A synthesis of deimatic behaviour.

Deimatic behaviours, also referred to as startle behaviours, are used against predators and rivals. Although many are spectacular, their proximate and ultimate causes remain unclear. In this review we aim to synthesise what is known about deimatic behaviour and identify knowledge gaps. We propose a working hypothesis for deimatic behaviour, and discuss the available evidence for the evolution, ontogeny, causation, and survival value of deimatic behaviour using Tinbergen's Four Questions as a framework. Our overarching aim is to direct future research by suggesting ways to address the most pressing questions in this field.

Coping with Danger and Deception: Lessons from Signal Detection Theory.

AbstractSignal detection theory (SDT) has been used to model optimal stimulus discrimination for more than four decades in evolutionary ecology. A popular standard model that maximizes payoff per encounter was recently criticized for being too simplistic, leading to erroneous predictions. We review a number of SDT models that have received less attention but have explicitly taken repeated encounters into account, focusing on prey choice, mate search, aggressive mimicry, and the aiding of kin. We show how these models can be seen as variants of a second standard model that can be analyzed in a unified framework. In contrast to the simpler model, in this second model a higher probability of an undesirable or dangerous event occurring may either decrease or increase the receiver's acceptance rates. In each instance, the latter outcome requires undesirable events to be undesirable in a relative rather than an absolute sense. Increasing the abundance of desirable signalers or the payoff from accepting them may also either raise or reduce acceptance rates. Our synthesis highlights fundamental similarities among models previously studied on a case-by-case basis and challenges some long-held beliefs. For example, some classic predictions of Batesian mimicry can be reversed when model prey are protected by low profitability rather than harmful defense.

Behavioural Ecology: Spiders Play the Imitation Game.

Examples of mimicry are widely celebrated because of the remarkable physical similarities they entail. A new study shows how an ant-mimicking spider uses behaviour to create the illusion of antennae, while walking in a manner resembling ants following pheromone trails.

How residency duration affects the outcome of a territorial contest: Complementary game-theoretic models.

While the first individuals to discover and maintain territories are generally respected as owners, under some conditions there may be ambiguity as to who got there first. Here we attempt to understand the evolutionary consequences of this ambiguity by developing a pair of game-theoretic models in which we explicitly consider rival residency-based claims to ownership. Following earlier qualitative explanations for residency effects, we assume that either the value of the territory (Model A) or an interloper׳s self-belief that it is the owner (Model B) increases with duration of residency. Model A clearly demonstrates that if the value of a territory increases to a resident over time, so should its motivation to fight in terms of the effort it invests in fighting. Indeed, only a small increase in territory value with residency duration can be sufficient for longer established residents to win disputes, even without any arbitrary convention or other form of priority effect. Likewise, Model B shows that the observed increase in fighting persistence with residency duration can be readily explained as a consequence of increasing confidence on behalf of the interloper that it is the rightful owner. Collectively, the models help to explain some general findings long observed by empiricists, and shed light on the nature of conflicts that can arise when individuals do not have complete information about rival claims to ownership.

Evolutionary stable investment in products that confer both an individual benefit and a public good.

Why should a microbe manufacture extracellular enzymes if its competitors can free-ride on these enzymes? Similarly, why should an animal place seeds into storage when others can exploit this stored resource? A solution to this general class of problems becomes apparent if one assumes that investors directly benefit from a proportion of the investments they make. Thus, when individuals benefit from a proportion p of their investments, but share the rest with other individuals in the system, then an evolutionarily stable level of investment can evolve which is higher the higher the value of p. These evolutionarily stable investment points mark the junction at which several classical games meet, so that changes in investment can move interactions from one game type to another. Non-zero optimal levels of investment also arise under conditions when investments are only shared locally, and even when producers lose more product to competitors than they save for themselves. Overall, this "personal gain" approach offers a simple yet robust explanation for why individuals engage in activities which may concomitantly benefit others.

Neighbor intervention: a game-theoretic model.

It has long been argued that a resident may benefit from helping its neighbor defend a territory against a challenger to avoid renegotiating its boundaries with a new and potentially stronger individual. We quantify this theory by exploring games involving challengers, residents and potential allies. In a simplified discrete game with zero variation of fighting strength, helping neighbors is part of an evolutionarily stable strategy (ESS) only if fighting costs are low relative to those of renegotiation. However, if relative fighting costs are high then an interventional ESS remains possible with finite variation of strength. Under these conditions, neighbors may help residents fight off intruders, but only when the resident does not stand a reliable chance of winning alone. We show that neighbor intervention is more likely with low home advantage to occupying a territory, strengths combining synergistically or low probability that an ally will be usurped, amongst other factors. Our parameterized model readily explains occasional intervention in the Australian fiddler crab, including why the ally tended to be larger than both the assisted neighbor and the intruder. Reciprocity is not necessary for this type of cooperation to persist, but also it is by no means inevitable in territorial species.

A screening level index for assessing the impacts of veterinary medicines on dung flies.

Veterinary parasiticides are administered to livestock to control a wide range of parasites. Following excretion, these substances may persist in the environment and impact nontarget organisms. This paper describes a simple screening-based index for predicting the effects of veterinary parasiticides on dung flies using data on parasiticide toxicity, animal husbandry, and parasiticide use. The utility of the index has been assessed, at the farm scale for a number of dipteran species, using data from a survey of farms in England and insect ecology and ecotoxicological data. The results indicate that a large proportion (35%) of parasiticide treatments in England will have no impact on dung fly populations. In terms of individual parasiticides, the macrocyclic lactone doramectin was predicted to have the highest impact on English dipteran populations with a maximum reduction in the population of horn flies on one farm of 28%. Ivermectin pour-on had the next highest impact (6.8%), followed by eprinomectin (6.4%), and ivermectin injection (4.1%). Due to a lack of data, it was not possible to assess the effects of the benzimidazole parasiticides (oxfendazole and fenbendazole), morantel and permethrin. The approach is simple, nondata-intensive and has the potential to be a valuable tool for use in environmental risk assessment or management of new and existing veterinary parasiticides.

Social eavesdropping: a game-theoretic analysis.

Here we extend the classic Hawk-Dove model of animal conflict to allow for continuous variation in fighting strengths. Whereas the winner of a fight is chosen at random in the discrete game, in our continuous game, the winner of any fight is the stronger individual, and costs are higher for more evenly matched opponents. We identify the evolutionary stable strength threshold beyond which an animal should be prepared to engage in aggressive behaviour and show that this threshold increases with variance in fighting strength when the costs of aggression are insensitive to the level of strength asymmetry, but decreases with variance when the costs are sensitive to the level of asymmetry. In contrast to the classic discrete game, population-wide aggressive behaviour occurs only when the costs of fighting are zero. It is now known that animals can eavesdrop on the outcome of contests between neighbours and modify their behaviour towards observed winners and losers. We therefore further extend our model to allow for social eavesdropping within networks comprising three individuals. Whereas earlier work showed that eavesdropping increases the frequency of mutually aggressive contests in the discrete game by enhancing the value of victory, here we show that aggression thresholds in the continuous game are always higher with eavesdropping than without it: for sufficiently weak animals, avoiding the costs of challenging an observed winner over-rides the potential benefit of winning, so that eavesdropping reduces the frequency of aggressive encounters. Thus, even though strength is not directly observable, information is extracted from the variation in fighting ability that the classic Hawk-Dove game ignores.

How realistic are outdoor microcosms? A comparison of the biota of microcosms and natural ponds.

This study investigated the extent to which aquatic plant and macroinvertebrate assemblages in small outdoor microcosms (cylinders 1.25-m diameter x 1.25 m deep) resembled assemblages found in natural ponds in Britain. Comparisons were made in terms of community structure, species richness, and numbers of uncommon species. Multivariate analysis indicated that, although the microcosms had no exact natural analogues, their plant and animal assemblages were most like those of deep, circumneutral ponds. Unlike natural ponds, the microcosms supported relatively species-poor invertebrate assemblages, lacking uncommon species. Among individual taxa, microcosms supported similar numbers of species of Gastropoda, Isopoda, Amphipoda, and Odonata as natural ponds but significantly fewer Coleoptera, Hemiptera, and Trichoptera species. This was most likely due to the absence of a shallow littoral area in the microcosms. Because of their vertical sides, the microcosms supported no marginal wetland plants, but submerged and floating-leaved plant assemblages were similar in community type and species richness to natural ponds. Refinements to microcosm and mesocosm designs are identified that would enable experimental systems to more closely replicate the assemblages found in natural ponds. In particular, the incorporation of natural margins would be likely to lead to experimental communities that were closer analogues of natural ponds.