Enemy damage of exotic plant species is similar to that of natives and increases with productivity

1 .In their colonized ranges, exotic plants may be released from some of the herbivores or pathogens of their home ranges but these can be replaced by novel enemies. It is of basic and practical interest to understand which characteristics of invaded communities control accumulation of the new pests. Key questions are whether enemy load on exotic species is smaller than on native competitors as suggested by the enemy release hypothesis (ERH) and whether this difference is most pronounced in resource-rich habitats as predicted by the resource–enemy release hypothesis (R-ERH). 2. In 72 populations of 12 exotic invasive species, we scored all visible above-ground damage morphotypes caused by herbivores and fungal pathogens. In addition, we quantified levels of leaf herbivory and fruit damage. We then assessed whether variation in damage diversity and levels was explained by habitat fertility, by relatedness between exotic species and the native community or rather by native species diversity. 3. In a second part of the study, we also tested the ERH and the R-ERH by comparing damage of plants in 28 pairs of co-occurring native and exotic populations, representing nine congeneric pairs of native and exotic species. 4. In the first part of the study, diversity of damage morphotypes and damage levels of exotic populations were greater in resource-rich habitats. Co-occurrence of closely related, native species in the community significantly increased the probability of fruit damage. Herbivory on exotics was less likely in communities with high phylogenetic diversity. 5. In the second part of the study, exotic and native congeneric populations incurred similar damage diversity and levels, irrespective of whether they co-occurred in nutrient-poor or nutrient-rich habitats. 9. Synthesis. We identified habitat productivity as a major community factor affecting accumulation of enemy damage by exotic populations. Similar damage levels in exotic and native congeneric populations, even in species pairs from fertile habitats, suggest that the enemy release hypothesis or the R-ERH cannot always explain the invasiveness of introduced species.

The impact of welfare benefits on natives' and immigrants' attitudes towards immigration

We investigate whether the dependence of immigrants on welfare benefits leads to opposition to further immigration by natives and immigrants in a pooled cross-section of 21 European countries for the 2004-2010 period. Explicitly controlling for the dependence of immigrants and natives on benefits we find that higher benefit take-up rates among immigrants than among natives lead to less favourable attitudes of natives towards immigration. Interestingly, we do not find similar stylised facts for immigrants' attitudes towards immigration.

The impact of welfare benefits on natives' and immigrants' attitudes towards immigration

We investigate whether the dependence of immigrants on welfare benefits leads to opposition to further immigration by natives and immigrants in a pooled cross-section of 21 European countries for the 2004-2010 period. Explicitly controlling for the dependence of immigrants and natives on benefits we find that higher benefit take-up rates among immigrants than among natives lead to less favourable attitudes of natives towards immigration. Interestingly, we do not find similar stylised facts for immigrants' attitudes towards immigration.

Catching-up: The educational mobility of migrants’ and natives’ children in Europe

Migrants into European countries are often less educated than European natives. We investigate whether migrants' children are able to catch up to their native counterparts in educational attainment, and analyze the drivers of differences in intergenerational educational upward mobility between natives' versus migrants' descendants. We find that migrants' children are more likely than natives' children to surpass their parents' educational attainment in the majority of countries studied. Their parents' low education is often the strongest determinant for their ability to move up in education class across generations.

Invasive plant species do not create more negative soil conditions for other plants than natives

Abstract A major task in ecology is to establish the degree of generality of ecological mechanisms. Here we present results from a multi-species experiment that tested whether a set of invasive species altered the soil conditions to the detriment of other species by releasing allelopathic compounds or inducing shifts in soil biota composition, and whether this effect was more pronounced relative to a set of closely related native species. We pre-cultivated soil with 23 exotic invasive, 19 related native and 6 related exotic garden species and used plain soil as a control. To separate allelopathy from effects on the soil biota, we sterilized half of the soil. Then, we compared the effect of soil pre-cultivation and sterilization on germination and growth of four native test species in two experiments. The general effect of soil sterilization was positive. The effect of soil pre-cultivation on test species performance was neutral to positive, and sterilization reduced this positive effect. This indicates general absence of allelopathic compounds and a shift toward a less antagonistic soil biota by cultivation species. In both experiments, pre-cultivation effects did not differ systematically between exotic invasive, exotic garden or native species. Our results do not support the hypothesis that invasive plants generally inhibit the growth of others by releasing allelopathic compounds or accumulating a detrimental soil biota.

Pulmonary-artery pressure and exhaled nitric oxide in Bolivian and Caucasian high altitude dwellers

There is evidence that high altitude populations may be better protected from hypoxic pulmonary hypertension than low altitude natives, but the underlying mechanism is incompletely understood. In Tibetans, increased pulmonary respiratory NO synthesis attenuates hypoxic pulmonary hypertension. It has been speculated that this mechanism may represent a generalized high altitude adaptation pattern, but direct evidence for this speculation is lacking. We therefore measured systolic pulmonary-artery pressure (Doppler chocardiography) and exhaled nitric oxide (NO) in 34 healthy, middle-aged Bolivian high altitude natives and in 34 age- and sex-matched, well-acclimatized Caucasian low altitude natives living at high altitude (3600 m). The mean+/-SD systolic right ventricular to right atrial pressure gradient (24.3+/-5.9 vs. 24.7+/-4.9 mmHg) and exhaled NO (19.2+/-7.2 vs. 22.5+/-9.5 ppb) were similar in Bolivians and Caucasians. There was no relationship between pulmonary-artery pressure and respiratory NO in the two groups. These findings provide no evidence that Bolivian high altitude natives are better protected from hypoxic pulmonary hypertension than Caucasian low altitude natives and suggest that attenuation of pulmonary hypertension by increased respiratory NO synthesis may not represent a universal adaptation pattern in highaltitude populations.

"Fascinating Voids: Alexander von Humboldt and the Myth of Chimborazo"

When Alexander von Humboldt reached the village of Calpi in the Andes on 22 June 1802, he was greeted with reverence and enthusiasm. Triumphal arches adorned with cotton, cloth, and silver decorated his path. The natives performed a dance in festive dress. A singer praised the explorer's expedition, which had departed three years earlier from the Spanish port of La Coruña. Like Odysseus on the isle of the Phaeacians, the traveler listened to a local rhapsodist singing about his heroic deeds. Before his adventure ended, it had already spun a popular myth. This episode, which Humboldt recorded in his diary, occurred at a significant moment. One day later, the “Second Discoverer of America” rose to even greater fame on an excursion marking in more ways than one the climax of his enterprise. Humboldt set out to climb Chimborazo (6,310 m/20,702 ft.), the mountain then thought to be the highest in the world. He was accompanied by the French botanist Aimé Bonpland (1773–1858) and the Creole nobleman and future activist Carlos Montúfar (1780–1816), as well as native guides and assistants. They climbed to heights never reached before, setting a new record and catapulting Humboldt to fame on both continents.

Allelopathic effects of three plant invaders on germination of native species: a field study

The ability of some invasive plant species to produce biochemical compounds toxic to native species, called allelopathy, is thought to be one of the reasons for their success when introduced to a novel range, an idea known as the Novel Weapons Hypothesis. However, support for this hypothesis mainly comes from bioassays and experiments conducted under controlled environments, whereas field evidence is rare. In a field experiment, we investigated whether three plant species invasive in Europe, Solidago gigantea, Impatiens glandulifera and Erigeron annuus, inhibit the germination of native species through allelopathy more than an adjacent native plant community. At three sites for each invasive species, we compared the germination of native species that were sown on invaded and non-invaded plots. Half of these plots were amended with activated carbon to reduce the influence of potential allelopathic compounds. The germination of sown seeds and of seeds from the seedbank was monitored over a period of 9 weeks. Activated carbon generally enhanced seed germination. This effect was equally pronounced in invaded and adjacent non-invaded plots, indicating that invasive species do not suppress germination more than a native plant community. In addition, more seeds germinated from the seedbank on invaded than on non-invaded soil, probably due to previous suppression of germination by the invasive species. Our field study does not provide evidence for the Novel Weapons Hypothesis with respect to the germination success of natives. Instead, our results suggest that if invasive species release allelopathic compounds that suppress germination, they do so to a similar degree as the native plant community.

The relative importance of immediate allelopathy and allelopathic legacy in invasive plant species

Abstract Some introduced invasive species may be competitively superior to natives because they release allelochemicals, which negatively affect native species. Allelochemicals can be immediately effective after being released but can also persist in soils, resulting in a legacy effect. However, to our knowledge there are no studies which distinguish between allelopathic legacy and immediate allelopathy of invasive species and also test for their relative importance and possible interdependence. We used eleven invasive species and tested whether they show immediate allelopathy and allelopathic legacy effects in a factorial pairwise competition experiment using field-collected soil (invaded/non-invaded) and activated carbon to neutralize allelochemicals. We grew two native and the invasive species in both monocultures and pairwise mixtures. In monocultures, the native species did not experience an allelopathic legacy effect of the invasives, suggesting that invaders generally lack persistent allelochemicals. However, the effects of invader allelochemicals were modulated by competitive interactions. In competition, immediate allelopathy decreased competitive ability of natives, while allelopathic legacy positively affected the natives. Moreover, immediate allelopathic and allelopathic legacy effects were strongly negatively correlated. Our results suggest that both immediately released allelochemicals and the allelochemical legacy of invasive species are important for plant performance under natural conditions, and that natives should be able to recover once the invaders are removed. To test whether immediate allelopathy is responsible for plant invasion success, further studies should compare allelopathic effects between invasive and closely related native species.

Redistribution and attitudes toward immigrants: A European perspective

We investigate whether the dependence of immigrants on welfare benefits leads to opposition to further immigration by natives and immigrants in a pooled cross-section of 21 European countries for the 2004{2010 period. Explicitly controlling for the dependence of immigrants and natives on benefits we find that higher benefit take-up rates among immigrants than among natives lead to less favourable attitudes of natives towards immigration. Interestingly, we do not find similar stylised facts for immigrants' attitudes towards immigration.

Redistribution and attitudes toward immigrants: A European perspective

We investigate whether the dependence of immigrants on welfare benefits leads to opposition to further immigration by natives and immigrants in a pooled cross-section of 21 European countries for the 2004-2010 period. Explicitly controlling for the dependence of immigrants and natives on benefits we find that higher benefit take-up rates among immigrants than among natives lead to less favourable attitudes of natives towards immigration. Interestingly, we do not find similar stylised facts for immigrants' attitudes towards immigration.

Reciprocity as a trigger of social cooperation in contemporary immigration societies?

While the system stabilizing function of reciprocity is widely acknowledged, much less attention has been paid to the argument that reciprocity might initiate social cooperation in the first place. This paper tests Gouldner’s early assumption that reciprocity may act as a ‘starting mechanism’ of social cooperation in consolidating societies. The empirical test scenario builds on unequal civic engagement between immigrants and nationals, as this engagement gap can be read as a lack of social cooperation in consolidating immigration societies. Empirical analyses using survey data on reciprocal norms and based on Bayesian hierarchical modelling lend support for Gouldner’s thesis, underlining thereby the relevance of reciprocity in today’s increasingly diverse societies: individual norms of altruistic reciprocity elevate immigrants’ propensity to volunteer, reducing thereby the engagement gap between immigrants and natives in the area of informal volunteering. In other words, compliance with altruistic reciprocity may trigger cooperation in social strata, where it is less likely to occur. The positive moderation of the informal engagement gap through altruistic reciprocity turns out to be most pronounced for immigrants who are least likely to engage in informal volunteering, meaning low, but also high educated immigrants.