Pollen-mediated gene dispersal within continuous and fragmented populations of a forest understorey species, Trillium cuneatum

Pollen movement plays a critical role in the distribution of genetic variation within and among plant populations. Direct measures of pollen movement in the large, continuous populations that characterize many herbaceous plant species are often technically difficult and biologically unreliable. Here, we studied contemporary pollen movement in four large populations of Trillium cuneatum. Three populations, located in the Georgia Piedmont, are exposed to strong anthropogenic disturbances, while the fourth population, located in the Southern Appalachian Mountains, is relatively undisturbed. Using the recently developed TwoGener analysis, we extracted estimates of the effective number of pollen donors (N(ep)), effective mating neighbourhood size (A(ep)) and the average distance of pollen movement (delta) for each population. We extended the TwoGener method by developing inference on the paternal gametic contribution to the embryo in situations where offspring genotypes are inferred from seeds and elaiosomes of species with bisporic megagametogenesis. Our estimates indicate that maternal plants do not sample pollen randomly from a global pool; rather, pollen movement in all four populations is highly restricted. Although the effective number of pollen donors per maternal plant is low (1.22-1.66) and pollen movement is highly localized in all populations, N(ep) in the disturbed Piedmont populations is higher and there is more pollen movement than in the mountains. The distance pollen moves is greater in disturbed sites and fragmented populations, possibly due to edge effects in Trillium habitats.     

Distribution of genetic diversity among disjunct populations of the rare forest understory herb, Trillium reliquum

We assessed genetic diversity and its distribution in the rare southeastern US forest understory species, Trillium reliquum. In all, 21 loci were polymorphic (PS=95.5%) and the mean number of alleles per polymorphic locus was 3.05. However, genetic diversity was relatively low (Hes=0.120) considering the level of polymorphism observed for this outcrossing species. A relatively high portion of the genetic diversity (29.7%) was distributed among populations. There was no relationship between population size and genetic diversity, and we did not detect significant inbreeding. These results are best explained by the apparent self-incompatibility of this species, its longevity and clonal reproduction. To address questions regarding the history of T. reliquum's rarity, we compared results for T. reliquum with that of its more common and partially sympatric congener, T. cuneatum. Despite shared life history traits and history of land use, we observed significant genetic differences between the two species. Although T. cuneatum contains slightly lower polymorphism (Ps=85%), we detected significantly higher genetic diversity (Hes=0.217); most of its genetic diversity is contained within its populations (GST=0.092). Our results suggest that not only is there little gene flow among extant T. reliquum populations, but that rarity and population isolation in this species is of ancient origins, rather than due to more recent anthropogenic fragmentation following European colonization. The Chattahoochee River was identified as a major barrier to gene exchange.     

Bird species diversity in forest understory: Analysis of mist-net samples

Summary Mist-netted samples of forest understory birds in neotropical (Costa Rica) and temperate (Illinois) forests (during spring migration) supported certain earlier observations: the neotropical understory sample contained more species, more rare species, and more species that use resources not sufficiently available in temperate forest.During spring migration in Illinois, the number of bird species in a mist-netted sample of the community approaches (albeit temporarily) that of neotropical forests and is sometimes even equivalent. But the constitution of these samples seems to be quite different in different regions. Costa Rican samples showed greater within-habitat variability and individual recapture distances were shorter, implying a greater local patchiness of bird distributions than in Illinois in spring.     

Patterns of diversity of flower-visitor assemblages to the understory Araceae in a tropical mountain forest in Colombia

In the Araceae, pollination biology has been extensively evaluated in several genera mainly in lowland tropical areas. However, the influence of physical factors such as elevation or precipitation on plant/flower-visitor interactions at the community level remains challenging for this plant family, specifically in tropical mountain forests. The aim of this study was to analyze how the species diversity and abundance of flowering Araceae and their flower-visitor assemblages change along an elevation gradient and through time, in response to changes in mean monthly precipitation in a tropical mountain forest located in Jardín, Antioquia, Colombia. Eighteen flowering Araceae species and floral visitors belonging to seven orders were recorded. Flower-visitor diversity decreased with elevation. A trend of increasing flowering Araceae and flower-visitor abundance richness at intermediate levels of precipitation was observed. Diptera were dominant in the lower part and Thysanoptera were dominant in the upper part of the gradient. The pattern of plant species distribution along the elevation and the amount of precipitation influenced the availability of flower resources, and, as a consequence, affected the spatial and temporal composition of flower-visitor assemblages. Local strategies for the conservation of the diversity of insect flower-visitors and their interactions should be focused on the implementation of agricultural practices that reduce the use of pesticides within adjacent commercial plantations and the avoidance of illegal clearings, maintaining unbroken elevational gradients of forest, which is the only way to protect the flowering resources for anthophilous insects. At the same time, continuous forest promotes the maintenance of macro and microclimatic conditions, preserving the stability of insect populations and diversity amongst several functional groups.     

辽东山区林权制度改革中林下种植模式对林下植物物种多样性的影响

以样方调查数据为基础,采用物种丰富度指数、均匀度指数和多样性指数,对辽宁省东部山区森林生态系统中种植林下参和大叶芹这两种作物对林下植物物种多样性的影响进行了研究,并分析了不同作物种植样地和未种植样地以及不同种植作物样地之间的各种指数的差异程度。结果表明:(1)种植两种作物均对灌木层物种产生了显著的影响,降低了物种多样性。(2)种植林下参使得草本层的物种丰富度显著降低,均匀度显著增加,而多样性指数差异不显著。(3)种植大叶芹使得草本层的物种丰富度、均匀度和多样性指数均显著降低。(4)林下参种植样地和大叶芹种植样地之间草本层的物种丰富度指数、均匀度指数和多样性指数之间存在显著差异。     

Growth and competition in clonal plants-persistence of shoot populations and species diversity

This paper reviews studies on growth and size-structure dynamics of shoots and clones in clonal plants in comparison with those in non-clonal plants, and discusses the characteristics of clonal plants. The mode of competition between individuals (symmetric versus asymmetric, degree of competitive asymmetry), growth dynamics of individuals, allocation pattern between organs and spatial pattern of individuals are closely correlated with each other in non-clonal plant populations. Theoretical and field studies based on the diffusion model revealed that plants of “height-growth” type (mostly early-successional tree species) and plants of “diameter-growth” type (mostly late-successional tree species) tend to exhibit asymmetric competition and symmetric competition respectively. Moreover, asymmetrically competing plants show smaller effects of variation in individual growth rate and spatial pattern on the size-structure dynamics of the population than symmetrically competing plants. Thefefore, the spatial pattern of inviduals should be considered especially for plants undergoing symmetric competition. These results for non-clonal plants should have a significant implication also for the growth dynamics and competition in clonal plants. The mean growth rate of shoots [G(t,x) function] and hence the mode of competition between shoots differs among clonal plant species as in non-clonal plants. However, a large magnitude and size-independence (or slightly negative size-dependence) of the variation in growth rate of shoots [D(t,x) function], especially at the early stage in a growing season is a common characteristic of many clonal plant species, in contrast to the positively size-dependent variation in individual growth rate in non-clonal plants. This type of variation in shoot growth rate leads to the persistence of stable shoot populations even when the mean growth rate function is changed, and also in cases where the shoot population structure would be unstable in the absence of variation in growth rate. It is suggested that competition between clones is symmetric in most clonal plant species, which brings about small-scale spatio-temporal changes in species abundance and hence species diversity.     

Identification of glacial refugia in south-eastern North America by phylogeographical analyses of a forest understorey plant, Trillium cuneatum

Aim We examine several hypotheses emerging from biogeographical and fossil records regarding glacial refugia of a southern thermophilic plant species. Specifically, we investigated the glacial history and post‐glacial colonization of a forest understorey species, Trillium cuneatum. We focused on the following questions: (1) Did T. cuneatum survive the Last Glacial Maximum (LGM) in multiple refugia, and (if so) where were they located, and is the modern genetic structure congruent with the fossil record‐based reconstruction of refugia for mesic deciduous forests? (2) What are the post‐glacial colonization patterns in the present geographical range? Location South‐eastern North America. Methods We sampled 45 populations of T. cuneatum throughout its current range. We conducted phylogeographical analyses based on maternally inherited chloroplast DNA (cpDNA haplotypes) and used TCS software to reconstruct intraspecific phylogeny. Results We detected six cpDNA haplotypes, geographically highly structured into non‐overlapping areas. With one exception, none of the populations had mixed haplotype composition. TCS analysis resulted in two intraspecific cpDNA lineages, with one clade subdivided further by shallower diversification. Main conclusions Our investigation revealed that T. cuneatum survived the LGM in multiple refugia, belonging to two (western, eastern) genealogical lineages geographically structured across south‐eastern North America. The western clade is confined to the south‐western corner of T. cuneatum’s modern range along the Lower Mississippi Valley, where fossil records document a major refugium of mesic deciduous forest. For the eastern clade, modern patterns of cpDNA haplotype distribution suggest cryptic vicariance, in the form of forest contractions and subsequent expansions associated with Pleistocene glacial cycles, rather than simple southern survival and subsequent northward colonization. The north–south partitioning of cpDNA haplotypes was unexpected, suggesting that populations of this rather southern thermophilic species may have survived in more northern locations than initially expected based on LGM climate reconstruction, and that the Appalachian Mountains functioned as a barrier to the dispersal of propagules originating in more southern refugia. Furthermore, our results reveal south‐west to north‐east directionality in historical migration through the Valley and Ridge region of north‐west Georgia.     

Trillium sulcatum (Liliaceae), a new species of the southern Appalachians

Trillium sulcatum, a new species with two petal color forms, was first circumscribed by Barksdale as a variety in 1938, but without a Latin diagnosis. It superficially resembles the mainly northernT. erectum and appears to be closely related to the primarily midwesternT. flexipes. Its distinguishing features are ringent flowers, short sepals, and long pedicels; additional characters are presented in a chart contrasting it with species with which it has been confused. Distribution suggesting relictual significance is documented. Except that intermediates withT. flexipes are occasional,T. sulcatum maintains its distinctiveness throughout its southern Appalachian range.     

Changes in forest structure, species diversity and spatial pattern following hurricane disturbance in a Piedmont North Carolina forest, USA

Aims: Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarelybeen examined in detail. In 1996, Hurricane Fran significantlydamaged many long-term tree census plots in the Duke Foreston the North Carolina Piedmont, thereby providing an exceptionalopportunity to examine pre- and post-hurricane forest compositionaltrajectories. Our goal was to examine immediate, short-term(0–4 years) and longer term (5 year) hurricane-inducedstructural, spatial and compositional changes in the tree population(stem d.b.h > 1 cm) in the context of our detailed, long-termknowledge of the dynamics of these forests. Methods: We surveyed stem damage and tree mortality in 34 long-term permanentplots (ca. 70-year record; 404–1 012 m²) and 7 large mappedtree stands (ca. 20-year record; 5 250–65 000 m²) representingboth transition-phase, even-aged pine stands and uneven-agedupland hardwood forests. We employed three types of damage measuresto quantify stand-level damage severity: percentage of stemsdamaged, percentage of basal area lost and a ‘stand-leveldamage index’. Second-order spatial analysis (Ripley'sK-function) was used to investigate patterns in tree mortality. Important findings: Our study found hurricane effects on the structural attributesof Piedmont forests to be variable and patchy. Changes in treespecies composition, however, were modest. Uprooting was themajor damage type for the overstory trees [diameter at breastheight (d.b.h.) >10 cm] apparently due to the exposure ofthe crowns to high wind combined with heavy rainfall prior toand during the storm. Saplings, juvenile trees and small trees(1–10 cm d.b.h.) of the understory and midstory were mainlydamaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remainedup to 2-fold higher than pre-hurricane background mortality5 years after the hurricane. Spatial point pattern analysisrevealed a patchy distribution of tree mortality during thehurricane sampling interval. Hurricane Fran resulted in a dramaticincrease in average gap size from ca. 400 m² pre-hurricane toca 1100 m² after the hurricane, whereas maximum gap sizes reached18–34 times larger than the pre-hurricane levels.     

Sexual reproduction and clonal growth in Reinhardtia gracilis (Palmae), an understory tropical palm

Patterns of sexual reproduction and clonal growth were investigated in the understory palm Reinhardtia gracilis var. gracilior over a 3-yr period. R. gracilis is a very abundant clonal palm in the tropical rain forest of Los Tuxtlas, Veracruz, México. Because ramets form clumps, genets are easily identified in the field. Genets were monitored in a 0.5-ha area, and classified by size according to the number of ramets they possessed. In contrast to clonal growth, sexual reproduction was highly dependent on genet size. The probability of reproduction, the number of inflorescences, and the number of fruits produced were positively correlated with genet size. However, neither the probability of producing a ramet, nor the number of ramets produced per genet were correlated with genet size. Over the 3 yr of study, 55% of the genet population had at least one ramet with reproductive structures, while <1% (a single genet in one year) had six ramets with flowers. Thirty-two percent of the mature genets reproduced during each of three consecutive years. In contrast, 58% of the genets produced no new ramets during these 3 yr. No evidence was found of a trade-off between clonal growth and sexual reproduction. Ramet production increases genet size and this in turn increases genet reproductive performance. Clonal growth in this species may be viewed as a growth strategy that tends to maximize genet fitness.     

Diversity and seasonal variation of ground and understory spiders from a tropical mountain cloud forest

We made intensive samplings to study the seasonal response of spiders across different forest strata (ground and understory) in a tropical mountain cloud forest from Mexico. We sampled spiders from ten plots in six sampling events during the dry and rainy season, to analyze their abundance, structure (distribution of abundance among species), diversity and the response of the five dominant species at each stratum. Results demonstrated that seasonal patterns of spider communities differed among strata, revealing a complex spatiotemporal dynamic. Abundance, structure, diversity of ground spiders, as well as the responses of four dominant species at this stratum, showed low seasonal variations. In contrast, a strong seasonal variation was observed for the understory assemblage, with lowest abundance and highest diversity in the rainy season, and different assemblage structures for each season. Seasonal patterns of each assemblage seem linked to the responses of their dominant species. We found high co‐occurrence among most of the ground dominant species with similar habitat use and with multivoltine patterns, contrasting with low co‐occurrence among most of the understory dominant species with similar habitat use and univoltine patterns. Our results showed that the spiders’ assemblages of tropical mountain cloud forest (opposed to what is found in temperate and boreal forests) increase their species richness with the height, and that their responses to seasonal change differ between strata. Management programs of these habitats should consider the spatial and temporal variations found here, as a better understanding of their ecological dynamics is required to support their sustainable management.     

Importance of the understory stratum to entomofaunal diversity in a temperate deciduous forest

The vertical stratification of lepidopteran and coleopteran communities in a cool-temperate deciduous forest in Japan was examined to evaluate the hypothesis of an expected uniform distribution of mobile flying insects between the canopy and understory of temperate forests. Lepidopteran and coleopteran insects were trapped using light traps at three sites in each of the canopy and understory for three consecutive nights each month from April to October 2001. For Lepidoptera, species richness, abundance, and family richness were significantly higher in the understory than in the canopy. For Coleoptera, only abundance was larger in the canopy relative to the understory; species and family richness did not differ between the strata. The beta diversity of the lepidopteran community was larger between the strata than among sites, but the coleopteran community showed an inverse pattern. These results imply the presence of vertical stratification within the lepidopteran community, but not within the coleopteran community, in the temperate forest. The understory contributes more than the canopy to lepidopteran diversity in the temperate forest, although this stratification may be relatively weak because, in contrast to the situation in tropical forests, the canopy and understory assemblages share many species.     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

Landslide-facilitated species diversity in a beech-dominant forest

To evaluate the extent to which landslides affect community dynamics and consequent species diversity in a beech-dominated forest, differences in the composition and size structure of tree species were compared between landslide and adjacent stable (control) stands. Demography and changes in size were compared between the two stands over a 5-year period about 60 years after a landslide. In the control stand, replacement occurred even amongst late-successional species, with beech (Fagus crenata)—the most dominant species—increasing in relative abundance. In the landslide stand, very few large individuals of late-successional species occurred, whereas large individuals of early-successional species occurred only in the landslide stand. The traits indicate that the landslide strongly facilitated species diversity, not only by reducing the dominance of late-successional species, but also by promoting recruitment of early-successional species. However, new recruitment of early-successional species was inhibited in the landslide stand, although we observed succeeding regeneration and subsequent population growth of late-successional species there. As a result, the relative dominance of late-successional species increased with succession after the landslide, thus decreasing future species diversity. In beech-dominant forest landscapes in Japan that include communities with different developmental stages, the mosaic of serial stages may facilitate species diversity after a landslide.     

Habitat niche specialization in an understory species in a warm temperate forest

Relationships between microhabitat variables; understory light conditions in summer and winter, altitude, slope inclination and topographic categories (valley, ridge, and slope) and the distribution of Aucuba japonica Thunb. (Cornaceae), a common understory shrub species in Japan were examined using non-contagious 66, 20 × 20 m² quadrats. The Morishita’s I _δ suggested that A. japonica distributions were strongly heterogeneous among the quadrats. Therefore positive spatial autocorrelation of A. japonica at a within-quadrat level (≤20 m) was obvious. Moran’s I statistics showed a significant positive spatial autocorrelation in A. japonica abundance within the distance shorter than 60 m. But the partial Mantel tests suggested that the mass effect from neighboring quadrats would little explain A. japonica abundance in a quadrat. The partial Mantel tests also clearly showed that A. japonica distributions were strongly structured by topography and understory light conditions. Using Monte Carlo randomization tests, we found that A. japonica was aggregately distributed in quadrats in valley which were covered by deciduous canopies. Better understory light conditions in winter together with valley edaphic conditions may increase the abundance of A. japonica there. It is concluded that habitat niche specialization is important in structuring distribution of A. japonica in this forest community.     

Tree species composition and diversity of tropical mountain cloud forest in the Yunnan, southwestern China

Species composition, physiognomy, and plant diversity of the less known cloud forests in Yunnan were studied based on data collected from 35 sample plots at seven sites. In floristic composition, the cloud forests are mainly comprised of Fagaceae, Ericaceae, Vacciniaceae, Aceraceae, Magnoliaceae, Theaceae, Aquifoliaceae, Illiciaceae, Lauraceae, and Rosaceae. Physiognomically, the forests are dominated by tree and shrub species. Lianas are rare in the forests. The plants with microphyllous or nanophyllous leaves comprise 44.32–63.46% of the total species, and plants with an entire leaf margin account for more than 50% of the tree and shrub species. There are few tree and shrub species with a drip tip leaf apex and papery leaves. Evergreen species make up more than 75% of the total tree and shrub species. In a 2,500 m² sampling area, the number of vascular species ranged between 57 and 110; Simpson’s diversity index ranged from 0.7719 to 0.9544, Shannon–Winner’s diversity index from 1.8251 to 3.2905, and Pielou’s evenness index from 0.5836 to 0.8982 for trees. The cloud forests in Yunnan are physiognomically similar to the tropical cloud forests in America and Southeast Asia. They very much resemble the mountain dwarf mossy forest in Hainan Island, southeastern China, and the Mountain ericaceous forests in the Malay Peninsula. The cloud forests in Yunnan are considered to be developed, as are the tropical upper montane cloud forests in Asia.     

竹叶眼子菜居群遗传多样性和克隆结构

采用ISSR技术对长江中游南岸豹澥湖和大冶湖不同生境中的竹叶眼子菜(Potamogeton malaianus)居群的遗传多样性及克隆结构进行了研究.结果表明,在两居群的106株个体中,利用6条ISSR引物共得到40条符合3/N标准并无连锁不平衡的清晰位点,竹叶眼子菜具有较高的遗传多样性,其多态位点百分率为75.0％,Shannon多样性指数为0.3736, 两居群的遗传分化很小.竹叶眼子菜的克隆多样性很高(D=0.9917),两居群间的克隆分化很大,不具有共有的基因型.竹叶眼子菜的基株分布为游击型构型,位于湖心的大冶居群克隆距离(3.0～31.5 m)明显地大于湖岸豹澥居群(2.4～6.7 m).