Relative Importance Of Dispersal Research Articles

Complex patterns of Gondwanan biogeography revealed in a dispersal‐limited arachnid

AbstractAimWe explore the biogeographic history of the Gondwanan lineage Triaenonychidae, a dispersal‐limited arachnid taxon that underwent a recent taxonomic revision based on phylogenomic data. We explicitly test hypotheses related to a biogeographical pattern of ‘common vicariance, rare dispersal’, predicted for dispersal‐limited taxa.LocationContinental landmasses of former temperate Gondwanan terranes (southern South America, southern Africa, Madagascar, Australia, New Zealand, and New Caledonia).TaxonTriaenonychidae, Opiliones, Arachnida.MethodsUtilizing a recently published phylogenomic data set based on ultra‐conserved elements, we conduct Bayesian divergence dating analyses, ancestral area estimation in a likelihood model testing framework, and analyses of macroevolutionary dynamics. Results are correlated with geological history and palaeoclimate reconstructions to infer biogeographic history and distribution.ResultsWe find that divergence dates of ancestral Triaenonychidae pre‐date continental breakup of Gondwana and could be attributed to palaeoclimatic differentiation across Gondwana. There is evidence for two separate expansion routes that span eastern and western Gondwana corresponding to northern warmer climate and southern cooler climate lineages. Many divergences across intercontinental lineages coincide with the timing of continental fragmentation, supporting vicariance as a dominant force. However, some lineages are supported as obvious examples of rare long‐distance dispersal. Biogeographic results support the predicted pattern of common vicariance and rare dispersal for these dispersal‐limited organisms.Main conclusionsVicariance due to continental fragmentation was important in the early diversification of Triaenonychidae. Their unique combination and degrees of dispersal ability and microhabitat preference resulted in complex phylogenetic patterns of geographic distribution not typically seen in other animal taxa. Examining biogeographic patterns across recent studies of arachnid taxa with varying dispersal ability, it is clear that biological characteristics play an important role in the relative importance of dispersal and vicariance (dispersal–vicariance continuum) for any given taxon and can be useful in forming testable a priori hypotheses.

Structure and thermodynamics of nondipolar molecular liquids and solutions from integral equation theory

ABSTRACTSolvent-induced solute polarisation of nondipolar solvents originates mainly from specific directional interactions and higher electrostatic multipole moments. Popular continuum solvation models such as the polarisable continuum models ignore such interactions and, therefore, cannot adequately model solvation effects on electronic structure in these environments. Important examples of nondipolar solvents that are indistinguishable by continuum methods are benzene and hexafluorobenzene. Both substances have very similar macroscopic properties, while solutes dissolved in either benzene or hexafluorobenzene behave differently due to their inverted electrostatic quadrupole moments and slightly different size. As a first step towards a proper and computationally feasible description of nondipolar molecular solvents, we present here integral equation theory results based on various forms of the reference interaction site model coupled to quantum-chemical calculations for benzene and hexafluorobenzene solutions of small molecules. We analyse solvation structures, also in comparison with molecular dynamics simulations, and show that predictions of transfer Gibbs energies, which define partition constants, benefit substantially from considering the exact, wave function-derived electrostatic field distribution beyond a simple point charge solute model in comparison with experimental data. Moreover, by constructing artificial uncharged and charge-inverted toy models of the solvents, it is possible to dissect the relative importance of dispersion and quadrupolar electrostatic effects on the partitioning equilibria. Such insight can help to design specifically optimised solvents to control solubility and selectivity for a wide range of applications.

INVESTIGATING PROCESSES OF NEOTROPICAL RAIN FOREST TREE DIVERSIFICATION BY EXAMINING THE EVOLUTION AND HISTORICAL BIOGEOGRAPHY OF THE PROTIEAE (BURSERACEAE)

Andean uplift and the collision of North and South America are thought to have major implications for the diversification of the Neotropical biota. However, few studies have investigated how these geological events may have influenced diversification. We present a multilocus phylogeny of 102 Protieae taxa (73% of published species), sampled pantropically, to test hypotheses about the relative importance of dispersal, vicariance, habitat specialization, and biotic factors in the diversification of this ecologically dominant tribe of Neotropical trees. Bayesian fossil-calibrated analyses date the Protieae stem at 55 Mya. Biogeographic analyses reconstruct an initial late Oligocene/early Miocene radiation in Amazonia for Neotropical Protieae, with several subsequent late Miocene dispersal events to Central America, the Caribbean, Brazil's Atlantic Forest, and the Chocó. Regional phylogenetic structure results indicate frequent dispersal among regions throughout the Miocene and many instances of more recent regional in situ speciation. Habitat specialization to white sand or flooded soils was common, especially in Amazonia. There was one significant increase in diversification rate coincident with colonization of the Neotropics, followed by a gradual decrease consistent with models of diversity-dependent cladogenesis. Dispersal, biotic interactions, and habitat specialization are thus hypothesized to be the most important processes underlying the diversification of the Protieae.

Flow intermittency alters longitudinal patterns of invertebrate diversity and assemblage composition in an arid‐land stream network

Summary1. Temporary streams comprise a large proportion of the total length of most stream networks, and the great majority of arid‐land stream networks, so it is important to understand their contribution to biotic diversity at both local and landscape scales.2. In late winter 2010, we sampled invertebrate assemblages in 12 reaches of a large arid‐land stream network (including perennial and intermittent headwaters, intermittent middle reaches and perennial rivers) in south‐east Arizona, U.S.A. Intermittent reaches had then been flowing for c. 60 days, following a dry period of more than 450 days. We sampled a subset of the perennial study reaches three more times between 2009 and 2011. Since intermittent reaches were dry during these additional sampling periods, we used assemblage data from two other intermittent streams in the study network (sampled in 2004–05 and 2010) to explore interannual variability in intermittent stream assemblage composition.3. Invertebrate richness was lowest in intermittent reaches, despite their often being connected to species‐rich perennial reaches. The assemblages of these intermittent reaches were not simply a subset of the species in perennial streams, but rather were dominated by a suite of stoneflies, blackflies and midges with adaptations to intermittency (e.g. egg and/or larval diapause). On average, 86% of individuals in these samples were specialists or exclusive to intermittent streams. Predators were 7–14 times more abundant in perennial than in intermittent reaches.4. Despite being separated by long distances (12–25 km) and having very different physical characteristics, the assemblages of perennial headwaters and rivers were more similar to one another than to intervening intermittent reaches, emphasising the prime importance of local hydrology in this system.5. The duration and recurrence intervals of dry periods, and the relative importance of dispersal from perennial refuges, probably influence the magnitude of biological differences between neighbouring perennial and temporary streams. Although perennial headwaters supported the highest diversity of invertebrates, intermittent reaches supported a number of unique or locally rare species and as such contribute to regional species diversity and should be included in conservation planning.

Demographic bottlenecks in tropical plant regeneration: A comparative analysis of causal influences

Abstract Mortality factors that act sequentially through the demographic transitions from seed to sapling may have critical effects on recruitment success. Understanding how habitat heterogeneity influences the causal factors that limit propagule establishment in natural populations is central to assess these demographic bottlenecks and their consequences. Bamboos often influence forest structure and dynamics and are a major factor in generating landscape complexity and habitat heterogeneity in tropical forests. To understand how patch heterogeneity influences plant recruitment we studied critical establishment stages during early recruitment of Euterpe edulis , Sloanea guianensis and Virola bicuhyba in bamboo and non-bamboo stands in the Brazilian Atlantic forest. We combined observational studies of seed rain and seedling emergence with seed addition experiments to evaluate the transition probabilities among regeneration stages within bamboo and non-bamboo stands. The relative importance of each mortality factor was evaluated by determining how the loss of propagules affected stage-specific recruitment success. Our results revealed that the seed addition treatment significantly increased seedling survivorship for all three species. E. edulis seedling survival probability increased in the addition treatment in the two stand types. However, for S. guianensis and V. bicuhyba this effect depended strongly on artificially protecting the seeds, as both species experienced increased seed and seedling losses due to post-dispersal seed predators and herbivores. Propagules of all three species had a greater probability of reaching subsequent recruitment stages when protected. The recruitment of large-seeded V. bicuhyba and E. edulis appears to be much more limited by post-dispersal factors than by dispersal limitation, whereas the small-seeded S. guianensis showed an even stronger effect of post-dispersal factors causing recruitment collapse in some situations. We demonstrated that E. edulis , S. guianensis and V. bicuhyba are especially susceptible to predation during early compared with later establishment stages and this early stage mortality can be more crucial than stand differences as determinants of successful regeneration. Among-species differences in the relative importance of dispersal vs. establishment limitation are mediated by variability in species responses to patch heterogeneity. Thus, bamboo effects on the early recruitment of non-bamboo species are patchy and species-specific, with successional bamboo patches exerting a far-reaching influence on the heterogeneity of plant species composition and abundance.

Importance of dispersal and thermal environment for mycorrhizal communities: lessons from Yellowstone National Park

The relative importance of dispersal and niche restrictions remains a controversial topic in community ecology, especially for microorganisms that are often assumed to be ubiquitous. We investigated the impact of these factors for the community assembly of the root-symbiont arbuscular mycorrhizal fungi (AMF) by sampling roots from geothermal and nonthermal grasslands in Yellowstone National Park (YNP), followed by sequencing and RFLP of AMF ribosomal DNA. With the exception of an apparent generalist RFLP type closely related to Glomus intraradices, a distance-based redundancy analysis indicated that the AMF community composition correlated with soil pH or pH-driven changes in soil chemistry. This was unexpected, given the large differences in soil temperature and plant community composition between the geothermal and nonthermal grasslands. RFLP types were found in either the acidic geothermal grasslands or in the neutral to alkaline grasslands, one of which was geothermal. The direct effect of the soil chemical environment on the distribution of two AMF morphospecies isolated from acidic geothermal grasslands was supported in a controlled greenhouse experiment. Paraglomus occultum and Scutellospora pellucida were more beneficial to plants and formed significantly more spores when grown in acidic than in alkaline soil. Distance among grasslands, used as an estimate of dispersal limitations, was not a significant predictor of AMF community similarity within YNP, and most fungal taxa may be part of a metacommunity. The isolation of several viable AMF taxa from bison feces indicates that wide-ranging bison could be a vector for at least some RFLP types among grasslands within YNP. In support of classical niche theory and the Baas-Becking hypothesis, our results suggest that AMF are not limited by dispersal at the scale of YNP, but that the soil environment appears to be the primary factor affecting community composition and distribution.

Responses to historical climate change identify contemporary threats to diversity in Dodecatheon.

Anthropogenic climate change may threaten many species with extinction. However, species at risk today survived global climate change in recent geological history. Describing how habitat tracking and adaptation allowed species to survive warming since the end of the Pleistocene can indicate the relative importance of dispersal and natural selection during climate change. By taking this historical perspective, we can identify how contemporary climate change could interfere with these mechanisms and threaten the most vulnerable species. We focused on a group of closely related plant species in the genus Dodecatheon (Primulaceae) in eastern North America. Two rare species (Dodecatheon amethystinum and Dodecatheon frenchii) that are endemic to patchy cool cliffs may be glacial relicts whose ranges constricted following the last glacial maximum. Alternatively, these species may be extreme ecotypes of a single widespread species (Dodecatheon meadia) that quickly adapted to microclimatic differences among habitats. We test support for these alternative scenarios by combining ecophysiological and population genetic data at a regional scale. An important ecophysiological trait distinguishes rare species from D. meadia, but only a few northern populations of D. amethystinum are genetically distinctive. These relict populations indicate that habitat tracking did occur with historical climate change. However, relatively stronger evidence for isolation by distance and admixture suggests that local adaptation and genetic introgression have been at least as important. The complex response of Dodecatheon to historical climate change suggests that contemporary conservation efforts should accommodate evolutionary processes, in some cases by restoring genetic connectivity between ecologically differentiated populations.

The relative importance of dispersal and the local environment for species richness in two aquatic plant growth forms

Local species richness can be affected by both the dispersal process and by environmental conditions (species sorting process). The evaluation of the relative roles of these two processes contributes not only to further understanding of the mechanisms determining species richness but also to biodiversity conservation. We studied the relative importance of hydrological dispersal and water chemistry for species richness of submerged and floating‐leaved macrophytes using 31 sets of interconnected ponds with different numbers of component ponds (defined as connection class). Connection class was slightly more important than, or equally important to, water chemistry in determining species richness of floating‐leaved macrophytes. In contrast, submerged macrophyte richness was much more influenced by water chemistry than by connection class, although increasing connection class had some positive effect. Similarly, the occurrence of a particular species of submerged macrophyte was better explained by pond water chemistry than by the occurrence of the same species in the pond immediately upstream. The reverse was true for floating‐leaved macrophytes; the presence of a given species was better explained by its presence in the pond immediately upstream than by water chemistry. These results indicated that the relative importance of the two processes that shape the species richness of aquatic plants is a consequence of the growth form of the plants. However, both the dispersal process via hydrologic connection and species sorting by water chemistry play some role in determining the species richness of both floating‐leaved and submerged macrophytes.

Relative importance of dispersion and rate‐limited mass transfer in highly heterogeneous porous media: Analysis of a new tracer test at the Macrodispersion Experiment (MADE) site

A single‐well injection‐withdrawal (SWIW) bromide tracer test was conducted to further investigate transport processes at the Macrodispersion Experiment (MADE) site on Columbus Air Force Base in Mississippi. The bromide breakthrough curve is highly asymmetric and exhibits an early time high‐concentration peak followed by an extended period of low‐concentration tailing. Comparisons of results simulated by advection‐dispersion (AD) and dual‐domain mass transfer (DDMT) models with the field data show that the DDMT model more accurately represents the magnitudes of both the early high‐concentration peak and the later low‐concentration tail. For both the AD and DDMT models, the match with field data is enhanced by incorporating hydraulic conductivity information from new direct‐push profiling methods. The Akaike information criterion for the DDMT models is much smaller than that for the AD models in both the homogeneous and heterogeneous cases investigated in this work. The improved match of the DDMT model with the SWIW test data supports the hypothesis of mass transfer processes occurring at this highly heterogeneous site.

The relative importance of dispersal and local processes in structuring phytoplankton communities in a set of highly interconnected ponds

Summary1. The recognition that both local and regional processes act together in shaping local communities makes determining their relative roles in natural communities central to understanding patterns in community structure.2. We investigated the relative influence of these processes on the phytoplankton communities of a highly interconnected pond system. We sampled the phytoplankton communities of 28 ponds concurrently with 20 local environmental variables.3. We found that phytoplankton community variation, in terms of both phytoplankton community composition (PCC) and diversity, was only significantly explained by local environmental variables. These were mainly associated with the contrasting clear‐water and turbid ecological states of the shallow ponds studied. Clear‐water conditions favoured only a few taxa, resulting in a significantly lower taxon diversity and richness under these conditions.4. The failure to explain variation in PCC by a dispersal model based on the water flow between ponds points at very effective species sorting. This is attributed to the high population turn‐over rates and sensitivity to environmental conditions of phytoplankton communities. Some evidence was found, however, that dispersal influences local communities through mass effects between neighbouring ponds.5. Overall, our results emphasize both the strong selection pressure that components of the food web exert on phytoplankton communities and the high potential of these communities to respond to such environmental change, thereby effectively opposing the homogenizing effects of continuous dispersal.

Out‐of‐Africa origin and dispersal‐mediated diversification of the butterfly genus Junonia (Nymphalidae: Nymphalinae)

The relative importance of dispersal and vicariance in the diversification of taxa has been much debated. Within butterflies, a few studies published so far have demonstrated vicariant patterns at the global level. We studied the historical biogeography of the genus Junonia (Nymphalidae: Nymphalinae) at the intercontinental level based on a molecular phylogeny. The genus is distributed over all major biogeographical regions of the world except the Palaearctic. We found dispersal to be the dominant process in the diversification of the genus. The genus originated and started diversifying in Africa about 20 Ma and soon after dispersed into Asia possibly through the Arabian Peninsula. From Asia, there were dispersals into Africa and Australasia, all around 5 Ma. The origin of the New World species is ambiguous; the ancestral may have dispersed from Asia via the Beringian Strait or from Africa over the Atlantic, about 3 Ma. We found no evidence for vicariance at the intercontinental scale. We argue that dispersal is as important as vicariance, if not more, in the global diversification of butterflies.

Mountaintop island age determines species richness of boreal mammals in the American Southwest

Models that describe the mechanisms responsible for insular patterns of species richness include the equilibrium theory of island biogeography and the nonequilibrium vicariance model. The relative importance of dispersal or vicariance in structuring insular distribution patterns can be inferred from these models. Predictions of the alternative models were tested for boreal mammals in the American Southwest. Age of mountaintop islands of boreal habitat was determined by constructing a geographic cladogram based on characteristics of intervening valley barriers. Other independent variables included area and isolation of mountaintop islands. Island age was the most important predictor of species richness. In contrast with previous studies of species richness patterns in this system, these results supported the nonequilibrium vicariance model, which indicates that vicariance has been the primary determinant of species distribution patterns in this system.

On the Viscosity and Physical Origin of Stability of Weakly Bound Complexes CdZn, HgZn and HgCd

Supermolecular CCSD(T)ab initiocalculations of potential energy curves for the electronic ground states of heteronuclear van der Waals complexes formed from the atoms of IIB group are presented. The physical origin of stability of the studied structures was analyzed by the symmetry-adapted perturbation theory. The magnitude of dispersion term increases with the increase of diatomic mass, but the relative importance of dispersion vs Hartree- Fock induction energies decreases in the order CdZn > HgZn > HgCd. Theoretical calculations of the temperature dependence of the shear viscosity for low-density binary mixtures are in good agreement with the temperature dependences of the shear viscosity obtained from empirical formula.

The Pattern and Timing of Diversification of Philippine Endemic Rodents: Evidence from Mitochondrial and Nuclear Gene Sequences

The 22 genera and 64 species of rodents (Muridae: Murinae) distributed in the Philippine Islands provide a unique opportunity to study patterns and processes of diversification in island systems. Over 90% of these rodent species are endemic to the archipelago, but the relative importance of dispersal from the mainland, dispersal within the archipelago, and in situ differentiation as explanations of this diversity remains unclear, as no phylogenetic hypothesis for these species and relevant mainland forms is currently available. Here we report the results of phylogenetic analyses of the endemic Philippine murines and a wide sampling of murine diversity from outside the archipelago, based on the mitochondrial cytochrome b gene and the nuclear-encoded IRBP exon 1. Analysis of our combined gene data set consistently identified five clades comprising endemic Philippine genera, suggesting multiple invasions of the archipelago. Molecular dating analyses using parametric and semiparametric methods suggest that colonization occurred in at least two stages, one ca. 15 Mya, and another 8 to 12 million years later, consistent with the previous recognition of "Old" and "New" endemic rodent faunas. Ancestral area analysis suggests that the Old Endemics invaded landmasses that are now part of the island of Luzon, whereas the three New Endemic clades may have colonized through either Mindanao, Luzon, or both. Further, our results suggest that most of the diversification of Philippine murines took place within the archipelago. Despite heterogeneity between nuclear and mitochondrial genes in most model parameters, combined analysis of the two data sets using both parsimony and likelihood increased phylogenetic resolution; however, the effect of data combination on support for resolved nodes was method dependent. In contrast, our results suggest that combination of mitochondrial and nuclear data to estimate relatively ancient divergence times can severely compromise those estimates, even when specific methods that account for rate heterogeneity among genes are employed. [Biogeography; divergence date estimation; mitochondrial DNA; molecular systematics; Murinae; nuclear exon; Philippines; phylogeny.].

Assortative mating and differential male mating success in an ash hybrid zone population

BackgroundThe structure and evolution of hybrid zones depend mainly on the relative importance of dispersal and local adaptation, and on the strength of assortative mating. Here, we study the influence of dispersal, temporal isolation, variability in phenotypic traits and parasite attacks on the male mating success of two parental species and hybrids by real-time pollen flow analysis. We focus on a hybrid zone population between the two closely related ash species Fraxinus excelsior L. (common ash) and F. angustifolia Vahl (narrow-leaved ash), which is composed of individuals of the two species and several hybrid types. This population is structured by flowering time: the F. excelsior individuals flower later than the F. angustifolia individuals, and the hybrid types flower in-between. Hybrids are scattered throughout the population, suggesting favorable conditions for their local adaptation. We estimate jointly the best-fitting dispersal kernel, the differences in male fecundity due to variation in phenotypic traits and level of parasite attack, and the strength of assortative mating due to differences in flowering phenology. In addition, we assess the effect of accounting for genotyping error on these estimations.ResultsWe detected a very high pollen immigration rate and a fat-tailed dispersal kernel, counter-balanced by slight phenological assortative mating and short-distance pollen dispersal. Early intermediate flowering hybrids, which had the highest male mating success, showed optimal sex allocation and increased selfing rates. We detected asymmetry of gene flow, with early flowering trees participating more as pollen donors than late flowering trees.ConclusionThis study provides striking evidence that long-distance gene flow alone is not sufficient to counter-act the effects of assortative mating and selfing. Phenological assortative mating and short-distance dispersal can create temporal and spatial structuring that appears to maintain this hybrid population. The asymmetry of gene flow, with higher fertility and increased selfing, can potentially confer a selective advantage to early flowering hybrids in the zone. In the event of climate change, hybridization may provide a means for F. angustifolia to further extend its range at the expense of F. excelsior.

Dispersal, cladistics and the nature of biogeography

Dispersal, cladistics and the nature of biogeography

Spatial occurrence and colonisations in patch‐tracking metapopulations: local conditions versus dispersal

We studied the relative importance of local variables and dispersal for the occurrence and colonisation of the epiphytic bryophytes Orthotricum speciosum (spore dispersed), and O. obtusifolium (spore and asexual gemmae) on aspen trees (‘patches’) in two forest landscapes (one old‐growth and one fragmented) using multiple logistic regression. The relative importance of dispersal was quantified as the reduction of residual deviance for a connectivity variable. In modelling dispersal, we assumed that trees with low local abundance were recent colonisations, and that trees with high local abundance were diaspore sources for colonisation. The occurrence of O. speciosum in the fragmented landscape was most affected by shading, but also by connectivity, aspen diameter and vitality. In the old‐growth landscape, connectivity was the single most important variable for recent colonisations, but its effect was lower than the sum of the effects of all local environmental variables. The occurrence of O. obtusifolium in the fragmented landscape was related to similar variables but the relative importance of these variables was different, and connectivity did not affect the probability of a recent colonisation in this species. We describe the epiphyte‐tree system in the patch‐tracking metapopulation model. In this model colonisations are distance dependent, but in contrast to the classical metapopulation model local extinctions are caused by deterministic patch destruction – once the epiphyte has colonised the tree it remains until the tree dies.

Natural Gradient Tracer Test to Evaluate Natural Attenuation of MTBE Under Anaerobic Conditions

AbstractA natural gradient tracer test using perdeuterated MTBE was conducted in an anaerobic aquifer to determine the relative importance of dispersion and degradation in reducing MTBE concentrations in ground water. Preliminary ground water chemistry and hydraulic conductivity data were used to place the tracer within an existing dissolved MTBE plume at Port Hueneme, California. Following one year of transport, the tracer plume was characterized in detail.Longitudinal dispersion was identified as the dominant mechanism for lowering the perdeuterated MTBE concentrations. The method of moments was used to determine the longitudinal and lateral dispersion coefficients (0.85 m2/day and 0.08 m2/day, respectively). A mass‐balance analysis, carried out after one year of transport, accounted for 110% of the injected mass and indicated that no significant mass loss occurred. The plume structure created by zones of higher and lower hydraulic conductivity at the site was complex, consisting of several localized areas of high tracer concentration in a lower concentration plume. This is important because the aquifer has generally been characterized as exhibiting fairly minor heterogeneity. In addition, the tracer plume followed a curved flowpath that deviated from the more macroscopic direction of ground water flow inferred from local ground water elevation measurements and the behavior of the existing plume. Understanding the mass balance, plume structure, curvature of the tracer plume, and consequently natural attenuation behavior required the detailed sampling approach employed in this study. These data imply that a detailed understanding of site hydrogeology and an extensive sampling network may be critical for the correct interpretation of monitored natural attenuation of MTBE.

Global patterns of environmental synchrony and the Moran effect

There is considerable debate over the relative importance of dispersal and environmental disturbances (the Moran effect) as causes of spatial synchrony in fluctuations of animal populations. If environmental factors generally exhibit high levels of spatial autocorrelation, they may be playing a more important role in synchronizing animal populations than sometimes recognized. Here I examine this issue by analyzing spatial autocorrelation in annual rainfall and mean annual temperatures from sites throughout the world using the database maintained by the Global Historical Climatology Network. Both annual precipitation and mean annual temperatures exhibit high synchrony declining with distance and are statistically significant over large distance, often on a continental scale. In general, synchrony was slightly higher in annual precipitation at short distances, but greater in mean annual temperatures at long distances. No latitudinal gradient in synchrony of either variable was detected. The high overall synchrony observed in these environmental variables combined with a pattern of decline with distance similar to that observed in many animal populations suggest that the Moran effect can potentially play an important role in driving synchrony in a wide variety of ecological phenomena regardless of scale.

Possible role of the seed bank in the restoration of open sand grassland in old fields

The species composition of the seed bank and aboveground vegetation of an old field was compared to a reference grassland stand. The relative importance of dispersal and recruitment as limiting factors was analysed, and measures for appropriate restoration are proposed. Grassland species were able to re-establish in the old field soon after abandonment of cultivation, with Stipa borysthenica as the dominant species. Five years after abandonment of cultivation, the seed bank was still dominated by weedy annuals while grassland species made a relatively high contribution to the seed bank in the reference site. The results do not support recruitment to be the limiting factor in recently abandoned fields, because grassland species that occurred in the seed bank were also present in the vegetation. A rapid regeneration of the matrix species is predicted due to their good dispersal capacity and the vicinity of the open sand grassland. However, the introduction of subordinate species and the control of invasive plants might require human intervention.