An explanatory model for food-web structure and evolution

Food webs are networks describing who is eating whom in an ecological community. By now it is clear that many aspects of food-web structure are reproducible across diverse habitats, yet little is known about the driving force behind this structure. Evolutionary and population dynamical mechanisms have been considered. We propose a model for the evolutionary dynamics of food-web topology and show that it accurately reproduces observed food-web characteristics in the steady state. It is based on the observation that most consumers are larger than their resource species and the hypothesis that speciation and extinction rates decrease with increasing body mass. Results give strong support to the evolutionary hypothesis. (C) 2005 Elsevier B.V. All rights reserved.

Soil resource supply influences faunal size-specific distributions in natural food webs

The large range of body-mass values of soil organisms provides a tool to assess the ecological organization of soil communities. The goal of this paper is to identify graphical and quantitative indicators of soil community composition and ecosystem functioning, and to illustrate their application to real soil food webs. The relationships between log-transformed mass and abundance of soil organisms in 20 Dutch meadows and heathlands were investigated. Using principles of allometry, maximal use can be made of ecological theory to build and explain food webs. The aggregate contribution of small invertebrates such as nematodes to the entire community is high under low soil phosphorus content and causes shifts in the mass-abundance relationships and in the trophic structures. We show for the first time that the average of the trophic link lengths is a reliable predictor for assessing soil fertility responses. Ordered trophic link pairs suggest a self-organizing structure of food webs according to resource availability and can predict environmental shifts in ecologically meaningful ways.

Rigorous conditions for food-web intervality in high-dimensional trophic niche spaces

Food webs represent trophic (feeding) interactions in ecosystems. Since the late 1970s, it has been recognized that food-webs have a surprisingly close relationship to interval graphs. One interpretation of food-web intervality is that trophic niche space is low-dimensional, meaning that the trophic character of a species can be expressed by a single or at most a few quantitative traits. In a companion paper we demonstrated, by simulating a minimal food-web model, that food webs are also expected to be interval when niche-space is high-dimensional. Here we characterize the fundamental mechanisms underlying this phenomenon by proving a set of rigorous conditions for food-web intervality in high-dimensional niche spaces. Our results apply to a large class of food-web models, including the special case previously studied numerically.

Food-web structure in low- and high-dimensional trophic niche spaces

A question central to modelling and, ultimately, managing food webs concerns the dimensionality of trophic niche space, that is, the number of independent traits relevant for determining consumer-resource links. Food-web topologies can often be interpreted by assuming resource traits to be specified by points along a line and each consumer's diet to be given by resources contained in an interval on this line. This phenomenon, called intervality, has been known for 30 years and is widely acknowledged to indicate that trophic niche space is close to one-dimensional. We show that the degrees of intervality observed in nature can be reproduced in arbitrary-dimensional trophic niche spaces, provided that the processes of evolutionary diversification and adaptation are taken into account. Contrary to expectations, intervality is least pronounced at intermediate dimensions and steadily improves towards lower- and higher-dimensional trophic niche spaces.

Chronic treatment with a stable obestatin analogue significantly alters plasma triglyceride levels but fails to influence food intake, fluid intake, body weight, or body composition in rats.

Obestatin (OB(1-23) is a 23 amino acid peptide encoded on the preproghrelin gene, originally reported to have metabolic actions related to food intake, gastric emptying and body weight. The biological instability of OB(1-23) has recently been highlighted by studies demonstrating its rapid enzymatic cleavage in a number of biological matrices. We assessed the stability of both OB(1-23) and an N-terminally PEGylated analogue (PEG-OB(1-23)) before conducting chronic in vivo studies. Peptides were incubated in rat liver homogenate and degradation monitored by LC-MS. PEG-OB(1-23) was approximately 3-times more stable than OB(1-23). Following a 14 day infusion of Sprague Dawley rats with 50 mol/kg/day of OB(1-23) or a N-terminally PEGylated analogue (PEG-OB(1-23)), we found no changes in food/fluid intake, body weight and plasma glucose or cholesterol between groups. Furthermore, morphometric liver, muscle and white adipose tissue (WAT) weights and tissue triglyceride concentrations remained unaltered between groups. However, with stabilised PEG-OB(1-23) we observed a 40% reduction in plasma triglycerides. These findings indicate that PEG-OB(1-23) is an OB(1-23) analogue with significantly enhanced stability and suggest that obestatin could play a role in modulating physiological lipid metabolism, although it does not appear to be involved in regulation of food/fluid intake, body weight or fat deposition.

Contingency Fit, Institutional Fit, and Firm Performance: A Metafit Approach to Organization–Environment Relationships

In this paper, we attempt to reconcile contingency and institutional fit approaches concerning the organization-environment relationship. While prior scholarly research has examined both theories and compared their impacts on organizational fit and performance, we lay the groundwork for a meta-fit approach by investigating how contingency and institutional fit interact to influence firm performance. We test our theoretical framework using a dataset of 3,259 respondents from 1,904 companies regarding task environmental demands and institutional demands on organizational design across a broad range of industries and firm size classes. Our results show that contingency and institutional fit provide complementary and interdependent explanations of firm performance. Importantly, our findings indicate that for firms under conditions of “quasi-fit” rather than perfect contingency fit or optimal institutional fit, improvements in contingency and/or institutional fit will result in better performance. However, firms with high contingency fit are less vulnerable to deviation from institutional fit in the formation of firm performance, while firms with perfect institutional fit will slightly decrease their performance when they strive to achieve contingency fit.

In vitro bioassays for the study of endocrine-disrupting food additives and contaminants

Endocrine-disrupting chemicals (EDCs) are capable of interfering with normal hormone homeostasis by acting on several targets and through a wide variety of mechanisms. Unwanted exposure to EDCs can lead to a wide spectrum of adverse health effects, especially when exposure is during critical windows of development. Feed and food are considered to be among the main routes of inadvertent exposure to EDCs, so there is an important need for efficient detection of EDCs in these matrices.

Business representation and the UK regions: mapping institutional change

Political devolution in Scotland, Wales and Northern Ireland and the developing regional agenda in England are prompting changes in the organization of business interest representation within the devolved and decentralized territories. In this paper we seek to describe the realignment of business interest representation at the 'regional' scale, first through a detailed review of changes underway across specific business associations and representative fora, and secondly through an initial attempt to compare and 'map' the patterns of institutional change recorded in the various territories. In broad terms the overall scale, operation and degree of formalization of the new political arrangements for business representation tend broadly to reflect the established institutional and political contexts of the respective nations and regions and the level of devolution ceded to the territories. However, there are important variations in a complex process of uneven development. In the concluding section we present some initial thoughts on the nature of the changes observed in the institutional framework for business representation. A key argument is that to date such changes suggest a reconfiguration of business political activity rather than a step-change in the institutional foundation for sub-national business interest representation in the UK. (C) 2003 Elsevier Ltd. All rights reserved.

Towards an Acceptable Level of Violence: Institutional Lessons from Northern Ireland

Institutional and economic development has recently returned to the forefront of economic analysis. The use of case studies (both historical and contemporary) has been important in this revival. Likewise, it has been argued recently by economic methodologists that historical context provides a kind of ‘‘laboratory’’ for the researcher interested in real world economic phenomena. Counterterrorism economics, in contrast with much of the rest of the literature on terrorism, has all too rarely drawn upon detailed contextual case studies. This article seeks to help remedy this problem. Archival evidence, including previously unpublished material on the DeLorean case, is an important feature of this article. The article examines how an inter-related strategy, which traded-off economic, security, and political considerations, operated during the Troubles. Economic repercussions of this strategy are discussed. An economic analysis of technical and organizational change within paramilitarism is also presented. A number of institutional lessons are discussed including: the optimal balance between carrot versus stick, centralization relative to decentralization, the economics of intelligence operations, and tit-for-tat violence. While existing economic models are arguably correct in identifying benefits from politico-economic decentralization, they downplay the element highlighted by institutional analysis.