Effects of Habitat Fragmentation on Abundance, Larval Food and Parasitism of a Spider-Hunting Wasp.

Habitat fragmentation strongly affects species distribution and abundance. However, mechanisms underlying fragmentation effects often remain unresolved. Potential mechanisms are (1) reduced dispersal of a species or (2) altered species interactions in fragmented landscapes. We studied if abundance of the spider-hunting and cavity-nesting wasp Trypoxylon figulus Linnaeus (Hymenoptera: Crabronidae) is affected by fragmentation, and then tested for any effect of larval food (bottom up regulation) and parasitism (top down regulation). Trap nests of T. figulus were studied in 30 agricultural landscapes of the Swiss Plateau. The sites varied in the level of isolation from forest (adjacent, in the open landscape but connected, isolated) and in the amount of woody habitat (from 4 % to 74 %). We recorded wasp abundance (number of occupied reed tubes), determined parasitism of brood cells and analysed the diversity and abundance of spiders that were deposited as larval food. Abundances of T. figulus were negatively related to forest cover in the landscape. In addition, T. figulus abundances were highest at forest edges, reduced by 33.1% in connected sites and by 79.4% in isolated sites. The mean number of spiders per brood cell was lowest in isolated sites. Nevertheless, structural equation modelling revealed that this did not directly determine wasp abundance. Parasitism was neither related to the amount of woody habitat nor to isolation and did not change with host density. Therefore, our study showed that the abundance of T. figulus cannot be fully explained by the studied trophic interactions. Further factors, such as dispersal and habitat preference, seem to play a role in the population dynamics of this widespread secondary carnivore in agricultural landscapes.

Exposure of silver-nanoparticles and silver-ions to lung cells in vitro at the air-liquid interface

BACKGROUND: Due to its antibacterial properties, silver (Ag) has been used in more consumer products than any other nanomaterial so far. Despite the promising advantages posed by using Ag-nanoparticles (NPs), their interaction with mammalian systems is currently not fully understood. An exposure route via inhalation is of primary concern for humans in an occupational setting. Aim of this study was therefore to investigate the potential adverse effects of aerosolised Ag-NPs using a human epithelial airway barrier model composed of A549, monocyte derived macrophage and dendritic cells cultured in vitro at the air-liquid interface. Cell cultures were exposed to 20 nm citrate-coated Ag-NPs with a deposition of 30 and 278 ng/cm2 respectively and incubated for 4 h and 24 h. To elucidate whether any effects of Ag-NPs are due to ionic effects, Ag-Nitrate (AgNO3) solutions were aerosolised at the same molecular mass concentrations. RESULTS: Agglomerates of Ag-NPs were detected at 24 h post exposure in vesicular structures inside cells but the cellular integrity was not impaired upon Ag-NP exposures. Minimal cytotoxicity, by measuring the release of lactate dehydrogenase, could only be detected following a higher concentrated AgNO3-solution. A release of pro-inflammatory markers TNF-alpha and IL-8 was neither observed upon Ag-NP and AgNO3 exposures as well as was not affected when cells were pre-stimulated with lipopolysaccharide (LPS). Also, an induction of mRNA expression of TNF-alpha and IL-8, could only be observed for the highest AgNO3 concentration alone or even significantly increased when pre-stimulated with LPS after 4 h. However, this effect disappeared after 24 h. Furthermore, oxidative stress markers (HMOX-1, SOD-1) were expressed after 4 h in a concentration dependent manner following AgNO3 exposures only. CONCLUSIONS: With an experimental setup reflecting physiological exposure conditions in the human lung more realistic, the present study indicates that Ag-NPs do not cause adverse effects and cells were only sensitive to high Ag-ion concentrations. Chronic exposure scenarios however, are needed to reveal further insight into the fate of Ag-NPs after deposition and cell interactions.

Bioavailability of silver nanoparticles and ions: from a chemical and biochemical perspective

Owing to their antimicrobial properties, silver nanoparticles (NPs) are the most commonly used engineered nanomaterial for use in a wide array of consumer and medical applications. Many discussions are currently ongoing as to whether or not exposure of silver NPs to the ecosystem (i.e. plants and animals) may be conceived as harmful or not. Metallic silver, if released into the environment, can undergo chemical and biochemical conversion which strongly influence its availability towards any biological system. During this process, in the presence of moisture, silver can be oxidized resulting in the release of silver ions. To date, it is still debatable as to whether any biological impact of nanosized silver is relative to either its size, or to its ionic constitution. The aim of this review therefore is to provide a comprehensive, interdisciplinary overview--for biologists, chemists, toxicologists as well as physicists--regarding the production of silver NPs, its (as well as in their ionic form) chemical and biochemical behaviours towards/within a multitude of relative and realistic biological environments and also how such interactions may be correlated across a plethora of different biological organisms.

Social skills as predictors of communication, performance and quality of collaboration in project-based learning

The assumption that social skills are necessary ingredients of collaborative learning is well established but rarely empirically tested. In addition, most theories on collaborative learning focus on social skills only at the personal level, while the social skill configurations within a learning group might be of equal importance. Using the integrative framework, this study investigates which social skills at the personal level and at the group level are predictive of task-related e-mail communication, satisfaction with performance and perceived quality of collaboration. Data collection took place in a technology-enhanced long-term project-based learning setting for pre-service teachers. For data collection, two questionnaires were used, one at the beginning and one at the end of the learning cycle which lasted 3 months. During the project phase, the e-mail communication between group members was captured as well. The investigation of 60 project groups (N���=���155 for the questionnaires; group size: two or three students) and 33 groups for the e-mail communication (N���=���83) revealed that personal social skills played only a minor role compared to group level configurations of social skills in predicting satisfaction with performance, perceived quality of collaboration and communication behaviour. Members from groups that showed a high and/or homogeneous configuration of specific social skills (e.g., cooperation/compromising, leadership) usually were more satisfied and saw their group as more efficient than members from groups with a low and/or heterogeneous configuration of skills.

Social milieus and worldviews in Mamluk adab-encyclopedias: The example of poverty and wealth

The economic and cultural rise of parts of the ����mma due to the particular economic and infrastructural conditions of the Mamluk era fostered the emergence of new intermediate levels of literature that were situated between the literature of the elite and that of the utterly ignorant and unlettered populace, between the Arabic koin�� (al-��arab��ya al-fu��������) and the local dialects (����mm��ya-s), between written and oral composition, performance and transmission. The paper proposes to analyze the composition of three Mamluk adab-encyclopedias and their treatment of poverty and wealth in light of the social milieus of their authors and publics.

Tagesschule und Schulerfolg?

Die Nutzung der sekund��ren Sozialisationsinstanz Schule durch die Kinder ��� wie sie darin zurechtkommen, in welcher Weise sie von ihr profitieren ��� h��ngt vom sozialen, kulturellen und ��konomischen Kapital der Familie ab. Bourdieu (1983) spricht hier von Habitus. Der Einfluss der sozialen Herkunft auf die schulischen Leistungen konnte in vielen Untersuchungen nachgewiesen werden (z.B. Coradi Vellacott 2007). Bereits bei Kindergarten- und Schuleintritt unterscheiden sich die Kinder in sprachlichen und mathematischen Kompetenzbereichen, insbesondere weil sie in ihren Familien unterschiedliche Entwicklungsm��glichkeiten erfahren (Moser & Bayer, 2010). Schlechtere Startbedingungen durchziehen alle Lebensbereiche ��� in der Schule, im Wohnumfeld oder bei der Freizeitgestaltung an weiteren institutionellen Bildungsorten. Es stellt sich die Frage, ob es dem Bildungssystem gelingt, diese Unterschiede zu kompensieren. Verschiedene Studien zeigen, dass es der Schule nicht im erhofften Umfang gelingt, die prim��ren Disparit��ten zu kompensieren. Damit dies besser gelingen kann, m��ssen sich die Bildungsinstitutionen und die Familie zu Beginn des 21. Jahrhunderts an die ver��nderten gesellschaftlichen Rahmenbedingungen anpassen. Damit sie auch in der Zukunft ihrer Kernaufgabe ��� Kinder auf ihrem Weg des Erwachsenwerdens zu unterst��tzen ��� gerecht werden k��nnen. Der Tagesschule in der Schweiz werden in der erziehungswissenschaftlichen Literatur verbreitet p��dagogische M��glichkeiten einger��umt, die dargestellte Situation im Bildungssystem zu verbessern (Holtappels, 2006). Die Tagesschule soll erm��glichen, weg von einer reinen Unterrichtsschule hin zu einer Schule als Erfahrungs- und Lebensraum zu kommen. In einer solchen Schule sollen ��� nebst der F��rderung von kognitiven Kompetenzen aller Sch��lerinnen und Sch��ler (Schulleistung) ��� eine individuelle F��rderung, soziales Lernen sowie insbesondere eine Erh��hung der Chancengerechtigkeit im Bildungssystem im Fokus stehen (Herzog, 2009). Im Hinblick auf Letzteres erhofft man sich durch eine ganzt��gige Bildung und Betreuung eine kompensatorische Wirkung hinsichtlich sozialer Disparit��ten. Ganzt��gige Bildung und Betreuung f��r Schulkinder kann in Form einer Tagesschule oder mit Blockzeitenunterricht und zus��tzlichen Bildungs- und Betreuungsangeboten an oder erg��nzend zur Schule realisiert werden. Unter einer Tagesschule versteht man heute in der Schweiz ��berwiegend eine schulische Institution mit einem den ganzen Tag abdeckenden Angebot. Sie setzt sich aus dem Unterricht und (Tagesschul-)Angeboten wie Mittagessen, Hausaufgabenbetreuung, freiem Spiel, geleiteten Sequenzen und Kursen u.a. zusammen. Teilweise verschmelzen die beiden Teile im Schultag (Sch��pbach, 2010).