Island Invasion by a Threatened Tree Species: Evidence for Natural Enemy Release of Mahogany (Swietenia macrophylla) on Dominica, Lesser Antilles

Despite its appeal to explain plant invasions, the enemy release hypothesis (ERH) remains largely unexplored for tropical forest trees. Even scarcer are ERH studies conducted on the same host species at both the community and biogeographical scale, irrespective of the system or plant life form. In Cabrits National Park, Dominica, we observed patterns consistent with enemy release of two introduced, congeneric mahogany species, Swietenia macrophylla and S. mahagoni, planted almost 50 years ago. Swietenia populations at Cabrits have reproduced, with S. macrophylla juveniles established in and out of plantation areas at densities much higher than observed in its native range. Swietenia macrophylla juveniles also experienced significantly lower leaf-level herbivory (~3.0%) than nine co-occurring species native to Dominica (8.4–21.8%), and far lower than conspecific herbivory observed in its native range (11%–43%, on average). These complimentary findings at multiple scales support ERH, and confirm that Swietenia has naturalized at Cabrits. However, Swietenia abundance was positively correlated with native plant diversity at the seedling stage, and only marginally negatively correlated with native plant abundance for stems ≥1-cm dbh. Taken together, these descriptive patterns point to relaxed enemy pressure from specialized enemies, specifically the defoliator Steniscadia poliophaea and the shoot-borer Hypsipyla grandella, as a leading explanation for the enhanced recruitment of Swietenia trees documented at Cabrits.

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.

Sizing up your enemy: individual predation vulnerability predicts migratory probability

Partial migration, in which a fraction of a population migrate and the rest remain resident, occurs in an extensive range of species and can have powerful ecological consequences. The question of what drives differences in individual migratory tendency is a contentious one. It has been shown that the timing of partial migration is based upon a trade-off between seasonal fluctuations in predation risk and growth potential. Phenotypic variation in either individual predation risk or growth potential should thus mediate the strength of the trade-off and ultimately predict patterns of partial migration at the individual level (i.e. which individuals migrate and which remain resident). We provide cross-population empirical support for the importance of one component of this model—individual predation risk—in predicting partial migration in wild populations of bream Abramis brama, a freshwater fish. Smaller, high-risk individuals migrate with a higher probability than larger, low-risk individuals, and we suggest that predation risk maintains size-dependent partial migration in this system.

Victims of War must be loyal to deserve protection: International law and national legislation on enemy aliens 1907-1918

In international law the internment of civilians has only been regulated in writing in the context of the 4th Geneva Convention of 1949. Nevertheless this did not mean that civilians were not protected by at least some rules of customary international law before that date and especially in World War I. Furthermore specialists of international law expected states – at least those considered to be part of the community of civilized nations – to continue to treat all men equal before the law even in wartime. As research already conducted (Bird, Panayi, Fischer) has shown, this was not the case during World War I. Based on these findings the presentation proposed here wants to look into the development of international law and into some national preparations for treating so called “enemy aliens” in the period before 1914 (Austria-Hungary, Australia, United Kingdom), in order to see to what extent principles of international law protecting civilians from the consequences of war can be detected in the pre-war preparations. As far as can be judged so far the issue of loyalty was central in this context. Looking at the war itself, the presentation proposed here will try to look at how far the principles of international law alluded to above continued to influence the policies on “enemy aliens” in the countries mentioned and to see, how the International Committee of the Red Cross tried to use them to legitimize and expand its protective policies in regard to civilians interned in belligerent as well as neutral countries throughout the war.

Fluids and barriers of the CNS establish immune privilege by confining immune surveillance to a two-walled castle moat surrounding the CNS castle

Neuronal activity within the central nervous system (CNS) strictly depends on homeostasis and therefore does not tolerate uncontrolled entry of blood components. It has been generally believed that under normal conditions, the endothelial blood-brain barrier (BBB) and the epithelial blood-cerebrospinal fluid barrier (BCSFB) prevent immune cell entry into the CNS. This view has recently changed when it was realized that activated T cells are able to breach the BBB and the BCSFB to perform immune surveillance of the CNS. Here we propose that the immune privilege of the CNS is established by the specific morphological architecture of its borders resembling that of a medieval castle. The BBB and the BCSFB serve as the outer walls of the castle, which can be breached by activated immune cells serving as messengers for outside dangers. Having crossed the BBB or the BCSFB they reach the castle moat, namely the cerebrospinal fluid (CSF)-drained leptomeningeal and perivascular spaces of the CNS. Next to the CNS parenchyma, the castle moat is bordered by a second wall, the glia limitans, composed of astrocytic foot processes and a parenchymal basement membrane. Inside the castle, that is the CNS parenchyma proper, the royal family of sensitive neurons resides with their servants, the glial cells. Within the CSF-drained castle moat, macrophages serve as guards collecting all the information from within the castle, which they can present to the immune-surveying T cells. If in their communication with the castle moat macrophages, T cells recognize their specific antigen and see that the royal family is in danger, they will become activated and by opening doors in the outer wall of the castle allow the entry of additional immune cells into the castle moat. From there, immune cells may breach the inner castle wall with the aim to defend the castle inhabitants by eliminating the invading enemy. If the immune response by unknown mechanisms turns against self, that is the castle inhabitants, this may allow for continuous entry of immune cells into the castle and lead to the death of the castle inhabitants, and finally members of the royal family, the neurons. This review will summarize the molecular traffic signals known to allow immune cells to breach the outer and inner walls of the CNS castle moat and will highlight the importance of the CSF-drained castle moat in maintaining immune surveillance and in mounting immune responses in the CNS.

Kognitive Grundlagen und motivationale Effekte individueller Gruppenwirksamkeitserwartungen. Ein informationsintegrationstheoretischer Zugang

Verschiedene Autoren gehen davon aus, dass der Glaube einer Gruppe an ihre Handlungsfähigkeit ein handlungs- und leistungsrelevanter Parameter ist (z. B. Bandura, 1997; Feltz, Short & Sullivan, 2008). Empirische Untersuchungen unterstützen diese Vermutung (z. B. Hodges & Carron, 1992) und es wird angenommen, dass Gruppenwirksamkeitserwartungen über motivationale Faktoren und Zielsetzungen kausal auf Gruppenleistungen wirken. Zur empirischen Theorieprüfung werden u. a. Fragebogen zur Erfassung individueller Gruppenwirksamkeitserwartungen eingesetzt. Solchen Fragebogen liegen Messmodelle zu Grunde, die Annahmen über die kognitiven Prozesse bei der Bildung individueller Gruppenwirksamkeitserwartungen machen und dazu dienen, individuelle Gruppenwirksamkeitserwartungen extern zu konstruieren (Anderson, 1996). Tatsächlich ist über die kognitiven Prozesse, durch die Personen zu ihren individuellen Gruppenwirksamkeitserwartungen gelangen, bislang wenig bekannt (Myers & Feltz, 2007). Diese kognitiven Prozesse stehen im Fokus dieser Arbeit und es soll untersucht werden, welche Gruppeneigenschaften und kontextuellen Bedingungen bei der Bildung individueller Gruppenwirksamkeitserwartungen berücksichtigt werden, wie sie zu einer subjektiven Handlungserwartung integriert werden und ob sich Unterschiede in den individuellen Konzepten aufgabenspezifischer Gruppenwirksamkeitserwartungen finden lassen. Aufgrund der Berichte über kausale Wirkbeziehungen zwischen Gruppenwirksamkeitserwartungen und Gruppenleistungen werden zudem die Zusammenhänge zwischen Gruppenwirksamkeitserwartungen und aufgabenbezogener Leistungsmotivation überprüft. Basierend auf einem theoretischen Modell zur Bildung individueller Gruppenwirksamkeitserwartungen werden Hypothesen zu kognitiven Informationsverarbeitungsprozessen formuliert. Als methodischer Zugang dient Andersons (1981, 1996) Informationsintegrationstheorie. Dreiundzwanzig Bachelor-Studierende der Sportwissenschaft (M = 23.30 Jahre; SD = 3.39; 35% Frauenanteil) der Universität Bern nahmen an den insgesamt sieben Erhebungen teil. Im Rahmen von Gruppenhandlungsszenarien wurden sie nach ihren Gruppenwirksamkeitserwartungen und/oder ihrer aufgabenspezifischen Leistungsmotivation gefragt. Zur statistischen Analyse wurden Mehrebenmodelle berechnet. Zusätzlich wurden graphische Informationsin-tegrationsdiagramme inhaltlich analysiert. Die Resultate weisen auf Abgleiche zwischen Aufgabenanforderungen und Mannschaftsressourcen als eine kognitive Grundlage individueller Gruppenwirksamkeitserwartungen hin. Diese Abgleiche beziehen sich auf physisch-technische wie auch psychologische Eigenschaften des Gruppenkontexts und scheinen durch Handlungspläne beeinflusst zu sein. Die Ergebnisse liefern zudem Anhaltspunkte für die externe Konstruktion von individuellen Gruppenwirksamkeitserwartungen und weisen auf bislang ungelöste Probleme bei der Operationalisierungen von Gruppenwirksamkeitserwartungen im Rahmen von Fragebogen hin. Mögliche weitere Einsatzgebiete für informationsintegrationstheoretische Methoden werden diskutiert.