Trends and Patterns of Global Refugee Migration

This paper studies long-term trends and patterns in global refugee migration. We explore the intensity, spread, and distance of refugee migration at a global, regional, and country level between 1951 and 2018. The analysis did not detect a long-term increase in the global intensity of refugee migration. Primarily depending on levels of conflict, refugee numbers have fluctuated at levels of between 0.1 and 0.3 percent of the world population. Apparent increases in numbers of the globally displaced are driven by the inclusion of populations and countries that were previously excluded from the data. While refugee populations continue to be concentrated in countries with low-to-medium income levels, the analysis reveals several geographic shifts in refugee migration. Refugees tend to come from a shrinking number of origin countries and move to an increasing variety of destination countries. This trend seems to reflect a concentration of recurrent conflict cycles in a relatively small number of countries and a parallel increase in the number of safe destinations. Although the vast majority of refugees remain near to origin countries, the average distance between origin and destination countries has increased over time, presumably linked to the greater ease of travel and migration-facilitating networks.</p

Speciation with gene flow in marine systems

Over the last century, a large body of literature emerged on mechanisms driving speciation. Most of the research into these questions focussed on terrestrial systems, while research in marine systems lagged behind. Here, we review the population genetic mechanisms and geographic context of 33 potential cases of speciation with gene flow in the marine realm, using six criteria inferred from theoretical models of speciation. Speciation with gene flow occurs in a wide range of marine taxa. Single traits, which induce assortative mating and are subjected to disruptive selection, such as differences in host-associations in invertebrates or colour pattern in tropical fish, are potentially responsible for a decrease in gene flow and may be driving divergence in the majority of cases. However, much remains unknown, and with the current knowledge, the frequency of ecological speciation with gene flow in marine systems remains difficult to estimate. Standardized, generally applicable statistical methods, explicitly testing different hypotheses of speciation, are, going forward, required to confidently infer speciation with gene flow

Leidraad beheersing eikenprocessierups

De beheersing van de eikenprocessierups is geen eenvoudige opgave. Het blijkt in de praktijk niet eenvoudig een juiste mix te vinden tussen het voorkómen van gezondheidsklachten, het vermijden van ongewenste ecologische effecten en het opzetten van een adequate monitoring en bestrijding van deze plaag. Met deze leidraad worden voor de professionele beheerders bouwstenen aangereikt om goede beheerkeuzen te maken. De huidige versie van de Leidraad is in voorjaar 2008 door een afvaardiging van de Expertgroep Eikenprocessierups geactualiseerd op basis van nieuwe inzichten en praktijkervaringe