Migrant Pool Research Articles

Cognitive and non-cognitive abilities of immigrants: New perspectives on migrant quality from a selective immigration country

We study innate ability – a traditionally unobserved component of migrant quality – in Australia, one of the top six destination countries worldwide. We proxy innate ability with validated and widely used measures of non-cognitive (personality) and cognitive (task performance) skills. We find that both first- and second-generation immigrants consistently outperform Australian-born residents with no immediate migration background (natives) on socially beneficial personality traits (Conscientiousness, Openness to Experience) and cognitive ability measures associated with high levels of executive function (coding speed), independent of their gender. The migrant pool resulting from the phase in of a selective immigration policy since 1974 was significantly better educated and more diversified in terms of language background relative to earlier arrivals. Although this meant that the point system attracted migrants with poorer English-language skills relative to natives with equal educational attainment, it did not change their innate ability composition or labor market outcomes. We conclude that selecting migrants based on observable quality characteristics did not lead to a migrant pool of lower quality in traditionally unobservable characteristics in the Australian immigration context.

Self-consistent dispersal puts tight constraints on the spatiotemporal organization of species-rich metacommunities

Biodiversity is often attributed to a dynamic equilibrium between the immigration and extinction of species. This equilibrium forms a common basis for studying ecosystem assembly from a static reservoir of migrants-the mainland. Yet, natural ecosystems often consist of many coupled communities (i.e., metacommunities), and migration occurs between these communities. The pool of migrants then depends on what is sustained in the ecosystem, which, in turn, depends on the dynamic migrant pool. This chicken-and-egg problem of survival and dispersal is poorly understood in communities of many competing species, except for the neutral case-the "unified neutral theory of biodiversity." Employing spatiotemporal simulations and mean-field analyses, we show that self-consistent dispersal puts rather tight constraints on the dynamic migration-extinction equilibrium. When the number of species is large, species are pushed to the edge of their global extinction, even when competition is weak. As a consequence, the overall diversity is highly sensitive to perturbations in demographic parameters, including growth and dispersal rates. When dispersal is short range, the resulting spatiotemporal abundance patterns follow broad scale-free distributions that correspond to a directed percolation phase transition. The qualitative agreement of our results for short-range and long-range dispersal suggests that this self-organization process is a general property of species-rich metacommunities. Our study shows that self-sustaining metacommunities are highly sensitive to environmental change and provides insights into how biodiversity can be rescued and maintained.

Genomic time-series data show that gene flow maintains high genetic diversity despite substantial genetic drift in a butterfly species.

Effective population size affects the efficacy of selection, rate of evolution by drift and neutral diversity levels. When species are subdivided into multiple populations connected by gene flow, evolutionary processes can depend on global or local effective population sizes. Theory predicts that high levels of diversity might be maintained by gene flow, even very low levels of gene flow, consistent with species long-term effective population size, but tests of this idea are mostly lacking. Here, we show that Lycaeides butterfly populations maintain low contemporary (variance) effective population sizes (e.g. ~200 individuals) and thus evolve rapidly by genetic drift. However, populations harboured high levels of genetic diversity consistent with an effective population size several orders of magnitude larger. We hypothesized that the differences in the magnitude and variability of contemporary versus long-term effective population sizes were caused by gene flow of sufficient magnitude to maintain diversity but only subtly affect evolution on generational timescales. Consistent with this hypothesis, we detected low but nontrivial gene flow among populations. Furthermore, using short-term population-genomic time-series data, we documented patterns consistent with predictions from this hypothesis, including a weak but detectable excess of evolutionary change in the direction of the mean (migrant gene pool) allele frequencies across populations and consistency in the direction of allele frequency change over time. The documented decoupling of diversity levels and short-term change by drift in Lycaeides has implications for our understanding of contemporary evolution and the maintenance of genetic variation in the wild.

Low effective population size and high spatial genetic structure of black poplar populations from the Oder valley in Poland

ContextBlack poplar (Populus nigra L.) is a keystone species of European riparian ecosystems that has been negatively impacted by riverside urbanization for centuries. Consequently, it has become an endangered tree species in many European countries. The establishment of a suitable rescue plan of the remaining black poplar forest stands requires a preliminary knowledge about the distribution of genetic variation among species populations. However, for some parts of the P. nigra distribution in Europe, the genetic resources and demographic history remain poorly recognized.AimsHere, we present the first study on identifying and characterizing the genetic resources of black poplar from the Oder valley in Poland. This study (1) assessed the genetic variability and effective population size of populations and (2) examined whether gene flow is limited by distance or there is a single migrant pool along the studied river system.MethodsA total of 582 poplar trees derived from nine black poplar populations were investigated with nuclear microsatellite markers.Results(1) The allelic richness and heterozygosity level were high and comparable between populations. (2) The genetic structure of the studied poplar stands was not homogenous. (3) The signatures of past bottlenecks were detected.ConclusionOur study (1) provides evidence for genetic substructuring of natural black poplar populations from the studied river catchment, which is not a frequent phenomenon reported for this species in Europe, and (2) indicates which poplar stands may serve as new genetic conservation units (GCUs) of this species in Europe.Key messageThe genetic resources of black poplar in the Oder River valley are still substantial compared to those reported for rivers in Western Europe. On the other hand, clear signals of isolation by distance and genetic erosion reflected in small effective population sizes and high spatial genetic structure of the analyzed populations were detected. Based on these findings, we recommend the in situ and ex situ conservation strategies for conserving and restoring the genetic resources of black poplar populations in this strongly transformed by human river valley ecosystem.

Super Aging in South Korea Unstoppable but Mitigatable: A Sub-National Scale Population Projection for Best Policy Planning

This research portrays the spatial and temporal progression of super-aging in regions throughout South Korea. Using a single-year population projection considering gross domestic migration, this research identifies which regions will shortly become a super-aged society. A cohort-component method with a migrant pool model is applied. The county-level national population registration data (2000–2018) are aggregated into 37 regions for the model run. In 2020, 16 rural regions will become super-aged societies. By 2029, all 37 regions, including the metropolitan areas, will join the group, with Sejong, the administrative capital, being the last to enter. In brief, the rural areas become super-aged earlier than the metropolitan areas, and within a decade, those 65 years old or older will make up the majority of the national population. Among all the metropolitan areas, Busan, the largest harbor city, will be the first to be super-aged in 2023. Sejong will experience the most radical change between 2020 and 2050. The research outcomes demonstrate that demographic changes in the rural and metropolitan areas are different; hence, the recent population policies, such as promoting fertility, may not work in the rural areas as they have already lost their population momentum due to the extreme and on-going urbanization throughout the nation. The unstoppable aging will pose adverse effects on future citizens (who are mostly senior) both financially and medically. An increase in health care expenditure and a nationwide blood shortage for transfusion are anticipated, for example.

The impact of migration on tuberculosis in the United States.

Due to greater exposure to Mycobacterium tuberculosis infection before migration, migrants moving to low-incidence settings can experience substantially higher tuberculosis (TB) rates than the native-born population. This review describes the impact of migration on TB epidemiology in the United States, and how the TB burden differs between US-born and non-US-born populations. The United States has a long history of receiving migrants from other parts of the world, and TB among non-US-born individuals now represents the majority of new TB cases. Based on an analysis of TB cases among individuals from the top 30 countries of origin in terms of non-US-born TB burden between 2003 and 2015, we describe how TB risks vary within the non-US-born population according to age, years since entry, entry year, and country of origin. Variation along each of these dimensions is associated with more than 10-fold differences in the risk of developing active TB, and this risk is also positively associated with TB incidence estimates for the country of origin and the composition of the migrant pool in the entry year. Approximately 87 000 lifetime TB cases are predicted for the non-US-born population resident in the United States in 2015, and 5800 lifetime cases for the population entering the United States in 2015.

Migrant pool model of dispersal explains strong connectivity of Avicennia officinalis within Sundarban mangrove areas: Effect of fragmentation and replantation

Abstract The ability of mangrove trees to reproduce and disperse in highly dynamic tidal environments is reflected in the contemporary genetic diversity and structure of their populations. Resilience and establishment may occur through either local recruitment (propagule pool model) or over longer distances with mixed origins (migrant pool model), thereby affecting the connectivity between natural populations. Anthropogenic activities such as encroachment and fragmentation or from mitigating reforestation could cause strategy switches and thus the connectivity and genetic structure of populations. In this study, we considered Avicennia officinalis, a dominant component of the Sundarban mangrove forest in Bangladesh to estimate dispersal dynamics over various distances within estuaries. A total of 423 individuals of A. officinalis, distributed over thirteen sites in the Sundarbans were sampled at both large and fine-scaled spatial level, the latter for comparison of natural and dense with fragmented sites. Up to 62 alleles showed a comparable level of allele diversity and gene diversities at both juvenile and adult life stages, assuming overall high levels of outcrossing. Significant inbreeding levels and high kinship values were solely observed at a reforested A. officinalis site. Genetic variables revealed high levels of connectivity between sites at close vicinity, with only a weak structure over larger geographic distances, between natural core Sundarban and coastal edge populations. Kinship coefficients were mostly low though significant up to several kilometers along estuarine branches, thereby suggesting propagule dispersal beyond each site. A fine-scaled analysis of kinship levels estimated for fragmented and natural forest plots along both sides of a river revealed that fragmentation induced higher kinship levels over 25–50 m distance, whereas dense natural populations were composed of less related individuals at shortest distances. A. officinalis populations might stay resilient through a mixture of unrelated propagules, clearly adhering a migrant pool model in natural sites and propagule pool model in fragmented sites. A poor gene diversity of planted trees might jeopardize the sustainability of mangrove plantation practices. Furthermore, high levels of diversity and connectivity indicated that the core Sundarban populations are a relevant source of germplasm in afforestation programmes.

TO THE NEW WORLD AND BACK AGAIN: RETURN MIGRANTS IN THE AGE OF MASS MIGRATION.

The authors compile large data sets from Norwegian and US historical censuses to study return migration during the Age of Mass Migration (1850-1913). Norwegian immigrants who returned to Norway held lower-paid occupations than did Norwegian immigrants who stayed in the United States, both before and after their first transatlantic migration, suggesting they were negatively selected from the migrant pool. Upon returning to Norway, return migrants held higher-paid occupations relative to Norwegians who never moved, despite hailing from poorer backgrounds. These patterns suggest that despite being negatively selected, return migrants had been able to accumulate savings and could improve their economic circumstances once they returned home.

Hidden founder effects: small-scale spatial genetic structure in recently established populations of the grassland specialist plant Anthyllisvulneraria.

The long-term establishment success of founder plant populations has been commonly assessed based on the measures of population genetic diversity and among population genetic differentiation, with founder populations expected to carry sufficient genetic diversity when population establishment is the result of many colonists from multiple source populations (the 'migrant pool' colonization model). Theory, however, predicts that, after initial colonization, rapid population expansion may result in a fast increase in the extent of spatial genetic structure (SGS), independent of extant genetic diversity. This SGS can reduce long-term population viability by increasing inbreeding. Using 12 microsatellite markers, we inferred colonization patterns in four recent populations of the grassland specialist plant Anthyllisvulneraria and compared the extent of SGS between recently established and old populations. Assignment analyses of the individuals of recent population based on the genetic composition of nine adjacent putative source populations suggested the occurrence of the 'migrant pool' colonization model, further confirmed by high genetic diversity within and low genetic differentiation among recent populations. Population establishment, however, resulted in the build-up of strong SGS, most likely as a result of spatially restricted recruitment of the progeny of initial colonists. Although reduced, significant SGS was nonetheless observed to persist in old populations. The presence of SGS was in all populations associated with elevated inbreeding coefficients, potentially affecting the long-term viability of these populations. In conclusion, this study illustrates the importance of studying SGS next to population genetic diversity and differentiation to adequately infer colonization patterns and long-term establishment success of plant species.

Infectious diseases in North Africa and North African immigrants to Europe.

The epidemiological transition has reduced infectious diseases mortality in most European countries, yet increased migrant influx risks importing diseases. All reported prevalence rates must be considered on a case-by-case basis depending on the disease in question, respective European Union (EU) country and migratory patterns at work. Tuberculosis has seen a re-emergence in Europe and is concentrated among migrants. Migrants arriving from North Africa (NA) and sub-Saharan Africa (SSA) carry higher rates of hepatitis C and B than the local EU population. The human immunodeficiency virus (HIV) impact of NA migrants to Europe is very low but a hallmark of the HIV epidemic is the penetration and circulation of non-B strains, recombinant forms and HIV-drug-resistant profiles through SSA migrants using NA as a transit point into Europe. Leishmaniasis is a re-emerging zoonotic disease prevalent to Southern Europe although not specifically isolated in migrant groups. Although not endemic in NA countries, malaria represent S: a risk in terms of re-emergence in Europe through transitory migrants arriving from SSA with the destination to Europe. Schistosomiasis has been largely eliminated from NA. High migrant flux into European countries has resulted in changing patterns of communicable disease and collectively requires a continuous surveillance. World Health Organization guidelines recommend targeted screening and preventative vaccination, followed by integration of migrants into the local health-care systems allowing for long-term treatment and follow-up. Finally, effective public health campaigns as a form of prevention are essential for the mitigation of disease dissemination in the migrant pool and for second-generation children of migrants.

Intraspecific phenotypic variation in a fish predator affects multitrophic lake metacommunity structure

Contemporary insights from evolutionary ecology suggest that population divergence in ecologically important traits within predators can generate diversifying ecological selection on local community structure. Many studies acknowledging these effects of intraspecific variation assume that local populations are situated in communities that are unconnected to similar communities within a shared region. Recent work from metacommunity ecology suggests that species dispersal among communities can also influence species diversity and composition but can depend upon the relative importance of the local environment. Here, we study the relative effects of intraspecific phenotypic variation in a fish predator and spatial processes related to plankton species dispersal on multitrophic lake plankton metacommunity structure. Intraspecific diversification in foraging traits and residence time of the planktivorous fish alewife (Alosa pseudoharengus) among coastal lakes yields lake metacommunities supporting three lake types which differ in the phenotype and incidence of alewife: lakes with anadromous, landlocked, or no alewives. In coastal lakes, plankton community composition was attributed to dispersal versus local environmental predictors, including intraspecific variation in alewives. Local and beta diversity of zooplankton and phytoplankton was additionally measured in response to intraspecific variation in alewives. Zooplankton communities were structured by species sorting, with a strong influence of intraspecific variation in A. pseudoharengus. Intraspecific variation altered zooplankton species richness and beta diversity, where lake communities with landlocked alewives exhibited intermediate richness between lakes with anadromous alewives and without alewives, and greater community similarity. Phytoplankton diversity, in contrast, was highest in lakes with landlocked alewives. The results indicate that plankton dispersal in the region supplied a migrant pool that was strongly structured by intraspecific variation in alewives. This is one of the first studies to demonstrate that intraspecific phenotypic variation in a predator can maintain contrasting patterns of multitrophic diversity in metacommunities.

Rapid Buildup of Genetic Diversity in Founder Populations of the Gynodioecious Plant Species Origanum vulgare after Semi-Natural Grassland Restoration

In most landscapes the success of habitat restoration is largely dependent on spontaneous colonization of plant species. This colonization process, and the outcome of restoration practices, can only be considered successful if the genetic makeup of founding populations is not eroded through founder effects and subsequent genetic drift. Here we used 10 microsatellite markers to investigate the genetic effects of recent colonization of the long-lived gynodioecious species Origanum vulgare in restored semi-natural grassland patches. We compared the genetic diversity and differentiation of fourteen recent populations with that of thirteen old, putative source populations, and we evaluated the effects of spatial configuration of the populations on colonization patterns. We did not observe decreased genetic diversity in recent populations, or inflated genetic differentiation among them. Nevertheless, a significantly higher inbreeding coefficient was observed in recent populations, although this was not associated with negative fitness effects. Overall population genetic differentiation was low (FST = 0.040). Individuals of restored populations were assigned to on average 6.1 different source populations (likely following the ‘migrant pool’ model). Gene flow was, however, affected by the spatial configuration of the grasslands, with gene flow into the recent populations mainly originating from nearby source populations. This study demonstrates how spontaneous colonization after habitat restoration can lead to viable populations in a relatively short time, overcoming pronounced founder effects, when several source populations are nearby. Restored populations can therefore rapidly act as stepping stones and sources of genetic diversity, likely increasing overall metapopulation viability of the study species.

Editorial -Left out, left off, left over: Why migrants from non-English speaking backgrounds are not adequately recognised in health promotion policy and programs

Australia has a long history of migration. Up to 1945 there was a ?white Australia? policy, which changed to accepting a more diverse migrant pool, including forced migrants (e.g. refugees).There is increasingly a need to understand and cater for the specific health needs of migrants, especially those from non-English speaking (NES) backgrounds, many of whom are not adequately recognised in population health planning. The vast increase in investment in prevention and health promotion may not cater for their needs without their participation in research and planning. Below we discuss the main five challenges.

Short‐distance partial migration of Neotropical birds: a community‐level test of the foraging limitation hypothesis

Partial migration of tropical birds was long believed to be driven by variation in food abundance. Recent evidence from a partially‐migratory species suggests that in contrast, limited foraging opportunities at high elevations during severe wet season storms drives the most metabolically‐challenged individuals down to elevations where rainfall is lighter. Here, I test community‐level predictions of this hypothesis by examining the relationship between high‐elevation rainfall in the second half of the year and counts of migrant birds in lowland forest during late December each year from 1990–2009. I contrast results derived from analysis of all migrant species with both analyses of only the frugivorous migrants, and analyses of resident species. Counts of migrant species were on average positively associated with montane rainfall with differences of up to 72% in the numbers of birds counted in drier or wetter years. Frugivores and smaller birds responded more strongly to variation in rainfall compared to the broader migrant species pool. Interestingly, counts of resident species were also higher following wetter montane wet seasons. Results of analyses exploring the cause of resident responses were not consistent with climatic effects on breeding productivity or short‐term weather effects on detectability. Results were, however, consistent with cryptic down‐slope migration of individuals breeding at higher elevations augmenting lowland resident populations in wet years. These results suggest that changes in rainfall amount, storm intensity, and timing of severe weather events would lead to large increases in or losses of an important behaviour.

Exploring the dynamics of migration to mega-delta cities in Asia and Africa: Contemporary drivers and future scenarios

This paper uses a content analysis of the published literature to take stock of current understanding of key social and policy drivers of migration to cities in 11 Asian and African mega-deltas and identifies commonalities and differences among them. The analysis shows that migration to urban centers in mega-deltas is an outcome of many forces: economic policies and incentives, local and destination institutions, government policies to develop small towns, and the geographic concentration of investments. Massive influx of capital to many deltas has transformed the local economic base from a primarily agricultural one to a manufacturing and processing economy. This has created uneven spatial economic development which is the underlying driver of migration to cities in the mega-deltas regardless of geographic context or size. Going forward to 2060, one critical challenge for all the deltas is to increase the labor skill of their workforce and foster technology innovation. Continued economic growth in these regions will require substantial investments in education and capacity building and the ability of urban centers to absorb the migrant labor pool.

Evolution in metacommunities

A metacommunity can be defined as a set of communities that are linked by migration, and extinction and recolonization. In metacommunities, evolution can occur not only by processes that occur within communities such as drift and individual selection, but also by among-community processes, such as divergent selection owing to random differences among communities in species composition, and group and community-level selection. The effect of these among-community-level processes depends on the pattern of migration among communities. Migrating units may be individuals (migrant pool model), groups of individuals (single-species propagule pool model) or multi-species associations (multi-species propagule pool model). The most interesting case is the multi-species propagule pool model. Although this pattern of migration may a priori seem rare, it becomes more plausible in small well-defined 'communities' such as symbiotic associations between two or a few species. Theoretical models and experimental studies show that community selection is potentially an effective evolutionary force. Such evolution can occur either through genetic changes within species or through changes in the species composition of the communities. Although laboratory studies show that community selection can be important, little is known about how important it is in natural populations.

Size and genetic composition of the colonizing propagules in a butterfly metapopulation

The amount and spatial distribution of genetic variation that is maintained in a metapopulation depends critically on the colonization process. Here, we use molecular markers to determine the number and genetic relatedness of individuals establishing new local populations in a large metapopulation of the Glanville fritillary butterflyMelitaea cinxia. The empirical results are compared with the predictions of a dispersal model based on a diffusion approximation of correlated random walk, which serves as a base‐line hypothesis about the rate and pattern of colonization. The results show that half of the new local populations consisted of a single larval group of full sibs and hence necessarily of the offspring of a single female. If the colonization involved two or more larval groups, these were usually oviposited by two different females that were unrelated to each other. The pattern of colonizations is thus intermediate between the propagule pool and the migrant pool models. These results elucidate the generation of genetic stochasticity, which may influence the dynamics of small populations. The dispersal model predicted well the pattern of habitat occupancy and the pattern of colonizations in relation to landscape structure, though which particular habitat patches became colonized was influenced also by measures of habitat quality not included in the model.

An exact sampling formula for the Wright-Fisher model and a solution to a conjecture about the finite-island model.

An exact sampling formula for a Wright-Fisher population of fixed size N under the infinitely many neutral alleles model is deduced. This extends the Ewens formula for the configuration of a random sample to the case where the sample is drawn from a population of small size, that is, without the usual large-N and small-mutation-rate assumption. The formula is used to prove a conjecture ascertaining the validity of a diffusion approximation for the frequency of a mutant-type allele under weak selection in segregation with a wild-type allele in the limit finite-island model, namely, a population that is subdivided into a finite number of demes of size N and that receives an expected fraction m of migrants from a common migrant pool each generation, as the number of demes goes to infinity. This is done by applying the formula to the migrant ancestors of a single deme and sampling their types at random. The proof of the conjecture confirms an analogy between the island model and a random-mating population, but with a different timescale that has implications for estimation procedures.

High nuclear genetic diversity, high levels of outcrossing and low differentiation among remnant populations of Quercus petraea at the margin of its range in Ireland.

Quercus petraea colonized Ireland after the last glaciation from refugia on mainland Europe. Deforestation, however, beginning in Neolithic times, has resulted in small, scattered forest fragments, now covering less than 12,000 ha. Plastid (three fragments) and microsatellite variation (13 loci) were characterized in seven Irish populations sampled along a north-south gradient. Using Bayesian approaches and Wright's F-statistics, the effects of colonization and fragmentation on the genetic structure and mating patterns of extant oak populations were investigated. All populations possessed cytotypes common to the Iberian Peninsula. Despite the distance from the refugial core and the extensive deforestation in Ireland, nuclear genetic variation was high and comparable to mainland Europe. Low population differentiation was observed within Ireland and populations showed no evidence for isolation by distance. As expected of a marker with an effective population size of one-quarter relative to the nuclear genome, plastid variation indicated higher differentiation. Individual inbreeding coefficients indicated high levels of outcrossing. Consistent with a large effective population size in the historical migrant gene pool and/or with high gene flow among populations, high within-population diversity and low population differentiation was observed within Ireland. It is proposed that native Q. petraea populations in Ireland share a common phylogeographic history and that the present genetic structure does not reflect founder effects.

Population subdivision and molecular sequence variation: theory and analysis of Drosophila ananassae data.

Population subdivision complicates analysis of molecular variation. Even if neutrality is assumed, three evolutionary forces need to be considered: migration, mutation, and drift. Simplification can be achieved by assuming that the process of migration among and drift within subpopulations is occurring fast compared to mutation and drift in the entire population. This allows a two-step approach in the analysis: (i) analysis of population subdivision and (ii) analysis of molecular variation in the migrant pool. We model population subdivision using an infinite island model, where we allow the migration/drift parameter Theta to vary among populations. Thus, central and peripheral populations can be differentiated. For inference of Theta, we use a coalescence approach, implemented via a Markov chain Monte Carlo (MCMC) integration method that allows estimation of allele frequencies in the migrant pool. The second step of this approach (analysis of molecular variation in the migrant pool) uses the estimated allele frequencies in the migrant pool for the study of molecular variation. We apply this method to a Drosophila ananassae sequence data set. We find little indication of isolation by distance, but large differences in the migration parameter among populations. The population as a whole seems to be expanding. A population from Bogor (Java, Indonesia) shows the highest variation and seems closest to the species center.