Pool Of Migrants Research Articles

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.

TIME, SPACE, AND SKILLS IN DESIGNING MIGRATION POLICY

AbstractThis paper proposes a multi-country model of international migration in which college-educated workers choose destination countries, preferred types of visas, and the optimal durations of stay. In this framework, I investigate the global implications of further development of the European Union (EU) program of preferential temporary visas for the highly skilled immigrants and compare them to the effects of income tax allowances for medium-term, college-educated, foreign workers. The two counterfactuals indicate a significant rise in the yearly inflows and total stocks of college-educated immigrants into the EU. The outcomes of the former policy are driven by a “visa-substitution” effect within the group of current migrants, while the latter scenario results in an increase in the pool of international migrants. Both policies induce a “destination–substitution” effect: losses of skilled migrants by non-EU states, which is reinforced by multilateral resistance to migration that is micro-founded in the model.

Age composition of winter irruptive Snowy Owls in North America

Patterns of winter irruptions in several owl species apparently follow the ‘lack of food’ hypothesis, which predicts that individuals leave their breeding grounds in search of food when prey populations do not allow breeding and are too small to ensure survival. Recent analyses, however, suggest an alternative mechanism dubbed the ‘breeding success’ hypothesis, which predicts that winter irruptions might instead be the result of a very successful breeding season, with a large pool of young birds subsequently migrating south from the breeding grounds. Here we assessed age‐class (juvenile vs. non‐juvenile) composition of winter irruptive Snowy Owls Bubo scandiacus over a 25‐year period (winter 1991–1992 to 2015–2016) between regular (North American Prairies and Great Plains) and irregular wintering areas (northeastern North America) using live‐trapped individuals and high‐resolution images of individual owls. Our results show that the proportion of juveniles (birds less than 1 year of age) varies considerably annually but is positively correlated with irruption intensity in both regions. In irregular wintering areas, it can constitute the majority (up to more than 90%) of winter irruptive Snowy Owls over a large geographical area. These results are consistent with the idea that large winter irruptions at temperate latitudes are not the result of adults massively leaving the Arctic in search of food after a breeding failure but are more likely to be a consequence of good reproductive conditions in the Arctic that create a large pool of winter migrants.

The effectiveness and cost-effectiveness of screening for latent tuberculosis among migrants in the EU/EEA: a systematic review.

BackgroundMigrants account for a large and growing proportion of tuberculosis (TB) cases in low-incidence countries in the European Union/European Economic Area (EU/EEA) which are primarily due to reactivation of latent TB infection (LTBI). Addressing LTBI among migrants will be critical to achieve TB elimination. Methods: We conducted a systematic review to determine effectiveness (performance of diagnostic tests, efficacy of treatment, uptake and completion of screening and treatment) and a second systematic review on cost-effectiveness of LTBI screening programmes for migrants living in the EU/EEA. Results: We identified seven systematic reviews and 16 individual studies that addressed our aims. Tuberculin skin tests and interferon gamma release assays had high sensitivity (79%) but when positive, both tests poorly predicted the development of active TB (incidence rate ratio: 2.07 and 2.40, respectively). Different LTBI treatment regimens had low to moderate efficacy but were equivalent in preventing active TB. Rifampicin-based regimens may be preferred because of lower hepatotoxicity (risk ratio = 0.15) and higher completion rates (82% vs 69%) compared with isoniazid. Only 14.3% of migrants eligible for screening completed treatment because of losses along all steps of the LTBI care cascade. Limited economic analyses suggest that the most cost-effective approach may be targeting young migrants from high TB incidence countries. Discussion: The effectiveness of LTBI programmes is limited by the large pool of migrants with LTBI, poorly predictive tests, long treatments and a weak care cascade. Targeted LTBI programmes that ensure high screening uptake and treatment completion will have greatest individual and public health benefit.

Bayesian estimation of the global biogeographical history of the Solanaceae

AbstractAimThe tomato family Solanaceae is distributed on all major continents except Antarctica and has its centre of diversity in South America. Its worldwide distribution suggests multiple long‐distance dispersals within and between the New and Old Worlds. Here, we apply maximum likelihood (ML) methods and newly developed biogeographical stochastic mapping (BSM) to infer the ancestral range of the family and to estimate the frequency of dispersal and vicariance events resulting in its present‐day distribution.LocationWorldwide.MethodsBuilding on a recently inferred megaphylogeny of Solanaceae, we conducted ML model fitting of a range of biogeographical models with the program ‘BioGeoBEARS’. We used the parameters from the best fitting model to estimate ancestral range probabilities and conduct stochastic mapping, from which we estimated the number and type of biogeographical events.ResultsOur best model supported South America as the ancestral area for the Solanaceae and its major clades. The BSM analyses showed that dispersal events, particularly range expansions, are the principal mode by which members of the family have spread beyond South America.Main conclusionsFor Solanaceae, South America is not only the family's current centre of diversity but also its ancestral range, and dispersal was the principal driver of range evolution. The most common dispersal patterns involved range expansions from South America into North and Central America, while dispersal in the reverse direction was less common. This directionality may be due to the early build‐up of species richness in South America, resulting in large pool of potential migrants. These results demonstrate the utility of BSM not only for estimating ancestral ranges but also in inferring the frequency, direction and timing of biogeographical events in a statistically rigorous framework.

Pulsed resources at tundra breeding sites affect winter irruptions at temperate latitudes of a top predator, the snowy owl.

Irruptive migration is mostly observed in species specialized on pulsed resources and is thought to be a response to unpredictable changes in food supply. We assessed two alternative hypotheses to explain the periodic winter irruptions of snowy owls Bubo scandiacus every 3-5years in temperate North America: (a) the lack-of-food hypothesis, which states that a crash in small mammal abundance on the Arctic breeding grounds forces owls to move out of the tundra massively to search for food in winter; (b) the breeding-success hypothesis, which states that high abundance of tundra small mammals during the summer allows for high production of young, thus increasing the pool of migrants moving south the following winter. We modeled winter irruptions of snowy owls in relation to summer food resources and geographic location. Winter abundance of owls was obtained from citizen-based surveys from 1994 to 2011 and summer abundance of small mammals was collected in summer at two distant sites in Canada: Bylot Island, NU (eastern High Arctic) and Daring Lake, NWT (central Low Arctic). Winter owl abundance was positively related to prey abundance during the previous summer at both sites and tended to decrease from western to eastern temperate North America. Irruptive migration of snowy owls was therefore best explained by the breeding success hypothesis and was apparently caused by large-scale summer variations in food. Our results, combined with previous findings, suggest that the main determinants of irruptive migration may be species specific even in a guild of apparently similar species.

Migration of skilled workers and innovation: A European Perspective

This paper analyzes the effect of skilled migration on two measures of innovation, patenting and bibliometric data, in a panel of 20 European countries between 1995 and 2008. The empirical findings show that a larger pool of migrants in the skilled professions is associated with higher levels of knowledge creation. Skilled migrants contribute both to the creation of “private” knowledge, measured by the number of patent applications through the Patent Cooperation Treaty, and to more “public” basic research, measured by the number of citations to published articles. This finding is robust, in that it uses both an occupation-based and an education-based index of skilled migration, as well as an instrumental variable estimation accounting for the endogeneity of the skilled migrants indicator and to a number of robustness checks. Our results suggest that policy efforts aiming at attracting skilled migrants to Europe and employing them in skilled professions, such as those put forward in the Europe 2020 Strategy, will indeed foster EU competitiveness in innovation.

Landscape‐scale habitat availability, and not local geography, predicts migratory landbird stopover across the Gulf of Maine

While it is clear that many migratory behaviors are shared across taxa, generalizable models that predict the distribution and abundance of migrating taxa at the landscape scale are rare. In migratory landbirds, ephemeral concentrations of refueling birds indicate that individual behaviors sometimes produce large epiphenomena in particular geographic locations. Identifying landscape factors that predict the distribution and abundance of birds during migratory stopover will both improve our understanding of the migratory process and assist in broad, regionally relevant conservation. In this study we used autumnal passerine stopover data from a five‐year period and eleven stopover sites across coastal Maine, USA, to test four broad hypotheses of migrant distribution and abundance that have been supported in other regions: a) the community characteristics of the pool of potential migrants, b) a site's local geography, c) landscape composition and configuration measured at different spatial scales, and d) interactions between these factors. Our final model revealed that birds concentrate at ‘habitat islands’, sites that possess a disproportionate percentage of the vegetated habitat in the 4‐km surrounding landscape. The strength of this pattern, however, was inversely proportional to a species' remaining migratory distance. Our results corroborate several studies that emphasize the importance of land cover composition at finer spatial scales (< 80 km2) for predicting the stopover distribution and abundances of migratory birds. This suggests that different migrants likely assess stopover sites with similar mechanisms along their migratory route, and these commonalities may be broadly applied to identify stopover locations of conservation importance across the continent.

Canine Gouging: A Taboo Resurfacing in Migrant Urban Population.

Cosmopolitan cities have become a pool of migrants from different parts of the world, who carry their cultural beliefs and superstitions with them around the globe. Canine gouging is a kind of infant oral mutilation (IOM) which is widely practiced among rural population of Africa where the primary tooth bud of the deciduous canine is enucleated. The belief is that the life threatening illnesses in children like vomiting, diarrhoea, and fevers are caused by worms which infest on tooth buds. This case report is of a 15-year-old Somalian born boy, who presented at the dental institute with intermittent pain in his lower right permanent canine which was associated with a discharging intra oral buccal sinus. The tooth was endodontically treated and then restored with composite. General dental practitioners need to be vigilant when encountered with tooth presenting unusual morphology, unilateral missing tooth, and shift in the midline due to early loss of deciduous/permanent canines. Identification of any such dental mutilation practice will need further counselling of the individual and family members. It is the duty of every dental professional to educate and safeguard the oral and dental health of general public.

The Cross-country Determinants of Potential and Actual Migration

In this study, we use cross-country bilateral data to quantify a two-step process of international migration and its aggregate determinants. We first analyze which country-specific factors affect the probability that individuals join the pool of potential (aspiring) migrants. Then, we consider the bilateral and destination country factors that affect the frequency at which potential migrants turn into actual migrants. Using information on potential migrants from World Gallup surveys and on actual migrants from national censuses for 138 origin countries and 30 major destinations between 2000 and 2010, we analyze economic, policy, cultural, and network determinants of each step. We find that the size of the network of previous migrants and the average income per person at destination are crucial determinants of the size of the pool of potential migrants. Economic growth in the destination country, on the other hand, is the main economic generator of migration opportunities for a given pool of potential migrants. We also find that college-educated exhibit greater actual emigration rates mainly because of better chances in realizing their immigration potentials, rather than because of higher willingness to migrate.

Costs and Benefits of Labour Mobility between the EU and the Eastern Partnership Partner Countries - Country Report: Ukraine

Ukraine is a migration-intensive country, with an estimated 1.5-2 million labour migrants (about 5% of the working-age population). Slightly over a half of these migrants travel for work to the EU. This study discusses the impact of this large pool of migrants on both the sending and receiving countries. It also assesses how liberalisation of the EU visa regime, something that the EU is currently negotiating with Ukraine, will affect the stream of Ukrainian labour migrants to EU countries. Our study suggests that the number of tourists will increase substantially, whereas the increase in the number of labour migrants is unlikely to be very large. We also suggest that the number of legal migrants is likely to increase, but at the same time the numer of illegal migrants will decline because currently only a third of migrants from Ukraine have both residence and work permits in the EU, while about a quarter of them stay there illegally.

Beta Diversity in Spatially Implicit Neutral Models: A New Way to Assess Species Migration

The spatially implicit neutral model (SINM) of S. P. Hubbell predicts species' abundance distributions at two levels: local communities where extinction balances immigration, characterized by the immigration number I, and the metacommunity, a source pool of migrants where speciation balances extinction. Previously, a plot's I was estimated from its species abundance distribution. Here, we relate neutral theory to the additive partitioning of species diversity and calculate the immigration rate into different plots from the variation in species composition among them. We revisit the G(ST) statistic of population genetics to introduce a new version, G(ST)(k), conditional on each community sample k. We derive an analytical expectation of G(ST)(k) as a function of the local immigration number, I(k), under a generalized version of the SINM, which allows the pool of migrants to deviate from the large-scale speciation-extinction balance. Simulations and field data suggest that G(ST)(k) provides reasonable estimates of immigration numbers, which were compared with the results from alternative likelihood-based estimations.

The Worldwide Market for Skilled Migrants: Can Australia Compete?

"The purpose of this article is to...[analyze] the relative importance of internal and external factors on the demand for skilled immigration visas to Australia. Our objectives are to determine how the size of the pool of potential migrants is influenced by factors such as relative economic conditions and U.S. and Canadian immigration policies and to determine what implications these factors have on the relative quality (skill level) of potential migrants to Australia. Our results indicate that the demand for skilled immigration visas to Australia is related to the number of immigrants accepted by the United States and Canada as well as employment possibilities in Australia. We do not find a relationship between U.S. and Canadian policy and the relative quality of the applicant pool."

International differences in the labor market performance of immigrants

The author provides substantive insights into the self-selection process that determines the composition of the pool of migrants. He also illustrates the importance of immigration policy in determining both the national origin and skill composition of migrant flow reaching a country of destination.

Group selection for a polygenic behavioral trait: a differential proliferation model.

Conditions for natural selection to increase a polygenic behavioral trait are derived for a model in which the population is divided into a very large number of partially isolated groups of variable and varying size. Specifically, we consider an altruistic trait that is deleterious to the individual but raises the mean fitness of the group. We assume, for each generation, that all groups have the same proportion of males, k, at the time of migration and that each group contributes Mf females and Mm males to a pool of migrants, from which Mf females and Mm males are randomly parceled out to each group. This assumption ensures that at equilibrium between random drift and a low level of migration and neglecting the small per locus effect of selection, each group has the same expected value of Wright's fixation index, FST = F. AT equilibrium, this is approximately 1/(1 + 4Me), where Me = 2kMf + 2(1 - k)Mm. The trait will increase when (b - c)/c greater than (1-F)/2F=2Me, where b is the expected benefit to the group and c is the expected cost of a unit change in the mean value of the altruistic trait. In particular, the group selection analogue of Hamilton's inequality, c/b less than r, where r is the coefficient of relationship, is obtained. The effect of isolation is enhanced if migration is mainly between adjacent groups and if group splitting is along family lines, as data on population structure of primates seem to indicate.