Species assembly in model ecosystems, I: Analysis of the population model and the invasion dynamics

Recently we have introduced a simplified model of ecosystem assembly (Capitan et al., 2009) for which we are able to map out all assembly pathways generated by external invasions in an exact manner. In this paper we provide a deeper analysis of the model, obtaining analytical results and introducing some approximations which allow us to reconstruct the results of our previous work. In particular, we show that the population dynamics equations of a very general class of trophic-level structured food-web have an unique interior equilibrium point which is globally stable. We show analytically that communities found as end states of the assembly process are pyramidal and we find that the equilibrium abundance of any species at any trophic level is approximately inversely proportional to the number of species in that level. We also find that the per capita growth rate of a top predator invading a resident community is key to understand the appearance of complex end states reported in our previous work. The sign of these rates allows us to separate regions in the space of parameters where the end state is either a single community or a complex set containing more than one community. We have also built up analytical approximations to the time evolution of species abundances that allow us to determine, with high accuracy, the sequence of extinctions that an invasion may cause. Finally we apply this analysis to obtain the communities in the end states. To test the accuracy of the transition probability matrix generated by this analytical procedure for the end states, we have compared averages over those sets with those obtained from the graph derived by numerical integration of the Lotka-Volterra equations. The agreement is excellent.Comment: 16 pages, 8 figures. Revised versio

An experimental customer satisfaction index to evaluate the performance of city logistics services

© 2016 Vilnius Gediminas Technical University (VGTU) Press. Freight transport in urban areas entails benefits (i.e. free access to goods when needed), but also negative externalities (environmental, social and transportation impacts). In response to these problems, the concept of city logistics emerged, for the purpose of planning, organizing, coordinating and controlling physical and information flows in order to find a compromise between efficient freight distribution in urban areas and protection of the environment. A typical city logistics initiative is the Urban Freight Consolidation Centre (UFCC), the benefits of which are significant. Its financial issues though represent a huge problem for public administrations. However, a large customer network, comprising retailers participating in the initiative, could make the UFCC a self-financing scheme. The key to expanding the scheme is closely linked with marketing campaigns and customer care. Therefore, customer care analysis represents an important tool in developing UFCC schemes. In this paper, a new Customer Satisfaction Index (CSI) is proposed for evaluating UFCC service quality. The new index, named CSImod, is a modified version of the traditional CSI, but places greater emphasis on customer dissatisfaction, so as to analyse the most critical areas of the service with a view to improving them. The index has been tested using experimental data collected within the CIVITAS RENAISSANCE Project, in which the Bristol and Bath Freight Consolidation Centre (BBFCC) scheme was evaluated. The evaluation was done from a user perspective, i.e. the participating retailers. The CSImod places more importance on the most dissatisfied customers making it possible to understand why they are dissatisfied and with what. Thus, it is possible to intervene with the aim of improving those areas of the service that are perceived as the worst. In spite of the high level of satisfaction with the overall service provided by the BBFCC, thanks to the CSImod the analysis pointed out that some retailers are dissatisfied with the delivery time arrangements and also with deliveries that were getting wet, issues about which the BBFCC manager was totally unaware. The CSImod could be used by UFCC operators to extend the network of the retailers involved and could therefore provide an implicit solution for making the scheme self-financing

Recent advances in understanding and measurement of mercury in the environment: Terrestrial Hg cycling

This review documents recent advances in terrestrial mercury cycling. Terrestrial mercury (Hg) research has matured in some areas, and is developing rapidly in others. We summarize the state of the science circa 2010 as a starting point, and then present the advances during the last decade in three areas: land use, sulfate deposition, and climate change. The advances are presented in the framework of three Hg "gateways" to the terrestrial environment: inputs from the atmosphere, uptake in food, and run off with surface water. Among the most notable advances:The Arctic has emerged as a hotbed of Hg cycling, with high stream fluxes and large stores of Hg poised for release from permafrost with rapid high-latitude warming.The bi-directional exchange of Hg between the atmosphere and terrestrial surfaces is better understood, thanks largely to interpretation from Hg isotopes; the latest estimates place land surface Hg re-emission lower than previously thought.Artisanal gold mining is now thought responsible for over half the global stream flux of Hg.There is evidence that decreasing inputs ofHg to ecosystems may bring recovery sooner than expected, despite large ecosystem stores of legacy Hg.Freshly deposited Hg is more likely than stored Hg to methylate and be incorporated in rice.Topography and hydrological connectivity have emerged as master variables for explaining the disparate response of THg and MeHg to forest harvest and other land disturbance.These and other advances reported here are of value in evaluating the effectiveness of theMinamata Convention on reducing environmental Hg exposure to humans and wildlife. (C) 2020 The Authors. Published by Elsevier B.V

Biologically Inspired Monocular Vision Based Navigation and Mapping in GPS-Denied Environments

This paper presents an in-depth theoretical study of bio-vision inspired feature extraction and depth perception method integrated with vision-based simultaneous localization and mapping (SLAM). We incorporate the key functions of developed visual cortex in several advanced species, including humans, for depth perception and pattern recognition. Our navigation strategy assumes GPS-denied manmade environment consisting of orthogonal walls, corridors and doors. By exploiting the architectural features of the indoors, we introduce a method for gathering useful landmarks from a monocular camera for SLAM use, with absolute range information without using active ranging sensors. Experimental results show that the system is only limited by the capabilities of the camera and the availability of good corners. The proposed methods are experimentally validated by our self-contained MAV inside a conventional building

Marine conservation : towards a multi-layered network approach

Valuing, managing and conserving marine biodiversity and a full range of ecosystem services is at the forefront of research and policy agendas. However, biodiversity is being lost at up to a thousand times the average background rate. Traditional disciplinary and siloed conservation approaches are not able to tackle this massive loss of biodiversity because they generally ignore or overlook the interactive and dynamic nature of ecosystems processes, limiting their predictability. To conserve marine biodiversity, we must assess the interactions and impacts among biodiversity and ecosystem services (BD-ES). The scaling up in complexity from single species to entire communities is necessary, albeit challenging, for a deeper understanding of how ecosystem services relate to biodiversity and the roles species have in ecosystem service provision. These interactions are challenging to map, let alone fully assess, but network and system-based approaches provide a powerful way to progress beyond those limitations. Here, we introduce a conceptual multi-layered network approach to understanding how ecosystem services supported by biodiversity drive the total service provision, how different stressors impact BD-ES and where conservation efforts should be placed to optimize the delivery of ecosystem services and protection of biodiversity

Health claims in the labelling and marketing of food products:: the Swedish food sector's Code of Practice in a European perspective

Since 1990 certain health claims in the labelling and marketing of food products have been allowed in Sweden within the food sector's Code of Practice. The rules were developed in close dialogue with the authorities. The legal basis was a decision by the authorities not to apply the medicinal products’ legislation to “foods normally found on the dinner table” provided the rules defined in the Code were followed. The Code of Practice lists nine well-established diet–health relationships eligible for generic disease risk reduction claims in two steps and general rules regarding nutrient function claims. Since 2001, there has also been the possibility for using “product-specific physiological claims (PFP)”, subject to premarketing evaluation of the scientific dossier supporting the claim. The scientific documentation has been approved for 10 products with PFP, and another 15 products have been found to fulfil the Code's criteria for “low glycaemic index”. In the third edition of the Code, active since 2004, conditions in terms of nutritional composition were set, i.e. “nutrient profiles”, with a general reference to the Swedish National Food Administration's regulation on the use of a particular symbol, i.e. the keyhole symbol. Applying the Swedish Code of practice has provided experience useful in the implementation of the European Regulation on nutrition and health claims made on foods, effective from 2007

Multiple Episodes of Convergence in Genes of the Dim Light Vision Pathway in Bats

The molecular basis of the evolution of phenotypic characters is very complex and is poorly understood with few examples documenting the roles of multiple genes. Considering that a single gene cannot fully explain the convergence of phenotypic characters, we choose to study the convergent evolution of rod vision in two divergent bats from a network perspective. The Old World fruit bats (Pteropodidae) are non-echolocating and have binocular vision, whereas the sheath-tailed bats (Emballonuridae) are echolocating and have monocular vision; however, they both have relatively large eyes and rely more on rod vision to find food and navigate in the night. We found that the genes CRX, which plays an essential role in the differentiation of photoreceptor cells, SAG, which is involved in the desensitization of the photoactivated transduction cascade, and the photoreceptor gene RH, which is directly responsible for the perception of dim light, have undergone parallel sequence evolution in two divergent lineages of bats with larger eyes (Pteropodidae and Emballonuroidea). The multiple convergent events in the network of genes essential for rod vision is a rare phenomenon that illustrates the importance of investigating pathways and networks in the evolution of the molecular basis of phenotypic convergence