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To what extent are bryophytes efficient dispersers?
Abstract
Bryophytes are typically seen as extremely efficient dispersers. Experimental evidence suggests that efficient short‐distance dispersal coupled with random long‐distance dispersal (LDD) leads to an inverse isolation effect. Under the latter, a higher genetic diversity of colonizing propagules is expected with increasing isolation, counteracting differentiation beyond the range of short‐distance dispersal. This expectation is tested from a review of evidence on spatial genetic structure and analyses of isolation‐by‐distance (IBD) at different scales. A decay of the IBD signal, characterized by non‐significant slopes between kinship coefficients and geographic distance was observed beyond 100 m. A second slope shift was observed at distances larger than 1 km, with a proportion of significant slopes in more than one third of the datasets. The decay of the IBD signal beyond 100 m, which reflects efficient LDD, is consistent with the inverse isolation hypothesis. Persistence of a significant IBD signal at medium ranges in one third of the analysed cases suggests, however, that the inverse isolation effect is not a rule in bryophyte spore dispersal. Furthermore, the higher proportion of significant IBD patterns observed at scales over 100 km likely marks the limits of regional dispersal, beyond which an increasingly smaller proportion of spores travel. Synthesis. We discuss the differences between experimental and genetic estimates of spore dispersal and conclude that geographic distance remains a significant proxy of spore colonization rates, with major consequences for our understanding of actual migration capacities in bryophytes, and hence, our capacity to model range shifts in a changing world. Experimental evidence suggests that, in bryophytes, random long‐distance dispersal counteracts genetic differentiation beyond the range of short‐distance dispersal. A meta‐analysis of spatial genetic structures reveals that, although a decay of the isolation‐by‐distance prevails at medium range, geographic distance remains a significant proxy of spore colonization rates, with major consequences for our capacity to model range shifts in a changing world.
... To compare the results with previous studies on IBD in bryophytes from a meta-analysis of datasets using haplotype frequencies and SNPs (Vanderpoorten et al., 2019), and in particular, to test the hypothesis that differences in the significance of the IBD signal observed come from an increased statistical power associated with the higher number of loci with RADseq data (Discussion), we sub-sampled the data matrix for three species (A. juliformis, B. hookeri and S. helicophyllus). ...
... In particular, a persisting signal of IBD was consistently reported beyond the range of short-distance dispersal (> 1 km). This contrasts with a recent meta-analysis of fine-scale spatial genetic structures in bryophytes, which reported the decay of the IBD pattern beyond that range in 30-50% of the datasets investigated (Vanderpoorten et al., 2019). We interpret the differences between the present and previous studies on IBD in bryophytes in terms of statistical power of the tests, since previous studies were based on haplotypic or SNP variation at a few loci. ...
... We interpret the differences between the present and previous studies on IBD in bryophytes in terms of statistical power of the tests, since previous studies were based on haplotypic or SNP variation at a few loci. This interpretation is supported by our sub-sampling analysis of three datasets, which revealed that, for a similar number of polymorphic markers as in Vanderpoorten et al. (2019), we observed significantly higher standard deviations of the IBD slopes between pairs of individuals located at > 1 km from each other in the randomly subsampled data matrices than in the full matrices, with a corresponding decay of the significance of the IBD signal beyond 1 km. ...
Lowland tropical bryophytes have been perceived as excellent dispersers. In such groups, the inverse isolation hypothesis proposes that spatial genetic structure is erased beyond the limits of short‐distance dispersal. Here, we determine the influence of environmental variation and geographic barriers on the spatial genetic structure of a widely dispersed and phylogenetically independent sample of Amazonian bryophytes. Single nucleotide polymorphism data were produced from a restriction site‐associated DNA sequencing protocol for 10 species and analyzed through F‐statistics and Mantel tests. Neither isolation‐by‐environment nor the impact of geographic barriers were recovered from the analyses. However, significant isolation‐by‐distance patterns were observed for 8 out of the 10 investigated species beyond the scale of short‐distance dispersal (>1 km), offering evidence contrary to the inverse isolation hypothesis. Despite a cadre of life‐history traits and distributional patterns suggesting that tropical bryophytes are highly vagile, our analyses reveal spatial genetic structures comparable to those documented for angiosperms, whose diaspores are orders of magnitude larger. Dispersal limitation for tropical bryophytes flies in the face of traditional assumptions regarding their dispersal potential, and suggests that the plight of this component of cryptic biodiversity is more dire than previously considered in light of accelerated forest fragmentation in the Amazon.
... Under this hypothesis, neither barriers nor geographic distance (but possibly local environmental conditions) would explain their distributions and spatial genetic structure, the latter being erased beyond the limits of short distance dispersal (inverse isolation hypothesis, Ledent et al. 2020). Experimental evidence suggests that efficient short distance dispersal together with random long-distance dispersal allow for an inverse isolation effect (Vanderpoorten et al. 2019), whereas genetic analyses neither found evidence for isolation-by-environment nor the impact of geographic barriers but significant isolation-by-distance patterns instead for the majority of analyzed liverwort and moss species (Ledent et al. 2020), contrary to the inverse isolation hypothesis. ...
... This result is consistent with the fact that bryophytes are freely dispersed throughout the landscape, and also shows that bryophyte communities behave as a metacommunity (Mota de Oliveira & ter Steege 2013). Since the distances between the Colombian localities of the samples exceed 200 km, long-distance dispersal can be assumed, where the isolation signals by distance are erased (Vanderpoorten et al. 2019). Contrary to the data found by Ledent et al. (2020) where 8 of the 10 species studied show evidence of isolation-by-distance, the data of the present study thus seem to show evidence in favor of the inverse isolation hypothesis, whereas isolation-by-distance at larger spatial scales (Colombia-Brazil) also seems to occur. ...
We studied the community structure and diversity of epiphytic bryophytes in a vertical gradient from tree base to canopy in four lowland rain forest sites of the Colombian Amazon (Amazonas, Caquetá, Putumayo, and Vaupés). Each of the 64 sampled phorophytes was divided into six height zones from the base (Z1) to the outer canopy (Z6). As a subproject, we carried out a genetic population study using the liverwort Cheilolejeunea rigidula (Lejeuneaceae) as our model species, which occurred in all six height zones. In addition to 65 successfully sequenced samples from the study sites, we included individuals of C. rigidula from Guiana and Brazil (Manaus and Tapajos) to investigate the connectivity and genetic structure of this species across the Amazon region and to evaluate the genetic structure based on phorophyte height zones. Each site in Colombia, Brazil and Guiana was considered a subpopulation. The sequenced chloroplast markers (partial atpB gene, partial psbA gene/psbA-trnH spacer) showed little variation across the Amazon and the height zones on the trees. The nuclear marker (ITS) showed a spatial structure indicating genetic differentiation of subpopulations across the Amazon, but little genetic differentiation of C. rigidula along the height of the trees. The gradient across the Amazon shows a relationship between genetic distance and geographic distance, indicating dispersal limitations (P<0.001). At local and regional scales, our results suggest that dispersal can have a dominant effect on populations and communities, increasing connectivity.
... Among H. ciliata populations, Euclidean genetic distances did not correlate with geographic distances (Fig. 6). Isolation by distance patterns have been studied repeatedly for other bryophytes, and in a metanalysis across 28 species Vanderpoorten et al. (2019) found most IBD signals at a range of less than 0.1 km (91% of tests being significant), but no IBD signals at 0.1 to 1 km. For distance classes greater than 1 km, they found that between 30 and 54% of tests were significant. ...
... careful removal of trees around boulders within forests; Hepenstrick et al. 2016). Colonisation of new boulders sourcing from boulder populations may only be realistic in close proximity (up to ca. 100 m distance; Vanderpoorten et al. 2019). Re-establishing the habitat quality of boulders where A. septentrionale went recently extinct and erratic boulders in general seems worthwhile, although spontaneous recolonisation of A. septentrionale is unlikely. ...
Erratic boulders provide habitat for rock-dwelling species and contribute to the biodiversity of landscapes. In the calcareous Swiss lowlands, siliceous erratic boulders are exclusive habitat islands for the regionally critically endangered fern Asplenium septentrionale, about 20 bryophyte species and numerous lichens. Focusing on island biogeographical processes, we analysed the conservation genomics of A. septentrionale and the moss Hedwigia ciliata on insular erratic boulders in the Swiss lowlands and the adjacent “mainland” in siliceous mountains. We genotyped both species using double digest restriction associated DNA sequencing (ddRAD). For the tetraploid A. septentrionale, abundant identical multilocus genotypes within populations suggested prevalent intragametophytic selfing, and six out of eight boulder populations consisting of a single multilocus genotype each indicated single spore founder events. The genetic structure of A. septentrionale mainland populations coincided with Pleistocene glacial refugia. Four genetic lineages of H. ciliata were identified, and populations consisting of a single multilocus genotype were less common than in A. septentrionale. For both taxa, multilocus genotype diversity on boulders was lower than in mainland populations. The absence of common genetic groups among boulder populations, and the absence of isolation by distance patterns, suggested colonisation of boulders through independent long-distance dispersal events. Successful boulder colonisation of A. septentrionale seems to be rare, while colonisation by H. ciliata appears to be more frequent. We conclude that pivotal principles of conservation biology, such as connectivity and genetic diversity, are of less importance for the studied cryptogams on insular erratic boulders because of long-distance dispersal, intragametophytic selfing and polyploidy.
... Long-distance dispersal is an important process that shapes bryophyte distribution patterns, especially at large scales (Vanderpoorten, 2019). Unlike what would be expected for plants with seeds, a greater genetic diversity of colonizing propagules is expected with greater isolation because bryophyte spores are carried through the air, thus neutralizing the differentiation process (Patiño et al., 2018;Vanderpoorten, 2019). ...
... Long-distance dispersal is an important process that shapes bryophyte distribution patterns, especially at large scales (Vanderpoorten, 2019). Unlike what would be expected for plants with seeds, a greater genetic diversity of colonizing propagules is expected with greater isolation because bryophyte spores are carried through the air, thus neutralizing the differentiation process (Patiño et al., 2018;Vanderpoorten, 2019). This ability of bryophytes reflects in a low rate of endemism (Frahm, 2007). ...
In forest enclaves known as Brejos de Altitude (forest refuges) in northeastern Brazil, floristic affinities are generally explained by historical processes of vicariance. However, for poikilohydric plants with long distance dispersal such as bryophytes, the present work predicts that floristic similarities result from environmental affinities between areas. The floristic relationships of forest refuges with different phytogeographic domains of Brazil were investigated based on the current distribution of bryophytes, and the processes that explain the distribution of species were discussed. A floristic database of 863 bryophyte species from 108 areas, including geoclimatic data, was used in the analysis. The floristic similarity between areas and their relationships with environmental and spatial variables were analyzed. The species composition was found to be distinct between biomes and phytogeographic domains. The floristic difference between the domains was mainly explained by turnover of species. Variables associated with water availability, i.e. aridity and water vapor pressure, drive the bryophyte assembly, leading to the conclusion that niche-based processes explain the distribution of bryophyte species in Brazilian biological refuges and tropical forests.
... disperse well and over long distances by wind (Frahm, 2008;Porley & Hodgetts, 2005) and are typically regarded as extremely efficient dispersers (Vanderpoorten et al., 2019). Some previous studies even suggested that long-distance dispersal of spores might be more common than previously appreciated (McDaniel & Shaw, 2003;Skotnicki et al., 2001) and dispersal limitation was not considered the major ecological process driving bryophyte assemblages (Liu et al., 2020;Patiño et al., 2013Patiño et al., , 2014. ...
To explore the taxon‐dependent contribution of dispersal limitation versus environmental filters to bryophyte assemblages. We investigated bryophytes and six environmental variables on 168 islands in the Thousand Island Lake,China. We compared the observed beta diversity with the expected values based on six null models (EE, EF, FE, FF, PE, and PF), detected the partial correlation of beta diversity with geographical distances. We quantified the contributions of spatial versus environmental variables and island isolation per se to species composition (SC) using variance partitioning. We modeled the species‐area relationships (SARs) for bryophytes and the other eight biotas. To explore the taxon‐dependent effects of spatial versus environmental filters on bryophytes, 16 taxa including five categories (total bryophytes, total mosses, liverworts, acrocarpous, and pleurocarpous mosses) and 11 species‐richest families were included in the analyses. The observed beta diversity values were significantly different from the predicted values for all 16 taxa. For all five categories, the observed partial correlations between beta diversity and geographical distance after controlling environmental effects were not only positive, but also significantly different from the predicted values based on the null models. Spatial eigenvectors are more important in shaping SC than environmental variables for all 16 taxa except Brachytheciaceae and Anomodontaceae. Spatial eigenvectors contributed more to SC variation in liverworts than in mosses and in pleurocarpous mosses than in acrocarpous mosses. The effects of island isolation on SC were significant for all five categories, highly varied at the family level. The z values of the SARs for the five bryophyte categories were all larger than those of the other eight biotas. In subtropical fragmented forests, dispersal limitation exerted significant, taxon‐dependent effects on bryophyte assemblages. It was dispersal limitation rather than environmental filtering that predominantly regulated the SC patterns of bryophytes. In subtropical fragmented forests, dispersal limitation exerted significant, taxon‐dependent effects on bryophyte distribution. It was dispersal limitation rather than environmental filtering that predominantly regulated SC patterns for most categories of bryophytes.
... Although epiphytes need to track patches of suitable trees (or leaves in the case of epiphylls) in a dynamic landscape for persistence (Snäll et al., 2005), mounting evidence suggests that dispersal capacity is counter-selected in epiphytic bryophytes. Epiphytic bryophytes typically exhibit spatially clustered distributions (Löbel et al., 2006;Snäll et al., 2003;Wagner et al., 2015) and their fine-scale patterns of genetic variation are strongly spatially structured (Ledent et al., 2020;Vanderpoorten et al., 2019), pointing to important effects of isolation-by-distance. These patterns are paralleled by morphological adaptations counter-favouring dispersal. ...
1. Epiphytic communities offer an original framework to disentangle the contributions of environmental filters, biotic interactions and dispersal limitations to community structure at fine spatial scales. We determine here whether variations in light, microclimatic conditions and host tree size affect the variation in species composition and phylogenetic structure of epiphytic bryophyte communities, and hence, assess the contribution of environmental filtering, phylogenetic constraints and competition to community assembly.
2. A canopy crane giving access to 1.1 ha of tropical rainforest in Yunnan (China) was employed to record hourly light and microclimatic conditions from 54 dataloggers and epiphytic bryophyte communities from 408 plots. Generalized Dissimilarity Modelling was implemented to analyse the relationship between taxonomic and phylogenetic turnover among epiphytic communities, host-tree characteristics and microclimatic variation.
3. Within-tree vertical turnover of bryophyte communities was significantly about 30% higher than horizontal turnover among-trees. Thus, the sharp vertical variations in microclimatic conditions from tree base to canopy are more important than differences in age, reflecting the likelihood of colonization, area, and habitat conditions between young and old trees, in shaping the composition of epiphytic bryophyte communities.
4. Our models, to which microclimatic factors contributed most (83–98%), accounted for 33% and 18% of the variation in vertical turnover in mosses and liverworts, respectively. Phylogenetic turnover shifted from significantly negative or non-significant within communities to significantly positive among communities, and was slightly, but significantly, correlated with microclimatic variation. These patterns highlight the crucial role of microclimates in determining the composition and phylogenetic structure of epiphytic communities.
5. Synthesis. The mostly non-significant phylogenetic turnover observed within communities does not support the idea that competition plays an important role in epiphytic bryophytes. Instead, microclimatic variation is the main driver of community composition and phylogenetic structure, evidencing the role of phylogenetic niche conservatism in community assembly.
... Regional genetic structure and IBD have been documented in other bryophytes. In a meta-analysis of 26 bryophyte species, Vanderpoorten et al. (2019) regressed genetic similarity among samples binned in seven groups defined by geographical separation. They found significant IBD at short distances separating samples (< 10 km), then a decay of IBD over intermediate distances, but an increase in the frequency of significant IBD at greater distances (e.g. ...
Bryophytes generally have broad geographical ranges that suggest high dispersal ability. The aim of this study was to test hypotheses about dispersal limitation, as indicated by isolation by distance, in four spore-producing species of the moss genus Sphagnum (Sphagnum carolinianum, Sphagnum missouricum, Sphagnum macrophyllum and Sphagnum pylaesii) and to assess whether plants in the southern USA harbour high levels of unique alleles and/or other indicators of exceptional genetic diversity. Isolation by distance was detected in all four species, but regional patterns of genetic structure were very species specific. Northern and southern genotype groups were detected in S. carolinianum and S. missouricum, but in S. pylaesii plants from the Adirondack Mountains of New York were genetically distinct from others to the north and south. One species, S. macrophyllum, exhibited differentiation between northern and southern genetic groups that appeared to reflect more ancient phylogenetic diversification.
... Alors et al., 2017;Hernández-Rojas et al., 2020). Among plants, bryophytes exhibit worldwide and disjunct distributions as evidence of their vagility (McDaniel & Shaw, 2005;Pisa et al., 2014;Kyrkjeeide et al., 2016a;Biersma et al., 2017;Patiño & Vanderpoorten, 2018;Vanderpoorten et al., 2019). The extensive distribution range of some bryophyte species [e.g. ...
Increasing evidence indicates that wide distributed bryophyte taxa with homogeneous morphology may represent separate evolutionary lineages. The evolutionary histories of these cryptic lineages may be related to historical factors, such as the climatic oscillations in the Quaternary. Thus, the post-glacial demographic signatures paired with cryptic speciation may result in complex phylogeographic patterns. This research has two aims: to determine whether the widespread moss Racomitrium lanuginosum represents cryptic molecular taxa across the Northern Hemisphere and to infer the effects of Quaternary glaciations on spatial genetic diversity. We used the internal transcribed spacer (ITS) marker to resolve the phylogeographic history of the species and single nucleotide polymorphisms (genotyping-by-sequencing) to infer the genetic structure and demographic history. Finally, we assessed the historical changes in the distribution range using species distribution models. Racomitrium lanuginosum comprises distinct molecular lineages sympatrically distributed in the Northern Hemisphere. We also uncovered long-distance dispersal from eastern North America to Scandinavia and potential in situ survival in northern Scandinavia. Due to the genetic signatures, the Alaska Peninsula could be considered a glacial refugium. The species experienced post-glacial expansion northwards in the Northern Hemisphere, mainly from the Alaska Peninsula. Our results exemplify the complex phylogeographic history in cold environments and contribute to recognizing evolutionary patterns in the Northern Hemisphere.
... Nevertheless, the higher colonization rates predicted for epiphytes based upon simulations with the Wald model are at odds with the counterselection of dispersal-efficient traits in epiphytic bryophytes and, in fact, epiphyte communities typically display aggregated patterns (Snäll et al., 2003;Löbel et al., 2006) and strong spatial genetic structures (Snäll et al., 2004;Ledent et al., 2020). We suggest that the apparent conflict between high colonization rates and Month 2022 | Volume 00 | Issue 00 | 1-3 counterselection of dispersal capacities in epiphytes, which results in aggregated patterns, can be interpreted in terms of a fat-tailed dispersal kernel that reflects a "dual" dispersal strategy (see Vanderpoorten et al., 2019 for review). On the one hand, spore density is higher within the near vicinity of the mother plant, resulting in the locally aggregated pattern. ...
The impact of climate change on biodiversity operates through a complex mixture of habitat loss and range shift through the emergence of newly suitable areas (Warren et al., 2013). The main question is therefore to determine whether species have the ability to balance the loss of suitable habitats by effectively shifting their ranges and track suitable areas under climate change (Nogués‐Bravo et al., 2018). Zanatta et al. (2020) most recently simulated the dispersal of apparently extremely efficient dispersers, namely bryophytes, whose tiny spores (less than 20 μm on average) are wind‐dispersed across large distances, under several climate change scenarios. This article is protected by copyright. All rights reserved.
... Further, high rates of LDD can lead to an inverse isolation effect in some cases, wherein more isolated sites (i.e., islands) receive a greater proportion of diaspores from increasingly distant sources and thus exhibit higher diversity than less isolated sites (Barbé et al., 2016;Lönnell et al., 2012;Sundberg, 2005Sundberg, , 2013Szövenyi et al., 2012). However, many moss species exhibit strong genetic structure at both local and regional scales, suggesting that dispersal alone cannot explain distribution patterns, and that establishment success may impose stronger limitations than dispersal (Ledent et al., 2020;Snäll et al., 2004;Vanderpoorten et al., 2019). Further, mosses do not exhibit a clear latitudinal alpha diversity gradient (Geffert et al., 2013;Möls et al., 2013;Shaw et al., 2005), likely due in part to the inverse isolation effect (Patiño & Vanderpoorten, 2018;Sundberg, 2005). ...
Digitization of herbarium specimens and DNA sequencing efforts in the past decade have enabled integrative analyses of patterns of diversity and endemism in a phylogenetic context. Here, we compare the best available floristic databases to a comprehensive specimen database to examine spatial patterns of moss phylogenetic assembly. We test the hypotheses that (1) mosses exhibit phylogenetic regionalization, (2) islands contain significantly high phylogenetic diversity and (3) that moss phylogenetic endemism is low on a global scale. Global. Mosses. We developed a phylogeny of 3654 moss species using 25 markers and compiled a global specimen database from online repositories. We calculated floristic and phylogenetic measures of diversity and endemism and performed randomizations to test for significant deviations from expectations. We use rarefaction and extrapolation to alleviate substantial differences in sampling effort across the globe. We used both phylogenetic and floristic methods to test for spatial regionalization. We compare our specimen‐based results to those obtained using a floristic dataset. Phylogenetic diversity is more robust to missing data than species richness. Mean phylogenetic distance was significantly higher than expected in areas with high species richness, indicating that reported richness in these areas is likely a product of repeated colonization. Phylogenetic endemism is low globally. Phylogenetic regionalizations cluster into a Holarctic/Holantarctic temperate region, a pantropical region, and a region composed of Australia, New Zealand and South Africa. Future efforts for collecting, sequencing and databasing moss species should focus on the tropics, particularly Africa and Southeast Asia. We provide further evidence to support several important theories developed in moss biogeography, including the role of long‐distance dispersal in shaping floristic patterns, the dominance of anagenesis in driving patterns of island diversity, and the role of climatic instability in driving patterns of assembly in the Holarctic.
... Bryophytes possess a particularly poikilohydric strategy of utilizing water and nutrients and have high sensitivity to variations in warm temperature to adapt to environmental conditions when occurring in extreme surroundings (Geffert et al., 2013;He et al., 2016). The specific ecophysiological and biological features of bryophytes make them as one of the most vulnerable groups to moving climatic state (Bates et al., 2005;Becker Scarpitta et al., 2017;Désamoré et al., 2012;He et al., 2016;Pardow & Lakatos, 2013), despite their strong dispersal capabilities (Vanderpoorten et al., 2019). A notable decrease in bryophyte diversity due to global warming was expected in the areas with many bryophytes, such as boreal forests at higher latitudes, alpine biomes, and high altitude forests (Geffert et al., 2013;He et al., 2016) or oceanic islands in Macaronesian biogeographic region (Patiño et al., 2016). ...
Identifying the danger and expressing the indeterminacy of forfeiting perching space of species induced by rapid climate warming is crucial for biodiversity risk management under future changes in climate conditions. The scenarios of climate shift named the representative concentration pathways, the categorizing technique with regard to fuzzy-set, and Monte Carlo scheme was employed to survey the indeterminacy and the danger of forfeiting perching space caused by climate warming for 115 bryophytes in China. For the deterministic scenarios of climate shift, the richness of 115 bryophytes improved in several areas in north-eastern China, while it dropped in some areas in southern, eastern, south-eastern, and central China. In addition, for the deterministic scheme of altering climatic state, the count for bryophytes with the proportion of contracting the present areal range as less than 20%, 20–40%, 40–60%, 60–80%, and over 80% was belike 34–38, 19–38, 24–35, 9–19, and 4–9, separately; the count of bryophytes with the ratio of the occupying entire areal range as over 80%, 60–80%, and less than 20% was roughly 97–109, 4–14, and 2–8, separately. For the scenarios of randomly change in climate state, the number of bryophytes with a various proportion of forfeiting the present perching space dropped with enhancing the possibility; with the likelihood beyond 0.6, the count of bryophytes with forfeiting present perching space as less than 20%, 20–40%, 40–60%, 60–80% and high than 80% of the present areal range was approximately 7–14, 2–10, 0–7, 2–9, and 13–20, separately; the number of bryophytes with the ratio of occupying the whole areal range as less than 20%, 20–40%, 40–60%, 60–80%, and over 80% was more or less 1–3, 0–3, 1–5, 1–3, and 38–44, separately. Roughly 48 bryophytes would face the risk of extinction from climate warming, including endemic and non-endemic species. Forfeiting perching space induced by climate warming would cause variations in species composition and the disappearance of some ecological functions associated with these bryophytes. The inconstancy of forfeiting areal range caused by climate warming should be incorporated into the policy-making of conservation bryophytes for adaptation of climate warming.
... We found no isolation-by-distance effects on intraspecific genetic composition in S. cossonii. This agrees with the results of a recent meta-analysis, where c. 50% of 26 investigated temperate bryophyte species did not show significant IBD signals at ranges of 100-1000 km, that compare to the distances between the sites in this study (Vanderpoorten et al., 2019). Haplotype (and nucleotide) diversity at the site level was higher in limed than in natural rich fens and relative haplotype frequencies differed, while haplotype number per fen was similar in the two fen types (Table 2A). ...
To understand colonization processes, it is critical to fully assess the role of dispersal
in shaping biogeographical patterns at the gene, individual, population, and community
levels. We test two alternative hypotheses (H I and H II) for the colonization of disturbed sites by clonal plants, by analyzing intraspecific genetic variation in one and reproductive traits in two typical fen mosses with separate sexes and intermittent spore dispersal, disturbed, early-succession (limed) fens and late-successional rich fens. H I suggests initial colonization of disturbed sites by diverse genotypes of which fewer remain in late-successional fens and an initially balanced sex ratio that develops into a possibly skewed population sex ratio. H II suggests initial colonization by few genotypes and gradual accumulation of additional genotypes and an initially skewed sex ratio that alters into the species-specific sex ratio, during succession. Under both scenarios, we expect enhanced sexual reproduction in late-successional fens due to resource gains and decreased ntermate distances when clones expand. We show that the intraspecific genetic diversity, assessed by two molecular markers, in Scorpidium cossonii was higher and the genetic variation among sites was smaller in disturbed than late-successional rich fens. Sex ratio was balanced in S. cossonii and Campylium stellatum in disturbed fens and skewed in C. stellatum in late-successional fens, thus supporting H I. In line with our prediction, sex expression incidence was higher in, and sporophytes were confined to, late-succession
compared to disturbed rich fens. Late-successional S. cossonii sites had more within-site
patches with two or more genotypes, and both species displayed higher sex expression levels in late-successional than in disturbed sites. We conclude that diverse genotypes and both sexes disperse efficiently to, and successfully colonize new sites, while patterns
of genetic variation and sexual reproduction in late-successional rich fens are gradually shaped by local conditions and interactions over extended time periods.
... Spores contribute to long distance dispersal across landscapes (Patiño and Vanderpoorten, 2018). Bryophytes are thought to be efficient spore-dispersing organisms, with 100 kilometers suggested as a likely distance a spore could travel (Vanderpoorten et al., 2019). Bryophytes have relatively low rates of endemism compared to seed plants, and species composition patterns match more closely with wind connectivity patterns than geographic proximity (Patiño and Vanderpoorten, 2018). ...
... Spores contribute to long distance dispersal across landscapes (Patiño and Vanderpoorten, 2018). Bryophytes are thought to be efficient spore-dispersing organisms, with 100 kilometers suggested as a likely distance a spore could travel (Vanderpoorten et al., 2019). Bryophytes have relatively low rates of endemism compared to seed plants, and species composition patterns match more closely with wind connectivity patterns than geographic proximity (Patiño and Vanderpoorten, 2018). ...
Biological soil crusts (BSCs) develop when various combinations of diminutive cyanobacteria, eukaryotic algae, non-lichenized fungi, lichens, and/or bryophytes occupy the upper few millimeters of the soil and raw material. They can be present in a wide range of ecological, including successional, and climatic conditions when and where disturbance and/or aridity have resulted in opportunities for colonization. However, they are most prevalent in arid, semiarid and polar ecosystems where vascular plant cover and diversity are characteristically low, leaving large areas available for colonization by some combination of the organismal groups mentioned above. The ecological roles of BSCs are numerous and diverse, and include the collection, accumulation and cycling of essential airborne and soil nutrients, redistribution of precipitated water, and soil formation and stabilization.
... Mosses found, are rather generalists, in comparison, both in terms of climatic and substrate requirements, as indicated by a lower number of obligate epixylic moss species. Also, the higher long-distance dispersal capacity of many moss species (Vanderpoorten et al., 2019, Patino andVanderpoorten, 2018) might have blurred the response to climate. Nevertheless, precipitation and deadwood still explained a notable 67% of the variance in site-level moss diversity data. ...
Deadwood is a habitat for numerous biota and serves as an indicator of forest biodiversity. Bryophytes significantly contribute to deadwood communities and epixylic bryophytes are particularly threatened. Additional to deadwood volumes, their occurrence depends on climatic conditions. However, the interactive effects of dead-wood and climate on epixylic bryophytes have hardly been assessed. Here, we analyse these effects based on 8 143 bryophyte specimens collected on 510 logs in 51 Austrian forests. We found that annual precipitation sum and deadwood volume explained 67%, 90%, and 82% of the variation in moss, liverwort and total species richness, respectively. Segmented regression indicated several breakpoints in these relationships, especially at c. 60 m 3 /ha of deadwood and 900 mm, respectively 1700 mm of annual precipitation. Epixylic bryophyte diversity increased strongly up to the deadwood threshold, but only moderately with still higher volumes. Nine hundred mm of annual precipitation was a macroclimatic limit for deadwood-specific bryophyte species. Below this value, obligate epixylic bryophytes were lost and liverworts were rare, even at sites with high deadwood amounts. At the wettest sites, the overall number of species decreased while deadwood-specific specialists further increased in number. The close tie of epixylic bryophytes to macroclimate may constrain the efficiency of deadwood management measures and suggests considerable impacts of climate change. A drier and warmer climate will probably decrease species richness and change the composition of epixylic bryophyte communities, with the most characteristic species, especially liverworts, facing the highest risk.
... and lichens) are dispersal-limited or not (Pharo & Zartman, 2007;Gjerde et al., 2014). One simple reason for this inconsistency might be that there is a large variability both between species in their dispersal capacity and between ecosystems in the likelihood that a propagule will establish (Barbé et al., 2016;Vanderpoorten et al., 2019). It is also important to be aware of the differences in both temporal and spatial scales when comparing results from different studies. ...
Questions
In some fire‐prone ecosystems, bryophytes play a crucial role by providing the surface fuel that controls the fire return interval. Afroalpine heathlands are such an ecosystem, yet almost nothing is known about the bryophytes in this system. We do not know the level of species richness, or if there is a successive accumulation of species over time, or if some species are adapted to specific phases along the successional gradient, for example early‐successional species sensitive to competition.
Location
Afroalpine heathlands in Ethiopia.
Methods
We made an inventory of all bryophytes in 48 plots of 5 m × 5 m, distributed along a chronosequence from 1 to 25 years post fire. The heathlands are located between 3500 m and 3800 m a.s.l. and are managed by traditional pasture burning with fire intervals of 8–20 years.
Results
We found in total 111 taxa of bryophytes. Post‐fire mortality was almost 100%. The youngest plots had only a few cosmopolitan species often found after fire. Initially, species richness increased monotonically while starting to level off around 15 years after fire, when many plots had around 30 species and a high cover of Breutelia diffracta, which is a key ground‐living species, important as surface fuel. Most species were found with sporophytes, a pattern even stronger for the most frequent species.
Conclusions
Interestingly, bryophyte diversity is already remarkably high by only 15 years after total eradication. The relatively slow accumulation of species in the first years after fire suggests that dispersal in space, and not time, is the major mechanism by which sites regain their diversity (i.e. spore banks play a smaller role than colonization of wind‐borne spores). This indicates that the high species richness is built up through colonization from surrounding heathlands, and perhaps also from higher‐altitude alpine grasslands and lower‐altitude forests, and that the bryophyte diversity in this system is maintained by the traditional fire and grazing management.
... However, most such studies in fragmented landscapes focus on the assembly mechanisms of woody or herbaceous plants (e.g., Burns et al. 2010, Keppel et al. 2010, Carvajal-Endara et al. 2017, and we know little about other organisms, such as bryophytes (but see Tiselius et al. 2019), which are broadly distributed (Heden€ as 2007, Frahm 2008 and play important functional roles in terrestrial ecosystems (Lindo andGonzalez 2010, Deane-Coe andStanton 2017). As bryophytes require specific microhabitats, establish on spatially discrete habitats rapidly (Zartman 2003), and have strong dispersal ability due to their small unicellular spores (Hutsemekers et al. 2008, Vanderpoorten et al. 2019, they can give us the opportunity to examine the role of habitat heterogeneity and dispersal limitation in community assembly processes. ...
Community assembly of island plants is a central topic in island biogeography. Most previous studies have focused on seed plants, while our understanding of bryophytes is limited. Specifically, how dispersal limitation and habitat heterogeneity shape beta diversity of bryophyte communities on islands remains unknown. We used two datasets of bryophyte communities from an artificial (~60 yr of isolation) and natural archipelago (~8500 yr of isolation) to understand their beta diversity patterns. The null model, in which species could disperse randomly and colonize successfully between islands, but the number of species on each island and the frequency of each species occurrence across all islands remain unchanged, was used to calculate expected beta diversity. Although we found significant differences in species composition between the two archipelagos, the difference in observed beta diversity was negligible. Further, there was no significant difference between observed and expected beta diversity in each archipelago. The difference in island area, rather than isolation, was significantly correlated with the beta diversity of bryophytes in both archipelagos. Our results suggest that the dispersal limitation is not the major ecological process driving the assembly of bryophyte communities in both archipelagos, but the habitat heterogeneity related to island area determines the beta diversity of bryophytes.
... Bryophyte spore-trapping experiments in fact revealed that the tail of the dispersal kernel is, beyond hundreds of meters, not distance-dependent, suggesting that, once a spore is airborne, it could disperse over hundreds to thousands of kilometers, regardless of the distance from the source 71 . Spatial genetic structures consistently show, however, significant isolation-by-distance patterns for all distance classes, evidencing that realized colonization rates are distant-dependent 72 and justifying the implementation of a mechanistic model such as WALD. Furthermore, the WALD model assumes that (i) the slippage velocity between the particles and surrounding air is zero, leading to an infinite drag coefficient, so that the particles and surrounding air parcels are tightly coupled, and that (ii) the diaspore terminal velocity is reached instantly after release. ...
The extent to which species can balance out the loss of suitable habitats due to climate warming by shifting their ranges is an area of controversy. Here, we assess whether highly efficient wind-dispersed organisms like bryophytes can keep-up with projected shifts in their areas of suitable climate. Using a hybrid statistical-mechanistic approach accounting for spatial and temporal variations in both climatic and wind conditions, we simulate future migrations across Europe for 40 bryophyte species until 2050. The median ratios between predicted range loss vs expansion by 2050 across species and climate change scenarios range from 1.6 to 3.3 when only shifts in climatic suitability were considered, but increase to 34.7-96.8 when species dispersal abilities are added to our models. This highlights the importance of accounting for dispersal restrictions when projecting future distribution ranges and suggests that even highly dispersive organisms like bryophytes are not equipped to fully track the rates of ongoing climate change in the course of the next decades.
... This was seen as evidence for in situ diversification within regions (mostly continents), which takes place at a faster rate than the intercontinental migration. The strong phylogeographic signal found in many bryophyte species at the intercontinental scale (Patiño & Vanderpoorten, 2018), along with the strong population genetic structuring observed in a number of continentally disjunct species Vanderpoorten & al., 2019), is in line with the notion that speciation has a spatial scale that depends on both area and levels of gene flow (Kisel & Barraclough, 2010). Our results suggest that in Epipterygium, large geographic areas seem to be required to allow speciation in allopatry. ...
A significant number of bryophyte species are thought to have transcontinental geographic ranges, often with multiple disjunct distribution areas. One of these cases is Epipterygium tozeri (Mniaceae), with a Holarctic distribution and disjunct ranges in western North America, the Mediterranean, Japan and central Asia. Collections from different geographic regions were lumped into E. tozeri based on morphology, but a molecular confirmation was lacking so far. Here, we tested species concepts in the genus Epipterygium, with a special focus on the E. tozeri species complex, combining morphological and DNA sequence data for the nuclear ribosomal ITS region and two plastid loci (trnG intron, trnT-psbD spacer). In a second step, we reconstructed the historical biogeography of the genus. We found that Epipterygium most likely originated in Asia or North/Central America and that the alleged single widespread species E. tozeri with disjunct ranges is in fact a group of genetically and morphologically distinct taxa, including four overlooked species, for which we provide descriptions: E. atlanticum sp. nov., E. biauritum sp. nov., E. oreophilum sp. nov., and E. yunnanense sp. nov. The biogeographical history of these species is best explained by a step-wise parallel colonization of the Eurasian and American continents followed by in-situ speciation.
... Spores contribute to long distance dispersal across landscapes (Patiño and Vanderpoorten, 2018). Bryophytes are thought to be efficient spore-dispersing organisms, with 100 kilometers suggested as a likely distance a spore could travel (Vanderpoorten et al., 2019). Bryophytes have relatively low rates of endemism compared to seed plants, and species composition patterns match more closely with wind connectivity patterns than geographic proximity (Patiño and Vanderpoorten, 2018). ...
Desiccation stress is frequently experienced by the moss Bryum argenteum and can influence survival, propagation and niche selection. We attempted to disentangle the interacting factors of life history phase (five categories) and rate of desiccation (time allotted for induction of desiccation tolerance) for 13 ecotypes of B. argenteum. Using chlorophyll fluorescence as a stress index, we determined how these parameters influenced desiccation tolerance. Rate of drying and life phase significantly affected desiccation tolerance. The reaction norms of desiccation tolerance displayed by the 13 ecotypes showed a substantial degree of variation in phenotypic plasticity. We observed differences in survival and fluorescence between rapid and slow drying events in juveniles. These same drying applications did not produce as large of a response for adult shoots (which consistently displayed high values). Some juvenile and protonemal ecotypes, such as those from the southwest United States, possessed higher innate tolerance to rapid drying, and greater resilience compared to ecotypes sourced from mesic localities in the United States. These results show a complex nuanced response to desiccation with ecotypes displaying a range of responses to desiccation reflecting both inherently different capacities for tolerating desiccation as well as variation in capacity for phenotypic plasticity. Our results suggest that we should expect few short-term effects of climate change due to high desiccation tolerance of adult shoots, but significant adverse long-term effects on colony establishment due to low tolerance of protonema and juvenile shoots. Further, we would recommend that future studies using mosses for habitat restoration of aridlands consider the desiccation tolerance capacity of individual ecotypes used for cultivation and later re-introduction. Understanding how mosses respond to desiccation is essential to interpret ecological roles, habitat preferences, selective pressures, and responses to climate change, and to estimate the potential effects of climate changes on bryophyte species and populations.
Understanding the effects of island shape and dispersal limitation on species assemblages is important for the conservation of bryophytes in fragmented landscapes. In order to explore the comparative contributions of dispersal limitation vs environmental filtering, island shape vs other island attributes to bryophyte species assemblages in fragmented landscapes, we investigated bryophyte flora and environmental variables (island shape, area, elevation, and isolation degree) of 71 islands in the Zhoushan Archipelago in the East China Sea. We used redundancy analysis, canonical correspondence analysis and generalized linear mixed models to explore comparative contributions of dispersal limitation vs environmental filtering, shape vs other explanatory variables to bryophyte species composition and species richness. Dispersal limitation independently accounted for 15% of the total variation in species composition, which was higher than environmental filtering (6.6%). When island shape was the only constraining explanatory variable, it explained 22.5% of the total species richness variation. Variance partitioning showed that island shape per se explained 3.8% of the total variation in species richness and 18.7% of the variation was confounded by island shape and other variables. Island shape combined with area and elevation was a good predictor of bryophyte species richness, independently explaining 40% of the total SR variation. Among twenty tested bryophyte categories, eighteen categories had positive relationships of their species richness with island shape irregularity, their species richness linearly increasing with island shape irregularity to varying extents. Island shape irregularity exerted a stronger effect on the species richness of acrocarpous mosses than that of pleurocarpous mosses. Therefore, dispersal limitation exerted significant effects on bryophyte species assemblages, and island shape imposed a significant and taxon-specific effect on bryophyte species richness. Our findings implied that a forest reserve with a high irregular shape is favourable for bryophyte conservation.
Introduction
Half a century since the creation of the International Association of Bryologists, we carried out a review to identify outstanding challenges and future perspectives in bryology. Specifically, we have identified 50 fundamental questions that are critical in advancing the discipline.
Methods
We have adapted a deep-rooted methodology of horizon scanning to identify key research foci. An initial pool of 258 questions was prepared by a multidisciplinary and international working group of 32 bryologists. A series of online surveys completed by a broader community of researchers in bryology, followed by quality-control steps implemented by the working group, were used to create a list of top-priority questions. This final list was restricted to 50 questions with a broad conceptual scope and answerable through realistic research approaches.
Key results
The top list of 50 fundamental questions was organised into four general topics: Bryophyte Biodiversity and Biogeography; Bryophyte Ecology, Physiology and Reproductive Biology; Bryophyte Conservation and Management; and Bryophyte Evolution and Systematics. These topics included 9, 19, 14 and 8 questions, respectively.
Conclusions
Although many of the research challenges identified are not newly conceived, our horizon-scanning exercise has established a significant foundation for future bryological research. We suggest analytical and conceptual strategies and novel developments for potential use in advancing the research agenda for bryology.
Purpose
Soil diaspore banks of bryophytes are poorly known in tundra grasslands, yet can be important for the maintenance of local bryophyte assemblages. We examined the effects of fertilization and grazing exclusion on above-ground bryophyte assemblages and soil diaspore banks in a tundra grassland.
Methods
We collected soil diaspore samples and recorded the cover of above-ground bryophytes from a full-factorial experiment with NPK fertilization and grazing exclusion treatments (a Nutrient Network site in NW Finland). Soil diaspore samples were germinated on trays in a greenhouse. We analyzed the compositions of diaspore bank assemblages and of above-ground assemblages and assessed their responses to the experimental treatments.
Results
The diaspore bank contained c. 50% of taxa found in above-ground assemblages; 26 bryophyte taxa germinated from the diaspore bank, while 40 taxa were found in the above-ground assemblages. These communities had distinct species compositions: the diaspore bank was dominated by Pohlia nutans, while above-ground assemblages were dominated by several species. NPK fertilization and grazing exclusion had negative effects on bryophyte richness and cover in above-ground assemblages, and weaker effects on these responses in the diaspore bank.
Conclusion
Soil diaspore banks comprise about half of the bryophyte taxa encountered in above-ground assemblages. Bryophyte diaspore banks are more buffered against nutrient enrichment and grazing exclusion than above-ground assemblages, suggesting that diaspore banks may enhance persistence and recovery of local bryophyte assemblages from environmental changes.
In the present review, we provide an updated account on the level of knowledge in island bryophyte biogeography. In the framework of the 50 most fundamental questions for present and future island biology research highlighted by Patiño et al. (2017), we summarize current knowledge in bryophyte island biogeography and outline main research avenues for the future in the field. We found that only about 50% of the key current questions in island biogeography have been addressed to some extent, at least once, in bryophytes. Even fundamental questions that have caught the attention of ecologists since more than one century, such as the species-area relationship, have only rarely been dealt with in bryophytes. The application of the Island Biogeography Theory therefore opens an avenue for research in bryology, and we discuss the most salient features, including species and community phylogenetics, biotic interactions, and invasion biology.
Climate change has and will have a dramatic impact on species ranges. Terrestrial species have accordingly already migrated poleward at a median speed of 16.9km per decade since the beginning of the industrial era. However, many species are not equipped to efficiently track the geographic changes of the conditions
matching their climatic niche, and are consequently prone to extinction. No less than about 20% of land plant species are hence threatened with extinction in the future, with major consequences on human food resources and health. In this context, Species distribution models (SDMs) offer an appealing framework to test the potential effects of climate change on species ranges. Like many biodiversity analyses, SDMs have traditionally been conducted at the species level. Cryptic speciation, which results in taxa that cannot rapidly be distinguished morphologically, but underwent divergent evolutionary histories, has been, however, increasingly reported, raising the question of whether SDMs should be fitted at the level of species (clade models), cryptic species or intraspecific lineages (subclade models). Projecting models through time further raises several questions and relies on several assumptions. In particular, projecting
species potential ranges in the future based on their niche inferred from extant climate conditions onto future climatic layers involves that (I) species climatic niches are conserved through time (niche
conservatism hypothesis) and that (ii) species are at equilibrium with their environment (i.e. their entire niche is filed), implying that they are not limited by their dispersal capacities, and are immediately able to
colonize any newly suitable area.
Focusing on bryophytes, whose ecophysiological characteristics, such as poikilohydry and reliance on rainfall for water uptake, make them excellent candidates to study the impact of climate change, but which exhibit reduced morphologies, raising concerns about broadly defined morphological species concepts, we address here the following questions:
1 At which taxonomic level should SDMs be computed? We compare the extent to which model projections generated at the level of species differ from those obtained for intraspecific lineages. Modelling at the level of infraspecific lineages raises a second issue, which is associated with the very small sample sizes that typically characterize molecularly defined lineages, that is: how can ensemble of small models calibrated from very small datasets be evaluated? In the light of analyses of niche overlap, we finally determine whether models should be calibrated at the level of the species or intraspecific lineages.
2 Is there climatic niche conservatism in bryophytes, and how does the tendency for closely related taxa to share the same climatic niche vary at increasing taxonomic depth?
3 To what extent will such efficient dispersers as bryophytes successfully track the shift of their suitable areas during the next decades? To address Q1, Ensembles of Small Models were evaluated by null models calibrated from randomly sampled presence points. We compared the extent of suitable area predicted by the projections of clade and subclade models. Niche overlaps were quantified using Schoener's D and Hellinger's I metrics, and the significance of these metrics in terms of niche conservatism or divergence was assessed by niche similarity tests. Combined predictions from subclade models contributed, on average, five times more than clade models to the total suitable area predicted by the combination of both subclade and clade models. Niche overlap was 0.71 on average, with evidence for niche conservatism in half of the species and no signal for niche divergence. Given the poor performance of models based on small datasets, we pragmatically suggest that, in the absence of evidence for niche divergence during diversification of closely related intraspecific
lineages, SDMs should be based on all available occurrence data at the species level. The hypothesis of climatic niche conservatism and its evolutionary ‘labillity’ was further tested at the level of an entire phylum of land plants, the Marchantiophyta, through analyses of the relationship between the spatial turnover of floras and macroclimatic variation. Phylogenetic turnover among floras was quantified
through πst statistics. πst-through-time profiles were generated at 1 myr intervals along the phylogenetic time-scale and were correlated with current geographic distance and macroclimatic variation with Mantel tests based on Moran spectral randomization to control for spatial autocorrelation. The contribution of macroclimatic variation to phylogenetic turnover was about four-times higher than that of geographic distance. The correlation between phylogenetic turnover and geographic distance rapidly decayed at increasing phylogenetic depth, whereas the relationship with macroclimatic variation remained constant until 100 myrs. Our analyses reveal that changes in the phylogenetic composition among liverwort floras across the globe are primarily shaped by macroclimatic variation. They demonstrate the relevance of macroclimatic niche conservatism for the assembly of liverwort floras over very large spatial and evolutionary time scales, which may explain why such a pervasive biodiversity pattern as the increase of species richness towards the tropics also applies to organisms with high dispersal capacities.
Finally, we developed a newly designed spatially-explicit model of dispersal by wind in the context of changing climate and presented an example of application in the case of the European flora. A grid of pixel specific environmental conditions and dispersal kernels, combining information on species dispersal traits, local wind conditions, as well as landscape features affecting dispersal by wind, was generated and used as input in simulations of species dispersal in the landscape under changing climate conditions. In European
bryophytes, the median ratios between predicted range loss vs expansion by 2050 across species and climate change scenarios ranged from 1.6 to 3.3 when only shifts in climatic suitability were considered, but increased to 34.7–96.8 when species dispersal abilities were added to our models. This highlights the importance of accounting for dispersal restrictions when projecting future distribution ranges and suggests that even highly dispersive organisms like bryophytes are not equipped to fully track the rates of ongoing climate change in the course of the next decades.
Bryophytes are potent metal absorbers, thriving well on heavy metal (HM)-polluted soils. Mechanisms controlling uptake, compartmentalization and impacts of HMs on bryophytes life cycle are largely unknown. The current study is an effort to decipher mechanisms of nickel (Ni) excess-induced effects on the phenological events of two bryophytes, Asterella wallichiana and Plagiochasma apendiculatum growing in natural habitats. Observations revealed Ni-excess induced negative impacts on abundance, frequency of occurrence of reproductive organs, population viability and morphological traits, spore viability and physiological attributes of both the liverworts. Results led us conclude that P . appendiculatum survived better with the lowest impact on its life cycle events than A . wallichiana under Ni excess in natural habitats. Our findings collectively provide insights into the previously unknown mechanisms of Ni-induced responses in liverworts with respect to phenological attributes, as well as demonstrate the potential of P . appendiculatum to survive better in Ni excess habitats.
Die neue Literaturzusammenstellung berücksichtigt hauptsächlich aktuelle bryologische Fachbücher und Fachartikel zu Studien und Fundberichten über Moose in Mitteleuropa und angrenzender Regionen, überwiegend Jahr 2019. Für aktuelle Veröffentlichungen mit Fokus auf Taxonomie und Systematik sei auf den Beitrag "Taxonomische und nomenklatorische Neuerungen-Moose, Vierte Folge" von Markus K. Meier in diesem Herzogiella-Heft verwiesen. Für Hinweise auf entsprechende Publikationen für die vierte Folge dieser Serie sind wir wie immer dankbar.
Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, sigmas pound 14 m, and moderate pollen flow, 70 m pound sigmap pound 140 m.
Climatic fluctuations during the Last Glacial Maximum (LGM) exerted a profound influence on biodiversity patterns, but their impact on bryophytes, the second most diverse group of land plants, has been poorly documented. Approximate Bayesian computations based on coalescent simulations showed that the post‐glacial assembly of European bryophytes involves a complex history from multiple sources. The contribution of allochthonous migrants was 95–100% of expanding populations in about half of the 15 investigated species, which is consistent with the globally balanced genetic diversities and extremely low divergence observed among biogeographical regions. Such a substantial contribution of allochthonous migrants in the post‐glacial assembly of Europe is unparalleled in other plants and animals. The limited role of northern micro‐refugia, which was unexpected based on bryophyte life‐history traits, and of southern refugia, is consistent with recent palaeontological evidence that LGM climates in Eurasia were much colder and drier than what palaeoclimatic models predict.
Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%–65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long‐distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long‐distance dispersal capacities, might be seen as a safe‐site strategy, forcing spores to land in appropriate (micro‐) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.
Criticism has been levelled at climate-change-induced forecasts of species range shifts that do not account explicitly for complex population dynamics. The relative importance of such dynamics under climate change is, however, undetermined because direct tests comparing the performance of demographic models vs. simpler ecological niche models are still lacking owing to difficulties in evaluating forecasts using real-world data. We provide the first comparison of the skill of coupled ecological-niche-population models and ecological niche models in predicting documented shifts in the ranges of 20 British breeding bird species across a 40-year period. Forecasts from models calibrated with data centred on 1970 were evaluated using data centred on 2010. We found that more complex coupled ecological-niche-population models (that account for dispersal and metapopulation dynamics) tend to have higher predictive accuracy in forecasting species range shifts than structurally simpler models that only account for variation in climate. However, these better forecasts are achieved only if ecological responses to climate change are simulated without static snapshots of historic land use, taken at a single point in time. In contrast, including both static land use and dynamic climate variables in simpler ecological niche models improve forecasts of observed range shifts. Despite being less skilful at predicting range changes at the grid-cell level, ecological niche models do as well, or better, than more complex models at predicting the magnitude of relative change in range size. Therefore, ecological niche models can provide a reasonable first approximation of the magnitude of species' potential range shifts, especially when more detailed data are lacking on dispersal dynamics, demographic processes underpinning population performance, and change in land cover.
1. Dispersal ecology is a broad topical discipline that tackles important conceptual and applied issues, such as the study of the ability of plants to transmit their propagules across fragmented and managed landscapes.
2. The relevance of dispersal for plant populations is threefold because: (i) dispersal processes scale from genes and individuals that disperse (or produce propagules to be dispersed) to population dynamics and both local and regional distribution patterns; (ii) by dispersing propagules or individu- als and the genes they carry, dispersal inherently links demographic and genetic dynamics across the landscape; and (iii) dispersal elicits key ecological and evolutionary processes that sustain biodiver- sity, such as species assembly in species-rich communities. The steady improvement of tracking devices and molecular tools that trace the movement or infer provenance of organisms and the press- ing need to address conservation issues have expanded the disciplinary boundaries of dispersal ecology.
3. The discussion on the main advances on and challenges for dispersal ecology was the main moti- vation for the organization of a thematic topic session entitled Dispersal processes driving plant movement: challenges for understanding and predicting range shifts in a changing world at the Annual Meeting of the British Ecological Society (2015, Edinburgh). This session brought together researchers with different types of expertise and interests on dispersal processes and their contribu- tions are now included in this special feature together with a few additional articles.
4. Synthesis. Overall, this special feature illustrates that dispersal ecology spans a broad range of research topics by integrating eight contributions that cover key aspects of this discipline: from con- ceptual and methodological advances to the study of the ecological and evolutionary outcomes.
The impact of variation in mating system on genetic diversity is a well-debated topic in evolutionary biology. The diploid sexual race of Cyrtomium falcatum (Japanese holly fern) shows mating system variation, i.e., it displays two different types of sexual expression (gametangia formation) in gametophytes: mixed (M) type and separate (S) type. We examined whether there is variation in the selfing rate among populations of this species, and evaluated the relationship between mating system, genetic diversity and effective population size using microsatellites. In this study, we developed eight new microsatellite markers and evaluated genetic diversity and structure of seven populations (four M-type and three S-type). Past effective population sizes (Ne) were inferred using Approximate Bayesian computation (ABC). The values of fixation index (FIS), allelic richness (AR) and gene diversity (h) differed significantly between the M-type (FIS: 0.626, AR: 1.999, h: 0.152) and the S-type (FIS: 0.208, AR: 2.718, h: 0.367) populations (when admixed individuals were removed from two populations). Although evidence of past bottleneck events was detected in all populations by ABC, the current Ne of the M-type populations was about a third of that of the S-type populations. These results suggest that the M-type populations have experienced more frequent bottlenecks, which could be related to their higher colonization ability via gametophytic selfing. Although high population differentiation among populations was detected (FST = 0.581, F’ST = 0.739), there was no clear genetic differentiation between the M- and S-types. Instead, significant isolation by distance was detected among all populations. These results suggest that mating system variation in this species is generated by the selection for single spore colonization during local extinction and recolonization events and there is no genetic structure due to mating system.
Metapopulation dynamics have been used to explain bryophyte dispersal patterns and they predict that population abundances vary with the spatial distribution of habitat and with species traits. However, results from stand and landscape studies are contradictory as both distance dependant and independent patterns have been found. These studies have typically included only a few species, which limits inter species comparison. It is the time to investigate bryophyte dispersal at the metacommunity scale. 2.We studied bryophyte dispersal patterns in a system made up of burned matrices containing unburned residual forest patches. The importance of short versus long distance dispersal was examined by comparing extant and propagule rain communities in residual forest patches of three fire sites using both species and life strategies. 3.Extant and propagule rain communities were distinct. Several propagule rain species, of all life strategies, did not originate from the closest extant community, suggesting that regional dispersal events are important, following the inverse isolation hypothesis. 4.Temporal, spatial and structural characteristics of the environment had a greater influence on dispersal than distance, which only influenced similarity patterns at the regional scale, highlighting the importance of propagule source attributes for the conservation of bryophyte metacommunities. 5.Synthesis. Long distance dispersal may be the rule and not the exception in bryophyte metacommunities. Therefore bryophyte metacommunity dynamics depend on several dispersal scales, and residual forest patches can contribute both to local and regional diaspore clouds. Species’ environmental tolerance during establishment and their ability to produce copious amounts of spores may be more important filters in bryophyte metacommunity dynamics than dispersal distance. This article is protected by copyright. All rights reserved.
Increasing biodiversity loss due to climate change is one of the most vital challenges of the 21(st) century. To anticipate and mitigate biodiversity loss, models are needed that reliably project species' range dynamics and extinction risks. Recently, several new approaches to model range dynamics have been developed to supplement correlative species distribution models (SDMs), but applications clearly lag behind model development. Indeed, no comparative analysis has been performed to evaluate their performance. Here, we build on process-based, simulated data for benchmarking five range (dynamic) models of varying complexity including classical SDMs, SDMs coupled with simple dispersal or more complex population dynamic models (SDM hybrids), and a hierarchical Bayesian process-based dynamic range model (DRM). We specifically test the effects of demographic and community processes on model predictive performance. Under current climate, DRMs performed best, although only marginally. Under climate change, predictive performance varied considerably, with no clear winners. Yet, all range dynamic models improved predictions under climate change substantially compared to purely correlative SDMs, and the population dynamic models also predicted reasonable extinction risks for most scenarios. When benchmarking data were simulated with more complex demographic and community processes, simple SDM hybrids including only dispersal often proved most reliable. Finally, we found that structural decisions during model building can have great impact on model accuracy, but prior system knowledge on important processes can reduce these uncertainties considerably. Our results reassure the clear merit in using dynamic approaches for modelling species' response to climate change but also emphasise several needs for further model and data improvement. We propose and discuss perspectives for improving range projections through combination of multiple models and for making these approaches operational for large numbers of species. This article is protected by copyright. All rights reserved.
Patterns of genetic variation and spatial genetic structure (SGS) were investigated in Crossocalyx hellerianus, a strictly epixylic dioicous liverwort (Scapaniaceae s.l., Marchantiophyta). Studied populations were located in Fennoscandia and Central Europe, with localities differing in availability of substrate and the population connectivity, and their populations consequently different in size, density, and prevailing reproductive mode. A set of nine polymorphic microsatellites was successfully developed and used. Identical individuals were only found within populations. Especially in large populations, the majority of the individuals were genetically unique. Resampled number of genotypes, mean number of observed alleles per locus after rarefaction, and Nei's gene diversity in large populations reached high values and ranged between 4.41-4.97, 3.13-4.45, and 0.94-0.99, respectively. On the contrary, the values in small populations were lower and ranged between 1.00-4.42, 1.00-2.73, and 0.00-0.95, respectively. As expected, large populations were found to be more genetically diverse than small populations but relatively big diversity of genotypes was also found in small populations. This indicated that even small populations are important sources of genetic variation in bryophytes and processes causing loss of genetic variation might be compensated by other sources of variability, of which somatic mutations might play an important role. The presence of SGS was discovered in all populations. Large populations possessed less SGS, with individuals showing a pronounced decrease in kinship over 50 cm of distance. Apparent SGS of small populations even at distances up to 16 meters suggests the aggregation of similar genotypes, caused predominantly by the deposition of asexually formed gemmae. Although no strong kinship was detectable at the distances over 16 meters in both small and large populations, identical genotypes were occasionally detected at longer distances (20-80 m), suggesting effective dispersal of asexual propagules.
The perceived low levels of genetic diversity, poor interspecific competitive and defensive ability, and loss of dispersal capacities of insular lineages have driven the view that oceanic islands are evolutionary dead ends. Focusing on the Atlantic bryophyte flora distributed across the archipelagos of the Azores, Madeira, the Canary Islands, western Europe, and northwestern Africa, we used an integrative approach with species distribution modeling and population genetic analyses based on approximate Bayesian computation to determine whether this view applies to organisms with inherent high dispersal capacities. Genetic diversity was found to be higher in island than in continental populations, contributing to mounting evidence that, contrary to theoretical expectations, island populations are not necessarily genetically depauperate. Patterns of genetic variation among island and continental populations consistently fitted those simulated under a scenario of de novo foundation of continental populations from insular ancestors better than those expected if islands would represent a sink or a refugium of continental biodiversity. We therefore suggest that the northeastern Atlantic archipelagos have played a key role as a stepping-stone for transoceanic migrants. Our results challenge the traditional notion that oceanic islands are the end of the colonization road and illustrate the significant role of oceanic islands as reservoirs of novel biodiversity for the assembly of continental floras.
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Most mosses have xerochastic dispersal (i.e., they open their capsules when conditions are dry), which is thought to favor long-distance dispersal. However, there are several species that use a hygrochastic strategy: spores are dispersed when conditions are wet. The significance of this strategy in the Mediterranean region is unknown. In this study, we explored whether ultrastructural features related to differences in spore resistance may explain these different strategies of spore dispersal. To this end, we examined the ultrastructural features of the spores of seven closely related species in the moss genus Orthotrichum. These species all grow as epiphytes in sub-Mediterranean forests, and the group includes both xerochastic and hygrochastic members. First, we found that the spore wall layers exhibit several features previously undescribed in mosses. Second, we discovered that there are only subtle differences in spore ultrastructure with regards to spore wall thickness, the degree of plastid development, or the storage substances used. We suggest that the hygrochastic dispersal in mosses from Mediterranean environments might be related to a safe-site strategy, rather than to drought avoidance, and we underscore the necessity of conducting spore ultrastructural studies on a greater number of bryophyte species.
Computer simulations of genetic data are increasingly used to investigate the impact of complex historical scenarios on patterns of genetic variation. Yet, in most empirical studies, relatively large portions of species ranges are often treated as panmictic populations, ignoring the underlying spatial context. In some cases, however, a more accurate spatial model is required. We use a spatially explicit model of coalescence (easily constructed by overlaying a 2-dimensional grid on maps displaying an estimate of past and current species ranges) to evaluate the potential of several summary statistics to differentiate three typical phylogeographic scenarios. We first explore the variation of each summary statistic within the boundaries of each phylogeographic scenario, and identify those that appear most promising for a comparison of historical scenarios and/or to infer historical parameters. We then combine a selected set of summary statistics in a single chi-square statistic and evaluate whether it can be used to differentiate past geographic fragmentation or range expansion from a simple scenario of isolation by distance. We also investigate the benefits of using a spatially explicit model by comparing its performance to alternative models that are less spatially explicit (lower geographic resolution). The results identify conditions in which each summary statistic is useful to infer the evolution of a species range, and allow us to validate our spatially explicit model of coalescence and our procedure to compare simulated and observed sequence data. We also provide a detailed description of the spatially explicit model of coalescence used, which is currently lacking.
Background and AimsClimate change is expected to alter the geographic range of many plant species dramatically. Predicting this response will be critical to managing the conservation of plant resources and the effects of invasive species. The aim of this study was to predict the response of temperate homosporous ferns to climate change.Methods
Genetic diversity and changes in distribution range were inferred for the diploid rock fern Asplenium fontanum along a South-North transect, extending from its putative last glacial maximum (LGM) refugia in southern France towards southern Germany and eastern-central France. This study reconciles observations from distribution models and phylogeographic analyses derived from plastid and nuclear diversity.Key ResultsGenetic diversity distribution and niche modelling propose that genetic diversity accumulates in the LGM climate refugium in southern France with the formation of a diversity gradient reflecting a slow, post-LGM range expansion towards the current distribution range. Evidence supports the fern's preference for outcrossing, contradicting the expectation that homosporous ferns would populate new sites by single-spore colonization. Prediction of climate and distribution range change suggests that a dramatic loss of range and genetic diversity in this fern is possible. The observed migration is best described by the phalanx expansion model.Conclusions
The results suggest that homosporous ferns reproducing preferentially by outcrossing accumulate genetic diversity primarily in LGM climate refugia and may be threatened if these areas disappear due to global climate change.
Neutral community models have shown that limited migration can have a pervasive influence on the taxonomic composition of local communities even when all individuals are assumed of equivalent ecological fitness. Notably, the spatially implicit neutral theory yields a single parameter I for the immigration-drift equilibrium in a local community. In the case of plants, seed dispersal is considered as a defining moment of the immigration process and has attracted empirical and theoretical work. In this paper, we consider a version of the immigration parameter I depending on dispersal limitation from the neighbourhood of a community. Seed dispersal distance is alternatively modelled using a distribution that decreases quickly in the tails (thin-tailed Gaussian kernel) and another that enhances the chance of dispersal events over very long distances (heavily fat-tailed Cauchy kernel). Our analysis highlights two contrasting situations, where I is either mainly sensitive to community size (related to ecological drift) under the heavily fat-tailed kernel or mainly sensitive to dispersal distance under the thin-tailed kernel. We review dispersal distances of rainforest trees from field studies and assess the consistency between published estimates of I based on spatially-implicit models and the predictions of the kernel-based model in tropical forest plots. Most estimates of I were derived from large plots (10-50 ha) and were too large to be accounted for by a Cauchy kernel. Conversely, a fraction of the estimates based on multiple smaller plots (1 ha) appeared too small to be consistent with reported ranges of dispersal distances in tropical forests. Very large estimates may reflect within-plot habitat heterogeneity or estimation problems, while the smallest estimates likely imply other factors inhibiting migration beyond dispersal limitation. Our study underscores the need for interpreting I as an integrative index of migration limitation which, besides the limited seed dispersal, possibly includes habitat filtering or fragmentation.
It is well-known that many species with small diaspores can disperse far during extended temporal scales (many years). However, studies on short temporal scales usually only cover short distances (in, e.g., bryophytes up to 15 m). By using a novel experimental design, studying the realized dispersal, we extend this range by almost two orders of magnitude. We recorded establishment of the fast-growing moss Discelium nudum on introduced suitable substrates, placed around a translocated, sporulating mother colony. Around 2,000 pots with acidic clay were placed at different distances between 5 m and 600 m, in four directions, on a raised bog, with increased pot numbers with distance. The experiment was set up in April-May and the realized dispersal (number of colonized pots) was recorded in September. Close to the mother colony (up to 10 m), the mean colonization rates (ratio of colonized pots) exceeded 50%. At distances between 10 and 50 m colonization dropped sharply, but beyond 50 m the mean colonization rates stabilized and hardly changed (1-3%). The estimated density of spores causing establishments at the further distances (2-6 spores/m²) was realistic when compared to the estimated spore output from the central colonies. Our study supports calculations from earlier studies, limited to short distances, that a majority of the spores disperse beyond the nearest vicinity of a source. The even colonization pattern at further distances raises interesting questions about under what conditions spores are transported and deposited. However, it is clear that regular establishment is likely at the km-scale for this and many other species with similar spore output and dispersal mechanism.
Abstract spagedi version 1.0 is a software primarily designed to characterize the spatial genetic structure of mapped individuals or populations using genotype data of codominant markers. It computes various statistics describing genetic relatedness or differentiation between individuals or populations by pairwise comparisons and tests their significance by appropriate numerical resampling. spagedi is useful for: (i) detecting isolation by distance within or among populations and estimating gene dispersal parameters; (ii) assessing genetic relatedness between individuals and its actual variance, a parameter of interest for marker based inferences of quantitative inheritance; (iii) assessing genetic differentiation among populations, including the case of haploids or autopolyploids.
Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, sigmas pound 14 m, and moderate pollen flow, 70 m pound sigmap pound 140 m.
Bryophytes include about 20,000 species characterized by their poikilohydric condition, high long-distance dispersal capacities, and cold tolerance. Despite these specific life-history traits, large-scale biogeographic patterns in bryophytes are consistent with those observed in other groups, wherein they have been interpreted in terms of historical factors. Comparative phylogeographic analyses in bryophytes and angiosperms suggest, however, that spatially congruent patterns may not necessarily arise from common processes. This is best illustrated by the strikingly lower rates of endemism at all taxonomic and spatial scales in bryophytes due to their failure to diversify in-situ and the rapidity at which they enlarge their distribution range. In particular, the striking transoceanic disjunctions that are typical for many bryophyte species and their low community turnover at broad geographic scales both point to the higher capacities of bryophytes for long-distance dispersal than angiosperms. Such high long-distance dispersal capacities are reflected in the lower spatial genetic structure of bryophytes as compared to angiosperms at large geographic scales. This explains why, as opposed to the expectations of MacArthur & Wilson's model, bryophyte species richness is not necessarily lower on islands than on continents, suggesting that community assembly is more constrained by ecological filtering than dispersal limitations in bryophytes. The low relevance of historical factors for global patterns of bryophyte species richness has contributed to the idea that, as opposed to the predictions of one of the most general rules in ecology, bryophyte species richness does not decrease with latitude due to a strong tropical niche conservatism. Recent evidence for the existence of a latitudinal species richness gradient in bryophytes raises, however, the question of why bryophytes diversified faster in the tropics. This and other avenues of research in bryophyte biogeography are discussed.
Analyses of fine-scale and macrogeographic genetic structure in plant populations provide an initial indication of how gene flow, natural selection, and genetic drift may collectively influence the distribution of genetic variation. The objective of our study is to evaluate the spatial dispersion of alleles within and among subpopulations of a tropical shrub, Psychotria officinalis (Rubiaceae), in a lowland wet forest in Costa Rica. This insect-pollinated, self-incompatible understory plant is dispersed primarily by birds, some species of which drop the seeds immediately while others transport seeds away from the parent plant. Thus, pollination should promote gene flow while at least one type of seed dispersal agent might restrict gene flow. Sampling from five subpopulations in undisturbed wet forest at Estación Biologíca La Selva, Costa Rica, we used electrophoretically detected isozyme markers to examine the spatial scale of genetic structure. Our goals are: 1) describe genetic diversity of each of the five subpopulations of Psychotria officinalis sampled within a contiguous wet tropical forest; 2) evaluate fine-scale genetic structure of adults of P. officinalis within a single 2.25-ha mapped plot; and 3) estimate genetic structure of P. officinalis using data from five subpopulations located up to 2 km apart. Using estimates of coancestry, statistical analyses reveal significant positive genetic correlations between individuals on a scale of 5 m but no significant genetic relatedness beyond that interplant distance within the studied subpopulation. Multilocus estimates of genetic differentiation among subpopulations were low, but significant (Fst = 0.095). Significant Fst estimates were largely attributable to a single locus (Lap-2). Thus, multilocus estimates of Fst may be influenced by microgeographic selection. If true, then the observed levels of IBD may be overestimates.
Understanding the complete dispersal process is important for making realistic predictions of species distributions, but mechanisms for diaspore release in wind-dispersed species are often unknown. However, diaspore release under conditions that increase the probability of longer dispersal distances and mechanisms that extend dispersal events in time may have evolutionary advantages. We quantified air humidity thresholds regulating spore release in the moss Brachythecium rutabulum. We also investigated the prevailing micrometeorological conditions when these thresholds occur in nature and how they affect dispersal distances up to 100 m, using a mechanistic dispersal model. We show that moss spores were mainly released when the peristome teeth were opening, as relative air humidity (RH) decreased from high values to relatively low (mainly between 90% and 75% RH). This most often occurred in the morning, when wind speeds were relatively low. Surprisingly, the model predicted that an equally high proportion of the spores would travel distances beyond 100 m (horizontally) when released in the wind conditions prevailing during events of RH decrease in the morning, that lead to peristome opening, as in the highest wind speeds. Moreover, a higher proportion of the spores reached high altitudes when released at the lower wind speeds during the morning compared to the higher speeds later in the day, indicating a possibility for extended dispersal distances when released in the morning. Dispersal in the morning is enhanced by a combination of a more unstable atmospheric surface layer that promotes vertical dispersal, and a lower wind speed that decreases the spore deposition probability onto the ground, compared to later in the day. Our study demonstrates an active spore release mechanism in response to diurnally changing air humidity. The mechanism may promote longer dispersal distances, because of enhanced vertical dispersal and because spores being released in the morning have more time to travel before the wind calms down at night. The mechanism also leads to a prolonged dispersal period over the season, which may be viewed as a risk spreading in time that ultimately also leads to a higher diversity of establishment conditions, dispersal distances and directions. © 2015 The Authors. Functional Ecology
Wind is the main dispersal agent for a wide array of species and for these species the environmental conditions under which diaspores are released can potentially modify the dispersal kernel substantially. Little is known about how bryophytes regulate spore release, but conditions affecting peristome movements and vibration of the seta may be important. We modelled airborne spore dispersal of the bryophyte species Discelium nudum (spore diameter 25 μm), in four different release scenarios, using a Lagrangian stochastic dispersion model and meteorological data. We tested the model predictions against experimental data on colonization success at five distances (5, 10, 30, 50 and 100 m) and eight directions from a translocated point source during seven two-day periods. The model predictions were generally successful in describing the observed colonization patterns, especially beyond 10 m. In the laboratory we established spore release thresholds; horizontal wind speed sd > 0.25 m s−1 induced the seta to vibrate and in relative humidity < 75% the peristome was open. Our dispersal model predicts that the proportion of spores dispersing beyond 100 m is almost twice as large if the spores are released under turbulent conditions than under more stable conditions. However, including release thresholds improved the fit of the model to the colonization data only minimally, with roughly the same amount of variation explained by the most constrained scenario (assuming both vibration of the seta and an open peristome) and the scenario assuming random release. Model predictions under realised experimental conditions suggest that we had a low statistical power to rank the release scenarios due to the lack of measurements of the absolute rate of spore release. Our results hint at the importance of release conditions, but also highlight the challenges in dispersal experiments intended for validating mechanistic dispersal models.
Abstract In this study, we analyzed the genetic structure and phylogeography of Sphaeropteris brunoniana from China and Laos. Combining cpDNA trnL-trnF and atpB-rbcL sequence variations, five haplotypes were identified from the 10 investigated populations. Moderate haplotype diversity (h= 0.66580) and low nucleotide diversity (π= 0.23 × 10−3) were detected. The S. brunoniana in Yunnan region had much higher genetic diversity (h= 0.60195, π= 0.35 × 10−3) than that of Hainan–Laos (h= 0.00000, π= 0.00). A high level of genetic differentiation (94.74%) between the two regions was revealed by amova. Nested clade analysis identified two major clusters of the five haplotypes, one clade in the Yunnan region and the other in Hainan–Laos. The analysis indicated that restricted gene flow with isolation by distance and allopatric fragmentation were likely the major processes that shaped the spatial distribution of the haplotypes. The isolated distribution of clades implied the emergence of independent refugia of this species in each region during Quaternary glaciations. The Yunnan populations frequently contained an ancestral haplotype, and most of them harbored other descendent haplotypes. Based on the distribution pattern of haplotypes and the nested clade analysis results, the Yunnan region potentially had several refugia of this species during glacial periods, whereas the Hainan populations were probable new colonizations.
While patterns of spore dispersal from single sources at short distances are fairly well known, information about ‘spore rain’ from numerous sources and at larger spatial scales is generally lacking. In this study, I sampled spore rain using a novel method consisting of 0.25–0.5 m2 cotton cloth traps at nine sites in the boreo-nemoral vegetation zone in eastern Sweden during two seasons, using Sphagnum spores as a model. Traps were located in various landscapes (mainland, islands). Additional trapping was done in an arctic area (Svalbard) without spore production. Spore densities were tested against distance from the nearest source and area of sources (open peatlands) within different radii around each site (5, 10, 20, 50, 100, 200, 300, 400 km). The cloth method appeared reliable when accounting for precipitation losses, retaining approximately 20–60% of the spores under the recorded amounts of precipitation. Estimated spore densities ranged from 6 million m−2 and season within a large area source, via regional deposition of 50 000–240 000 spores m−2, down to 1000 m−2 at Svalbard. Spore rain for all sites was strongly related to distance from the nearest source, but when excluding samples taken within a source peatland, the amount of sources within 200 km was most important. Spores were larger at isolated island sites, indicating that a higher proportion originated from distant, humid areas. Immense amounts of Sphagnum spores are dispersed across regional distances annually in boreal areas, explaining the success of the genus to colonise nutrient poor wetlands. The detectable deposition at Svalbard indicates that about 1% of the regional spore rain has a trans- or intercontinental origin. The regional spore rain, originating from numerous sources in the landscape, is probably valid for most organisms with small diaspores and provides a useful insight in ecology, habitat restoration and conservation planning.
1.Adequately describing the dispersal mechanisms of a species is important for understanding and predicting its distribution dynamics in space and time. For wind-dispersed species, the transportation of airborne propagules is comparatively well studied, while the mechanisms triggering propagule release are poorly understood, especially for cryptogams. 2.We investigated the effect of wind speed and turbulence on spore release in the moss Atrichum undulatum in a wind tunnel. Specifically, we measured the amount of spores released from sporophytes when exposed to different wind speeds, in high and low turbulence, using a particle counter. We also related spore release to variation in vibrations of the sporophyte, and investigated how the vibrations were affected by wind speed, turbulence and sporophyte length (here including capsule, seta and the top part of the shoot). 3.We show that in high turbulence, the amount of spores released increased with increasing wind speed, while in low turbulence it did not, within the wind speed range 0.8–4.3 m/s. However, there was a threshold in wind speed (~2.5–3 m/s) before large amounts of spores started to be released in turbulent flow, which coincided with incipient vibrations of the sporophyte. Thresholds in wind variation, rather than average wind speed, seemed to initiate sporophyte vibrations. The vibration threshold increased with decreasing sporophyte length. 4.The deposition of spores near the source decreased with increasing wind variation during the time of their release, based on simulated spore deposition from another study of moss dispersal. 5.Synthesis. We suggest that vibration of moss sporophytes is an important mechanism to regulate spore release, and that turbulence and sporophyte length regulate the onset of sporophyte vibration. Spore release thresholds affect dispersal distances and have implications for our understanding and predictions of species distribution patterns, population dynamics and persistence. The mechanisms of this phase of the dispersal process are also important to explore for other species, since there may be a substantial variation depending on the species’ different traits. This article is protected by copyright. All rights reserved.
Effective dispersal is crucial to species inhabiting transient substrates in order for them to be able to persist in a landscape. Bryophytes, pteridophytes, lichens and fungi all have wind-dispersed small diaspores and can be efficiently dispersed if their diaspores reach air masses above canopy height. However, empirical data on dispersal over landscape scales are scarce. We investigated how the colonization of an acrocarpous clay-inhabiting pioneer moss, Discelium nudum, varied between sites that differed in connectivity to potential dispersal sources at spatial scales from 1 to 20 km in a region in northern Sweden. We recorded the colonization on ˜25 introduced clay heaps at each of 14 experimental sites some months after the dispersal period. The colonization rate ranged from 0–82% and had a statistically significant relationship with a proxy for potential habitats (amount of clay-dominated soil) in a buffer of 20 km radius surrounding the experimental sites (and also weakly with the amount of substrate in a 10 km buffer). There were no significant relationships between colonization rate and connectivity at smaller scales (1 and 5 km). We made a rough estimate of the number of spores available for dispersal in a landscape, given the amount of clay-dominated soil, by recording the number of Discelium nudum colonies in two 25 × 25 km landscapes. The estimated available spore numbers in the different 20 km buffers were of the same order of magnitude as the deposition densities at the experimental sites calculated from the colonization rates. The results suggest that the spores of species with scattered occurrences and small diaspores (25 μm) in open landscapes can be deposited over extensive areas, at rates high enough to drive colonization patterns. This also implies that regional connectivity may be more important than local connectivity for these kinds of species.
It is well accepted that the shape of the dispersal kernel, especially its tail, has a substantial effect on the genetic structure of species. Theory predicts that dispersal by fat-tailed kernels reshuffles genetic material, and thus, preserves genetic diversity during colonization. Moreover, if efficient long-distance dispersal is coupled with random colonization, an inverse isolation effect is predicted to develop in which increasing genetic diversity per colonizer is expected with increasing distance from a genetically variable source. By contrast, increasing isolation leads to decreasing genetic diversity when dispersal is via thin-tailed kernels. Here, we use a well-established model group for dispersal biology (peat mosses: genus Sphagnum) with a fat-tailed dispersal kernel, and the natural laboratory of the Stockholm archipelago to study the validity of the inverse isolation hypothesis in spore-dispersed plants in island colonization. Population genetic structure of three species (Sphagnum fallax, Sphagnum fimbriatum and Sphagnum palustre) with contrasting life histories and ploidy levels were investigated on a set of islands using microsatellites. Our data show (ϕst ', amova, IBD) that dispersal of the two most abundant species can be well approximated by a random colonization model. We find that genetic diversity per colonizer on islands increases with distance from the mainland for S. fallax and S. fimbriatum. By contrast, S. palustre deviates from this pattern, owing to its restricted distribution in the region, affecting its source pool strength. Therefore, the inverse isolation effect appears to hold in natural populations of peat mosses and, likely, in other organisms with small diaspores.
Aim To test whether species richness of Sphagnum mosses on islands in a land uplift archipelago is related to island age, area or connectivity, and whether the frequency of different species can be predicted by their life history and autecology.
Location The northern Stockholm archipelago in the Baltic Sea, east-central Sweden, with a current land uplift rate of 4.4 mm year−1.
Methods We sampled 17 islands differing in area (0.55–55 ha), height (3.6–18 m, representing c. 800–4000 years of age) and distance from mainland (1.6–41 km). For each Sphagnum patch we measured area, height above sea level, horizontal distance from the shore and shading from vascular plants. Factors affecting island species richness, species frequency and habitats on the islands were tested by stepwise regressions. Species frequency was tested on nine life history and autecological variables, including estimated abundance and spore output on the mainland, habitat preference and distribution.
Results We recorded 500 patches of 19 Sphagnum species, distributed in 83 rock pools on 14 islands. Island species richness correlated positively with island area and with degree of shelter by surrounding islands, while distance from the mainland, connectivity, height or age did not add to the model. Species frequency (number of colonized islands and rock pools) was mainly predicted by spore output on the mainland and by habitat preference (swamp forest species were more frequent than others), while spore size, for example, did not add to the model. Species differed in mean height above and horizontal distance from the shore, area of occupied rock pools and in the degree of shading of patches. The mean horizontal distance from the shore and the area of occupied rock pools correlated positively with the normal growth position above the water table among species. Spore capsules were found in only 2% of patches, mostly in the bisexual Sphagnum fimbriatum.
Main conclusions The presence of Sphagnum in the Stockholm archipelago seems to be governed by regional spore production and habitat demands. Sphagnum does not appear to be dispersal limited at distances up to 40 km and time spans of centuries. Species with a high regional spore output have had a higher colonization rate, which, together with the rarity of spore capsules on the islands, indicate the mainland as a source for colonization rather than dispersal among islands. Swamp forest species seem more tolerant to the island conditions (summer droughts and some salt spray) than open mire species. The different distances from the sea occupied by the species indicate a slow, continuous succession and species replacement towards the island interior as islands are being uplifted and thus expand in area. This partly explains why larger islands harbour more species. Our results thus support some of the island biogeographical theories related to the species–area relationship.
The construction of the world's largest hydroelectric scheme across the Yangtze River, the Three Gorges Dams (TGD), in the centre of a southern-central Chinese biodiversity hot spot, the Three Gorges Reservoir Area (TGRA), has attracted international concern and conservation action. To examine whether landscape changes to date have impacted regional flora, and to establish long-term monitoring baselines, we assessed the distribution and dynamics of an endangered and TGRA endemic fern, Adiantum reniforme var. sinense. For eight nuclear microsatellites, high levels of genetic diversity (HE = 0.653–0.781) and slightly elevated inbreeding (FIS = 0.077–0.197) were found across 13 surveyed populations. The population history of this fern is characterized by a balance of gene flow and genetic drift, where historical dispersal, inferred from coalescent (F = 0.129) and genetic differentiation (FST = 0.094 and RST = 0.180) approaches, is moderate, reflecting an isolation by distance relationship. Importantly, most populations exhibited mutation-drift disequilibrium, suggesting a recent population decline, which is congruent with the known demographic history of the species following dam-related activities. Based on these results, populations of A. reniforme var. sinense are expected to lose genetic diversity and increase genetic structure as dam-related activities decrease size and increase genetic isolation of remnants.
I made a dispersal experiment with six Sphagnum (peat moss) species, representing a wide range of spore and capsule sizes. Spore deposition was recorded at nine distances up to 3.2 m during two four-day periods with sunny conditions in July and August.
Deposition patterns in all species fitted well to the inverse power law (deposition per unit area proportional to distanceb), with rates of decline b ranging from −1.84 to −2.35 among species (R2>0.99). However, even when these curves are extended to infinity for the four species with b<−2, they fail to explain all spores being dispersed (e.g. only 11% in S. squarrosum). Difference in rates of decline b between the periods, despite similar horizontal wind speeds and directions, indicates the importance of thermal updrafts. Spore capsule diameter negatively correlated with the proportions of spores remaining in dehisced capsules (range 5–16%), being deposited within the colony (range 2–14%), and being deposited between the colony edge and the outer sampled perimeter (range 7–22%), probably because a larger capsule shoots the spores higher into the air, in effect meaning an increased initial release height. Spore diameter positively affected deposition outside the colony edge. The deposition curves together with observed long-distance colonisations, omnipresence in mires of many Sphagnum species and genetic evidence, suggest that Sphagnum spores regularly travel far.
Spatial extension of the empirical deposition curves at a regional scale indicate that with increasing isolation of target sites, the higher the proportion of spores would originate from sources farther away than the nearest sources. Given spatial patterns in the source populations, this would result in higher genetic (and species) diversity per coloniser with increasing isolation, thus counteracting differentiation.
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Dispersal is of central importance to population biology, behavioral ecology and conservation. However, because field studies are based on finite study areas, nearly all dispersal distributions for vertebrates currently available are biased, often highly so. The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.
Asplenium fontanum subsp. fontanum and A. petrarchae subsp. bivalens are diploid rock ferns of limestone outcrops of the western Mediterranean region. Asplenium fontanum subsp. fontanum occurs from Valencia through northeastern Spain to the Alpes-Maritimes and Swiss Jura. Asplenium petrarchae subsp. bivalens occurs only on Majorca, in Valencia and possibly in southern Spain. We analysed allozyme and chloroplast genetic marker diversity in 75 populations of A. fontanum subsp. fontanum and 12 populations of A. petrarchae subsp. bivalens sampled from across their respective ranges. The two species show similar levels of species and population genetic diversity to one another and to other diploid European Asplenium taxa. Both are predominantly outbreeding, as indicated by F(IS) = 0.108 and 0.167 respectively. Substantial between-population differentiation results largely from differentiation between regions. Isolation by distance operates over limited geographic ranges, up to 50 km. In A. fontanum subsp. fontanum, the major geographical differentiation between Valencia and the rest of the taxon range probably represents an ancient range fragmentation. A less pronounced differentiation divides populations in the SW from those in the NE of the range, with evidence for a biogeographic link between the eastern Pyrenees and southeastern France. High diversity in the Pyrenees may either represent ancient population differentiation, or a suture zone. In A. petrarchae subsp. bivalens, populations on Majorca exhibit a subset of the genetic diversity present in Valencia, although the two regions are strongly differentiated by differing allele frequencies. Dispersal from the mainland may have founded Majorcan populations, although a role for in situ island survival cannot be excluded.
Analysis of the spatial genetic structure within continuous populations in their natural habitat can reveal acting evolutionary processes. Spatial autocorrelation statistics are often used for this purpose, but their relationships with population genetics models have not been thoroughly established. Moreover, it has been argued that the dependency of these statistics on variation in mutation rates among loci strongly limits their interest for inferential purposes. In the context of an isolation by distance process, we describe relationships between a descriptor of the spatial genetic structure used in empirical studies, Moran's I statistic and population genetics parameters. In particular, we point out that, when Moran's I statistic is used to describe correlation in allele frequencies at the individual level, it provides an estimator of Wright's coefficient of relationship. We also show that the latter parameter, as a descriptor of genetic structure, is not influenced by selfing rate or ploidy level. Under specific finite population models, numerical simulations show that values of Moran's I statistic can be predicted from analytical theory. These simulations are also used to estimate the time taken to approach a structure at equilibrium. Finally, we discuss the conditions under which spatial autocorrelation statistics are little influenced by variation in mutation rates, so that they could be used to estimate gene dispersal parameters.
Three different approaches were used to assess the kinship structure of two epiphytic bryophytes, Orthotrichum speciosum and O. obtusifolium, that have different dispersal strategies. The two species were sampled in a 200 ha landscape where species occurrence and host trees had been mapped previously. Local environmental conditions at sampled trees were recorded and kinship between individuals was calculated based on amplified fragment length polymorphism (AFLP)-marker data. We did not detect any association between AFLP-markers and investigated environmental conditions. In both species, significant kinship coefficients were found between individuals up to 300-350 m apart which shows that both species have a restricted dispersal range. The spatial kinship structure was detected with both autocorrelation analysis and generalized additive models (GAMs), but linear regression failed to detect any structure in O. speciosum. Although the dioecious O. obtusifolium is currently the more common species it may, none the less, due to its restricted dispersal range and reproduction mode, become threatened in the future by current silvicultural practices which enhance the distance between host trees and decrease their life span. Finally, GAMs seem most appropriate for analysing spatial genetic structure because the effects of local environmental conditions and spatial structure can be analysed simultaneously, no assumption of a parametric form between kinship coefficient and distance is required, and spatial data resolution is not lost in the arbitrary choice of distance classes characterizing autocorrelation analysis.
Many empirical studies have assessed fine-scale spatial genetic structure (SGS), i.e. the nonrandom spatial distribution of genotypes, within plant populations using genetic markers and spatial autocorrelation techniques. These studies mostly provided qualitative descriptions of SGS, rendering quantitative comparisons among studies difficult. The theory of isolation by distance can predict the pattern of SGS under limited gene dispersal, suggesting new approaches, based on the relationship between pairwise relatedness coefficients and the spatial distance between individuals, to quantify SGS and infer gene dispersal parameters. Here we review the theory underlying such methods and discuss issues about their application to plant populations, such as the choice of the relatedness statistics, the sampling scheme to adopt, the procedure to test SGS, and the interpretation of spatial autocorrelograms. We propose to quantify SGS by an 'Sp' statistic primarily dependent upon the rate of decrease of pairwise kinship coefficients between individuals with the logarithm of the distance in two dimensions. Under certain conditions, this statistic estimates the reciprocal of the neighbourhood size. Reanalysing data from, mostly, published studies, the Sp statistic was assessed for 47 plant species. It was found to be significantly related to the mating system (higher in selfing species) and to the life form (higher in herbs than trees), as well as to the population density (higher under low density). We discuss the necessity for comparing SGS with direct estimates of gene dispersal distances, and show how the approach presented can be extended to assess (i) the level of biparental inbreeding, and (ii) the kurtosis of the gene dispersal distribution.