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Migration System (migration + system)
Selected AbstractsPortugal as a Semi-peripheral Country in the Global Migration SystemINTERNATIONAL MIGRATION, Issue 3 2009Pedro Góis Although Portugal has traditionally produced many emigrants, the last 30 years have also shown increasing immigration. This increase in immigration has drawn attention away from the fact that significant emigration from Portugal continues. In this article, some of the main characteristics of migrations to and from Portugal are highlighted from a systemic perspective. The article shows that Portugal is both a receiving country and a sending country in the global migration system, and that it integrates several of the main migration systems at different levels. It is suggested that Portugal's participation in existing migration systems is best captured and explained by conceptualizing it as a semi-peripheral society, one that is part of a core region of the world system (the European Union) and displays a number of characteristics of both central and peripheral countries. The concept of semi-periphery enables one to recognize the existence of what could be termed a quasi or emergent migratory system: the Lusophone migration system, which one can conceive as communicating intensively with other macro migratory systems. Observing the country's migratory dynamics from the last two decades, and especially the migration flows that bond the Portuguese-speaking countries, one may view the Lusophone migration system as able to combine different levels of centers that (in some moments, and given certain conditions) could evolve into a bicephalous, or even tricephalous, center. These centers function as bonds among several other migration systems, and it is in the middle of this Lusophone migration system that the semi-peripheral role of Portugal becomes evident, as it can be core and periphery at the same time. [source] Population genetics of the European trout (Salmo trutta L.) migration system in the river Rhine: recolonisation by sea troutECOLOGY OF FRESHWATER FISH, Issue 1 2005A. Schreiber Abstract , Allozyme genetics (34 loci) is studied in up to 1010 European trout (Salmo trutta) from the Rhine, Meuse, Weser, Elbe and Danube river systems in Central Europe. Population samples from single collection sites, chiefly small streams (GCG = 0.2126), rather than the divergence of the trout from Atlantic and Danubian drainages (GSG = 0.0711), contributed to the overall gene diversity of GST = 0.2824. Sea trout (n = 164) and brown trout (n = 767) in Atlantic rivers adhere to the same biogeographical stock, but anadromous trout from the Rhine and the Elbe display more genetic cohesion than resident brown trout from the Rhine system alone. Strayers from the Elbe could have founded the recently re-established sea trout population of the Rhine, after a few decades of absence or precarious rarity. Migrants may even connect the Rhine and Elbe stocks by ongoing gene flow. A release,recapture study confirms that all trout in the Rhine belong to one partly migratory population network: Six of 2400 juvenile sea trout released into a tributary of the Rhine were later recorded as emigrants to the Rhine delta, against three of 1600 released brown trout. One migrant had entered the open North Sea, but the other dispersers were recorded in fresh waters of the Rhine delta (Ijsselmeer, Amstelmeer). Stocking presumably elevated both heterozygosity and fixation indices of brown trout, but this effect is subtle within the range of the Atlantic population group. Improved sea trout management in the Rhine, and modifications to brown trout stocking in the upper Danubian area are recommended. [source] AUTOMATICALLY OPERATING RADARS FOR MONITORING INSECT PEST MIGRATIONSINSECT SCIENCE, Issue 4 2002Alistair Drake Abstract, Over the last three decades, special-purpose "entomological" radars have contributed much to the development of our understanding of insect migration, especially of the nocturnal migrations at altitudes of up to , 1 km that are regularly undertaken by many important pest species. One of the limitations of early radar studies, the difficulty of maintaining observations over long periods, has recently been overcome by the development of automated units that operate autonomously and transmit summaries of their observations to a base laboratory over the public telephone network. These relatively low-cost Insect Monitoring Radars (IMRs) employ a novel "ZLC" configuration that allows high quality data on the migrants' flight parameters and identity to be acquired. Two IMRs are currently operating in the semi-arid inland of eastern Australia, in a region where populations of migrant moths (Lepidoptera) and Australian plague locusts Chortoicetes terminifera (Orthoptera) commonly originate, and some examples of outputs from one of these units are presented. IMRs are able to provide the data needed to characterize a migration system, i.e. to estimate the probabilities of migration events occurring in particular directions at particular seasons and in response to particular environmental conditions and cues. They also appear capable of fulfilling a "sentinel" role for pest-management organisations, alerting forecasters to major migration events and thus to the likely new locations of potential target populations. Finally, they may be suitable for a more general ecological monitoring role, perhaps especially for quantifying year-to-year variations in biological productivity. [source] Portugal as a Semi-peripheral Country in the Global Migration SystemINTERNATIONAL MIGRATION, Issue 3 2009Pedro Góis Although Portugal has traditionally produced many emigrants, the last 30 years have also shown increasing immigration. This increase in immigration has drawn attention away from the fact that significant emigration from Portugal continues. In this article, some of the main characteristics of migrations to and from Portugal are highlighted from a systemic perspective. The article shows that Portugal is both a receiving country and a sending country in the global migration system, and that it integrates several of the main migration systems at different levels. It is suggested that Portugal's participation in existing migration systems is best captured and explained by conceptualizing it as a semi-peripheral society, one that is part of a core region of the world system (the European Union) and displays a number of characteristics of both central and peripheral countries. The concept of semi-periphery enables one to recognize the existence of what could be termed a quasi or emergent migratory system: the Lusophone migration system, which one can conceive as communicating intensively with other macro migratory systems. Observing the country's migratory dynamics from the last two decades, and especially the migration flows that bond the Portuguese-speaking countries, one may view the Lusophone migration system as able to combine different levels of centers that (in some moments, and given certain conditions) could evolve into a bicephalous, or even tricephalous, center. These centers function as bonds among several other migration systems, and it is in the middle of this Lusophone migration system that the semi-peripheral role of Portugal becomes evident, as it can be core and periphery at the same time. [source] IN FOCUS: Partial migration in tropical birds: the frontier of movement ecologyJOURNAL OF ANIMAL ECOLOGY, Issue 5 2010Cagan H. Sekercioglu A. E. Jahn, D. J. Levey, J. A. Hostetler & A. M. Mamani (2010) Determinants of partial bird migration in the Amazon Basin. Journal of Animal Ecology, 79, 983,992. Partial migration, in which only some individuals of a species migrate, might be central to the evolution of migratory behaviour and is likely to represent an evolutionary transition between sedentariness and complete migration. In one of the few detailed, individual-based migration studies of tropical birds, Jahn et al. study the partial migration system of a South American bird species for the first time. Food limitation forces the large adult males and small, young females to migrate, contrary to the expectations of the body size and dominance hypotheses. This study confirms the importance of food variability as the primary driver of migratory behaviour. There is urgent need for similar studies on the movement ecology of understudied tropical bird species, whose diversity of migratory behaviour can shed light on the evolution of bird migration. [source] Changes in the timing of spring and autumn migration in North American migrant passerines during a period of global warmingIBIS, Issue 2 2005ALEXANDER M. MILLS Butler (2003) used first arrival dates (FADs) of 103 migrant birds in northeastern USA and found that both long-distance migrants (LDMs; wintering south of the USA) and short-distance migrants (SDMs; wintering in the southern USA) arrived earlier in the second half of the 20th century than they had in the first, consistent with scenarios of global warming; the trend was stronger in SDMs. Using FADs to characterize migration systems can be problematic because they are data from one tail of a distribution, they comprise a mostly male population and they may not correlate well with the balance of the migration period. FADs also provide no information about autumn migration. This paper uses a banding dataset from Long Point Bird Observatory, Ontario, for 14 passerines for a period of global warming (1975,2000), taking these issues into account. The data were filtered to minimize effects of unequal netting effort (147 491 resulting records), and the passage dates then calculated in each season of each year for the 1st, 2nd and 3rd quartiles for regression analysis. Only two of 13 species analysed in the spring showed significantly earlier passage times, although the overall trend was towards earlier spring migration, especially among SDMs. Autumn responses were more prevalent, however, and in some cases more dramatic with six of 13 species showing delayed migration (four SDMs, two LDMs). Two LDMs exhibited earlier autumn migration. Where earlier spring migration occurred, both sexes appeared to contribute to the change. Where delayed migration occurred in autumn, both sexes and both adults and hatch-year birds appeared to contribute in at least some cases. The spring FAD results are consistent with those of Butler, but when the whole migration is considered, change is far from universal in spring and is in fact more substantial and complex in autumn. [source] Portugal as a Semi-peripheral Country in the Global Migration SystemINTERNATIONAL MIGRATION, Issue 3 2009Pedro Góis Although Portugal has traditionally produced many emigrants, the last 30 years have also shown increasing immigration. This increase in immigration has drawn attention away from the fact that significant emigration from Portugal continues. In this article, some of the main characteristics of migrations to and from Portugal are highlighted from a systemic perspective. The article shows that Portugal is both a receiving country and a sending country in the global migration system, and that it integrates several of the main migration systems at different levels. It is suggested that Portugal's participation in existing migration systems is best captured and explained by conceptualizing it as a semi-peripheral society, one that is part of a core region of the world system (the European Union) and displays a number of characteristics of both central and peripheral countries. The concept of semi-periphery enables one to recognize the existence of what could be termed a quasi or emergent migratory system: the Lusophone migration system, which one can conceive as communicating intensively with other macro migratory systems. Observing the country's migratory dynamics from the last two decades, and especially the migration flows that bond the Portuguese-speaking countries, one may view the Lusophone migration system as able to combine different levels of centers that (in some moments, and given certain conditions) could evolve into a bicephalous, or even tricephalous, center. These centers function as bonds among several other migration systems, and it is in the middle of this Lusophone migration system that the semi-peripheral role of Portugal becomes evident, as it can be core and periphery at the same time. [source] A tale of networks and policies: prolegomena to an analysis of irregular migration careers and their developmental pathsPOPULATION, SPACE AND PLACE (PREVIOUSLY:-INT JOURNAL OF POPULATION GEOGRAPHY), Issue 3 2010Martina Cvajner Abstract In recent decades, large-scale irregular migration flows and systems have developed across Europe. Although such systems involve most European countries and are often treated as being similar, their structures and dynamics are quite different. Some irregular migration systems have developed through clandestine entries, while other systems are almost entirely the result of overstaying. Some systems have been structured around a sequence of self-contained spells of irregular work, while others have involved long-term irregular residence. Some have coupled specific flows with specific niches in the occupational structures, while others have shown no significant connections with specific sectors of employment. This paper is based on what has been learned from an immigrant life-history project carried out in Italy in recent years, and describes three different types of irregular migratory systems that are themselves rooted in three different kinds of migration careers: atomistic, volume-based and structured. The paper argues that the distinction between different irregular migration systems is crucial both for structural and developmental analysis. Differences in the structure of irregular migration systems should also be taken into account in the analyses of the impact of different migration control policies. Copyright © 2009 John Wiley & Sons, Ltd. 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