Rheagogies: modelling non-trophic effects in food webs

In a food web, nutrients flow via trophic links. For this reason, trophic interactions have a fundamental character due to the principle of mass conservation. To further comply with this principle, we consider a food web model that includes nutrient cycling. Non-trophic effects amongst species of the food web are modelled as interaction modifications, i.e., a functional change in the trophic interaction between two species caused by a third species (a three-party interaction that we call ‘‘rheagogy’’).We also consider that the ecological communities modelled by the food webs result from an assembly process that involves colonisations and extinctions. We find that two distinct classes of ecological communities must be distinguished: (a) ‘‘superefficient’’ communities, in which almost all available nutrients are incorporated into the biomass and (b) ‘‘sub-efficient’’ ones, in which a large proportion of nutrients is not fixed by living organisms. We show that rheagogies (that model non-trophic interactions) are crucial: the larger the effects of rheagogies, the easier the construction of super-efficient communities. These communities are characterized by positive rheagogies, meaning that a certain proportion of mutualistic interactions is necessary. Systems with few or weak rheagogies are less likely to use available abiotic resources efficiently. Although richness (i.e., number of species) is also positively related to efficient nutrient use, its importance is much smaller than that of rheagogies

Illusory Increases in Font Size Improve Letter Recognition

Visual performance of human observers depends not only on the optics of the eye and early sensory encoding but also on subsequent cortical processing and representations. In two experiments, we demonstrated that motion adaptation can enhance as well as impair visual acuity. Observers who experienced an expanding motion aftereffect exhibited improved letter recognition, whereas observers who experienced a contracting motion aftereffect showed impaired letter recognition. We conclude that illusory enlargement and shrinkage of a visual stimulus can modulate visual acuity

COMPARISON OF ANN AND CBR MODELS FOR EARLY COST PREDICTION OF STRUCTURAL SYSTEMS

Reasonably accurate cost estimation of the structural system is quite desirable at the early stages of the design process of a construction project. However, the numerous interactions among the many cost-variables make the prediction difficult. Artificial neural networks (ANN) and case-based reasoning (CBR) are reported to overcome this difficulty. This paper presents a comparison of CBR and ANN augmented by genetic algorithms (GA) conducted by using spreadsheet simulations. GA was used to determine the optimum weights for the ANN and CBR models. The cost data of twenty-nine actual cases of residential building projects were used as an example application. Two different sets of cases were randomly selected from the data set for training and testing purposes. Prediction rates of 84% in the GA/CBR study and 89% in the GA/ANN study were obtained. The advantages and disadvantages of the two approaches are discussed in the light of the experiments and the findings. It appears that GA/ANN is a more suitable model for this example of cost estimation where the prediction of numerical values is required and only a limited number of cases exist. The integration of GA into CBR and ANN in a spreadsheet format is likely to improve the prediction rates

Toll-Like Receptor 2 Signaling Protects Mice from Tumor Development in a Mouse Model of Colitis-Induced Cancer

Inflammatory bowel disease (IBD) is a disorder of chronic inflammation with increased susceptibility to colorectal cancer. The etiology of IBD is unclear but thought to result from a dysregulated adaptive and innate immune response to microbial products in a genetically susceptible host. Toll-like receptor (TLR) signaling induced by intestinal commensal bacteria plays a crucial role in maintaining intestinal homeostasis, innate immunity and the enhancement of intestinal epithelial cell (IEC) integrity. However, the role of TLR2 in the development of colorectal cancer has not been studied. We utilized the AOM-DSS model for colitis-associated colorectal cancer (CAC) in wild type (WT) and TLR2−/− mice. Colons harvested from WT and TLR2−/− mice were used for histopathology, immunohistochemistry, immunofluorescence and cytokine analysis. Mice deficient in TLR2 developed significantly more and larger colorectal tumors than their WT controls. We provide evidence that colonic epithelium of TLR2−/− mice have altered immune responses and dysregulated proliferation under steady-state conditions and during colitis, which lead to inflammatory growth signals and predisposition to accelerated neoplastic growth. At the earliest time-points assessed, TLR2−/− colons exhibited a significant increase in aberrant crypt foci (ACF), resulting in tumors that developed earlier and grew larger. In addition, the intestinal microenvironment revealed significantly higher levels of IL-6 and IL-17A concomitant with increased phospho-STAT3 within ACF. These observations indicate that in colitis, TLR2 plays a protective role against the development of CAC

An ongoing case-control study to evaluate the NHS Bowel Cancer Screening Programme

© 2014 Massat et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated

Chronic Eczematous Eruptions of the Elderly Are Associated with Chronic Exposure to Calcium Channel Blockers: Results from a Case–Control Study

It has been suggested that chronic eczematous eruptions of the elderly could be associated with chronic drug exposure. To determine the drugs associated with these eruptions, we conducted a case–control study on 102 cases and 204 controls. Cases were consecutive patients older than 60 years presenting with an eczematous eruption that had evolved continuously or recurrently for more than 3 months without a reliable cause. Two controls were matched to each case on age, sex, in/outpatient origin, and center. Information about drug exposure was obtained from patients and their pharmacists. Drug use for more than 3 months within the year preceding the eruption was compared between cases and controls. An association was found between calcium channel blockers (CCB) and eczema, with a matched OR (odds ratio) of 2.5 (95% CI (confidence interval): 1.3–4.6). To ascertain the course of patients after CCB withdrawal, two ancillary studies were performed on 74 patients with eczematous eruptions from our department before the case–control study period, and on 101 patients registered in the French “Pharmacovigilance” database. Healing of these eruptions after CCB withdrawal occurred in 83 and 68% of these cases, respectively. The long-term use of CCB is a risk factor for chronic eczematous eruptions of the elderly

Letter processing and font information during reading: beyond distinctiveness, where vision meets design

Letter identification is a critical front end of the reading process. In general, conceptualizations of the identification process have emphasized arbitrary sets of distinctive features. However, a richer view of letter processing incorporates principles from the field of type design, including an emphasis on uniformities across letters within a font. The importance of uniformities is supported by a small body of research indicating that consistency of font increases letter identification efficiency. We review design concepts and the relevant literature, with the goal of stimulating further thinking about letter processing during reading

The stability of ecosystems: a brief overview of the paradox of enrichment

In theory, enrichment of resource in a predator-prey model leads to destabilization of the system, thereby collapsing the trophic interaction, a phenomenon referred to as "the paradox of enrichment". After it was first proposed by Rosenzweig (1971), a number of subsequent studies were carried out on this dilemma over many decades. In this article, we review these theoretical and experimental works and give a brief overview of the proposed solutions to the paradox. The mechanisms that have been discussed are modifications of simple predator-prey models in the presence of prey that is inedible, invulnerable, unpalatable and toxic. Another class of mechanisms includes an incorporation of a ratio-dependent functional form, inducible defence of prey and density-dependent mortality of the predator. Moreover, we find a third set of explanations based on complex population dynamics including chaos in space and time. We conclude that, although any one of the various mechanisms proposed so far might potentially prevent destabilization of the predator-prey dynamics following enrichment, in nature different mechanisms may combine to cause stability, even when a system is enriched. The exact mechanisms, which may differ among systems, need to be disentangled through extensive field studies and laboratory experiments coupled with realistic theoretical models