Patch use and departure rules by gull-billed tern Gelochelidon nilotica

The gull-billed tern Gelochelidon nilotica feeds on the fiddler crab Leptuca uruguayensis, which settles forming patches in south-eastern temperate mudflats of Argentina. Through field observations, we evaluated whether gull-billed terns used patches following the marginal value theorem (MVT). Gull-billed tern residence time in a patch was not related to crab density or travel times. The number of captures was also unrelated to crab density. Most of the times (44.6%) terns captured only one crab from each patch, and 35% of the times they left without a capture. However, crab density was lower when terns left the patches than when they arrived. This suggests that following several capture attempts by terns, crabs hide, producing a temporary decrease in their availability, forcing tern departure from the patches, which are no longer profitable. Thus, when prey availability is affected more by predator activity than by consumption, the MVT may not necessarily apply.

Hide-and-seek strategies and post-contact immobility

To understand why an animal might gain by playing dead, or more precisely, exhibit post-contact immobility (PCI), we consider the context in which this behaviour occurs. Is it, for example, a method by which a potential victim encourages a predator to direct its attention elsewhere? We investigate this possibility by using the marginal value theorem to analyse predator behaviour in the context of this defence strategy by potential prey. We consider two models. In the first, (random revisiting) the predator may return to sites it has already depleted within the patch. In the second, (systematic search) the predator goes only to new sites within the patch. The results of the two models are qualitatively extremely similar. We show that when prey occur in patches, PCI favours prey survival. Indeed, certain antlion larvae have PCI durations characterized by very long half-lives. These appear to be of such long durations that further increases would convey no substantial benefits in redirecting potential predators to other antlions within the patch and subsequently to other patches.

Evolutionary Ecological Model of Defence Activation Disorders Via the Marginal Value Theorem

Objective Excessive activation of defence modules leads to some dysfunctional outcomes, which can be broadly classified to defence activation disorders. Defence activation disorders have high mortality, low fertility, high prevalence and high heritability. In this study, agent-based simulation model is formulated for solving this evolutionary paradox.Methods The emotional system is considered as a superordinate cognitive module for grasping the average resource amount and the average diminishing returns of resources, based on the Marginal Value Theorem. Under the assumption, the evolutionary ecological model was proposed and analysed.Results Individuals utilising suboptimal strategies can be stably maintained in agent-based evolutionary simulation environments. Individuals were adapted to have different <i>d-values</i> according to the local niche. The simulation runs stably within the calibrated range of the variables for a long time. Agents establish locally optimal strategies based on their given <i>d-values</i>, and the relative proportion of subpopulation maintained stably in the heterogeneous habitat with the resource gradient.Conclusion This study verifies the evolutionary mechanism of defence activation disorders in computer-simulated environments by using agent-based modelling with the Marginal Value Theorem. Balancing selection appears to be a plausible evolutionary mechanism that makes the suboptimal levels of defence activation the evolutionarily stable strategies.

Foraging optimally in social neuroscience: computations and methodological considerations

Research in social neuroscience has increasingly begun to use the tools of computational neuroscience to better understand behaviour. Such approaches have proven fruitful for probing underlying neural mechanisms. However, little attention has been paid to how the structure of experimental tasks relates to real-world decisions, and the problems that brains have evolved to solve. To go significantly beyond current understanding, we must begin to use paradigms and mathematical models from behavioural ecology, which offer insights into the decisions animals must make successfully in order to survive. One highly influential theory—marginal value theorem (MVT)—precisely characterises and provides an optimal solution to a vital foraging decision that most species must make: the patch-leaving problem. Animals must decide when to leave collecting rewards in a current patch (location) and travel somewhere else. We propose that many questions posed in social neuroscience can be approached as patch-leaving problems. A richer understanding of the neural mechanisms underlying social behaviour will be obtained by using MVT. In this ‘tools of the trade’ article, we outline the patch-leaving problem, the computations of MVT and discuss the application to social neuroscience. Furthermore, we consider the practical challenges and offer solutions for designing paradigms probing patch leaving, both behaviourally and when using neuroimaging techniques.

Foraging Optimally in Social Neuroscience: Computations and Methodological considerations

Research in social neuroscience has increasingly begun to use the tools of computational neuroscience to better understand behaviour. Such approaches have proven fruitful for probing underlying neural mechanisms. However, little attention has been paid to how the structure of experimental tasks relates to real-world decisions, and the problems that brains have evolved to solve. To go significantly beyond current understanding, we must begin to use paradigms and mathematical models from behavioural ecology, which offer insights into the decisions animals must make successfully in order to survive. One highly influential theory – Marginal Value Theorem (MVT) – precisely characterises and provides an optimal solution to a vital foraging decision that most species must make: the patch leaving problem. Animals must decide when to leave collecting rewards in a current patch (location) and travel somewhere else. We propose that many questions posed in social neuroscience can be approached as patch-leaving problems. A richer understanding of the neural mechanisms underlying social behaviour will be obtained by using MVT. In this ‘tools of the trade’ article, we outline the patch-leaving problem, the computations of MVT, and discuss is application to social neuroscience. Furthermore, we consider practical challenges and offer solutions for designing paradigms probing patch-leaving, both behaviourally and when using neuroimaging techniques.

Nahua mushroom gatherers use area-restricted search strategies that conform to marginal value theorem predictions

We develop a method of analysis for testing the marginal value theorem (MVT) in natural settings that does not require an independent definition or mapping of patches. We draw on recent theoretical work on area-restricted search (ARS) that links turning-angle and step-size changes to geographically localized encounter-rates. These models allow us to estimate “giving-up times” using encounter-annotated GPS tracking data. Applied to a case study of Nahua mushroom foragers, these models identify distinct forms of intrapatch and interpatch search behavior, with intrapatch search transitioning to interpatch search after a predictable interval of time since the last encounter with a harvested mushroom. Our empirical estimate of giving-up time coincides with the theoretically optimal giving-up time derived under the MVT in the same environment. The MVT is currently underused in studies of human foraging and settlement patterns, due in large part to the difficulty of identifying discrete resource patches and quantifying their characteristics. Our methods mitigate the need to make such discrete maps of patches and thus have the potential to broaden the scope for empirical evaluations of the MVT and related theory in humans. Beyond studies of naturalistic foraging in humans and other animals, our approach has implications for optimization of search behavior in a range of applied fields where search dynamics must be adapted to shifting patterns of environmental heterogeneity affecting prey density and patchiness.