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Conventional plant dispersal classification systems use simple binary assignment schemes classifying each species as either being dispersed by means of a certain dispersal vector or not. However, because the dispersal potential ranges continually, this dichotomy appears to be rather artificial, and the existing systems may not be very useful for addressing ecological questions. To quantify gradual differences in the dispersal potential, we developed a system assessing wind dispersal potentials. Wind dispersal potential is defined as the proportion of diaspores exceeding a predefined reference distance under certain weather conditions, to acknowledge that wind dispersal potential is scale and context specific. The system is based on an independently validated simulation model of wind dispersal that was used to compute the proportion of diaspores exceeding predefined reference distances. On an ordinal scale, the proposed system allows one to assess the wind dispersal potential of any plant species with known falling velocity and release height of its diaspores without further computing. The system mainly relies on two traits characterizing the plant species (falling velocity and initial release height of the diaspores) and two context-specific parameters (reference distance and weather conditions). We examined how wind dispersal potential is sensitive to these factors and found that it was most sensitive to weather conditions and falling velocity. The species-specific traits interact with reference distance: the greater the reference distance and the lower the release height in relation, the more relevant a low falling velocity becomes for achieving a high wind dispersal potential. We subsequently applied the system to 335 plant species and found a considerable variation in their wind dispersal potentials. Many species commonly assumed to be wind dispersed exhibit only a low wind dispersal potential. Comparing the wind dispersal potentials to the morphology of the diaspores also reveals a considerable variation of the wind dispersal potential of species classified as the same morphological type. The results show that the conventional assignment of a plant species to a certain mode of dispersal, which is primarily based on the morphology of its diaspores, will often result in misleading conclusions regarding the dispersal potential of the respective species.

Spatial synchrony in population dynamics can be caused by dispersal or spatially correlated variation in environmental factors like weather (Moran effect). Distinguishing between these mechanisms is challenging for natural populations, and the study of dispersal‐induced synchrony in particular has been dominated by theoretical modelling and laboratory experiments. The goal of the present study was to evaluate the evidence for dispersal as a cause of meso‐scale (distances of tens of kilometres) spatial synchrony in natural populations of the two cyclic geometrid moths Epirrita autumnata and Operophtera brumata in sub‐arctic mountain birch forest in northern Norway. To infer the role of dispersal in geometrid synchrony, we applied three complementary approaches, namely estimating the effect of design‐based dispersal barriers (open sea) on synchrony, comparing the strength of synchrony between E. autumnata (winged adults) and the less dispersive O. brumata (wingless adult females), and relating the directionality (anisotropy) of synchrony to the predominant wind directions during spring, when geometrid larvae engage in windborne dispersal (ballooning). The estimated effect of dispersal barriers on synchrony was almost three times stronger for the less dispersive O. brumata than E. autumnata. Inter‐site synchrony was also weakest for O. brumata at all spatial lags. Both observations argue for adult dispersal as an important synchronizing mechanism at the spatial scales considered. Further, synchrony in both moth species showed distinct anisotropy and was most spatially extensive parallel to the east–west axis, coinciding closely to the overall dominant wind direction. This argues for a synchronizing effect of windborne larval dispersal. Congruent with most extensive dispersal along the east–west axis, E. autumnata also showed evidence for a travelling wave moving southwards at a speed of 50–80 km/year. Our results suggest that dispersal processes can leave clear signatures in both the strength and directionality of synchrony in field populations, and highlight wind‐driven dispersal as promising avenue for further research on spatial synchrony in natural insect populations.

Wind disperses the pollen and seeds of many plants, but little is known about whether and how it shapes large-scale landscape genetic patterns. We address this question by a synthesis and reanalysis of genetic data from more than 1,900 populations of 97 tree and shrub species around the world, using a newly developed framework for modeling long-term landscape connectivity by wind currents. We show that wind shapes three independent aspects of landscape genetics in plants with wind pollination or seed dispersal: populations linked by stronger winds are more genetically similar, populations linked by directionally imbalanced winds exhibit asymmetric gene flow ratios, and downwind populations have higher genetic diversity. For each of these distinct hypotheses, partial correlations between the respective wind and genetic metrics (controlling for distance and climate) are positive for a significant majority of wind-dispersed or wind-pollinated genetic data sets and increase significantly across functional groups expected to be increasingly influenced by wind. Together, these results indicate that the geography of both wind strength and wind direction play important roles in shaping large-scale genetic patterns across the world’s forests. These findings have implications for various aspects of basic plant ecology and evolution, as well as the response of biodiversity to future global change.

Following a disturbance, dispersal shapes community composition as well as ecosystem structure and function. For fungi, dispersal is often wind or mammal facilitated, but it is unclear whether these pathways are complementary or redundant in the taxa they disperse and the ecosystem functions they provide. Here, we compare the diversity and morphology of fungi dispersed by wind and three rodent species in recently harvested forests using a combination of microscopy and Illumina sequencing. We demonstrate that fungal communities dispersed by wind and small mammals differ in richness and composition. Most wind-dispersed fungi are wood saprotrophs, litter saprotrophs, and plant pathogens, whereas fungi dispersed in mammal scat are primarily mycorrhizal, soil saprotrophs, and unspecified saprotrophs. We note substantial dispersal of truffles and agaricoid mushrooms by small mammals, and dispersal of agaricoid mushrooms, crusts, and polypores by wind. In addition, we find mammal-dispersed spores are larger than wind-dispersed spores. Our findings suggest that wind- and small-mammal-facilitated dispersal are complementary processes and highlight the role of small mammals in dispersing mycorrhizal fungi, particularly following disturbances such as timber harvest.

Abscission of seeds in some plant species occurs as a result of strong wind gusts that exert sufficient drag forces to liberate the seed from its parent. This may be an adaptive feature, as release into stronger wind gusts has been shown to lead to greater dispersal distances, which is likely to have evolutionary advantages. We test the hypotheses that (i) seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations and (ii) that the preferential abscission of seeds into upward wind gusts will result in the dispersal of seeds over greater distances. As a case study, we studied the abscission dynamics of Conyza bonariensis (L.) Cronquist (fleabane), which is an important weed with global distribution. Using abscission data obtained through a series of seed release experiments, we confirm that abscission of seeds in C. bonariensis is most likely to occur during strong and upward wind gusts. We demonstrate that, for a given wind speed, seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations. We also show that preferential release into upward wind gusts has some influence on the distance travelled, but the strength of this influence is dependent on the correlation between wind orientation and wind speed. For this particular study, the sensitivity of release to the horizontal wind speed seems to have a larger effect on the distance travelled than sensitivity to wind orientation.

In species that disperse by airborne propagules an inverse relationship is often assumed between propagule size and dispersal distance. However, for microscopic spores the evidence for the relationship remains ambiguous. Lagrangian stochastic dispersion models that have been successful in predicting seed dispersal appear to predict similar dispersal for all spore sizes up to ∼40 μm diameter. However, these models have assumed that spore size affects only the downwards drift of particles due to gravitation and have largely omitted the highly size-sensitive deposition process to surfaces such as forest canopy. On the other hand, they have assumed that spores are certain to deposit when the air parcel carrying them touches the ground. Here, we supplement a Lagrangian stochastic dispersion model with a mechanistic deposition model parameterized by empirical deposition data for 1-10 μm spores. The inclusion of realistic deposition improved the ability of the model to predict empirical data on the dispersal of a wood-decay fungus (aerodynamic spore size 3.8 μm). Our model predicts that the dispersal of 1-10 μm spores is in fact highly sensitive to spore size, with 97-98% of 1 μm spores but only 12-58% of 10-μm spores dispersing beyond 2 km in the simulated range of wind and canopy conditions. Further, excluding the assumption of certain deposition at the ground greatly increased the expected dispersal distances throughout the studied spore size range. Our results suggest that by evolutionary adjustment of spore size, release height and timing of release, fungi and other organisms with microscopic spores can change the expected distribution of dispersal locations markedly. The complex interplay of wind and canopy conditions in determining deposition resulted in some counterintuitive predictions, such as that spores disperse furthest under intermediate wind, providing intriguing hypotheses to be tested empirically in future studies.

Summary Plant species around the world invest in seed dispersal by producing large numbers of seeds, with a wide range of morphological adaptations that facilitate dispersal. Not all dispersed seeds reach suitable sites, however, and plants can significantly improve their fitness by increasing the proportion of seeds arriving at suitable sites for germination and establishment. Disproportionate dispersal to suitable sites is known as ‘directed dispersal’. Yet, mechanisms of directed dispersal are only known for a limited number of animal‐dispersed plant species. We tested the hypothesis that directed dispersal can also be driven by abiotic vectors, such as water or wind. We used a tiered approach, combining analyses of experimental, field and literature data on wetland plant species and evaluating the potential for evolution of directed dispersal with a spatially explicit individual‐based model. The data collected demonstrate that wetland plants produce seeds with adaptations to promote transportation and deposition by water towards microsites along the hydrological gradient where they germinate and establish best. Aquatic species produce seeds that sink and are transported by water as bed load towards inundated sites. In contrast, shoreline species produce seeds that float for very long periods of time so that they are eventually entrapped by shoreline vegetation or deposited at the waterline. Our model simulations confirm that the patterns we observed in nature can evolve under natural selection through adaptations in seed buoyancy. For wind dispersal, the situation is more complex. Wind does not provide directed dispersal in the strictest sense but, rather, simply appears to be the best available dispersal vector for more terrestrial wetland plant species to reach drier areas in a wet environment. Synthesis. We show that directed dispersal towards specific, suitable microsites is not exclusive to animal‐dispersed plant species, but may be far more common in plants – also in species dispersed by abiotic vectors, in particular water. As water and wind are very common dispersal vectors throughout the plant kingdom, directed dispersal (and not just dispersal distance) seems to be of general importance for the ecology of plants. A lay summary is available for this article. Lay Summary

Nematodes colonize almost all aquatic habitats worldwide. Despite their small size, restricted locomotion and lack of pelagic larvae, they can reach even isolated habitats within a short time. In this review, we examine the underlying dispersal modes, considering their active movement in substrates and water, their drift by water and wind, rafting, zoochory as well as human-mediated vectors. These modes are limited by morphology and habitat structure, ecological factors and especially by hydrodynamics. Active dispersal is effective over short distances, but with increasing water-flow velocity, passive dispersal modes, which enable long-range transfer, become important. In fact, the transport of nematodes over thousands of kilometers via ship water tanks and by hitchhiking on sea turtles has been documented. Overland dispersal vectors include wind and birds whereas rafting enables an aggregated distribution because food is available, and reproduction is possible onboard the rafts. The diversity of possible dispersal modes is high and offers a reasonably chance for gravid females or groups of nematodes to be transferred even to remote environments. Their immigration is continuous, and supported by their rapid, parthenogenetic reproduction, nematodes are effective pioneers with the ability to (re)colonize new or disturbed habitats or rebalance already existing communities.

Plant pathogens are responsible for the annual yield loss of crops worldwide and pose a significant threat to global food security. A necessary prelude to many plant disease epidemics is the shortrange dispersal of spores, which may generate several disease foci within a field. New information is needed on the mechanisms of plant pathogen spread within and among susceptible plants. Here, we show that self-propelled jumping dew droplets, working synergistically with low wind flow, can propel spores of a fungal plant pathogen (wheat leaf rust) beyond the quiescent boundary layer and disperse them onto neighboring leaves downwind. An array of horizontal water-sensitive papers was used to mimic healthy wheat leaves and showed that up to 25 spores/h may be deposited on a single leaf downwind of the infected leaf during a single dew cycle. These findings reveal that a single dew cycle can disperse copious numbers of fungal spores to other wheat plants, even in the absence of rain splash or strong gusts of wind.

Pines (n = 121 species) are important elements of forest ecosystems. They are economically and ecologically valuable and are often at the center of efforts to manage forests to reduce the risk of wildland fires. The pattern and process of pine seed dispersal and seedling establishment have important implications for maintaining healthy forests. 75% of pines are dispersed by wind, and 25% are dispersed by scatter-hoarding birds and rodents. Among the wind-dispersed pines, there are about 20 species that attract the attention of seed-caching animals that gather seeds and cache them in soil, so these species are dispersed by a combination of wind and animals. Animal-dispersed pines often occur in semi-arid ecosystems. The seeds cached by animals are a dynamic resource. Animals pilfer each other’s caches, move them to new sites and recache them. Some seed reside in dozens of different cache sites between seed maturation and seed germination. Many pines are adapted to fire. This involves serotinous cones (about 24 species), which are dense, woody, and lignified and remain closed at maturity. Serotiny establishes a canopy seed bank that can persist for several decades. Shortly after fire, these cones open and shed seeds onto the burned landscape. Pines often mast, producing large crops of seeds at intervals of several years. These large cone crops satiate the appetites of specialist seed predators, resulting in increased seedling establishment and also increases the effectiveness of seed dispersal. In the past, pines have responded to climate change by shifting geographic ranges, and some pines appear to be responding to warming climates in a similar way.