A note on density dependence in population models

One of the most studied phenomena in ecology is density dependent regulation. The model most frequently used to study this behaviour is the theta-logistic model. However, disagreement has developed within the ecology community pertaining to the interpretation of this model’s parameters, and thus as to appropriate values for the parameters to assume. In particular, the parameter θ$\theta$ has been allowed to take negative values, resulting in the ‘growth rate parameter’ estimated to be negative for species which are extant and exhibit no signs of becoming extinct in the short-term. Here we explain this phenomenon by formulating the theta-logistic model in the manner in which the original logistic model was formulated by Verhulst (1838), in doing so providing a simple interpretation of model parameters and thus restrictions on values the parameters may assume. We conclude that θ$\theta$ should (almost always) be restricted to values greater than −1$-1$. This has implications for studies assessing the form of density dependence from data. Additionally, another model appearing in the literature is presented which provides a more flexible model of density dependence at the expense of only one additional parameter.     

Meta-analysis: trophic level, habitat, and productivity shape the food web effects of resource subsidies

Studies of the effects of cross-habitat resource subsidies have been a feature of food web ecology over the past decade. To date, most studies have focused on demonstrating the magnitude of a subsidy or documenting its effect in the recipient habitat. Ecologists have yet to develop a satisfactory framework for predicting the magnitude of these effects. We used 115 data sets from 32 studies to compare consumer responses to resource subsidies across recipient habitat type, trophic level, and functional group. Changes in consumer density or biomass in response to subsidies were inconsistent across habitats, trophic, and functional groups. Responses in stream cobble bar and coastline habitats were larger than in other habitats. Contrary to expectation, the magnitude of consumer response was not affected by recipient habitat productivity or the ratio of productivity between donor and recipient habitats. However, consumer response was significantly related to the ratio of subsidy resources to equivalent resources in the recipient habitat. Broad contrasts in productivity are modified by subsidy type, vector, and the physical and biotic characteristics of both donor and recipient habitats. For this reason, the ratio of subsidy to equivalent resources is a more useful tool for predicting the possible effect of a subsidy than coarser contrasts of in situ productivity. The commonness of subsidy effects suggests that many ecosystems need to be studied as open systems.     

Public Nutrition in Emergencies: An Overview of Debates, Dilemmas and Decision-making

This paper introduces and discusses the main themes and issues arising from the workshop 'International Public Nutrition in Emergencies: The Potential for Improving Practice'.
Good co-ordination within the nutrition sector of the international humanitarian response system has led to a range of achievements in recent years. Major constraints to improving programme impact remain, however, including misconceptions about the scope of nutrition among the wider humanitarian system, which tends to give it a narrow focus on malnutrition and feeding people. In contrast to this limited view, the Public Nutrition approach brings a more broad-based emphasis to assessing and responding to nutritional problems in emergencies, and takes into account the wider social, economic and political causes of malnutrition.
Six case study presentations illustrated the various components of a Public Nutrition approach, including in-depth assessment, analysis and tailoring programmes accordingly. Additional presentations considered the nature of vulnerability, the concept of Public Nutrition, the responsibilities for addressing nutritional problems and some of the operational tools and frameworks in current use.
Participants agreed on the necessity of raising levels of awareness and understanding among all actors in the humanitarian sphere about the impact of their actions on nutrition. Strategies for achieving this included developing better multi-sectoral working relationships and also strengthening relationships with donors and key decision-makers in the humanitarian system. Other related strategies included institutional learning, training and capacity building, particularly in relation to institutions based in developing countries and building upon initiatives such as the Sphere Project, which has successfully brought together the various actors within the humanitarian system in order to improve quality of response.     

Identifying key needs for the integration of social–ecological outcomes in arctic wildlife monitoring

For effective monitoring in social–ecological systems to meet needs for biodiversity, science, and humans, desired outcomes must be clearly defined and routes from direct to derived outcomes understood. The Arctic is undergoing rapid climatic, ecological, social, and economic changes and requires effective wildlife monitoring to meet diverse stakeholder needs. To identify stakeholder priorities concerning desired outcomes of arctic wildlife monitoring, we conducted in-depth interviews with 29 arctic scientists, policy and decision makers, and representatives of indigenous organizations and nongovernmental organizations. Using qualitative content analysis, we identified and defined desired outcomes and documented links between outcomes. Using network analysis, we investigated the structure of perceived links between desired outcomes. We identified 18 desired outcomes from monitoring and classified them as either driven by monitoring information, monitoring process, or a combination of both. Highly cited outcomes were make decisions, conserve, detect change, disseminate, and secure food. These reflect key foci of arctic monitoring. Infrequently cited outcomes (e.g., govern) were emerging themes. Three modules comprised our outcome network. The modularity highlighted the low strength of perceived links between outcomes that were primarily information driven or more derived (e.g., detect change, make decisions, conserve, or secure food) and outcomes that were primarily process driven or more derived (e.g., cooperate, learn, educate). The outcomes expand monitoring community and disseminate created connections between these modules. Key desired outcomes are widely applicable to social–ecological systems within and outside the Arctic, particularly those with wildlife subsistence economies. Attributes and motivations associated with outcomes can guide development of integrated monitoring goals for biodiversity conservation and human needs. Our results demonstrated the disconnect between information- and process-driven goals and how expansion of the monitoring community and improved integration of monitoring stakeholders will help connect information- and process-derived outcomes for effective ecosystem stewardship.     

Prenatal diagnosis of Harlequin ichthyosis presenting as distal arthrogryposis using three-dimensional ultrasound

We describe a case of Harlequin Icthyosis where the main 2D and 3D ultrasound findings were digital contractures as opposed to the more commonly described severe facial dysmorphisms. A prenatal finding of distal arthrogryposis can therefore include harlequin icthyosis as a differential diagnosis, where 3D ultrasound may then disclose the facial features more commonly associated with the condition. Copyright © 2007 John Wiley & Sons, Ltd.     

Laboratory and field estimates of the rate of faecal pellet production by Antarctic krill,Euphausia superba

The time course of faecal pellet production (egestion) was monitored in January 1985 for a population of Antarctic krill, Euphausia superba Dana, maintained in flowing seawater aquaria at Palmer Station, Antarctica. Following transfer to filtered seawater, krill produced faecal strings for roughly 40 min, after which time faecal egestion virtually ceased. Similar results were obtained for freshly-trawled krill at sea in February and March 1985. There were wide daily variations in total faecal egestion rate; mean rates varied from 0.54 to 1.66 mg dry wt h^-1 and individual rates from 0.25 to 2.35 mg h^-1 (all data corrected to a standard krill of 600 mg fresh weight). Despite these wide fluctuations in total faecal egestion, the loss of organic matter showed no significant daily variation, with a mean value of 0.13 mgh^-1. The relationship between faecal egestion rate and faecal organic content suggested that feeding rate was governed by food quality; when inorganic load was high, feeding rate increased to ensure sufficient energy intake. The data suggest that superfluous feeding does not occur in krill and that values of gut-clearance time calculated from time intervals greater than about 40 min will not be representative of previous feeding history. the rates of faecal egestion observed in this study indicate that the flux of faecal pellets from krill is substantial. They imply an energy intake in E. superba of 17 to 28% body weight per day, much higher than estimated previously for this species by summing known energy losses, but similar to estimates for other euphausiids.