Balancing direct and indirect sources of navigational information in a leaderless model of collective animal movement

Navigation is an important movement process that enables individuals and groups of animals to find targets in space at different spatio-temporal scales. Earlier studies have shown how being in a group can confer navigational advantages to individuals, either through following more experienced leaders or through the pooling of many inaccurate compasses, a process known as the ‘many wrongs principle’. However, the exact mechanisms for how information is transferred and used within the group in order to improve both individual- and group-level navigational performance are not fully understood. Here we explore the relative weighting that should be given to different sources of navigational information by an individual within a navigating group at each step of the movement process. Specifically, we consider a direct goal-oriented source of navigational information such as the individual׳s own imperfect knowledge of the target (a ‘noisy compass’) alongside two indirect sources of navigational information: the previous movement directions of neighbours in the group (social information) and, for the first time in this context, the previous movement direction of the individual (persistence). We assume that all individuals are equal in their abilities and that direct navigational information is prone to higher errors than indirect information. Using computer simulations, we show that in such situations giving a high weighting to either type of indirect navigational information can serve to significantly improve the navigation success of groups. Crucially, we also show that if the quality of social information is reduced, e.g. by an individual׳s limited cognitive abilities, the best navigational strategy for groups assigns a considerable weighting to persistence, a behaviour that is neither social, nor directly aimed at navigating

Navigational efficiency in a biased and correlated random walk model of individual animal movement

Understanding how an individual animal is able to navigate through its environment is a key question in movement ecology that can give insight into observed movement patterns and the mechanisms behind them. Efficiency of navigation is important for behavioral processes at a range of different spatio-temporal scales, including foraging and migration. Random walk models provide a standard framework for modeling individual animal movement and navigation. Here we consider a vector-weighted biased and correlated random walk (BCRW) model for directed movement (taxis), where external navigation cues are balanced with forward persistence. We derive a mathematical approximation of the expected navigational efficiency for any BCRW of this form and confirm the model predictions using simulations. We demonstrate how the navigational efficiency is related to the weighting given to forward persistence and external navigation cues, and highlight the counter-intuitive result that for low (but realistic) levels of error on forward persistence, a higher navigational efficiency is achieved by giving more weighting to this indirect navigation cue rather than direct navigational cues. We discuss and interpret the relevance of these results for understanding animal movement and navigation strategies

21st century fisheries management: a spatio-temporally explicit tariff-based approach combining multiple drivers and incentivising responsible fishing

Abstract Kraak, S. B. M., Reid, D. G., Gerritsen, H. D., Kelly, C. J., Fitzpatrick, M., Codling, E. A., and Rogan, E. 2012. 21st century fisheries management: a spatio-temporally explicit tariff-based approach combining multiple drivers and incentivising responsible fishing. – ICES Journal of Marine Science, 69: 590–601. Traditionally fisheries management has focused on biomass and mortality, expressed annually and across large management units. However, because fish abundance varies at much smaller spatio-temporal scales, fishing mortality can potentially be controlled more effectively if managed at finer scale. The ecosystem approach requires more indicators at finer scales as well. Incorporating ecosystem targets would need additional management tools with potentially conflicting results. We present a simple, integrated, management approach that provides incentives for “good behaviour”. Fishers would be given a number of fishing-impact credits, called real-time incentives (RTIs), to spend according to spatio-temporally varying tariffs per fishing day. RTI quotas and tariffs could be based on commercial stocks and ecosystem targets. Fishers could choose how to spend their RTIs, e.g. by limited fishing in high-catch or sensitive areas or by fishing longer in lower-catch or less sensitive areas. The RTI system does not prescribe and forbid, but instead allows fishers to fish wherever and whenever they want; ecosystem costs are internalized and fishers have to take them into account in their business decisions. We envisage no need for traditional landings or catch quotas for the fleets while operating under the scheme. The approach could facilitate further devolution of responsibility to industry.</jats:p

Role of infochemical mediated zooplankton grazing in a phytoplankton competition model

Infochemicals released by marine phytoplankton play important roles in food web interactions by influencing the feeding behavior and selectivity of zooplanktonic predators. Recent modeling efforts have focused on the role of such chemicals as toxic grazing deterrents in phytoplankton competition. However, infochemicals may also be utilized as grazing cues, leading predators to profitable foraging patches. Here we investigate the role of infochemical mediated zooplankton grazing in a standard 3-species phytoplankton competition model, with the aim of further elucidating the ecological role of phytoplankton derived infochemicals. We then extend this to consider a more realistic 4-species model. The models produce a range of solutions depending on the strength of competition and microzooplankton grazing selectivity. Our key result is that infochemical chemoattractants, which increase the susceptibility of the producer to grazing, can provide a refuge for both competing phytoplankton species by attracting carnivorous copepods to consume microzooplankton grazers in a multi-trophic interaction. Our results indicate that infochemicals potentially have important consequences for the dynamics of marine food webs. © 2012 Elsevier B.V

Health surveillance for occupational asthma in the UK

Background Periodic health surveillance (HS) of workers can identify early cases of occupational asthma. Information about its uptake and its content in the UK is lacking. Aims To identify the overall levels of uptake and quality of HS for occupational asthma within three high risk industry sectors in the UK. Methods A telephone survey of employers, and their occupational health (OH) professionals, carried out in three sectors with exposures potentially capable of causing occupational asthma (bakeries, wood working and motor vehicle repair). Results A total of 457 organizations participated (31% response rate). About 77% employed <10 people, 17% between 10 and 50 and 6% >50. Risk assessments were common (67%) and 14% carried out some form of HS for occupational asthma, rising to 19% if only organizations reporting asthma hazards and risks were considered. HS was carried out both by in-house (31%) and external providers (69%). Organizational policies were often used to define HS approaches (80%), but infrequently shared with the OH provider. OH providers described considerable variation in practice. Record keeping was universal, but worker-held records were not reported. HS tools were generally developed in-house. Lung function was commonly measured, but only limited interpretation evident. Referral of workers to local specialist respiratory services was variable. Conclusions This study provided new insights into the real world of HS for occupational asthma. We consider that future work could and should define simpler, more practical and evidence-based approaches to HS to ensure maximal consistency and use of high-quality approaches

Emergence of the wrapped Cauchy distribution in mixed directional data

Inferring the most appropriate distribution (or distributions) to describe observed directional data is important in many applications of circular statistics. In particular, animal movement paths are typically analysed and modelled by considering the distribution of step lengths and turning (or absolute) angles. Here we demonstrate that a single-wrapped Cauchy distribution can appear to fit directional data mixed from two different underlying wrapped normal distributions. We derive mathematical expressions to calculate the parameter space for which this occurs and illustrate the result by analysing an example data set of the movements of African bull elephants (Loxodonta Africana). We conclude that the presence of a wrapped Cauchy distribution in observed directional data can, in certain cases, be explained by data coming from two distinct underlying distributions. We discuss how this may relate to the presence of multiple movement modes within an observed path when analysing animal movement data

Diffusion about the mean drift location in a biased random walk

Random walks are used to model movement in a wide variety of contexts: from the movement of cells undergoing chemotaxis to the migration of animals. In a two- dimensional biased random walk, the diffusion about the mean drift position is entirely dependent on the moments of the angular distribution used to determine the movement direction at each step. Here we consider biased random walks using several different angular distributions and derive expressions for the diffusion coefficients in each direction based on either a fixed or variable movement speed, and we use these to generate a probability density function for the long-time spatial distribution. we demonstrate how diffusion is typically anisotropic around the mean drift position and illustrate these theoretical results using computer simulations. we relate these results to earlier studies of swimming microorganisms and explain how the results can be generalized to other types of animal movement. © 2010 by the Ecological Society of America

Correlation dynamics between electrons and ions in the fragmentation of D2_2 molecules by short laser pulses

We studied the recollision dynamics between the electrons and D$_2^+$ ions following the tunneling ionization of D$_2$ molecules in an intense short pulse laser field. The returning electron collisionally excites the D$_2^+$ ion to excited electronic states from there D$_2^+$ can dissociate or be further ionized by the laser field, resulting in D$^+$ + D or D$^+$ + D$^+$, respectively. We modeled the fragmentation dynamics and calculated the resulting kinetic energy spectrum of D$^+$ to compare with recent experiments. Since the recollision time is locked to the tunneling ionization time which occurs only within fraction of an optical cycle, the peaks in the D$^+$ kinetic energy spectra provides a measure of the time when the recollision occurs. This collision dynamics forms the basis of the molecular clock where the clock can be read with attosecond precision, as first proposed by Corkum and coworkers. By analyzing each of the elementary processes leading to the fragmentation quantitatively, we identified how the molecular clock is to be read from the measured kinetic energy spectra of D$^+$ and what laser parameters be used in order to measure the clock more accurately.Comment: 13 pages with 14 figure

Exploring Determinants of Pre-movement Delays in a Virtual Crowd Evacuation Experiment

Understanding evacuations of high-occupancy buildings presents a major challenge in fire safety science. The total time individuals require to exit a building includes the time it takes them to respond to an alarm and decide to evacuate (pre-movement) and the time it takes them to walk along their chosen exit route (movement). Previous work has shown that variation in pre-movement times is responsible for substantial evacuation delays, but few controlled experiments on this have been conducted. Here, we present a virtual experiment that investigates the level of risk individuals take by collecting virtual objects before evacuating. We determine how over 1200 participants, who were recruited from visitors to the London Science Museum, respond to three factors: a reduction in their knowledge of a building, a change in the behaviour of other simulated evacuees and a change in how they are attached to the objects they can collect (potential gain versus loss). We confirm that collecting more objects is risky, as it affects evacuation success. In our experiment, 44.6% of participants choose extreme strategies by collecting either all or none of the available objects before evacuating. While the adoption of extreme strategies is affected by all three factors we investigate, the only factor that significantly increases the average number of objects participants collect, regardless of extreme strategies, is loss aversion. Our work shows the potential of virtual experiments to safely, quickly and cheaply scope processes causing pre-movement time delays in crowd evacuations. This provides a starting point for further research