Passive Dispersal Research Articles

Inconsistent response of taxonomic groups to space and environment in mediterranean and tropical pond metacommunities.

The metacommunity concept provides a theoretical framework that aims at explaining organism distributions by a combination of environmental filtering, dispersal, and drift. However, few works have attempted a multitaxon approach and even fewer have compared two distant biogeographical regions using the same methodology. We tested the expectation that temperate (mediterranean-climate) pond metacommunities would be more influenced by environmental and spatial processes than tropical ones, because of stronger environmental gradients and a greater isolation of waterbodies. However, the pattern should be different among groups of organisms depending on their dispersal abilities. We surveyed 30 tropical and 32 mediterranean temporary ponds from Costa Rica and Spain, respectively, and obtained data on 49 environmental variables. We characterized the biological communities of bacteria and archaea (from the water column and the sediments), phytoplankton, zooplankton, benthic invertebrates, amphibians and birds, and estimated the relative role of space and environment on metacommunity organization for each group and region, by means of variation partitioning using generalized additive models. Purely environmental effects were important in both tropical and mediterranean ponds, but stronger in the latter, probably due to their larger limnological heterogeneity. Spatially correlated environment and pure spatial effects were greater in the tropics, related to higher climatic heterogeneity and dispersal processes (e.g., restriction, surplus) acting at different scales. The variability between taxonomic groups in the contribution of spatial and environmental factors to metacommunity variation was very wide, but higher in active, compared with passive, dispersers. Higher environmental effects were observed in mediterranean passive dispersers, and higher spatial effects in tropical passive dispersers. The unexplained variation was larger in the tropical setting, suggesting a higher role for stochastic processes, unmeasured environmental factors, or biotic interactions in the tropics, although this difference affected some actively dispersing groups (insects and birds) more than passive dispersers. These results, despite our limitations in comparing only two regions, provide support, for a wide variety of aquatic organisms, for the classic view of stronger abiotic niche constraints in temperate areas compared with the tropics. The heterogeneous response of taxonomic groups between regions also points to a stronger influence of regional context than organism adaptations on metacommunity organization.

Design and construction of 3D printed devices to investigate active and passive bacterial dispersal on hydrated surfaces

BackgroundTo disperse in water-unsaturated environments, such as the soil, bacteria rely on the availability and structure of water films forming on biotic and abiotic surfaces, and, especially, along fungal mycelia. Dispersal along such “fungal highways” may be driven both by mycelial physical properties and by interactions between bacteria and fungi. However, we still do not have a way to disentangle the biotic and abiotic elements.ResultsWe designed and 3D printed two devices establishing stable liquid films that support bacteria dispersal in the absence of biotic interactions. The thickness of the liquid film determined the presence of hydraulic flow capable of transporting non-motile cells. In the absence of flow, only motile cells can disperse in the presence of an energy source. Non-motile cells could not disperse autonomously without flow but dispersed as “hitchhikers” when co-inoculated with motile cells.ConclusionsThe 3D printed devices can be used as an abiotic control to study bacterial dispersal on hydrated surfaces, such as plant roots and fungal hyphae networks in the soil. By teasing apart the abiotic and biotic dimensions, these 3D printed devices will stimulate further research on microbial dispersal in soil and other water-unsaturated environments.

Benthic foraminifera in the Nakdong River Delta (southeast Korea) and their response to middle Holocene climatic change in the coastal environment of the East Asian margin

• Benthic foraminifera in the NRD contain the Marine, Bay, and Opportunistic taxa. • Precipitation and resultant river discharge increased in Korean Peninsula at ∼ 4 ka. • Two small maxima of low oxygen-resistant taxon represent the fluctuated TWC. • Replacement of two species implies the enhanced East Asian winter monsoon at 4.6 ka. Fossil benthic foraminifera from five cores in the Nakdong River Delta (southeast Korea) were investigated to reveal paleoenvironmental changes across the middle/late Holocene transition, particularly focusing on ∼4 ka climatic event. Based on multi-dimensional scaling, benthic foraminifera are divided into (1) Marine taxa, (2) Bay taxa, and (3) Opportunistic taxa. Planktonic/total (benthic and planktonic) foraminiferal ratio decreased abruptly during 4.6–3.3 ka, and Nonionella stella was found commonly across ∼4 ka in core ND-01 (intermediate site among the five cores). These results imply that the ∼4 ka climatic event led to the stratification of less saline epilimnetic water underlain by more saline oxygen-poor hypolimnetic water in the Nakdong River Delta. This indicates temporal increase in precipitation in the Nakdong River drainage, which can be attributed to the intensified rainfall with the second Changma peak, associated with typhoons toward the Korean Peninsula. The small twin maxima of N. stella across ∼4 ka in core ND-01 were similar to those of the total sulfur contents in both Yeja Bay (southern Korea) and Lake Togo-ike (southwestern Japan). Such similarity in the stratigraphic patterns among the remote locations can be explained by the small-scale sea-level variations with the fluctuation of the Tsushima Warm Current, in addition to changes in precipitation. The common species of Haynesina sp. A was replaced by Elphidium somaense after ∼4.6 ka, which is likely due to the shift of passive dispersal as a result of the enhanced East Asian winter monsoon and/or the change in the westerly jet path.

Oceanic Fronts Shape Biodiversity of Gelatinous Zooplankton in the European Arctic

Oceanic fronts constitute boundaries between hydrologically distinct water masses and comprise one of the most productive regions of the world’s ocean. Fronts associated with density gradients (active fronts) profoundly structure planktonic communities in adjacent waters, but less is known about the impacts of density-compensated (passive) fronts. Two such fronts are found in the European Arctic, the Arctic Front (AF) and the Polar Front (PF), that both separate warmer and saltier, Atlantic water from the colder, but fresher Arctic water. As scrutinized research on the influence of passive fronts on zooplankton at large spatial and temporal scales had been lacking, we tackled the question of their role in maintaining distinct communities, employing globally unique, 12-year-long gelatinous zooplankton (GZ) and hydrological time series from the European Arctic. The GZ, owing to their fast reproductive cycles and passive dispersal, reflect particularly well the local environment. We therefore compared GZ communities between zones separated by the two fronts, disentangled their drivers, and analyzed community shifts occurring whenever front relocation occurred. We have identified fifteen GZ taxa, distributed among three distinct communities, specific for front-maintained zones, and selected the following taxa as indicators of each zone: W—west of the AF, within the Greenland Sea Gyre, Beroe spp.; C—central, in between the AF and the PF, Aglantha digitale; and E—east of the PF, in the West Spitsbergen Shelf Mertensia ovum. Taxonomic composition of these communities, and their specific abundance, persisted throughout time. We also showed that relocation of either front between the sampling years was subsequently followed by the restructuring of the GZ community. Our results indicate that passive oceanic fronts maintain distinct GZ communities, with probable limited exchange across a front, and provide a new perspective for the Arctic ecosystem evolution under progressing Atlantification.

Modelling the effects of currents and migratory behaviours on the dispersal of Atlantic salmon (Salmo salar) post-smolts in a coastal embayment

The post-smolt phase is considered a critical period for Atlantic salmon ( Salmo salar). Hence, identifying migration routes used by post-smolts is needed to protect the habitats they require to successfully complete their life cycle. We used a biophysical model coupled with output from a water circulation model (FVCOM) to simulate dispersal of Atlantic salmon post-smolts in a semi-enclosed bay: Passamaquoddy Bay, New Brunswick, Canada. The model was run with nine post-smolt behaviours and six swimming speeds, and then tested against acoustic telemetry data. While no modelled behaviour entirely captured observed salmon migration routes, we identified some behaviours that could allow salmon to successfully leave the bay and resulted in predictions that matched observations reasonably well (e.g., swimming southwest, negative, or tide-varying rheotaxis). We could also rule out several behaviours as unlikely to be used by Atlantic salmon post-smolts in this area (e.g., passive dispersal, orienting based on salinity or temperature, and positive rheotaxis). Hence, with suitable behaviours and models, this approach can provide estimates of the essential habitats and migration routes of wild post-smolts.

Modelling Radiative and Convective Thermal Exchanges over a European City Center and Their Effects on Atmospheric Dispersion

Micro-meteorological studies of urban flow and pollution dispersion often assume a neutral atmosphere and often the three-dimensional variation in temperature fields and flow around buildings is neglected in most building energy balance models. The aim of this work is to present the results of development and validation of a three-dimensional tool coupling thermal energy balance of the buildings and modelling of the atmospheric flow and dispersion in urban areas. To do so, a 3D microscale atmospheric radiative scheme has been developed in the atmospheric module of the computational fluid dynamics (CFD) code Code_Saturne adapted to detailed building geometries. The full coupling of the radiative transfer and fluid dynamics models has been validated with idealized cases. In this paper, our focus is to simulate and compare with measurements the diurnal evolution of the brightness surface temperatures and the momentum and energy fluxes for a neighborhood in the city center of Toulouse, in the southwest part of France. This is performed by taking into account the 3D effects of the flow around the buildings and all thermal exchanges, in real meteorological conditions, and compare them to aircraft infrared images and in situ measurements on a meteorological mast. The calculation mesh developed for the city center and the simulation conditions for the selected day of the field campaign are presented. The results are evaluated with the measurements from the Canopy and Aerosol Particles Interactions in TOulouse Urban Layer experiment (CAPITOUL). In addition, the second purpose of this work is to investigate a hypothetical release of passive pollutant dispersion in the same area of Toulouse under different thermal transfer conditions for the street and the buildings surfaces: neutral and 3D radiative transfer heating. The presence of heat transfer continually modifies the airflow field while the airflow in the neutral case reaches a stationary state. Compared to the neutral case, taking into account the thermal transfer enhances the turbulence kinetic energy and vertical velocity (especially at the roof level) due to buoyancy forces. The simulation results also show that the thermal effects considerably alter the plume shape.

The nature of dispersal barriers and their impact on regional species pool richness and turnover

AbstractAimWe document realized and potential global species ranges based on empirically vetted species concepts in conjunction with global climate databases and climate suitability modelling. From this we investigate the nature of dispersal barriers and illustrate how they generate ecological uniqueness.LocationHolarctic.MethodsFifty‐two small body‐size (i.e. < 5 mm) land snail taxa within the genera Euconulus, Pupilla and Vertigo were considered. These represent ~10% of all small body‐size Holarctic land snails and are among the most proficient known passive dispersers. Their potential climatic ranges were determined using Maxent modelling based on 9205 occurrence records. From these we inferred the location, width and nature of isolating barriers and tested for their effects on regional species pool richness and turnover.ResultsUse of unvetted traditional taxonomic concepts and unverified occurrence records would have created up to threefold higher or lower estimates of species‐specific climatic tolerances than the actual values. Modelling must thus only use high quality occurrence data. All but one taxon were shown at a global scale to possess multiple isolated areas of appropriate climate. While oceans represented the most common barrier (37%), intra‐continental barriers were in total almost twice as frequent (inappropriate climate – 29%, habitat/history – 27% and the Greenland ice sheet – 7%). These barriers restricted taxa to only a subset of their potential range, with European taxa possessing approximately twice the global occupancy rates as North American ones (median scores of 62 vs. 34%). As a result, regional taxa pools were three times smaller than their potential sizes, with 50% change in composition occurring over ~2600‐km distances.Main conclusionsEven for these readily dispersing taxa, isolation barriers prevented species from saturating their potential global range, reduced the size of regional species pools by 2/3, and generated ecological uniqueness between them.

From microbes to mammals: Pond biodiversity homogenization across different land‐use types in an agricultural landscape

AbstractLocal biodiversity patterns are expected to strongly reflect variation in topography, land use, dispersal boundaries, nutrient supplies, contaminant spread, management practices, and other anthropogenic influences. Contrary to this expectation, studies focusing on specific taxa revealed a biodiversity homogenization effect in areas subjected to long‐term intensive industrial agriculture. We investigated whether land use affects biodiversity levels and community composition (α‐ and β‐diversity) in 67 kettle holes (KH) representing small aquatic islands embedded in the patchwork matrix of a largely agricultural landscape comprising grassland, forest, and arable fields. These KH, similar to millions of standing water bodies of glacial origin, spread across northern Europe, Asia, and North America, are physico‐chemically diverse and differ in the degree of coupling with their surroundings. We assessed aquatic and sediment biodiversity patterns of eukaryotes, Bacteria, and Archaea in relation to environmental features of the KH, using deep‐amplicon‐sequencing of environmental DNA (eDNA). First, we asked whether deep sequencing of eDNA provides a representative picture of KH aquatic biodiversity across the Bacteria, Archaea, and eukaryotes. Second, we investigated if and to what extent KH biodiversity is influenced by the surrounding land use. We hypothesized that richness and community composition will greatly differ in KH from agricultural land use compared with KH in grasslands and forests. Our data show that deep eDNA amplicon sequencing is useful for in‐depth assessments of cross‐domain biodiversity comprising both micro‐ and macro‐organisms, but has limitations with respect to single‐taxa conservation studies. Using this broad method, we show that sediment eDNA, integrating several years to decades, depicts the history of agricultural land‐use intensification. Aquatic biodiversity was best explained by seasonality, whereas land‐use type explained little of the variation. We concluded that, counter to our hypothesis, land use intensification coupled with landscape wide nutrient enrichment (including atmospheric deposition), groundwater connectivity between KH and organismal (active and passive) dispersal in the tight network of ponds, resulted in a biodiversity homogenization in the KH water, leveling off today's detectable differences in KH biodiversity between land‐use types. These findings have profound implications for measures and management strategies to combat current biodiversity loss in agricultural landscapes worldwide.

An evaluation of the genetic connectivity and temporal stability of the blue and red shrimp Aristeus antennatus: a case study of spawning females\u2019 grounds in the Western Mediterranean Sea

The blue and red shrimp Aristeus antennatus has been intensively exploited by trawling fishery in the Western Mediterranean Sea. Implementation of an adequate management plan needs complete genetic data of the non-spawning and spawning grounds of the species. During the reproductive period, the species forms spawning aggregations in the middle slope, mainly constituted of mature females carrying spermatophores. Seven spawning females’ grounds in the Western Mediterranean Sea from Gulf of Lions (France) to Cabo de Palos (Spain) were sampled during two consecutive years, 2016 and 2017. This study assessed for the first time the levels of genetic diversity within spawning grounds, the genetic divergence among them and estimated the degree of temporal genetic stability using multilocus genotyping. Our results showed a high connectivity of the spawning females’ grounds that remains stable during the two analysed years, explained by passive larval dispersal, together with juveniles and adults’ migration. We advise that a future management plan for A. antennatus fishery should consider the Mediterranean Subarea GSA6 as a single unit, but it should be combined with local monitoring in order to ensure the sustainable exploitation of the populations.

Influence of milk proteins on the adhesion and formation of Bacillus sporothermodurans biofilms: Implications for dairy industrial processing

Bacillus sporothermodurans is a producer of highly heat-resistant spores, which is a problem for the dairy industry worldwide. In this work, we studied the attachment and biofilm formation on stainless steel surfaces in contact with milk proteins (casein and whey). The results of the biofilm formation were obtained by the plate count method. In conjunction, biofilms (niches and cell sizes) were measured by scanning electron microscopy (SEM) on the 1 st , 5 th and 10 th day. X-ray photoelectron spectroscopy (XPS) was a complementary technique that probed the conditioning of the substrate surface after 24 h. The milk proteins affected the total bacterial count in the samples, and also influenced the biofilm architecture. Sessile cell counts varied from 4.3 log CFU/cm 2 in the attachment stage to up to 10.2 log CFU/cm 2 in the matured biofilm stage. The spore counts varied from <1.4 ± 0.02 (1 st day) to 3.7 log ± 1.1 log spores/cm 2 (10 th day). The control group at the biofilm maturation stage (5 th day) had higher niches than at the cell fixation (1 st day) and was different from the other groups that showed active dispersion in the presence of milk proteins. The same occurred on the 10 th day for the control group. Circular patterns in the biofilm with casein, passive dispersal and elongated cells were also observed. Enzyme treatment and disinfectants may be used to remove or reduce biofilm formation. • This is the first report on the B. sporothermodurans biofilm life cycle. • The distributions of B. sporothermodurans biofilms were influenced by milk proteins. • Active and passive dispersal were observed in the biofilm life cycle. • Enzymatic and chemical treatments are efficient for the removal of biofilm. • Eventual pitting or corrosion and biofilm formation at the air-liquid interface were observed.

Micro-/Meso-Scale Distinction and Horizontal Migration of Tintinnid (Ciliophora: Tintinnida) Assemblages in Three Regions Around the North Pacific Ocean

We explored the relationships among different tintinnid populations on micro-, meso-, and basin-scales from three regions across the Pacific Ocean, including the Costa Rica Dome (CRD) in the Eastern Pacific Ocean, the Celebes Sea (CS), and the Tokara Strait (TS) in the Western Pacific Ocean. We quantified the species occurrence, vertical and biogeographic distribution patterns, and morphological parameters of tintinnid assemblages. A total of 46 tintinnid species were observed, with more than half (63.0%) in common among the three areas, accounting for 97.1% of the total abundances. The numerically abundant forms remained more or less the same set of species in the three areas. However, community structure analyses, in terms of species, lorica oral diameter (LOD) size classes, and genera, revealed clear distinctions among different regions, as well as among different water depths. A Lagrangian simulation of passive dispersal in ocean currents across the Pacific Ocean, supported the hypothesis that greater similarity between tintinnid populations in the CS and TS (relative to CRD), was related to ocean circulation linkages between the populations. A latitudinal decline of tintinnid species richness was observed, mainly as a result of a decline of redundant species and warm-water species in colder areas. These data provide information unique insight into population variability of microzooplankton communities on micro- to meso- and even large scales in the world oceans.

Wave‐Enhanced Tracer Dispersion

AbstractRecent oceanic datasets indicate high gravity wave‐to‐balance energy ratio at submesoscales. Idealized investigations exploring such wave‐dominated regimes have found that waves can break up coherent vortices and generate energetic small scale flow structures, indicating that the turbulence phenomenology is very different in wave‐dominated regimes when compared to the quasi‐geostrophic regime. Motivated by these recent investigations revealing significant differences in the flow dynamics in quasi‐geostrophic and wave‐dominated regimes and multiple oceanic observations pointing out enhanced tracer stirring at submesoscales, in this paper we compare and contrast passive tracer dispersion by barotropic flows in quasi‐geostrophic and wave‐dominated turbulent regimes using the reduced model explored by Thomas and Yamada (2019), https://doi.org/10.1017/jfm.2019.465. On comparing passive tracer dispersion by barotropic flows in the two different regimes, we find that wave‐dominated turbulent flows stir and mix tracer fields much more rapidly than quasi‐geostrophic turbulent flows that consist of well‐defined coherent vortices. The presence of energetic small‐scale features in wave‐dominated flows increases small‐scale turbulent diffusivity and results in steeper tracer variance spectrum in wave‐dominated flows compared to the quasi‐geostrophic flows. Our findings point out that gravity waves can play an indirect role in enhancing tracer dispersion: waves modify the flow, generating energetic small‐scale structures, that makes stirring of tracers more efficient. Despite our study being idealized, we speculate the qualitative phenomenology of waves indirectly enhancing tracer dispersion to be of significance at submesoscales in the world's oceans.

Environmental heterogeneity, dispersal mode and habitat specialisation modify within‐site beta diversity of spring macroinvertebrates

AbstractSpring helocrenes are a unique aquatic environment with high biotic diversity. Although environmental heterogeneity has traditionally been assumed to explain the high species richness of spring habitats, this assumption has never been properly tested. Here, we sampled macroinvertebrates from two calcareous helocrenes in Slovakia with visually distinguishable mesohabitat heterogeneity. We hypothesise that macroinvertebrate beta diversity significantly increases with environmental heterogeneity even at a small within‐site spatial scale. We also examined four species‐trait categories, that is, active or passive dispersers and habitat specialists or generalists. Significant spatial structuring of environmental heterogeneity was found at one site, whereas the other site did not show a clear spatial pattern. Strong associations were found between beta diversity of all species trait categories and environmental heterogeneity at the first site, while there were virtually no associations at the second site. Specialists were not spatially structured at any of the sites examined. Our results suggest that invertebrate beta diversity responds positively to environmental heterogeneity at a site by also tracking spatial structuring of abiotic conditions. However, the response may vary depending on the dispersal mode and habitat specialisation of the invertebrates.

Machine Learning to Predict Area Fugitive Emission Fluxes of GHGs from Open-Pit Mines

Greenhouse gas (GHG) emissions from open-pit mines pose a global climate challenge, which necessitates appropriate quantification to support effective mitigation measures. This study considers the area-fugitive methane advective flux (as a proxy for emission flux) released from a tailings pond and two open-pit mines, denominated “old” and “new”, within a facility in northern Canada. To estimate the emission fluxes of methane from these sources, this research employed near-surface observations and modeling using the weather research and forecasting (WRF) passive tracer dispersion method. Various machine learning (ML) methods were trained and tested on these data for the operational forecasting of emissions. Predicted emission fluxes and meteorological variables from the WRF model were used as training and input datasets for ML algorithms. A series of 10 ML algorithms were evaluated. The four models that generated the most accurate forecasts were selected. These ML models are the multi-layer perception (MLP) artificial neural network, the gradient boosting (GBR), XGBOOST (XGB), and support vector machines (SVM). Overall, the simulations predicted the emission fluxes with R2 (-) values higher than 0.8 (-). Considering the bias (Tonnes h−1), the ML predicted the emission fluxes within 6.3%, 3.3%, and 0.3% of WRF predictions for the old mine, new mine, and the pond, respectively.

Dispersão potencial de caramujos por endozoocoria de aves aquáticas em áreas úmidas neotropicais

Abstract Waterbird-mediated zoochory is one of the main ecological mechanisms by which non-flying freshwater invertebrates can disperse between isolated wetlands. Passive dispersal through gut passage inside waterbirds (endozoochory) may explain how many organisms spread in the landscape. Here, we evaluate the potential for dispersal of aquatic snails by three waterbird species in neotropical wetlands. A total of 77 faecal samples from Coscoroba coscoroba (n = 28), Dendrocygna viduata (n = 36) and Anas flavirostris (n = 13) were collected in the field and taken to the laboratory. There, the samples were examined under a stereomicroscope to check for the presence of gastropod shells. We found 496 intact gastropod shells, and Heleobia piscium was the most abundant species (n= 485). We also found two shells of Drepanotrema sp. and nine others distributed between two different morphotypes of Planorbidae. Snails were present in 20.8 % of all samples, and were more frequent in faeces of coscoroba swan (50%) than the other two bird species. Our data suggest that aquatic snails may disperse by avian endozoochory between neotropical wetlands, with vectors including migratory bird species.

A relação entre distribuição regional e abundância de espécies zooplanctônicas numa planície de inundação é mediada pelo regime hidrológico

Abstract: Aim Positive relationships between occupancy and abundance are often found for different groups of organisms and ecosystem types. However, to our knowledge, no study has sought to assess this relationship considering a context in which a particular mechanism is the most likely explanation. In this study, in addition to the positive relationship with abundance, we tested the hypothesis that occupancy of zooplankton species should be greater during the flood season because in this period the hydrological connectivity is greater than in the dry season, facilitating passive dispersal between floodplain environments. Methods Our study was carried out at 52 sites - including lakes and rivers - on the Araguaia River floodplain. We used an analysis of covariance to test the effects of abundance and hydrological period on zooplankton occupancy. Results We found, as expected, a positive relationship between occupancy and abundance of zooplankton species in each hydrological period. Our results also indicated that, with the increase in abundance, species occupancies were higher in the flood than in the dry season. Conclusions The positive effect of the flood on zooplankton occupancy can be explained by the increase in water level that increases the hydrological connectivity and the potential for plankton passive dispersal.

Uncertainty Quantification of Inflow on Passive Scalar Dispersion in Urban Environment

Uncertainty Quantification of Inflow on Passive Scalar Dispersion in Urban Environment

Vertebrates as uninfected disseminators of helminth eggs and larvae.

The passive dispersal of non-mobile organisms by vertebrates (zoochory) is a common mechanism used to explain their often widespread distribution. Transport occurs either internally via the vertebrate digestive tract (endozoochory), or externally be adhering to skin, feathers or fur (ectozoochory), and its success is due to both physiological and ecological factors associated with the disseminating 'hosting' animal. Helminth eggs and larvae are generally non-mobile stages that are largely dependent on the movement of another animal, typically a host, for geographical dissemination. Studies on the zoochory of helminths by vertebrates are extensive and particularly long-standing, stretching back to the 19th century, although this literature is often overlooked when considering the biogeography of parasites. This review assesses the potential of helminths to be dispersed passively by zoochory examining evidence from both laboratory and field studies. The physiological dynamics of the vertebrate intestines and skin surface as hostile environments, as well as the characteristics of eggs and larvae which may facilitate successful transport are evaluated. The various mechanisms of helminth endo- and ectozoochory are presented and the likelihood of long-distance dispersal determined. It is concluded that zoochory is a potentially important means of disseminating parasites.

Wind Speed and Direction Drive Assisted Dispersal of Asian Citrus Psyllid.

Wind directly influences the spread of vector-borne plant pathogens by driving the passive dispersal of vectors to potentially new areas. Here, we evaluated the effect of wind speed and direction on the dispersal of the Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama) (Hemiptera: Psyllidae), the vector of the bacteria causing huanglongbing (HLB), a lethal disease of citrus. The effect of different wind speeds on short or long-distance dispersal of ACP was investigated using a high-speed wind tunnel under laboratory conditions. The effect of wind direction on ACP dispersal under field conditions was evaluated using custom-made wind vane-style traps. In wind tunnel assays, ACP remained on plants until wind treatments reached ≥48 km/h when psyllids were mostly dislodged from plants and moved by the wind. For a short-distance, wind-driven movement (movement by the wind from one plant to another), the effect of wind speed was not significant at any of the wind speed treatments tested. Wind vane traps placed in a Florida citrus grove captured significantly more ACP on the windward side, suggesting that ACP were moved with the wind. The number of ACP found on the windward side of traps was significantly higher from May to August. These results indicate that ACP is likely to disperse with prevailing wind direction and that settled ACP may become dislodged and moved at random by high wind speeds occurring in areas of significant citrus production (southern California, Florida, or Texas).

Disentangling the roles of electric fields and wind in spider dispersal experiments

Observations of spiders' pre-dispersal behavior can be used to answer various ecological and evolutionary questions. So far, dispersal experiments have often used air currents as a stimulating factor. Effects of electric fields on the pre-dispersal behavior of spiders have recently been discovered. Electric fields may lead to unexplained variation in results and limit comparability between previous studies. Here we aim to disentangle the roles of wind and electric fields on the passive aerial dispersal of three linyphiid spider species. Our results confirm that strong electric fields in the air elicit pre-dispersal behavior, and in combination with a light wind, facilitate dispersal (take-off). Nevertheless, even the strong electric fields employed here played a rather supplementary role in spiders' dispersal with wind remaining the most influential factor. We recommend that studies of passive aerial dispersal should control for electric field strength but otherwise use wind as the primary stimulating factor.