Short-range Dispersal Research Articles

Effects of different dispersal patterns on the presence-absence of multiple species

Predicting which species will be present (or absent) across a geographical region remains one of the key problems in ecology. Numerous studies have suggested several ecological factors that can determine species presence-absence: environmental factors (i.e. abiotic environments), interactions among species (i.e. biotic interactions) and dispersal process. While various ecological factors have been considered, less attention has been given to the problem of understanding how different dispersal patterns, in interaction with other factors, shape community assembly in the presence of priority effects (i.e. where relative initial abundances determine the long-term presence-absence of each species). By employing both local and non-local dispersal models, we investigate the consequences of different dispersal patterns on the occurrence of priority effects and coexistence in multi-species communities. In the case of non-local, but short-range dispersal, we observe agreement with the predictions of local models for weak and medium dispersal strength, but disagreement for relatively strong dispersal levels. Our analysis shows the existence of a threshold value in dispersal strength (i.e. saddle-node bifurcation) above which priority effects disappear. These results also reveal a co-dimension 2 point, corresponding to a degenerate transcritical bifurcation: at this point, the transcritical bifurcation changes from subcritical to supercritical with corresponding creation of a saddle-node bifurcation curve. We observe further contrasting effects of non-local dispersal as dispersal distance changes: while very long-range dispersal can lead to species extinctions, intermediate-range dispersal can permit more outcomes with multi-species coexistence than short-range dispersal (or purely local dispersal). Overall, our results show that priority effects are more pronounced in the non-local dispersal models than in the local dispersal models. Taken together, our findings highlight the profound delicacy in the mediation of priority effects by dispersal processes: “big steps” can have more influence than many “small steps”.

Short range dispersal of western flower thrips in field-grown French beans in Kenya

AbstractThe short-range diurnal dispersal pattern of adult western flower thripsFrankliniella occidentalis(Pergande), in relation to spatial distribution of French beans, was determined in the field. A total of 1200 adult femaleF. occidentaliswere released on 60 French bean plants with 20 adult thrips per plant at the central release point of 3.14 m2. Dispersal was determined in terms of the number of thrips recorded on French beans planted on concentric circles at 0.9, 1.8, 3.6, 7.2 and 14.4 m radii from a circular central release point for five days. Results indicated that there was a steady increase in the proportion of dispersing adultF. occidentalisfrom the first to the fourth day in the first planting season, and from the first to the third day in the second planting season. The peak hour for dispersal was 10.15 h in the first season while it was 13.15 h in the second season. Temperature and wind speed were positively associated with the dispersal activity of adultF. occidentalis. Minimal flight activity was at temperatures below 15 °C and peak flight activity was at 19 °C. The prevailing wind direction did not influence the dispersal pattern of adultF. occidentalisin both seasons. AdultF. occidentalismoved up to 7.2 m on French beans on the first day. In both seasons, the mean direction of thrips dispersal was mostly uniformly distributed (not oriented to a particular compass direction) around the central release point. The results provide an insight into developing integrated management strategies against the pest based on isolation of farm fields, management of alterative hosts around French bean fields and insecticide application.

Dispersal of the Invasive Pasture Pest Heteronychus arator into Areas of Low Population Density: Effects of Sex and Season, and Implications for Pest Management.

African black beetle, Heteronychus arator (Scarabaeidae), is an exotic pest of pastures in northern New Zealand. Both adults and larvae feed on pasture grasses. Adults disperse by walking (short range) or flying (long range). Dispersal flights are triggered by warm night temperatures in spring and autumn. Short range adult dispersal in search of mates, food or oviposition sites is poorly understood. This study investigated walking activity of H. arator adults over three seasons in New Zealand pastures. Adult walking activity was monitored using pitfall traps along fence lines and in pasture plots on a dairy farm in Waikato, New Zealand, in spring 2013, spring 2014, and autumn 2015. Beetle populations were reduced by application of a biopesticide bait to compare walking activity between treated and control plots for up to 26 days post-treatment. Marked beetles were released into the pasture plots to measure the distance traveled by recaptured individuals. Trap catches along the fence lines were correlated with air temperatures in 2013. Trap catches were male biased in spring 2014 compared with autumn 2015. Trap numbers in the control plots were nearly double that of treated plots in both seasons. More beetles were caught in the pitfall traps at the edges of the treated plots than in the center. Trap catches were consistent throughout the control plot in spring 2014, but in autumn 2015 more beetles were caught in the center of the control plot than at the edges. Few marked beetles were recaptured with dispersal rates estimated as <0.5 m per day. Warmer temperatures encouraged short range dispersal in H. arator. Males were more active than females during the spring mating season. Edge effects were strong and should be considered in the design of field experiments.

Spatial spread of dengue in a non-endemic tropical city in northern Argentina

After more than eighty years dengue reemerged in Argentina in 1997. Since then, the largest epidemic in terms of geographical extent, magnitude and mortality, was recorded in 2009. In this report we analyzed the DEN-1 epidemic spread in Orán, a mid-size city in a non-endemic tropical area in Northern Argentina, and its correlation with demographic and socioeconomic factors. Cases were diagnosed by ELISA between January and June 2009. We applied a space-time and spatial scan statistic under a Poisson model. Possible association between dengue incidence and socio-economic variables was studied with the Spearman correlation test. The epidemic started from an imported case from Bolivia and space-time analysis detected two clusters: one on February and other in April (in the south and the northeast of the city respectively) with risk ratios of 25.24 and 4.07 (p<0.01). Subsequent cases spread widely around the city without significant space-temporal clustering. Maximum values of the entomological indices were observed in January, at the beginning of the epidemic (B=21.96; LH=8.39). No statistically significant association between socioeconomic variables and dengue incidence was found but positive correlation between population size and the number of cases (p<0.05) was detected. Two mechanisms may explain the observed pattern of epidemic spread in this non-endemic tropical city: a) Short range dispersal of mosquitoes and people generates clusters of cases and b) long-distance (within the city) human movement contributes to a quasi-random distribution of cases.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Tumor cell dispersal: A little movement goes a long way

In a spatial model, short-range dispersal of tumor cells has a major impact on limiting tumor genetic heterogeneity, tumor growth rate, and resistance to chemotherapy.

Sincronismo em um Modelo com Multi-Espécies

Apresentamos um modelo metapopulacional composto por sitios distribuidos em duas escalas geograficas e habitados por multi-especies. Na escala regional, os sitios estao acoplados por processo de dispersao curta formando um grupo de sitios, ou conglomerado. Na escala global, consideramos grupos de sitios conectados por processo de longo alcance. Analisamos a sincronizacao do modelo e apresentamos um criterio analitico para a sincronizacao onde todos os grupos de sitios evoluem com a mesma densidade. Atraves de simulacoes numericas, discutimos os diferentes modos de sincronizacao que dependem de como os individuos se distribuem nos sitios que compoem um conglomerado.

A spatial model predicts that dispersal and cell turnover limit intratumour heterogeneity.

Most cancers in humans are large, measuring centimetres in diameter, and composed of many billions of cells. An equivalent mass of normal cells would be highly heterogeneous as a result of the mutations that occur during each cell division. What is remarkable about cancers is that virtually every neoplastic cell within a large tumour often contains the same core set of genetic alterations, with heterogeneity confined to mutations that emerge late during tumour growth. How such alterations expand within the spatially constrained three-dimensional architecture of a tumour, and come to dominate a large, pre-existing lesion, has been unclear. Here we describe a model for tumour evolution that shows how short-range dispersal and cell turnover can account for rapid cell mixing inside the tumour. We show that even a small selective advantage of a single cell within a large tumour allows the descendants of that cell to replace the precursor mass in a clinically relevant time frame. We also demonstrate that the same mechanisms can be responsible for the rapid onset of resistance to chemotherapy. Our model not only provides insights into spatial and temporal aspects of tumour growth, but also suggests that targeting short-range cellular migratory activity could have marked effects on tumour growth rates.

Seasonal Movement Patterns and Long-Range Dispersal of Asian Citrus Psyllid in Florida Citrus.

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the bacterial pathogen, Candidatus Liberibacter asiaticus, which is the causal agent of huanglongbing (HLB) in the United States. Both short-range and long-range dispersal of D. citri adults affect the spread of HLB; however, little is known about the long-range dispersal capabilities of D. citri in the field or the seasonality of flight behavior. In the present study, an in situ protein marking technique was used to determine the dispersal of D. citri by trapping marked adults under natural field conditions. D. citri movement from abandoned citrus groves to adjacent managed citrus groves was greatest during the spring and summer months and decreased significantly during the colder months (September-March). D. citri were able to traverse potential geographic barriers such as roads and fallow fields. In an experiment conducted to determine long-range dispersal capacity in the absence of severe weather events, D. citri were able to disperse at least 2 km within 12 d. Wind direction was not correlated with the number of marked psyllids captured, indicating substantial flight capability by D. citri. Finally, the number of marked psyllids captured increased with the density of emerging young leaves on surrounding trees. The results confirm that abandoned citrus groves in Florida serve as reservoirs for D. citri, which can disperse across long distances despite geographical barriers.

Consequences of Dispersal Heterogeneity for Population Spread and Persistence

Dispersal heterogeneity is increasingly being observed in ecological populations and has long been suspected as an explanation for observations of non-Gaussian dispersal. Recent empirical and theoretical studies have begun to confirm this. Using an integro-difference model, we allow an individual's diffusivity to be drawn from a trait distribution and derive a general relationship between the dispersal kernel's moments and those of the underlying heterogeneous trait distribution. We show that dispersal heterogeneity causes dispersal kernels to appear leptokurtic, increases the population's spread rate, and lowers the critical reproductive rate required for persistence in the face of advection. Wavespeed has been shown previously to be determined largely by the form of the dispersal kernel tail. We qualify this by showing that when reproduction is low, the precise shape of the tail is less important than the first few dispersal moments such as variance and kurtosis. If the reproductive rate is large, a dispersal kernel's asymptotic tail has a greater influence over wavespeed, implying that estimating the prevalence of traits which correlate with long-range dispersal is critical. The presence of multiple dispersal behaviors has previously been characterized in terms of long-range versus short-range dispersal, and it has been found that rare long-range dispersal essentially determines wavespeed. We discuss this finding and place it within a general context of dispersal heterogeneity showing that the dispersal behavior with the highest average dispersal distance does not always determine wavespeed.

Population distribution and synchronized dynamics in a metapopulation model in two geographic scales

In this paper, a metapopulation model composed of patches distributed in two spatial scales is proposed in order to study the stability of synchronous dynamics. Clusters of patches connected by short-range dispersal are assumed to be formed. Long distance dispersal is responsible to link patches that are in different clusters. During each time step, we assume that there are three processes involved in the population dynamics: (a) the local dynamics, which consists of reproduction and survival; (b) short-range dispersal of individuals between the patches of each cluster; and (c) the movement between the clusters. First we present an analytic criterion for regional synchronization, where the clusters evolve with the same dynamics. We then discuss the possibility of a full synchronism, where all patches in the network follow the same time evolution. The existence of such a state is not always ensured, even considering that all patches have the same local dynamics. It depends on how the individuals are distributed among the local patches that compose a cluster after long-range dispersal takes place in the regional scale. An analytic criterion for the stability of synchronized trajectories in this case is obtained.

Global attractor for a nonlocal model for biological aggregation

We investigate the long term behavior in terms of global attractors, as time goes to infinity, of solutions to a continuum model for biological aggregations in which individuals experience long-range social attraction and short range dispersal. We consider the aggregation equation with both degenerate and non-degenerate diffusion in a bounded domain subject to various boundary conditions. In the degenerate case, we prove the existence of the global attractor and derive some optimal regularity results. Furthermore, in the non-degenerate case we give a complete structural characterization of the global attractor, and also discuss the convergence of any bounded solutions to steady states. In particular, under suitable assumptions on the parameters of the problem, we establish the convergence of the bounded solution u(t) to a single steady state u(*), and the rate of convergence parallel to u(t)-u(*)parallel to(Lp(Omega)) similar to (1+t)(-rho), as t -> infinity for any p> 1, and some rho=rho(u(*),rho)is an element of(0,1). Finally, the existence of an exponential attractor is also demonstrated for sufficiently smooth kernels in the case of non-degenerate diffusion. Our analysis extends and complements the analysis from [17] and many other fundamental works.

Dispersal analysis of three Peltigera species based on landscape genetics data

Lichens can either disperse sexually through fungal spores or asexually through vegetative propagules and fragmentation. Understanding how genetic variation in lichens is distributed across a landscape can be useful to infer dispersal and establishment events in space and time as well as the conditions needed for this establishment. Most studies have sampled lichens across large spatial distances on the order of hundreds of kilometers, while here we sequence the internal transcribed spacer (ITS) for 113 samples of three Peltigera species sampling at a variety of small spatial scales. The maximum distance between sampled lichens was 3.7 km and minimum distance was approximately 20 cm. We find significant amounts of genetic diversity across all three species. For P. praetextata, two out of the three most common ITS genotypes exhibit spatial autocorrelation supporting short-range dispersal. Using rarefaction we estimate that all ITS genotypes in our sampling area have been found for P. praetextata and P. evansiana, but not P. canina. Comparing our results with other ITS data in the literature provides evidence for global dispersal for at least one sequence followed by the evolution of endemic haplotypes with wide dispersal and rare haplotypes with more local dispersal.

Spores of lichen-forming fungi in the mycoaerosol and their relationships with climate factors

Fungal particulates are a dominant component of the bioaerosol, but aerobiological studies traditionally focused on a limited set of fungi having relevance as allergens or plant pathogens. This study first analyzes the occurrence of lichen meiospores in the mycoaerosol, quantitatively evaluating in the atmosphere of an alpine environment the occurrence of polar diblastic spores, unequivocally attributable to the lichen family Teloschistaceae. The analysis of air-samples collected one week per month for one year with a Hirst-type sampler displayed a low percentage occurrence of polar-diblastic spores (<0.1%) with respect to the whole mycoaerosol, dominated by Cladosporium. Spearman's correlation tests on aerobiological and climatic data highlighted a strong relationship between the detection of Teloschistaceae spores and rainfall events, excluding seasonal patterns or daily rhythms of dispersion. The fact that all the air-sampled spores were attributable to the species of Teloschistaceae occurring in the site, together with laboratory observations of predominant short range dispersal patterns for polar diblastic and other lichen spores, indicated that sexual reproduction is mostly involved in the local expansion of colonization, dispersal from a long distance appearing a less probable phenomenon. These findings indicated that responses of lichen communities to climate factors, usually related to physiological processes, also depend on their influence on meiospore dispersal dynamics. Spatial limitations in dispersal, however, have to be taken into account in evaluating lichen distributional shifts as indicators of environmental changes.

Gene flow across a hybrid zone maintained by a weak heterogametic incompatibility and positive selection of incompatible alleles

Hybridization between incipient species is more likely to produce sterile or inviable F(1) offspring in the heterogametic (XY or ZW) sex than in the homogametic (XX or ZZ) sex, a phenomenon known as Haldane's rule. Population dynamics associated with Haldane's rule may play an important role in early speciation of sexually reproducing organisms. The dynamics of the hybrid zone maintained by incomplete hybrid inferiority (sterility/inviability) in the heterogametic sex (a 'weak' Haldane's rule) caused by a Bateson-Dobzhansky-Muller incompatibility was modelled. The influences and interplays of the strengths of incompatibility, dispersal, density-dependent regulation (DDR) and local adaptation of incompatible alleles in a scenario of short-range dispersal (the stepping-stone model) were examined. It was found that a partial heterogametic hybrid incompatibility could efficiently impede gene flow and maintain characteristic clinal noncoincidence and discordance of alleles. Density-dependent regulation appears to be an important factor affecting hybrid zone dynamics: it can effectively skew the effects of the partial incompatibility and dispersal as measured by effective dispersal, clinal structures and density depression. Unexpectedly, local adaptation of incompatible alleles in the parental populations, which would be critical for the establishment of the incompatibility, exerts little effect on hybrid zone dynamics. These results strongly support the plausibility of the adaptive origin of hybrid incompatibility and ecological speciation: an adaptive mutation, if it confers a marginal fitness advantage in the local population and happens to cause epistatic inferiority in hybrids, could efficiently drive further genetic divergence that may result in the gene becoming an evolutionary hotspot.

Mosaic structure of native ant supercolonies

According to the inclusive fitness theory, some degree of positive relatedness is required for the evolution and maintenance of altruism. However, ant colonies are sometimes large interconnected networks of nests, which are genetically homogenous entities, causing a putative problem for the theory. We studied spatial structure and genetic relatedness in two supercolonies of the ant Formica exsecta, using nuclear and mitochondrial markers. We show that there may be multiple pathways to supercolonial social organization leading to different spatial genetic structures. One supercolony formed a genetically homogenous population dominated by a single mtDNA haplotype, as expected if founded by a small number of colonizers, followed by nest propagation by budding and domination of the habitat patch. The other supercolony had several haplotypes, and the spatial genetic structure was a mosaic of nuclear and mitochondrial clusters. Genetic diversity probably originated from long-range dispersal, and the mosaic population structure is likely a result of stochastic short-range dispersal of individuals. Such a mosaic spatial structure is apparently discordant with the current knowledge about the integrity of ant colonies. Relatedness was low in both populations when estimated among nestmates, but increased significantly when estimated among individuals sharing the same genetic cluster or haplogroup. The latter association indicates the important historical role of queen dispersal in the determination of the spatial genetic structure.

Host selection and establishment of striped mealybug, Ferrisia virgata, on cotton cultivars

The striped mealybug, Ferrisia virgata (Hemiptera: Pseudococcidae), is a polyphagous and cosmopolitan species, which attacks a wide variety of crops, including cotton. Lately, it has been found infesting colored fiber cotton and emerging as an important pest in the Northeast of Brazil. Therefore, this study investigated the effects of colonization, establishment, plant distribution and dispersal of F. virgata on cotton cultivars. Preference experiments were set up in the laboratory and in the greenhouse, in which cultivars were offered simultaneously to nymphs or females and the number of insects on each cultivar was counted after 24 h, 48 h, 22 days and 60 days, respectively. Meanwhile, attack of different plant structures and dispersal were investigated under field conditions. Results showed that F. virgata is able to become established on colored cotton fiber cultivars (BRS Verde, BRS Rubi, and BRS Safira) as well as on white cotton cultivars (BRS 201 and CNPA 7H) without showing any preference among these cultivars. Females produce a large number of offspring to enhance nymph survival and host plant colonization, since the number of first instars successfully established after migration is low (<10%). In addition, its short range dispersal can easily occur from plant to plant. Therefore, strategies to manage F. virgata will be needed to facilitate colored cotton production, especially in organic farms infested by this mealybug species.

Rafting rocks reveal marine biological dispersal: A case study using clasts from beach-cast macroalgal holdfasts

Tracking and quantifying biological dispersal presents a major challenge in marine systems. Most existing methods for measuring dispersal are limited by poor resolution and/or high cost. Here we use geological data to quantify the frequency of long-distance dispersal in detached bull-kelp (Phaeophyceae: Durvillaea) in southern New Zealand. Geological resolution in this region is enhanced by the presence of a number of distinct and readily-identifiable geological terranes. We sampled 13,815 beach-cast bull-kelp plants across 130 km of coastline. Rocks were found attached to 2639 of the rafted plants, and were assigned to specific geological terranes (source regions) to quantify dispersal frequencies and distances. Although the majority of kelp-associated rock specimens were found to be locally-derived, a substantial number (4%) showed clear geological evidence of long-distance dispersal, several having travelled over 200 km from their original source regions. The proportion of local versus foreign clasts varied considerably between regions. While short-range dispersal clearly predominates, long-distance travel of detached bull-kelp plants is shown to be a common and ongoing process that has potential to connect isolated coastal populations. Geological analyses represent a cost-effective and powerful method for assigning large numbers of drifted macroalgae to their original source regions.

Cost of movement in the multicellular stage of the social amoebae Dictyostelium discoideum and D. purpureum

One of the challenges of microbial life is that the best location for feeding and growth may not be the best location for dispersal. This is likely to be the case for the social amoebae Dictyostelium discoideum and Dictyostelium purpureum that feed on soil bacteria in the amoeba stage, but then group into a multicellular slug that moves towards light before forming a fruiting body. Here we examine this short-range social dispersal in the social amoebae, Dictyostelium discoideum and D. purpureum. We predicted D. purpureum would have higher migration costs and travel less far because it forms a dead stalk from living cells as it moves, while D. discoideum delays stalk formation until movement ceases. We found that D. purpureum migrated shorter distances than D. discoideum, in accord with our prediction. D. discoideum slugs moved an average of 2.46 ± 0.19 cm while D. purpureum slugs moved an average of 1.04 ± 0.06 cm. In both species, migration incurred a cost in reduced spore production, compared to experimental conditions where slugs did not migrate. D. discoideum under the no migration treatment produced 0.55± 0.05 spores per cell and under the migration treatment produced 0.25 ± 0.04 spores per cell. D. purpureum under the no migration treatment produced 1.01± 0.06 spores per cell and under the migration treatment produced 0.85 ± 0.06 spores per cell. We also found that D. discoideum produced fruiting bodies with fewer spores after migrating while D. purpureum did not. It appears that the evolutionary loss of stalked migration gives D. discoideum cells the advantage of delaying specialization and the ability to colonize more distant locations, but has significant costs due to migration distance, such as the fraction of cells that become fertile spores.

Colony- and age-specific seasonal dispersal of Herring Gulls Larus argentatus breeding in The Netherlands

The Herring Gull population in The Netherlands went through phases of exploitation, protection, persecution and again (partial) protection during the nineteenth and twentieth centuries. The numbers of breeding pairs peaked in the 1980s at approximately 90,000 pairs, at which point a colour-ringing campaign was organised to evaluate dispersal and distribution patterns. Herring Gulls were ringed as chicks, predominately near-fledglings, in 12 colonies in 1986 (1,247 individuals), 13 colonies in 1987 (1,354 individuals) and 14 colonies in 1988 (1,396 individuals). Between 1986 and 2009, of the 3,997 Herring Gull chicks colour-ringed, 3,124 individuals (78.2%) were seen and reported at least once, while 453 (11.3%) were recovered dead. In total, 86,247 ring-readings of living gulls were received and processed, originating from 1,358 locations by 868 observers. One-fifth (20.5%) of all sightings originated from the home-ranges (areas within a radius of 5 km around the ringing place). Only 691 sightings (0.8%) were reported at over 300 km from the natal colony (10.7% at 6–10 km, 8.9% at 11–25 km, 17.7% at 26–50 km, 22.9% at 51–100 km, 14.4% at 101–200 km and 4.1% at 201–300 km). Colony-specific differences in travelling distance, dispersal rate and direction of movements suggest a grouping of colonies in three areas: (1) eastern Wadden Sea islands (Rottumeroog–Vlieland), with significantly higher dispersal rates and movements mostly towards the south-west to south-east; (2) Texel and the four colonies along the mainland coast (Callantsoog–Wassenaar), with shorter mean range and movements mostly to the south; (3) colonies in the Delta area (Europoort–Saeftinghe), with rather short range movements and dispersal in many directions. The maximum distance travelled did not vary much between adults, immatures and juveniles, but the timing of outward and return movements was different for each of these age categories. Adult birds reached their greatest mean distances on average 1 month earlier than immatures, which in turn arrived at this point 1 month earlier than juveniles. These age-specific differences were enhanced in the spring, when birds were moving towards the (natal) colonies, but when adults moved on average closer and 2 months ahead of immatures, which in turn moved earlier and closer to the natal home-range than juveniles. With reference to findings from other studies in other European countries, Herring Gulls breeding in The Netherlands occupies a mid-position between dispersive and sedentary tendencies.