Independence and interdependence in the nest-site choice by honeybee swarms: Agent-based models, analytical approaches and pattern formation

In a recent paper List, Elsholtz and Seeley (List et al., 2009) have devised an agent-based model of the nest-choice dynamics in swarms of honeybees, and have concluded that both interdependence and independence are needed for the bees to reach a consensus on the best nest site. We here present a simplified version of the model which can be treated analytically with the tools of statistical physics and which largely has the same features as the original dynamics. Based on our analytical approaches it is possible to characterize the co-ordination outcome exactly on the deterministic level, and to a good approximation if stochastic effects are taken into account, reducing the need for computer simulations on the agent-based level. In the second part of the paper we present a spatial extension, and show that transient non-trivial patterns emerge, before consensus is reached. Approaches in terms of Langevin equations for continuous field variables are discussed.     

The behavioral context of common dolphin (Delphinus sp.) vocalizations

Correlations between surface behavior and concurrent underwater vocalizations were modeled for common dolphins (Delphinus spp.) in the Southern California Bight (SCB) over multiple field seasons. Clicks, pulsed calls, and whistles were examined, with a total of 50 call features identified. Call features were used to classify behavior using random forest decision trees, with rates of correct classification reaching 80.6% for fast travel, 84.6% for moderate travel, 59.8% for slow travel, and 58% for foraging behavior. Common dolphins spent most of their time traveling. The highest number of clicks, pulsed calls, and complex whistles were produced during fast travel. In contrast, during foraging there were few pulsed calls and whistles produced, and the whistles were simple with narrow bandwidths and few harmonics. Behavior and vocalization patterns suggest nocturnal foraging in offshore waters as the primary feeding strategy. Group size and spacing were strongly correlated with behavior and rates of calling, with higher call rates in dispersed traveling groups and lower call rates in loosely aggregated foraging groups. These results demonstrate that surface behavior can be classified using vocalization data, which builds the framework for behavioral studies of common dolphins using passive acoustic monitoring techniques.     

A fruit in hand is worth many more in the bush: steep spatial discounting by free-ranging rhesus macaques (Macaca mulatta)

Decision making is one of the principal cognitive processes underlying goal-directed behaviour and thus there is justifiably strong interest in modeling it. However, many of these models have yet to be tested outside of the laboratory. At the same time, field work would benefit from the use of experimental methods developed in the laboratory to determine the causal relationships between environmental variables and behaviour. We therefore adapted a laboratory-derived experimental paradigm to test decision making in the wild. The experiment used an indifference-point procedure to determine the influence of both the amount and distance of food on choice behaviour. Free-ranging rhesus monkeys were given the choice between a smaller amount of food at a closer distance and a larger amount farther away. In four conditions, we held the closer amount constant across trials and varied the farther amount to determine the point at which the monkeys were indifferent to the choice alternatives. For example, in condition one, we used one piece of food at the closer location, and determined how many pieces would be equivalent in the farther location. Four different closer amounts were tested to obtain an indifference point curve, with the indifference amounts at the farther location plotted against the closer amounts. The slope of the obtained linear indifference curve was surprisingly high, suggesting that rhesus monkeys significantly discount food that is farther away. Possible reasons for this steep spatial discounting are discussed.     

Context-dependent decisions among options varying in a single dimension

Contrary to theories of rational choice, adding alternatives to a choice set can change the choices made by both humans and animals. This is usually done by adding an inferior decoy to a choice set of two favoured options that are characterized on two distinct dimensions. We presented wild, free-living rufous hummingbirds (Selasphorus rufus) with choices between two or three options that varied in a single dimension only. The options varied in concentration, in volume or in corolla length. When the options varied in concentration, the addition of a medium option to a choice set of a low and a high concentration caused birds to increase their preference for the high option. However, they decreased their preference for the high concentration option when a low option was added to a choice set of high and medium concentrations. When the options varied only in volume, the addition of a high volume option to a choice set of low and medium options decreased the birds’ preference for the medium option. We saw no effects of adding a third option when the options varied in corolla length alone. Hummingbirds, then, make context-dependent decisions even when the options vary in only a single dimension although which effect occurs seems to depend on the dimension being manipulated. None of the current theories alone adequately explain these results.     

The need for systematic reviews of reasons

There are many ethical decisions in the practice of health research and care, and in the creation of policy and guidelines. We argue that those charged with making such decisions need a new genre of review. The new genre is an application of the systematic review, which was developed over decades to inform medical decision-makers about what the totality of studies that investigate links between smoking and cancer, for example, implies about whether smoking causes cancer. We argue that there is a need for similarly inclusive and rigorous reviews of reason-based bioethics, which uses reasoning to address ethical questions. After presenting a brief history of the systematic review, we reject the only existing model for writing a systematic review of reason-based bioethics, which holds that such a review should address an ethical question. We argue that such a systematic review may mislead decision-makers when a literature is incomplete, or when there are mutually incompatible but individually reasonable answers to the ethical question. Furthermore, such a review can be written without identifying all the reasons given when the ethical questions are discussed, their alleged implications for the ethical question, and the attitudes taken to the reasons. The reviews we propose address instead the empirical question of which reasons have been given when addressing a specified ethical question, and present such detailed information on the reasons. We argue that this information is likely to improve decision-making, both directly and indirectly, and also the academic literature. We explain the limitations of our alternative model for systematic reviews.     

Visual extrapolation under risk: human observers estimate and compensate for exogenous uncertainty

Humans commonly face choices between multiple options with uncertain outcomes. Such situations occur in many contexts, from purely financial decisions (which shares should I buy?) to perceptuo-motor decisions between different actions (where should I aim my shot at goal?). Regardless of context, successful decision-making requires that the uncertainty at the heart of the decision-making problem is taken into account. Here, we ask whether humans can recover an estimate of exogenous uncertainty and then use it to make good decisions. Observers viewed a small dot that moved erratically until it disappeared behind an occluder. We varied the size of the occluder and the unpredictability of the dot''s path. The observer attempted to capture the dot as it emerged from behind the occluded region by setting the location and extent of a ‘catcher’ along the edge of the occluder. The reward for successfully catching the dot was reduced as the size of the catcher increased. We compared human performance with that of an agent maximizing expected gain and found that observers consistently selected catcher size close to this theoretical solution. These results suggest that humans are finely tuned to exogenous uncertainty information and can exploit it to guide action.     

Spatial Multiobjective Optimization of Agricultural Conservation Practices using a SWAT Model and an Evolutionary Algorithm

Finding the cost-efficient (i.e., lowest-cost) ways of targeting conservation practice investments for the achievement of specific water quality goals across the landscape is of primary importance in watershed management. Traditional economics methods of finding the lowest-cost solution in the watershed context (e.g.,^5,12,20) assume that off-site impacts can be accurately described as a proportion of on-site pollution generated. Such approaches are unlikely to be representative of the actual pollution process in a watershed, where the impacts of polluting sources are often determined by complex biophysical processes. The use of modern physically-based, spatially distributed hydrologic simulation models allows for a greater degree of realism in terms of process representation but requires a development of a simulation-optimization framework where the model becomes an integral part of optimization.Evolutionary algorithms appear to be a particularly useful optimization tool, able to deal with the combinatorial nature of a watershed simulation-optimization problem and allowing the use of the full water quality model. Evolutionary algorithms treat a particular spatial allocation of conservation practices in a watershed as a candidate solution and utilize sets (populations) of candidate solutions iteratively applying stochastic operators of selection, recombination, and mutation to find improvements with respect to the optimization objectives. The optimization objectives in this case are to minimize nonpoint-source pollution in the watershed, simultaneously minimizing the cost of conservation practices. A recent and expanding set of research is attempting to use similar methods and integrates water quality models with broadly defined evolutionary optimization methods^{3,4,9,10,13-15,17-19,22,23,25}. In this application, we demonstrate a program which follows Rabotyagov et al.''s approach and integrates a modern and commonly used SWAT water quality model⁷ with a multiobjective evolutionary algorithm SPEA2²⁶, and user-specified set of conservation practices and their costs to search for the complete tradeoff frontiers between costs of conservation practices and user-specified water quality objectives. The frontiers quantify the tradeoffs faced by the watershed managers by presenting the full range of costs associated with various water quality improvement goals. The program allows for a selection of watershed configurations achieving specified water quality improvement goals and a production of maps of optimized placement of conservation practices.     

Expected utility violations evolve under status-based selection mechanisms

The expected utility theory of decision making under uncertainty, a cornerstone of modern economics, assumes that humans linearly weight “utilities” for different possible outcomes by the probabilities with which these outcomes occur. Despite the theory's intuitive appeal, both from normative and from evolutionary perspectives, many experiments demonstrate systematic, though poorly understood, patterns of deviation from EU predictions. This paper offers a novel theoretical account of such patterns of deviation by demonstrating that EU violations can emerge from evolutionary selection when individual “status” affects inclusive fitness. In humans, battles for resources and social standing involve high-stakes decision making, and assortative mating ensures that status matters for fitness outcomes. The paper therefore proposes grounding the study of decision making under uncertainty in an evolutionary game-theoretic framework.     

Monitoring in the Context of Structured Decision-Making and Adaptive Management

Abstract: In a natural resource management setting, monitoring is a crucial component of an informed process for making decisions, and monitoring design should be driven by the decision context and associated uncertainties. Monitoring itself can play ≥3 roles. First, it is important for state-dependent decision-making, as when managers need to know the system state before deciding on the appropriate course of action during the ensuing management cycle. Second, monitoring is critical for evaluating the effectiveness of management actions relative to objectives. Third, in an adaptive management setting, monitoring provides the feedback loop for learning about the system; learning is sought not for its own sake but primarily to better achieve management objectives. In this case, monitoring should be designed to reduce the critical uncertainties in models of the managed system. The United States Geological Survey and United States Fish and Wildlife Service are conducting a large-scale management experiment on 23 National Wildlife Refuges across the Northeast and Midwest Regions. The primary management objective is to provide habitat for migratory waterbirds, particularly during migration, using water-level manipulations in managed wetlands. Key uncertainties are related to the potential trade-offs created by management for a specific waterbird guild (e.g., migratory shorebirds) and the response of waterbirds, plant communities, and invertebrates to specific experimental hydroperiods. We reviewed the monitoring program associated with this study, and the ways that specific observations fill ≥1 of the roles identified above. We used observations from our monitoring to improve state-dependent decisions to control undesired plants, to evaluate management performance relative to shallow-water habitat objectives, and to evaluate potential trade-offs between waterfowl and shorebird habitat management. With limited staff and budgets, management agencies need efficient monitoring programs that are used for decision-making, not comprehensive studies that elucidate all manner of ecological relationships.     

Egg rejection behaviour in the great reed warbler (<Emphasis Type="Italic">Acrocephalus arundinaceus</Emphasis>): the effect of egg type

Egg discrimination in hosts of the common cuckoo Cuculus canorus is frequently studied by experimental parasitism, using model cuckoo eggs. We compared egg rejection behaviour of the great reed warbler Acrocephalus arundinaceus to either model cuckoo eggs made of plastic or painted real host eggs. We simultaneously parasitised host nests by two different egg types to simulate cuckoo parasitism. A previous study revealed very similar, ca. 70%, rejection rates against both of these egg types (beige or bluish background colour maculated with dark brown) when they were used for single parasitism. In the present study we showed 96% average rejection rates against these egg types when they were applied in multiple experimental parasitism, causing a more predictable output for rejection behaviour. Hard plastic eggs and painted real eggs were rejected at similar frequencies, and videotaping revealed that model egg rejection caused extra work for great reed warblers. We revealed a new type of rejection behaviour, when hosts tried to eject hard-shelled model cuckoo eggs: Hosts made little holes in the middle part of these plastic eggs by pecking them several times before ejection, as if seeking the possibility to pierce and hold these eggs in their bills. Painted real eggs were rejected by actually puncturing the eggshell and holding them in the bill during ejection. No instances of grasp ejection were recorded during filming. Most experimental eggs of either type were ejected within 1 day after the introduction of the eggs, indicating that hosts made their rejection decisions quickly. Our observations suggest the lack of plasticity in the mode and timing of ejection behaviour towards experimental cuckoo eggs of different types in great reed warblers.