Estimating the tolerance of species to the effects of global environmental change

Global environmental change is affecting species distribution and their interactions with other species. In particular, the main drivers of environmental change strongly affect the strength of interspecific interactions with considerable consequences to biodiversity. However, extrapolating the effects observed on pair-wise interactions to entire ecological networks is challenging. Here we propose a framework to estimate the tolerance to changes in the strength of mutualistic interaction that species in mutualistic networks can sustain before becoming extinct. We identify the scenarios where generalist species can be the least tolerant. We show that the least tolerant species across different scenarios do not appear to have uniquely common characteristics. Species tolerance is extremely sensitive to the direction of change in the strength of mutualistic interaction, as well as to the observed mutualistic trade-offs between the number of partners and the strength of the interactions.Comment: Nature Communications 4, Article number: 2350, (2013

How structurally stable are global socioeconomic systems?

The stability analysis of socioeconomic systems has been centered on answering whether small perturbations when a system is in a given quantitative state will push the system permanently to a different quantitative state. However, typically the quantitative state of socioeconomic systems is subject to constant change. Therefore, a key stability question that has been under-investigated is how strong the conditions of a system itself can change before the system moves to a qualitatively different behavior, i.e., how structurally stable the systems is. Here, we introduce a framework to investigate the structural stability of socioeconomic systems formed by the network of interactions among agents competing for resources. We measure the structural stability of the system as the range of conditions in the distribution and availability of resources compatible with the qualitative behavior in which all the constituent agents can be self-sustained across time. To illustrate our framework, we study an empirical representation of the global socioeconomic system formed by countries sharing and competing for multinational companies used as proxy for resources. We demonstrate that the structural stability of the system is inversely associated with the level of competition and the level of heterogeneity in the distribution of resources. Importantly, we show that the qualitative behavior of the observed global socioeconomic system is highly sensitive to changes in the distribution of resources. We believe this work provides a methodological basis to develop sustainable strategies for socioeconomic systems subject to constantly changing conditions

Nestedness in mutualistic networks

James et al. (2012) presented simulations that apparently falsify the analytical result by Bastolla et al. (2009), who showed that nested mutualistic interactions decrease interspecific competition and increase biodiversity in model ecosystems. This contradiction, however, mainly stems from the incorrect application of formulas derived for fully connected networks to empirical, sparse networks.Comment: 2 pages, 1 figur

XANES Study of Structural Disorder in Amorphous Silicon

An investigation of the structure of several amorphous silicon (a-Si) films is presented. Samples were prepared by using the ion beam sputtering technique at different substrate deposition temperatures. X-ray absorption spectroscopy and multiple scattering formalism have been used to detect structural variations of the a-Si films. The analysis of the XANES (X-ray absorption near-edge structure) spectra shows that increasing the substrate deposition temperature leads to a structural change toward a higher-level short-range order.

Randomised controlled trial of primary school based intervention to reduce risk factors for obesity

OBJECTIVE: To assess if a school based intervention was effective in reducing risk factors for obesity. DESIGN: Group randomised controlled trial. SETTING: 10 primary schools in Leeds. PARTICIPANTS: 634 children aged 7­-11 years. INTERVENTION: Teacher training, modification of school meals, and the development of school action plans targeting the curriculum, physical education, tuck shops, and playground activities. MAIN OUTCOME MEASURES: Body mass index, diet, physical activity, and psychological state. RESULTS: Vegetable consumption by 24 hour recall was higher in children in the intervention group than the control group (weighted mean difference 0.3 portions/day, 95% confidence interval 0.2 to 0.4), representing a difference equivalent to 50% of baseline consumption. Fruit consumption was lower in obese children in the intervention group ( - 1.0, - 1.8 to - 0.2) than those in the control group. The three day diary showed higher consumption of high sugar foods (0.8, 0.1 to 1.6)) among overweight children in the intervention group than the control group. Sedentary behaviour was higher in overweight children in the intervention group (0.3, 0.0 to 0.7). Global self worth was higher in obese children in the intervention group (0.3, 0.3 to 0.6). There was no difference in body mass index, other psychological measures, or dieting behaviour between the groups. Focus groups indicated higher levels of self reported behaviour change, understanding, and knowledge among children who had received the intervention. CONCLUSION: Although it was successful in producing changes at school level, the programme had little effect on children's behaviour other than a modest increase in consumption of vegetables

Evaluation of implementation and effect of primary school based intervention to reduce risk factors for obesity

OBJECTIVES: To implement a school based health promotion programme aimed at reducing risk factors for obesity and to evaluate the implementation process and its effect on the school. DESIGN: Data from 10 schools participating in a group randomised controlled crossover trial were pooled and analysed. SETTING: 10 primary schools in Leeds. Participants 634 children (350 boys and 284 girls) aged 7­11 years. MAIN OUTCOME MEASURES: Response rates to questionnaires, teachers' evaluation of training and input, success of school action plans, content of school meals, and children's knowledge of healthy living and self reported behaviour. RESULTS: All 10 schools participated throughout the study. 76 (89%) of the action points determined by schools in their school action plans were achieved, along with positive changes in school meals. A high level of support for nutrition education and promotion of physical activity was expressed by both teachers and parents. 410 (64%) parents responded to the questionnaire concerning changes they would like to see implemented in school. 19 out of 20 teachers attended the training, and all reported satisfaction with the training, resources, and support. Intervention children showed a higher score for knowledge, attitudes, and self reported behaviour for healthy eating and physical activity. CONCLUSION: This programme was successfully implemented and produced changes at school level that tackled risk factors for obesity

The evolutionary linguist's divining-rod : restrictive theory

CITATION: Botha, R. P. 2004. The evolutionary linguist's divining-rod : restrictive theory. Stellenbosch Papers in Linguistics, 35:43-54, doi:10.5774/35-0-10.The original publication is available at http://spil.journals.ac.zaNo abstract available.https://spil.journals.ac.za/pub/article/view/10Publisher’s versio

Fraction auctions: the tradeoff between effciency and running time

This paper studies the sales of a single indivisible object where bidders have continuous valuations. In Grigorieva et al. [13] it was shown that, in this setting, query auctions necessarily allocate inefficiently in equilibrium. In this paper we propose a new sequential auction, called the c-fraction auction. We show c-fraction auctions guarantee approximate efficiency at any desired level of accuracy, independent of the number of bidders. We discuss the running time and the efficiency in the ex-post equilibrium of the auction. We show that by changing the parameter c of the auction we can trade off efficiency against running time.operations research and management science;