vegetation was destroyed during the last eruption. Furthermore, the clustered distributions of different haplotypes within each patch or plot suggested that newly colonized genets tended to be generated from seeds dispersed near the initially established mother genets. These results revealed that the establishment of the S. reinii population on the southeastern slope of Mount Fuji involved two sequential modes of seed dispersal: long-distance dispersal followed by short-distance dispersal.     

Effect of population density of compatible neighbours on inbreeding level within a Primula sieboldii population

We investigated the effect of population density of compatible neighbours on inbreeding level of Primula sieboldii, a heterostylous clonal herb. Pollinator availability, seed set, selfing rate, diversity of pollen donors, and fitness of progenies were compared between less and more isolated genets, which differed in the number of compatible opposite-morph genets within 20 m, the range at which most pollen flow occurred. Although pollinator availability did not differ between the two groups, seed set and diversity of pollen donors in more isolated genets were significantly lower than in less isolated genets. Additionally, the mean selfing rates of less and more isolated genets were 1.3 and 36.7%, respectively, and the mean leaf area of the self-fertilized seedlings was 70 to 40% smaller than that of outcrossed seedlings of the same mother genet. Due to this large inbreeding depression, it is unlikely that self-fertilized seedlings could successfully establish in natural habitats and hence the inbreeding level in the next generation around the more isolated genet would not increase rapidly. However, the possibility of mating between full-sibs would increase because the diversity of pollen donors was low and both pollen and seed dispersal were spatially restricted. Thus the inbreeding level of the next generations would gradually increase around the more isolated genets owing to biparental inbreeding. This study suggested that the population density of compatible neighbours has a critical impact on the future inbreeding level within P. sieboldii populations.     

Local genetic structure in a clonal dioecious angiosperm

We used seven microsatellite loci to characterize genetic structure and clonal architecture at three different spatial scales (from meters to centimetres) of a Cymodocea nodosa population. C. nodosa exhibits both sexual reproduction and vegetative propagation by rhizome elongation. Seeds remain buried in the sediment nearby the mother plant in a dormant stage until germination. Seed dispersal potential is therefore expected to be extremely restricted. High clonal diversity (up to 67% of distinct genotypes) and a highly intermingled configuration of genets at different spatial scales were found. No significant differences in genetic structure were found among the three spatial scales, indicating that genetic diversity is evenly distributed along the meadow. Autocorrelation analyses of kinship estimates confirmed the absence of spatial clumping of genets at small spatial scale and the expectations of a very restricted seed dispersal (observed dispersal range 1-21 m) in this species.     

Fine-scale spatial genetic structure and gene dispersal in Silene latifolia

Plants are sessile organisms, often characterized by limited dispersal. Seeds and pollen are the critical stages for gene flow. Here we investigate spatial genetic structure, gene dispersal and the relative contribution of pollen vs seed in the movement of genes in a stable metapopulation of the white campion Silene latifolia within its native range. This short-lived perennial plant is dioecious, has gravity-dispersed seeds and moth-mediated pollination. Direct measures of pollen dispersal suggested that large populations receive more pollen than small isolated populations and that most gene flow occurs within tens of meters. However, these studies were performed in the newly colonized range (North America) where the specialist pollinator is absent. In the native range (Europe), gene dispersal could fall on a different spatial scale. We genotyped 258 individuals from large and small (15) subpopulations along a 60 km, elongated metapopulation in Europe using six highly variable microsatellite markers, two X-linked and four autosomal. We found substantial genetic differentiation among subpopulations (global F_ST=0.11) and a general pattern of isolation by distance over the whole sampled area. Spatial autocorrelation revealed high relatedness among neighboring individuals over hundreds of meters. Estimates of gene dispersal revealed gene flow at the scale of tens of meters (5–30 m), similar to the newly colonized range. Contrary to expectations, estimates of dispersal based on X and autosomal markers showed very similar ranges, suggesting similar levels of pollen and seed dispersal. This may be explained by stochastic events of extensive seed dispersal in this area and limited pollen dispersal.     

Variation in stand structure,light and seedling abundance across a tropical moist forest chronosequence,Panama

Abstract. We asked whether forest structure and understory light environments across a tropical moist forest chronosequence followed predictions of a 4‐phase model of secondary succession (establishment, thinning, transition and steady‐state) and whether seedling density and diversity were functions of light availability as predicted by this model. Using aerial photographs, we identified eight second‐growth stands (two each aged ca. 20, 40, 70, and 100 yr) and two old‐growth stands within Barro Colorado Nature Monument, Panama. Trees and seedlings were sampled in nested, contiguous quadrats in 2 160‐m transects in each stand. Light was measured as percent transmittance of diffuse photosynthetically active radiation (TPAR) at each seedling quadrat and by estimation of percent total incident radiation during the growing season from hemispherical canopy photographs. Basal area, tree density, and canopy height followed predictions of the 4‐phase model. Percent total radiation, but not TPAR, declined with stand age as did seedling density. While seedlings were more likely to occur in quadrats at higher light levels, much variation in seedling density was not related to light availability. Seedling patch sizes were small irrespective of light patches, estimated as semivariance ranges. Seedling species richness was a function of seedling density; estimates of species diversity unbiased by density did not vary systematically as a function of stand age. Proximate seed sources, efficient dispersal mechanisms, and appropriate establishment conditions can promote establishment of species‐rich communities early in successions of heterogeneous tropical moist forest.     

Plant Parentage,Pollination, and Dispersal: How DNA Microsatellites Have Altered the Landscape

DNA microsatellites provide plant ecologists with molecular markers precise enough to assign parentage to seeds and seedlings. This allows the exact distance and trajectory of successful pollen to be traced to characterize pollination patterns. Parentage assignment of established seedlings also allows researchers to accurately determine how far new recruits have traveled from their seed parent. This paper reviews the history and development of molecular parentage assignment in studies of native plants, as well as the limitations and constraints to this approach. This paper also reviews 53 articles published in the past 15 years that use parentage assignment to study pollination and seed dispersal in native plants. These parentage studies have overturned many common assumptions regarding pollen and seed dispersal patterns. They show that long-distance dispersal of pollen is common in both wind and animal dispersed systems, with average pollination distances commonly being hundreds of meters. The pollination neighborhood is often extremely large, and simple dispersal functions based on distance alone fail to make accurate predictions of pollination. Rather than hindering gene flow, fragmentation and isolation sometimes, and perhaps even commonly, results in increased pollination distances. Studies of seed dispersal using parentage assignment have also yielded some surprises. We now know that it may be erroneous to assume that seeds growing under the crown of a conspecific adult are growing beneath their mother, or that seed dispersal distances are more limited than pollen dispersal distances. Taken together, the studies to date demonstrate that both seed and pollen dispersal are quite complex phenomena influenced by many ecological processes.     

Variation in pollen dispersal between years with different pollination conditions in a tropical emergent tree

We examined differences in pollen dispersal efficiency between 2 years in terms of both spatial dispersal range and genetic relatedness of pollen in a tropical emergent tree, Dipterocarpus tempehes. The species was pollinated by the giant honeybee (Apis dorsata) in a year of intensive community-level mass-flowering or general flowering (1996), but by several species of moths in a year of less-intensive general flowering (1998). We carried out paternity analysis based on six DNA microsatellite markers on a total of 277 mature trees forming four spatially distinct subpopulations in a 70 ha area, and 147 and 188 2-year-old seedlings originating from seeds produced in 1996 and 1998 (cohorts 96 and 98, respectively). Outcrossing rates (0.93 and 0.96 for cohorts 96 and 98, respectively) did not differ between years. Mean dispersal distances (222 and 192 m) were not significantly different between the 2 years but marginally more biased to long distance in 1996. The mean relatedness among cross-pollinated seedlings sharing the same mothers in cohort 96 was lower than that in cohort 98. This can be attributed to the two facts that the proportion of intersubpopulations pollen flow among cross-pollination events was marginally higher in cohort 96 (44%) than in cohort 98 (33%), and that mature trees within the same subpopulations are genetically more related to each other than those between different subpopulations. We conclude that D. tempehes maintained effective pollen dispersal in terms of outcrossing rate and pollen dispersal distance in spite of the large difference in foraging characteristics between two types of pollinators. In terms of pollen relatedness, however, a slight difference was suggested between years in the level of biparental inbreeding.     

Maintenance of high pollen dispersal in Eucalyptus wandoo, a dominant tree of the fragmented agricultural region in Western Australia

Pollen dispersal was investigated in five remnant populations of Eucalyptus wandoo, a dominant insect-pollinated tree in the fragmented agricultural region of southern Western Australia. Paternity analysis using six microsatellite loci identified a pollen source for 45% of seedlings, and the remainder were assumed to have arisen from pollen sources outside the stands. Outcrossing was variable, ranging from 52 to 89%, and long distance pollen dispersal was observed in all populations with up to 65% of pollen sourced from outside the populations over distances of at least 1 km. Modelling dispersal functions for pollination events within the two larger populations showed little difference between the four two-parameter models tested and indicated a fat-tailed dispersal curve. Similarity of direct and indirect historical estimates of gene flow indicates maintenance of gene flow at levels experienced prior to fragmentation. The study revealed extensive long distance pollen dispersal in remnant patches of trees within a fragmented agricultural landscape in the southern temperate region and highlighted the role of remnant patches in maintaining genetic connectivity at the landscape scale.     

The reproductive biology of Polytrichum formosum: clonal structure and paternity revealed by microsatellites

Using highly polymorphic microsatellite markers, we assessed clonal structure and paternity in a population of the bryophyte species Polytrichum formosum. Identical multilocus genotypes of individual shoots were almost never observed in spatially separated cushions, but were found to be highly clustered within moss cushions. Therefore, asexual reproduction through dispersal of gametophyte fragments is not very important in P. formosum. However, asexual reproduction on a very localized scale through vegetative growth of genets (branching of gametophytes via clonal growth of rhizomes) is very extensive. The patchy spatial distribution of genets and the absence of intermingling among genets suggest that this species follows a 'phalanx' clonal growth strategy. Vegetative proliferation of genets will increase their size, and, consequently, will have considerable fitness consequences for individuals in terms of increased genet longevity and reproductive output. Although paternity analysis of sporophytes confirmed male genet size, i.e. gamete production, to be an important determinant of male reproductive fitness, it also showed that the spatial distance to female genets is the predominant factor that governs male reproductive success. Moreover, we showed that male gamete dispersal distances in P. formosum are much further than generally assumed, and are in the order of metres rather than centimetres. Combining the findings, we conclude that the high genotypic diversity observed for this facultatively clonal species is most likely explained by a preponderance of sexual reproduction over clonal reproduction.     

Limited seed dispersal shapes fine-scale spatial genetic structure in a Neotropical dioecious large-seeded palm

Seed and pollen dispersal contribute to gene flow and shape the genetic patterns of plants over fine spatial scales. We inferred fine-scale spatial genetic structure (FSGS) and estimated realized dispersal distances in Phytelephas aequatorialis, a Neotropical dioecious large-seeded palm. We aimed to explore how seed and pollen dispersal shape this genetic pattern in a focal population. For this purpose, we genotyped 138 seedlings and 99 adults with 20 newly developed microsatellite markers. We tested if rodent-mediated seed dispersal has a stronger influence than insect-mediated pollen dispersal in shaping FSGS. We also tested if pollen dispersal was influenced by the density of male palms around mother palms in order to further explore this ecological process in large-seeded plants. Rodent-mediated dispersal of these large seeds occurred mostly over short distances (mean 34.76 ± 34.06 m) while pollen dispersal distances were two times higher (mean 67.91 ± 38.29 m). The spatial extent of FSGS up to 35 m and the fact that seed dispersal did not increase the distance at which male alleles disperse suggest that spatially limited seed dispersal is the main factor shaping FSGS and contributes only marginally to gene flow within the population. Pollen dispersal distances depended on the density of male palms, decreasing when individuals show a clumped distribution and increasing when they are scattered. Our results show that limited seed dispersal mediated by rodents shapes FSGS in P. aequatorialis, while more extensive pollen dispersal accounts for a larger contribution to gene flow and may maintain high genetic diversity. Abstract in Spanish is available with online material.     

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.     

Fine-scale clonal structure and diversity within patches of a clone-forming dioecious shrub, Ilex leucoclada (Aquifoliaceae)

BACKGROUND AND AIMS: The mode of reproduction (sexual vs. asexual) is likely to have important effects on genetic variation and its spatial distribution within plant populations. An investigation was undertaken of fine-scale clonal structure and diversity within patches of Ilex leucoclada (a clone-forming dioecious shrub). METHODS: Six patches were selected in a 1-ha plot previously established in an old-growth beech forest. Two of the selected patches were composed predominantly of stems with male flowers (male patch), and two contained stems with predominantly female flowers (female patch). The remaining two patches contained stems with male flowers and stems with female flowers in more or less equal proportions (mixed patch). Different genets were distinguished using random amplified polymorphic DNA (RAPD) markers. KEY RESULTS: One hundred and fifty-six genets with different RAPD phenotypes were identified among 1928 stems from the six patches. Among the six patches, the male patches had the lowest clonal diversity, and the mixed patches had the highest. Distribution maps of the genets showed that they extended downhill, reflecting natural layering that occurred when stems were pressed to the ground by heavy snow. In every patch, there were a few large genets with many stems and many small genets with a few stems. CONCLUSION: The differences in clonal diversity among patches may be due to differences in seedling recruitment frequencies. The skewed distribution of genet size (defined as the number of stems per genet) within patches may be due to differences in the timing of germination, or age (with early-establishing genets having clear advantages for acquiring resources) and/or intraspecific competition.     

Spatial genetic structure within a metallicolous population of Arabidopsis halleri, a clonal, self-incompatible and heavy-metal-tolerant species

Arabidopsis halleri, a close wild relative of A. thaliana, is a clonal, insect-pollinated herb tolerant to heavy metals (Zn, Pd, Cd) and a hyperaccumulator of Zn and Cd. It is of particular interest in the study of evolutionary processes and phytoremediation. However, little is known about its population gene flow patterns and the structure of its genetic diversity. We used five microsatellite loci to investigate the genetic structure at a fine spatial scale (10 cm to 500 m) in a metallicolous population of A. halleri. We also studied the contributions made by clonal propagation and sexual reproduction (seed and pollen dispersal) to the genetic patterns. Clonal diversity was high (D(G) > 0.9). Clonal spread occurs only at short distances (< 1 m). Both clonal spread and limited dispersal, associated with sexual reproduction, contribute to the significant spatial genetic structure revealed by spatial autocorrelation analysis. The shape of the autocorrelogram suggests that seed dispersal is restricted and pollen flow extensive, which may be related to intense activity by insect pollinators. Clonal spread was more extensive in the lowly polluted zone than in the highly polluted zone. This cannot be interpreted as a strategy for promoting the propagation of adapted genotypes under the harshest ecological constraints (highest heavy metal concentrations). The higher fine-scale spatial genetic structure found in the lowly polluted zone can be ascribed to plant densities that were lower than in the highly polluted zone. No evidence of genetic divergence due to spatial heavy metal heterogeneity was found between lowly and highly polluted zones.     

Genet structure and determinants of clonal structure in a temperate deciduous woodland herb, Uvularia perfoliata

1 We used isozyme variation to examine the genet structure of Uvularia perfoliata patches in gap and closed canopy habitats in a temperate deciduous forest in Maryland, USA.
2 A large patch in a gap habitat was composed of a small number of widely spread genets with many ramets, and a large number of genets with more restricted distribution and few ramets. Genets with many ramets were patchily distributed at a metre scale. Analysis of genet structure on a scale of square centimetres, however, revealed that the genets were highly intermingled with no clear boundaries between them. The presence at both scales of sampling of many genets with unique multilocus genotypes indicated continuing genet recruitment within the population.
3 In the closed canopy habitat, the patches examined were each composed of a single unique multilocus genotype, suggesting that each had developed by asexual propagation following the establishment of a single genet.
4 The clonal structure of U. perfoliata patches in both gap and closed canopy habitats therefore appears to depend on recruitment patterns of genets. Populations in closed canopy habitats are characterized by a 'waiting' strategy, in which asexual ramet production maintains populations until genet recruitment by seed production can occur under the more optimal conditions associated with canopy gaps. Extended sampling suggests that the genetic diversity of U. perfoliata populations is primarily controlled by the disturbance regime of the forest canopy.     

Extensive pollen dispersal in a bird-pollinated shrub, Calothamnus quadrifidus, in a fragmented landscape

Pollen dispersal was investigated in six populations of Calothamnus quadrifidus, a bird-pollinated shrub in the fragmented agricultural region of southern Western Australia. Paternity analysis using six microsatellite loci identified a pollen source within populations for 67% of seedlings, and the remainder were assumed to have arisen from pollen sources outside the populations. Outcrossing was variable, ranging from 5% to 82%, and long-distance pollen dispersal was observed in all populations with up to 43% of pollen sourced from outside the populations over distances of up to 5 km. This extensive pollen immigration was positively associated with population size but not isolation. Comparison of two populations of similar size but different density showed greater internal pollination and less selfing in the denser population, suggesting an influence of density on pollinator behaviour. The study revealed extensive long-distance pollen dispersal for C. quadrifidus within this fragmented agricultural landscape and highlighted the interaction between reserve populations and isolated road verge remnants in maintaining genetic connectivity at the landscape scale.     

Plasticity in fitness and fitness-related traits at ramet and genet levels in a tillering grass Panicum miliaceum under patchy soil nutrients

Seedling and root sprout recruitment after a volcanic deforestation was examined in a Prunus ssiori population. According to genotypes of five microsatellite (SSR) loci, 44 genets were identified among 188 ramets ≥ 5 cm DBH in a 2.3-ha plot in 2000. The genets formed mutually exclusive patches. Because only one repeat change in an SSR locus distinguished five genets from adjacent genets, there is a possibility that the five genets derived from somatic mutations as well as sexual reproduction. Thus, at least 39 genets originated from seedlings, and at least 144 ramets derived from root sprouts. The seedlings were recruited after the volcanic eruptions in 1739 and before 1972 because trees of 5 cm DBH were 28 years of age, estimated from annual rings. As the largest ramet recruited from a root sprout was estimated to be 94 years old, root sprout recruitment began between 1739 and 1906. Thus, the estimated minimum rates of recruitment from seedlings and root sprouts were 0.167 y^–1 and 0.618-2.182 y^–1, respectively. The clonal diversity of the P. ssiori population (Simpson's D = 0.92) was higher than that of other clonal plant populations. The inbreeding coefficient was significantly negative (Wright's F _IS = −0.069). These results suggest that the frequent seedling recruitment in an outbreeding system maintains the clonal diversity in the population. This revised version was published online in June 2006 with corrections to the Cover Date.     

Directional seed and pollen dispersal and their separate effects on anisotropy of fine‐scale spatial genetic structure among seedlings in a dioecious,wind‐pollinated,and wind‐dispersed tree species,Cercidiphyllum japonicum

Prevailing directions of seed and pollen dispersal may induce anisotropy of the fine‐scale spatial genetic structure (FSGS), particularly in wind‐dispersed and wind‐pollinated species. To examine the separate effects of directional seed and pollen dispersal on FSGS, we conducted a population genetics study for a dioecious, wind‐pollinated, and wind‐dispersed tree species, Cercidiphyllum japonicum Sieb. et Zucc, based on genotypes at five microsatellite loci of 281 adults of a population distributed over a ca. 80 ha along a stream and 755 current‐year seedlings. A neighborhood model approach with exponential‐power‐von Mises functions indicated shorter seed dispersal (mean = 69.1 m) and much longer pollen dispersal (mean = 870.6 m), effects of dispersal directions on the frequencies of seed and pollen dispersal, and the directions with most frequent seed and pollen dispersal (prevailing directions). Furthermore, the distance of effective seed dispersal within the population was estimated to depend on the dispersal direction and be longest at the direction near the prevailing direction. Therefore, patterns of seed and pollen dispersal may be affected by effective wind directions during the period of respective dispersals. Isotropic FSGS and spatial sibling structure analyses indicated a significant FSGS among the seedlings generated by the limited seed dispersal, but anisotropic analysis for the seedlings indicated that the strength of the FSGS varied with directions between individuals and was weakest at a direction near the directions of the most frequent and longest seed dispersal but far from the prevailing direction of pollen dispersal. These results suggest that frequent and long‐distance seed dispersal around the prevailing direction weakens the FSGS around the prevailing direction. Therefore, spatially limited but directional seed dispersal would determine the existence and direction of FSGS among the seedlings.     

Relative contribution of contemporary pollen and seed dispersal to the effective parental size of seedling population of California valley oak (Quercus lobata, Née)

For plant populations, gene movement through pollen and seed dispersal governs the size of local genetic neighbourhoods and shapes the opportunities for natural selection and genetic drift. A critical question is how together these two processes influence the evolutionary dynamics of local populations. To assess the respective contributions of pollen and seed flow, we propose a novel indirect assessment of the separate male and female gametic contributions to total effective parental size ( N _e), based on parental correlations estimated via kinship coefficients, that can be applied to data sets that include unambiguous genotypes for male and female gametic contributions. Using the endemic Californian valley oak ( Quercus lobata ) as our study species, we apply this method to a set of microsatellite genotypes for two distinct ecological sets of naturally recruiting seedlings with acorns attached. We found that the effective numbers of contributing male parents ( N _ep) exceed effective numbers of female parents ( N _em) for seedlings established beneath adult trees ( N _ep = 8.1 and N _em = 1.1), as well as for seedlings established away from adult trees ( N _ep = 15.4 and N _em = 2.7), illustrating that seed dispersal enhances pollen dispersal and increases the effective number of seed sources in open seedling patches. The resulting effective parental size of seedling populations translates into smaller effective numbers of parents for undispersed vs. dispersed seedlings ( N _e = 3.6 and N _e = 6.7, respectively). This study introduces a novel statistic method and provides important new evidence that, on a short-term temporal scale, seed dispersal shapes the local neighbourhood size of new recruits.     

Microsatellite analysis of seed dispersal and parentage of saplings in bur oak, Quercus macrocarpa

Microsatellite analysis was used to examine parentage and spatial distributions of 62 adult bur oaks Quercus macrocarpa, and 100 saplings in a single stand. Using genotypes scored by PCR products at four microsatellite loci, we determined that 94 saplings matched at least one parent in the stand. Saplings often occur as dense clusters of half-sibs around the presumed maternal parent, and only four adults were seed parents to a large proportion of the saplings sampled. A stump apparently was the seed parent of the largest cluster of half-sibs, which occupied a sizeable light gap opened up by the death of their maternal tree. Approximately half of the saplings appeared to have grown from seeds that had not been removed after falling from the tree, and half from seeds that were dispersed beyond the crown of their maternal parent. Long-distance seed dispersal may be more common than has been previously reported. Extremely high levels of long-distance pollination were indicated, and pollen donors within the stand were generally distributed randomly around maternal trees. More than half of the saplings had paternal parents outside of the stand. This study demonstrates the utility of microsatellite analysis for studying mating systems, seed dispersal and seedling establishment in natural plant populations.     

Linking the pattern to the mechanism: How an introduced mammal facilitates plant invasions

Non‐native mammals that are disturbance agents can promote non‐native plant invasions, but to date there is scant evidence on the mechanisms behind this pattern. We used wild boar (Sus scrofa) as a model species to evaluate the role of non‐native mammals in promoting plant invasion by identifying the degree to which soil disturbance and endozoochorous seed dispersal drive plant invasions. To test if soil disturbance promotes plant invasion, we conducted an exclosure experiment in which we recorded emergence, establishment and biomass of seedlings of seven non‐native plant species planted in no‐rooting, boar‐rooting and artificial rooting patches in Patagonia, Argentina. To examine the role of boar in dispersing seeds we germinated viable seeds from 181 boar droppings and compared this collection to the soil seed bank by collecting a soil sample adjacent to each dropping. We found that both establishment and biomass of non‐native seedlings in boar‐rooting patches were double those in no‐rooting patches. Values in artificial rooting patches were intermediate between those in boar‐rooting and no‐rooting treatments. By contrast, we found that the proportion of non‐native seedlings in the soil samples was double that in the droppings, and over 80% of the germinated seeds were native species in both samples. Lastly, an effect size test showed that soil disturbance by wild boar rather than endozoochorous dispersal facilitates plant invasions. These results have implications for both the native and introduced ranges of wild boar, where rooting disturbance may facilitate community composition shifts.