Dispersal Paths Research Articles

Correlating habitat suitability with landscape connectivity: A case study of Sichuan golden monkey in China

We examined the landscape suitability of the region currently occupied by the Sichuan golden money (Rhinopithecus roxellana) using occupancy models constructed in Maxent with presence-only data and environmental variables. The aim of the study was to estimate potential dispersal corridors between presently disjunct populations. Least-cost path analysis was used to estimate its dispersal paths across the fragmented landscape. The results indicate that core areas of suitable habitat are located in the Qinling, Dabashan, and Minshan Mountains, as well as small patches in the Qionglai, Daxiangling and Liangshan Mountains; the most suitable habitats are in nature reserves of the Minshan Mountain. Elevation and density of the human settlements were the most important factors for identifying suitable habitat; and we identified location of less populated areas where some suitable forest patches offer the potential for dispersal corridors for this species. The study implies that there is potential for expansion of the species distribution, if steps are taken to preserve current forest patches that maybe too small for residency but suitable for dispersal.

Collective modes in multipolar plasmonic lattices: control of interparticle-gap upward/downward energy streams

We numerically study the collective resonances and field profiles of two-dimensional arrays of large metallic nanodisks supporting multipolar plasmonic modes in nearly homogeneous environments. We show that, depending on the wavelength, these arrays can support two distinct collective modes with orthogonal field intensity distributions. In one of these modes (scattering mode), the optical scattering between the nanodisks forms a sharp optical feature with significant sensitivity to the refractive index of the environment. In the second mode (optical-band mode), the nanodisks are mainly coupled via an optical band with a field intensity profile perpendicular to the incident light polarization. This mode is associated with a subtle optical peak with much less sensitivity to the environment. We demonstrate that around this peak, the nanodisks support a unique asymmetrical field dispersion and energy flow paths. For a given wavelength range, the plasmon fields in this mode deeply penetrate into the substrate while energy moves up from the substrate between the gaps of the nanodisks, forming energy whirlpools in the superstrate. With a slight wavelength change, these fields switch to the superstrate, and the direction of the gap energy path is inverted. We investigate how such features can be tuned by adding a thin layer of silicon between the substrate and superstrate and discuss the applicability of the scattering mode for sensitive sensors.

Proximate influences on female dispersal in white‐tailed deer

ABSTRACTUltimate causes of animal dispersal have been hypothesized to benefit the dispersing individual because dispersal reduces competition for local resources, potential for inbreeding, and competition for breeding partners. However, proximate cues influence important features of dispersal behavior, including when dispersal occurs, how long it lasts, and direction, straightness, and distance of the dispersal path. Therefore, proximate cues that affect dispersal influence ecological processes (e.g., population dynamics, disease transmission, gene flow). We captured and radio‐marked 277 juvenile female white‐tailed deer (Odocoileus virginianus), of which 27 dispersed, to evaluate dispersal behavior and to determine proximate cues that may influence dispersal behavior. Female dispersal largely occurred at 1 year of age and coincided with the fawning season. Dispersal paths varied but generally were non‐linear and prolonged. Physical landscape features (i.e., roadways, rivers, residential areas) influenced dispersal path direction and where dispersal terminated. Additionally, forays outside of the natal range that did not result in dispersal occurred among 52% of global positioning system (GPS)‐collared deer (n = 25) during the dispersal period. Our results suggest intra‐specific social interactions and physical landscape features influence dispersal behavior in female deer. Female dispersal behavior, particularly the lack of directionality, the semi‐permeable nature of physical barriers, and the frequency of forays outside of the natal range, should be considered in regard to population management and controlling the spread of disease. © 2016 The Wildlife Society.

Connecting models to movements: testing connectivity model predictions against empirical migration and dispersal data

Connectivity has become a top conservation priority in response to landscape fragmentation. Many methods have been developed to identify areas of the landscape with high potential connectivity for wildlife movement. However, each makes different assumptions that may produce different predictions, and few comparative tests against empirical movement data are available. We compared predictive performance of the most-used connectivity models, cost-distance and circuit theory models. We hypothesized that cost-distance would better predict elk migration paths, while circuit theory would better predict wolverine dispersal paths, due to alignment of the methods’ assumptions with the movement ecology of each process. We used each model to predict elk migration paths and wolverine dispersal paths in the Greater Yellowstone Ecosystem, then used telemetry data collected from actual movements to assess predictive performance. Methods for validating connectivity models against empirical data have not been standardized, thus we applied and compared four alternative methods. Our findings generally supported our hypotheses. Circuit theory models consistently predicted wolverine dispersal paths better than cost-distance, though cost-distance models predicted elk migration paths only slightly better than circuit theory. In most cases, our four validation methods supported similar conclusions, but provided complementary perspectives. We reiterate suggestions that alignment of connectivity model assumptions with focal species movement ecology is an important consideration when selecting a modeling approach for conservation practice. Additional comparative tests are needed to better understand how relative model performance may vary across species, movement processes, and landscapes, and what this means for effective connectivity conservation.

Combining the least cost path method with population genetic data and species distribution models to identify landscape connectivity during the late Quaternary in Himalayan hemlock.

Himalayan hemlock (Tsuga dumosa) experienced a recolonization event during the Quaternary period; however, the specific dispersal routes are remain unknown. Recently, the least cost path (LCP) calculation coupled with population genetic data and species distribution models has been applied to reveal the landscape connectivity. In this study, we utilized the categorical LCP method, combining species distribution of three periods (the last interglacial, the last glacial maximum, and the current period) and locality with shared chloroplast, mitochondrial, and nuclear haplotypes, to identify the possible dispersal routes of T. dumosa in the late Quaternary. Then, both a coalescent estimate of migration rates among regional groups and establishment of genetic divergence pattern were conducted. After those analyses, we found that the species generally migrated along the southern slope of Himalaya across time periods and genomic makers, and higher degree of dispersal was in the present and mtDNA haplotype. Furthermore, the direction of range shifts and strong level of gene flow also imply the existence of Himalayan dispersal path, and low area of genetic divergence pattern suggests that there are not any obvious barriers against the dispersal pathway. Above all, we inferred that a dispersal route along the Himalaya Mountains could exist, which is an important supplement for the evolutionary history of T. dumosa. Finally, we believed that this integrative genetic and geospatial method would bring new implications for the evolutionary process and conservation priority of species in the Tibetan Plateau.

Expansion of bloom-forming Dolichospermum lemmermannii (Nostocales, Cyanobacteria) to the deep lakes south of the Alps: Colonization patterns, driving forces and implications for water use

Since the beginning of the 1990s, the largest lakes south of the Alps (Garda, Iseo, Como and Maggiore) showed a progressive colonization of Dolichospermum lemmermannii (Cyanobacteria). The appearance of surface blooms of this species raised serious concerns because of the impacts on the tourist economy and the potential toxigenic effects. Nevertheless, no detailed investigations were done to clarify the taxonomic position, ecology and toxicity of this species. In this work, phylogenetic analyses based on the 16S rRNA and rpoB genes demonstrated how the strains isolated from the Italian lakes were clustered together with other D. lemmermannii strains isolated in Northern Europe. The expansion of this species in the southern subalpine lakes contrasted with the prevailing south to north dispersion paths typical of other Nostocales (e.g. Cylindrospermopsis and Aphanizomenon). Conversely, the spread was consistent with the geographical areal of this cyanobacterium, which appears circumscribed between the 40th parallel and the Arctic Circle. This aspect highlights the ecological heterogeneity that characterizes the order Nostocales. In Lake Garda, D. lemmermannii always developed in the warmest months (>15°C) with low abundances (generally <200 cell mL−1). Nevertheless, owing to its ability to form surface water blooms, this species is considered as one of the most nuisance algae in the subalpine lake district. From the other side, different strains isolated from these large lakes tested negative for the biosynthesis of microcystins, anatoxin-a, nodularins and cylindrospermopsins, and for the presence of mcyE and anaC genes of the microcystins and anatoxin-a gene clusters.

Quantifying the reliability of dispersal paths in connectivity networks.

Many biological systems, from fragmented landscapes to host populations, can be represented as networks of connected habitat patches. Links between patches in these connectivity networks can represent equally diverse processes, from individuals moving through the landscape to pathogen transmissions or successive colonization events in metapopulations. Any of these processes can be characterized as stochastic, with functional links among patches that exist with various levels of certainty. This stochasticity then needs to be reflected in the algorithms that aim to predict the dispersal routes in these networks. Here we adapt the concept of reliability to characterize the likelihood that a specific path will be used for dispersal in a probabilistic connectivity network. The most reliable of the paths that connect two patches will then identify the most likely sequence of intermediate steps between these patches. Path reliability will be sensitive to targeted disruptions of individual links that form the path, and this can then be used to plan the interventions aimed at either preserving or disrupting the dispersal along that path. The proposed approach is general, and can be used to identify the most likely dispersal routes in various contexts, such as predicting patterns of migrations, colonizations, invasions and epidemics.

On the relevance of tidal forcing in modelling the Mediterranean thermohaline circulation

The four dominant constituents of the semi-diurnal and diurnal tides have been implemented in a regional eddy-resolving Mediterranean version of the Massachusetts Institute of Technology general circulation model to assess the role played by tides on the simulated Mediterranean thermohaline circulation. To this aim we have compared two 10-year hindcast simulations differing only for the inclusion/omission of tidal forcing. Following the recent recommendations suggested by Sannino et al. (2014) both simulations use the same model having a substantial increment of the horizontal resolution in the region of the Strait of Gibraltar. The results suggest that application of explicit tidal forcing in a Mediterranean model has non negligible effects on the simulated circulation in addition to the expected intensification of local mixing processes. The western basin exhibits an immediate response to the different characteristics of the inflowing AW observable in the modified deep water convection processes in the Gulf of Lion. The inclusion of tidal forcing also induces changes in the intermediate circulation of the Tyrrhenian Sea bringing to a better representation of local structures and a reinforcement of the global thermohaline cell. LIW dispersal paths in the eastern basin are also affected by tides.

Pathways and mechanisms of Late Ordovician (Katian) faunal migrations of Laurentia and Baltica

Late Ordovician strata within the Cincinnati Basin record a mass faunal migration event during the C4 and C5 depositional sequences. The geographic source region for the invaders and the paleoceanographic conditions that facilitated dispersal into the Cincinnati Basin has previously been poorly understood. Using Parsimony Analysis of Endemicity, biogeographic relationships among Laurentian and Baltic basins were analyzed for each of the C1-C5 depositional sequences to identify dispersal paths. The results support multiple dispersal pathways, including three separate dispersal events between Baltica and Laurentia. Within Laurentia, results support dispersal pathways between areas north of the Transcontinental Arch into the western Midcontinent, between the Upper Mississippi Valley into the Cincinnati Basin, and between the peri-cratonic Scoto-Appalachian Basin and the Cincinnati Basin. These results support the hypothesis that invasive taxa entered the Cincinnati Basin via multiple dispersal pathways and that the equatorial Iapetus current facilitated dispersal of organisms from Baltica to Laurentia. Within Laurentia, surface currents and large storms moving from northeast to southwest likely influenced the dispersal of organisms. Larval states were characterized for the Richmondian invaders, and most invaders were found to have had planktotrophic planktic larvae. These self-feeding larvae have high dispersal potential, which - in conjunction with oceanographic and climatic conditions - enabled long-distance dispersal and interbasinal species migrations.

Human‐aided and natural dispersal drive gene flow across the range of an invasive mosquito

Human-aided transport is responsible for many contemporary species introductions, yet the contribution of human-aided transport to dispersal within non-native regions is less clear. Understanding dispersal dynamics for invasive species can streamline mitigation efforts by targeting routes that contribute disproportionally to spread. Because of its limited natural dispersal ability, rapid spread of the Asian tiger mosquito (Aedes albopictus) has been attributed to human-aided transport, but until now, the relative roles of human-aided and natural movement have not been rigorously evaluated. Here, we use landscape genetics and information-theoretic model selection to evaluate 52 models representing 9240 pairwise dispersal paths among sites across the US range for Ae.albopictus and show that recent gene flow reflects a combination of natural and human-aided dispersal. Highways and water availability facilitate dispersal at a broad spatial scale, but gene flow is hindered by forests at the current distributional limit (range edge) and by agriculture among sites within the mosquito's native climatic niche (range core). Our results show that highways are important to genetic structure between range-edge and range-core pairs, suggesting a role for human-aided mosquito transport to the range edge. In contrast, natural dispersal is dominant at smaller spatial scales, reflecting a shifting dominance to natural movement two decades after introduction. These conclusions highlight the importance of (i) early intervention for species introductions, particularly those with readily dispersed dormant stages and short generation times, and (ii) strict monitoring of commercial shipments for transported immature stages of Ae.albopictus, particularly towards the northern edge of the US range.

Hydrographic and biological components of the seascape structure the meroplankton community in a frontal system

Studies investigating the environmental influence on the structure of meroplank- tonic communities generally focus on fish larvae. To our knowledge, no study to date has com- bined information on other important groups of the meroplankton such as decapod crustaceans and cephalopods. Here, we investigate the spatiotemporal distribution of a summer meroplankton community in the upper water column of the Balearic Sea (Western Mediterranean). The study compares 2 contrasting years (2004 and 2005) in terms of hydrographic (i.e. thermal pattern, spa- tial structure of the oceanic front) and biological (i.e. origin and composition of phytoplankton) components of the pelagic seascape. Our results reveal that both year-specific drivers, such as salinity gradient, and common factors between years, such as chlorophyll concentration, influence the community structure. This resulted in a contrasting influence between years of hydrographic and biological components of the seascape, which implies an alternating effect of dispersal path- ways and retention to coupling productive conditions. The study characterizes recurrent environ- mental scenarios associated with different co-occurring fish and decapod crustacean larvae (i.e. mixed assemblages), the most relevant being: (1) recent Atlantic waters of low salinity, (2) resident waters of higher salinity, and (3) high chlorophyll concentration at depth of chlorophyll maximum. This study sheds new light on the complex responses of plankton communities to exogenous drivers in highly variable environments such as frontal systems.

A Novel Scheme for Dynamic Triggering Of Packet Dispersion

Packet burst losses are proven to be detrimental to multimedia applications. Most of the burst losses in the Internet are the result of tail drop discipline, which drops packets when queues in routers are filled to their maximum capacity. A potential way of addressing the burst losses is to use packet dispersion over multiple and disjoint paths to destination. However, packet dispersion requires packet reordering and addressing the problems concerning packet latency and jitter. We are proposing a model that dynamically triggers packet dispersion depending on the high priority queue occupancy containing high priority traffic, whereas the need for packet dispersion and the number of dispersion paths is inferred from traffic load in other queues. Proposed mechanism reduces tail drops in queues containing high priority traffic by performing packet shifting to high priority queues that belong to other output interfaces designated for packet dispersion. It delivers significant benefits regarding packet loss and packet loss distance, which are considered imperative parameters for describing the quality of multimedia and real-time traffic. DOI: http://dx.doi.org/10.5755/j01.eee.20.5.5429

Tracing variability of run‐off generation in mountainous permafrost of semi‐arid north‐eastern Mongolia

AbstractThe headwaters of mountainous, discontinuous permafrost regions in north‐eastern Mongolia are important water resources for the semi‐arid country, but little is known about hydrological processes there. Run‐off generation on south‐facing slopes, which are devoid of permafrost, has so far been neglected and is totally unknown for areas that have been affected by recent forest fires. To fill this knowledge gap, the present study applied artificial tracers on a steppe‐vegetated south‐facing and on two north‐facing slopes, burned and unburned. Combined sprinkling and dye tracer experiments were used to visualize processes of infiltration and water fluxes in the unsaturated zone. On the unburned north‐facing slope, rapid and widespread infiltration through a wet organic layer was observed down to the permafrost. On the burned profile, rapid infiltration occurred through a combusted organic and underlying mineral layer. Stained water seeped out at the bottom of both profiles suggesting a general tendency to subsurface stormflow (SSF). Ongoing SSF could directly be studied 24 h after a high‐intensity rainfall event on a 55‐m hillslope section in the burned forest. Measurements of water temperature proved the role of the permafrost layer as a base horizon for SSF. Repeated tracer injections allowed direct insights into SSF dynamics: A first injection suggested rather slow dispersive subsurface flow paths; whereas 18 h later, a second injection traced a more preferential flow system with 20 times quicker flow velocities. We speculate that these pronounced SSF dynamics are limited to burned slopes where a thermally insulating organic layer is absent. On three south‐facing soil profiles, the applied tracer remained in the uppermost 5 cm of a silt‐rich mineral soil horizon. No signs of preferential infiltration could be found, which suggested reduced biological activity under a harsh, dry and cold climate. Instead, direct observations, distributed tracers and charcoal samples provided evidence for the occurrence of overland flow. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Large frugivorous birds facilitate functional connectivity of fragmented landscapes

Summary Quantifying ecosystem functions in spatially explicit ways is important for management decisions in increasingly fragmented landscapes. Between‐patch dispersal of seeds by frugivores constitutes a key ecosystem function to ensure connectivity for fleshy‐fruited plants. However, to date, methodological hurdles have limited our understanding of dispersal pathways on the landscape scale. We made use of newly available tracking devices and combined movement data of 30 trumpeter hornbills Bycanistes bucinator with gut passage times and high‐resolution habitat data in a fragmented forest landscape in South Africa. We identified each potential seed dispersal path and distinguished whether potential seed transport happened to a different forest patch (between‐patch dispersal), within the same patch (within‐patch dispersal) or into the habitat matrix (failed dispersal). To quantify functional landscape connectivity, we identified all possible between‐patch connections and used graph networks to estimate landscape connectivity provided by hornbills. Although potential between‐patch dispersal events were rare (on average 7% compared to 20% failed dispersal and 73% within‐patch dispersal), hornbills could cover distances of up to 15 km. Hornbills visited over 100 forest patches and connected a habitat network with an extent of about 50 km, which increased the potential functional connectivity of the landscape more than twofold. We identified habitat patches that were critical stepping stones for seed dispersal pathways. Without these stepping stones, the network would likely disintegrate into separated components and lead to isolation of forest fragments. Synthesis and applications. We showed that large frugivorous birds can greatly improve functional connectivity for fleshy‐fruited plants across broad scales, linking habitat patches in fragmented forest landscapes. Combining high‐resolution movement and landscape data in graph networks allows identifying seed dispersal pathways and critical stepping stones in fragmented landscapes. This approach addresses the general challenge of spatially explicit mapping of ecosystem services and can be widely incorporated in reserve design and landscape‐level conservation planning.

The influence of habitat structure on genetic differentiation in red fox populations in north-eastern Poland.

The red fox (Vulpes vulpes) has the widest global distribution among terrestrial carnivore species, occupying most of the Northern Hemisphere in its native range. Because it carries diseases that can be transmitted to humans and domestic animals, it is important to gather information about their movements and dispersal in their natural habitat but it is difficult to do so at a broad scale with trapping and telemetry. In this study, we have described the genetic diversity and structure of red fox populations in six areas of north-eastern Poland, based on samples collected from 2002–2003. We tested 22 microsatellite loci isolated from the dog and the red fox genome to select a panel of nine polymorphic loci suitable for this study. Genetic differentiation between the six studied populations was low to moderate and analysis in Structure revealed a panmictic population in the region. Spatial autocorrelation among all individuals showed a pattern of decreasing relatedness with increasing distance and this was not significantly negative until 93 km, indicating a pattern of isolation-by-distance over a large area. However, there was no correlation between genetic distance and either Euclidean distance or least-cost path distance at the population level. There was a significant relationship between genetic distance and the proportion of large forests and water along the Euclidean distances. These types of habitats may influence dispersal paths taken by red foxes, which is useful information in terms of wildlife disease management.Electronic supplementary materialThe online version of this article (doi:10.1007/s13364-014-0180-2) contains supplementary material, which is available to authorized users.

Environment and dispersal paths override life strategies and residence time in determining regional patterns of invasion by alien plants

Abstract We describe a novel dissimilarity framework to analyze spatial patterns of species diversity and illustrate it with alien plant invasions in Northern Portugal. We used this framework to test the hypothesis that patterns of alien invasive plant species richness and composition are differently affected by differences in climate, land use and landscape connectivity ( i.e. Geographic distance as a proxy and vectorial objects that facilitate dispersal such as roads and rivers) between pairs of localities at the regional scale. We further evaluated possible effects of plant life strategies (Grime's C-S-R) and residence time. Each locality consisted of a 1 km 2 landscape mosaic in which all alien invasive species were recorded by visiting all habitat types. Multi-model inference revealed that dissimilarity in species richness is more influenced by environmental distance (particularly climate), whereas geographic distance (proxies for dispersal limitations) is more important to explain dissimilarity in species composition, with a prevailing role for ecotones and roads. However, only minor differences were found in the responses of the three C-S-R strategies. Some effect of residence time was found, but only for dissimilarity in species richness. Our results also indicated that environmental conditions ( e.g. climate conditions) limit the number of alien species invading a given site, but that the presence of dispersal corridors determines the paths of invasion and therefore the pool of species reaching each site. As geographic distances ( e.g. ecotones and roads) tend to explain invasion at our regional scale highlights the need to consider the management of alien invasions in the context of integrated landscape planning. Alien species management should include (but not be limited to) the mitigation of dispersal pathways along linear infrastructures. Our results therefore highlight potentially useful applications of the novel multimodel framework to the anticipation and management of plant invasions.

Influence of spatial layout on airflow field and particle distribution on the workspace of a factory

The transport of raw materials within factories can lead to contamination in the form of suspended particles. This study used airflow velocity distribution and pollutant distribution to develop a reliable fluid mechanics model for the calculation of dispersion values. We then modified conventional air inlet models with the precondition of maintaining the same inlet volume and proposed a model to optimize airflow based on simulations of particle dispersion and accumulation. Finally, we altered the spatial layout of the building and compared the effects of various factors on the distribution of particulate pollution. Our results demonstrate that the spatial design of the factory significantly influences airflow and therefore the effectiveness of efforts to eliminate particulate matter. When designing factories, one must consider the operations of personnel and in-feed materials and configure air-conditioning systems within the overall layout of the space. To ensure a healthy work environment, airflow field control should be used to plan models for the discharge of harmful substances, according to their source and dispersion paths.

Understanding the salinity issue of coal mine spoils in the context of salt cycle

Coal mine spoils (CMSs), the solid wastes originated from the rock formations and soil cover overlying or interbedded with coal seams, are a worldwide environmental management challenge. Previous studies have shown that salinity is of most concern among the CMSs' environmental impacts, especially in Australia. With increasing concerns from both the governments and communities, there is a real need for the coal mining industry to understand the source, dynamics and management options of CMS salinity. We reviewed the general properties of CMSs from coal mine sites worldwide and the current understanding of the CMS salinity, which are in a limited number of available published reports. Properties (e.g., pH, electrical conductivity and hydraulic conductivity) of studied CMSs varied largely due to its complex lithological origination. A conceptual model was proposed to illustrate the origin, dispersion paths and transformations dynamics of salts in spoils, taking the scenario of a coal mine in Australia as an example. The major factors governing the salt dynamics in CMSs are summarized as mineral weatherability and salt leachability of the spoils. Management of CMS salinity is still a vague area awaiting more extensive studies. Three topics related to the management were explored in the review, which are pre-mining planning, spatial variability of spoil properties and remediation including electrokinetics and phytoremediation. Particularly, based on the geological classification of CMSs and the leachate chemistry of spoils of various sources, a clear relationship between salinity and geounits was established. This association has a potential application in pre-mining planning for the management of salinity from coal mine spoils.

Modelling dispersal and connectivity of broadcast spawning corals at the global scale

AbstractAimWe develop the first global model of connectivity for a generic broadcast spawning coral, and compare the results to connectivity estimates from genetic studies, general biogeographic patterns and theories. We also derive various ‘connectivity indices’ describing relative isolation and source potential between locations.LocationModelled oceans 47° S–47° N.MethodsDispersal of model coral ‘larvae’ was simulated over 8 years using an individual‐based biophysical dispersal model driven by 1/12°‐resolution surface ocean current data and incorporating individual trait variability (e.g. a phased pre‐competency period). Source and arrival locations of modelled larvae on suitable reef habitat gave standardized dispersal paths and relative levels of connectivity.ResultsIn the model c. 50% of connections occurred within 50–100 km, with rarer dispersal between regions linking entire oceans in a ‘stepping stone’ fashion. The central Pacific was an almost complete barrier to dispersal, only rarely breached westward from the Galapagos to Marquesas Islands. Areas showing strong isolation also included Hawaii, Easter Island, the Red Sea and the eastern Atlantic. The Indo‐West Pacific and Great Barrier Reef showed the highest levels of connectivity, with secondary peaks in the western Indian Ocean, corresponding to areas of enriched coral diversity. The central Indo‐Pacific diversity hotspot was overall a greater source than sink for dispersal.ConclusionsThis study provides a global view of connectivity that complements genetic and biogeographic work as well as providing a number of novel findings relevant to biogeographic theories (e.g. the central Indo‐Pacific as a dispersal source; Johnston Atoll as the sole ‘stepping‐stone’ into Hawaii). Discrepancies with proposed connectivity patterns (e.g. one‐way, westward, connectivity across the central Pacific) present hypotheses for future research. The model represents an effective tool for exploring the factors controlling connectivity on this scale and the effects of climate change on future connectivity, and will also aid predictions of future reef distributions.

The role of wind in hydrochorous mangrove propagule dispersal

Abstract. Although wind has been recognized to be an important factor in the dispersal of hydrochorous mangrove propagules, and hence in the quantification of (meta)population dynamics, the species-specific sensitivity to wind effects has not been studied. We combined observations from a controlled experiment (flume tank) and in situ experiments to understand wind and water current contributions to dispersal potential as well as to estimate real dispersal ranges due to immediate response to tidal currents (two outgoing tides). This was done for 4 species with propagules differing in morphological and buoyancy properties (i.e. Rhizophora mucronata, Ceriops tagal, Heritiera littoralis and Xylocarpus granatum). The flume experiments revealed that the influence of wind depends on the density of a propagule (and hence its buoyancy characteristics) and that typical morphological characteristics of the dispersal unit are additionally important. H. littoralis propagules were influenced most, because on the one hand their low density (613.58 g L−1; n =10) enables them to float on top of the water surface, and on the other hand their "sailboat-like" structure provides a relatively large surface area. The X. granatum fruits appeared to be the least influenced by ambient wind conditions, explained by the smooth surface and spherical shape of which, because of the fruit's high density (890.05 g L−1; n = 1), only a small part sticks above the water surface. Although the seeds of X. granatum are of a similar size class than H. littoralis propagules, they are (like the X. granatum fruits) largely submerged due to their high density (870.66 g L−1; n = 8), hence catching less wind than H. littoralis propagules. The influence of wind on the dispersal of the horizontally floating C. tagal and R. mucronata dispersal units was strong, comparable to that of H. littoralis propagules. A differential effect of wind was found within elongated propagules, which directly follows from the floating orientation of the propagules. While the dispersal path of vertically floating propagules was influenced by the strength and direction of the water currents and to a lesser extent by ambient wind conditions, the dispersal path of horizontally floating propagules was influenced by both strength and direction of the water currents and prevailing wind forces. To validate the flume results, propagules of C. tagal and R. mucronata were released during outgoing tide in a tidal creek in Gazi Bay (Kenya), followed by observation of their dispersal distance and direction, while knowing the actual dominant wind direction. In line with the flume results, this study showed that wind plays an important role in the dispersal distance of the propagules. The present study provides important mechanistic insight into the effect of wind on hydrochorous mangrove propagule dispersal, thereby yielding an essential step towards the construction and optimization of (particle-based) hydrodynamic dispersal models.