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Return migration of foreign students
No full textUsing unique administrative micro panel data, this paper presents a comprehensive empirical
analysis of the return of recent foreign students in The Netherlands. The life course
experiences of these students in the host, both on the labour market and in marriage
formation, impact their decision to leave. Using a “timing-of-events” model we estimate the
impact of these processes on the return intensity. The model allows for correlated
unobserved heterogeneity across the migration, the labour market and the marriage
formation processes. The large size of the data permits us to stratify the analysis by five
groups based on the country of birth. The empirical analyses reveal that employment induces
students to stay and unemployment induces them to leave. Forming a family in The
Netherlands makes the students more prone to stay. The size of the impact of these life
course experiences on return differs by age at entry and gender.
Keywords: student migration, timing of events method, labour dynamics, marriage
Effects of resources and mortality on the growth and reproduction of Nile perch in Lake Victoria
No full text1. A collapse of Nile perch stocks of Lake Victoria could affect up to 30million people. Furthermore, changes in Nile perch population size-structure and stocks make the threat of collapse imminent. However, whether eutrophication or fishing will be the bane of Nile perch is still debated. 2. Here, we attempt to unravel how changes in food resources, a side effect of eutrophication, and fishing mortality determine fish population growth and size structures. We parameterised a physiologically structured model to Nile perch, analysed the influence of ontogenetic diet shifts and relative resource abundances on existence boundaries of Nile perch and described the populations on either side of these boundaries. 3. Our results showed that ignoring ontogenetic diet shifts can lead to over-estimating the maximum sustainable mortality of a fish population. Size distributions can be indicators of processes driving population dynamics. However, the vulnerability of stocks to fishing mortality is dependent on its environment and is not always reflected in size distributions. 4. We suggest that the ecosystem, instead of populations, should be used to monitor long-term effects of human impact. [KEYWORDS: diet shift existence boundaries Nile perch population growth sustainable fishing lates-niloticus l size-structured populations life-history traits haplochromine cichlids east-africa mwanza gulf nyanza-gulf competition predation dynamics]
Initial reactivity and magnitude of the acute stress response associated with personality in wild great tits (Parus major)
No full textPhenotypic correlations, such as those between functionally distinct behavioral traits, can emerge through the action of selection on individual traits, on trait combinations, and through pleiotropic mechanisms. Steroid hormones are known to have pleiotropic effects on a suite of behavioral and physiological traits, including stable individual differences in coping with stress. Characterizing the stress axis in relation to personality, however, has typically focused on estimating baseline and peak levels of glucocorticoids, principally in captive animals. In contrast, the reactivity of the stress response—how quickly it turns on and persists—may better indicate the ability of an individual to cope with challenges, particularly in free-living animals. Using wild great tits (Parus major) we tested the hypothesis that cautious individuals respond to a standardized stressor with a more reactive stress response compared to bolder individuals. Wild birds were captured and tested for exploration behavior in a novel environment—an operational measure of personality in this species—and assessed separately for their glucocorticoid response to a standardized stressor. Slower explorers exhibited a greater elevation in glucocorticoid levels within the first three minutes after capture. Further, slower explorers reached a higher maximum CORT concentration and had higher total exposure to glucocorticoids during the stressor period. These data provide evidence that the temporal reactivity of the endocrine stress response, specifically its speed and magnitude, is associated with stable behavioral traits in free-living animals.
Keywords
Corticosterone;
Exploration;
Hypothalamic–pituitary–adrenal axis;
Personality;
Stress reactivity
Plants Know Where It Hurts: Root and Shoot Jasmonic Acid Induction Elicit Differential Responses in Brassica oleracea
No full textMethane as a carbon source for the food web in raised bog pools
No full textRaised bog pools are extremely nutrient poor and rich in humic substances, and these features
limit primary production. To assess the base of the invertebrate food web in bog pools we measured the
stable-isotopic signatures of primary producers, dead organic matter, and invertebrates, and the
composition and stable-C-isotope ratio of their phospholipid-derived fatty acids (PLFAs). The stableisotopic
signatures showed the presence of multiple trophic levels and differential use of basal food
sources by the invertebrates among and within species, individuals, and size classes. Carnivorous and
omnivorous invertebrates assimilated polyunsaturated fatty acids (PUFAs) derived from algae, and
possibly macrophytes, and fatty acids that are specific for methane-oxidizing bacteria (MOB). Part of the
bacterial biomass conveyed to higher trophic levels in the bog pools originated from MOB. Pelagic
zooplankton appeared to rely more on bacteria, whereas insects relied more on algae. Periphyton, a
primary algal food source, was the basal food source most depleted in 13C and was inferred to sustain §½
the invertebrate food web. The relatively depleted d13C values of PUFAs in invertebrates suggest a role for
methane-derived C. We argue that the CO2 assimilated by the algae could be derived from MOB.
Therefore, depleted d13C values of invertebrates do not necessarily indicate a direct pathway between MOB
and these invertebrates because algae may form an intermediate level.
Changes in community composition of ammonia-oxidizing betaproteobacteria from stands of Black mangrove (Avicennia germinans) in response to ammonia enrichment and more oxic conditions
No full textIn flooded and non-flooded impounded forests of Black mangrove (Avicennia germinans), the community structure of the ammonia-oxidizing betaproteobacteria (β-AOB) differed among distinct mangrove vegetation cover types and hydrological regimes. This had been explained by a differential response of lineages of β-AOB to the prevailing soil conditions that included increased levels of moisture and ammonium. To test this hypothesis, slurries of soils collected from a flooded and a non-flooded impoundment were subjected to enhanced levels of ammonium in the absence and presence of additional shaking. After a period of 6 days, the community composition of the β-AOB based on the 16S rRNA gene was determined and compared with the original community structures. Regardless of the incubation conditions and the origin of the samples, sequences belonging to the Nitrosomonas aestuarii lineage became increasingly dominant, whereas the number of sequences of the lineages of Nitrosospira (i.e. Cluster 1) and Nitrosomonas sp. Nm143 declined. Changes in community structure were related to changes in community sizes determined by quantitative PCR based on the amoA gene. The amoA gene copy numbers of β-AOB were compared to those of the ammonia-oxidizing archaea (AOA). Gene copy numbers of the bacteria increased irrespective of incubation conditions, but the numbers of archaea declined in the continuously shaken cultures. This observation is discussed in relation to the distribution of the β-AOB lineages in the impounded Black mangrove forests.