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ABSTRACT Despite a long roster of prey defences against predators now documented by biologists, any given species utilises only some of them, and we have few a priori predictions as to if, when or where they will be employed. In order to uncover general trends in the way in which crabs avoid predation attempts after they have been detected, we examined the antipredator behaviour of nine intertidal decapod species on three continents. We studied five different types of defensive behaviour and seven morphological and environmental factors which might affect such behaviours at different stages of the predatory sequence. In combination with other studies, we suggest that although intertidal crabs invest a great deal in crypticity to avoid detection, once discovered, they remain immobile, raise their chelae or flee but the extent to which these and other defences are exhibited differ markedly across species. We found that luminance contrast with the background, body size, chelae size and immediate habitat in which crabs were found affected antipredator behaviour whereas neither sex, nor chromatic contrast with the background were important. Our findings broaden understanding of defensive behaviour in several decapod species and highlight how species tailor the use of the same defences in different ways according to threat, morphology and local environment. [ABSTRACT FROM AUTHOR]

Intermittent locomotion is a common locomotor mode in small vertebrates. Pausing is thought to aid in locating a predator or prey, enhancing crypsis, lowering energy costs, and/or maneuvering around obstacles or toward a refuge. Many lizards flee predators by turning into potential refugia and subsequently pausing, presumably to conceal themselves. Intermittent locomotion may be associated with turning by allowing an animal time to assess its surroundings and/or decreasing the likelihood of losing its footing. In this study, we quantify locomotor performance and the use of intermittent locomotion in Florida scrub lizards (Sceloporus woodi) when navigating either a 45° or 90° turn. Lizards paused in 92.91% of all trials, and yet despite pausing, instantaneous speed was not different entering or exiting the turn. This result suggests that turning comes at minimal cost to forward speed for lizards under these conditions. Pausing during a turn, however, did slow speed in the turn. Interestingly, the speed in the turn did not differ in trials with a pause before the turn versus trials without a pause. The angle of the turn also had no effect on whether lizards paused. We found that lizards increase peak acceleration following pauses to compensate for lost speed during the pause, providing a mechanism that may minimize negative fitness effects associated with slow running speeds and allow intermittent locomotion to be such a common strategy in lizards. [ABSTRACT FROM AUTHOR]

We describe a natural situation that supports predictions of theoretical scenarios in which predators tactically influence the food - safety trade-off faced by prey to increase their vulnerability. By using low-cost 'false attacks' or otherwise advertising their presence, predators force prey to spend time in refuges or in other forms of safety-enhancing behavior, during which foraging is impaired or impossible. Prey must compensate by taking extra risks at other times or places to meet their energy requirements, and as a consequence become easier to capture. We used data on the occurrence of over-ocean flocking (OOF) by Pacific dunlins (Calidris alpina pacifica), and on the timing and success of attacks by peregrines. OOF is a safe but energetically expensive alternative to traditional roosting, and largely replaced the latter in Boundary Bay of southwest British Columbia as the presence of wintering peregrines rose during the 1990s. Peregrines appear to use 'false' or 'non-serious' attacks to shift the occurrence of OOF to a tidal time frame earlier than is ideal for dunlins, thereby creating later hunting opportunities during which dunlins were vulnerable than otherwise would have been the case. The shift increased dunlin mortality substantially. Tactics used by predators such as prominent perching, salient signals and unpredictable appearances, could have evolved because this forces prey to increase their level of caution, rendering them more vulnerable at other times or places. [ABSTRACT FROM AUTHOR]

Many species possess damage‐released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the "intended" recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade‐off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues. [ABSTRACT FROM AUTHOR]

Given the vulnerability of early life stages to predation, many species elicit antipredator responses to predator-associated cues (e.g. alarm cues, necromones). However, the response used may vary between predatory stimuli. Antipredator responses, while ostensibly enhancing survival, are costly, either resulting in missed opportunities (e.g. foraging) through decreased activity and crypsis strategies (i.e. predator avoidance) or incurring high energetic costs through the use of generalized stress responses and increased activity (i.e. predator evasion). Juvenile Port Jackson sharks, Heterodontus portusjacksoni , were exposed to the scent of dead conspecifics (conspecific necromones) coupled with a simulated predator chase to determine the energetic effects of a predator 'attack'. When exposed to necromone cues alone, juvenile sharks depressed their oxygen uptake rates for up to 3 h following exposure, indicating that they used crypsis to avoid detection by predators. However, when forced to swim and evade a predator, sharks increased their oxygen uptake rates, regardless of whether or not they were exposed to predatory cues. Juvenile sharks exposed to conspecific necromones may primarily rely on strategies that depress activity to avoid detection by predators; however, if forced to evade capture they use energetically costly escape strategies similar to typical 'fight or flight' responses. • Necromones elicit context-dependent antipredator responses. • Exercise, such as that from a predator chase, negates crypsis responses. • Changes in oxygen uptake rates persisted for at least 3 h. • Concomitant stressors will decrease effectiveness of these strategies. [ABSTRACT FROM AUTHOR]

In many animal taxa, the presence of injured conspecifics triggers escape or freezing behaviour. We examined these anti-predatory responses in the eriophyoid mite Aculops allotrichus from Robinia pseudoacacia. The mite was tested on leaflets in cages with two leaf chambers connected by a tunnel, on compound leaves, on which only two opposite leaflets remained, and on leaf discs placed on glass. We released females onto a site with freshly pierced individuals and allowed them to move to a "safe" place. Females did not escape from dangerous patches in any of our tests. They did not refrain from oviposition or become motionless in the presence of damaged conspecifics, either. On the contrary, in the test with old leaf discs, females prolonged their stay on "risky" patches. Additionally, after five hours the proportion of females in chambers with pierced conspecifics was significantly higher than in the control, and only after 24 hours were there no differences between the two combinations. It indicates that the presence of injured conspecifics is not a cue of predation risk for A. allotrichus. In contrast, the eriophyoid can be arrested on "dangerous" leaves, and possible factors underlying this phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Non‐consumptive predator effects (NCEs) are now widely recognised for their capacity to shape ecosystem structure and function. Yet, forecasting the propagation of these predator‐induced trait changes through particular communities remains a challenge. Accordingly, focusing on plasticity in prey anti‐predator behaviours, we conceptualise the multi‐stage process by which predators trigger direct and indirect NCEs, review and distil potential drivers of contingencies into three key categories (properties of the prey, predator and setting), and then provide a general framework for predicting both the nature and strength of direct NCEs. Our review underscores the myriad factors that can generate NCE contingencies while guiding how research might better anticipate and account for them. Moreover, our synthesis highlights the value of mapping both habitat domains and prey‐specific patterns of evasion success ('evasion landscapes') as the basis for predicting how direct NCEs are likely to manifest in any particular community. Looking ahead, we highlight two key knowledge gaps that continue to impede a comprehensive understanding of non‐consumptive predator–prey interactions and their ecosystem consequences; namely, insufficient empirical exploration of (1) context‐dependent indirect NCEs and (2) the ways in which direct and indirect NCEs are shaped interactively by multiple drivers of context dependence. [ABSTRACT FROM AUTHOR]

Insects have evolved various types of antipredator defenses. For example, many insects have evolved crypsis, and exhibit cryptic body colors and shapes for hiding from predators. Other insects produce toxins as a form of chemical defense against predators, and some toxic insects are aposematic, with conspicuous body colors for advertising their toxins. Insects can also develop hairs, spines or hard exoskeletons as morphological defenses to protect themselves from predation. In addition, insects can evolve behavioral defenses, in which insects exhibit autotomy or dropping, or feign death. This study investigated which predator types evoke these types of defenses, through a review of the effectiveness of antipredator defenses in insects against carnivorous animals that are commonly used as model predators in studies. These predators include other insects, spiders, fish, frogs, lizards, birds and mammals. The results provide the first step for clarifying the evolutionary drivers of antipredator defenses in insects. The following aspects should be considered for future studies: multiple predator species and sufficient replication, alternative prey and predator models, and tolerance to predators in insects. [ABSTRACT FROM AUTHOR]

Recent advances in neural circuitry techniques, like optogenetics and chemogenetics, have allowed for a greater understanding of the periaqueductal gray (PAG) and its importance in predator and prey behaviors. These studies in rodents have highlighted the role of the rostrolateral PAG in hunting behaviors, and have demonstrated functional differences across the dorsal-ventral/rostral-caudal axes of the PAG associated with defensive behaviors. Human imaging studies have further demonstrated that the PAG is active during situations involving imminent threat suggesting that the function of the PAG is likely largely conserved across species. This mini-review article highlights some of the recent advancements towards our understanding of the functional neuroanatomy of the PAG and its importance in the predator and prey behaviors that are critical for survival. [ABSTRACT FROM AUTHOR]

Female-limited polymorphism in colour and pattern has long been studied to understand how intraspecific phenotypic variation is maintained. Female Anolis sagrei lizards are polymorphic in their dorsal patterning, and this variation has been hypothesized to reduce predation through crypsis, with different patterns being associated with camouflage in different microhabitats or while adopting different modes of escape. However, previous studies testing this hypothesis remained inconclusive, potentially because this variation was classified categorically instead of being quantified continuously. Thus, we initially examined whether the dorsal pattern in female A. sagrei varies continuously and then investigated whether this variation is associated with habitat use or escape behaviour. Data from Gainesville, FL, USA suggests that dorsal pattern variation is both categorical and continuous. One-third of A. sagrei females have a distinct, male-like chevron dorsal pattern, whereas the remainder bear a striped dorsal pattern that varies continuously and does not fall into three discrete categories as reported previously. Chevroned females perched significantly higher than striped females, but other habitat use and escape behaviours did not vary with dorsal pattern. Our results thus do not support the hypothesis that dorsal pattern variation in female A. sagrei is an adaptation for predator avoidance by crypsis, and instead we speculate that the male-like chevron dorsal pattern in females is an adaptation to minimize sexual conflict. [ABSTRACT FROM AUTHOR]

Abstract: The consumptive effects of predators are widely acknowledged, but predation can also impact prey populations through non‐consumptive effects (NCEs) such as costly antipredator behavioral responses. The magnitude of antipredator behavioral responses by prey is determined by an assessment of risk using sensory cues, which in turn is modulated by the environmental context. We studied the detection behavior and escape response of the keyhole limpet Fissurella limbata from the predatory sea star Heliaster helianthus. Through laboratory and field experimental trials, we quantified the distance and time of predator detection behavior by the prey, and measured their active escape responses when elicited. We found that predator detection by the limpet was chiefly mediated by distance, with experimental individuals capable of detecting predator presence effectively up to distances of at least 50 cm in the field and 70 cm under laboratory conditions. Our results indicate that this prey species is able to evaluate the proximity of its predator and use it as an indication of predation risk; therefore, predator–prey distance appears to be a primary predictor of the magnitude of the antipredator response. Given the tight relationship between predator distance and prey movement and the important role herbivores can play, particularly in this ecosystem, we expect that NCEs will cascade to the patterns of abundance and composition of rocky shore communities through changes in prey foraging behavior under risk. [ABSTRACT FROM AUTHOR]

Flight initiation distance (FID), the distance at which an organism flees from an approaching threat, is an ecological metric of cost-benefit functions of escape decisions. We adapted the FID paradigm to investigate how fast- or slow-attacking "virtual predators" constrain escape decisions. We show that rapid escape decisions rely on "reactive fear" circuits in the periaqueductal gray and midcingulate cortex (MCC), while protracted escape decisions, defined by larger buffer zones, were associated with "cognitive fear" circuits, which include posterior cingulate cortex, hippocampus, and the ventromedial prefrontal cortex, circuits implicated in more complex information processing, cognitive avoidance strategies, and behavioral flexibility. Using a Bayesian decision-making model, we further show that optimization of escape decisions under rapid flight were localized to the MCC, a region involved in adaptive motor control, while the hippocampus is implicated in optimizing decisions that update and control slower escape initiation. These results demonstrate an unexplored link between defensive survival circuits and their role in adaptive escape decisions. [ABSTRACT FROM AUTHOR]

Theory predicts prey should flee to safety when the fitness benefits of flight meet or exceed the costs. Empirical work has shown the importance of predation risk (e.g., predator behavior, distance to refuge) to prey flight behavior. However, less is known about the influence of flight costs. We monitored nesting Painted Turtles ( Chrysemys picta (Schneider, 1783)) to examine their response to a human observer (potential predator) depending on the distance between a turtle and an observer, distance between a turtle and water (i.e., refuge), and nesting stage at the time of the encounter (i.e., searching for a nest site vs. constructing a nest). We found no evidence that the distance to an observer influenced flight decisions. However, turtles were less likely to flee as the distance to water increased, and turtles already constructing nests were more likely to continue nesting than those still searching for nest sites. Turtles that traveled farther from water and that were constructing nests may have continued nesting because they had invested considerable energy and were close to completing oviposition. Thus, the fitness benefits of being closer to successful oviposition may outweigh the costs of increased vulnerability to predators during this important and vulnerable period of reproduction. [ABSTRACT FROM AUTHOR]

Satiation of predispersal seed predators by mast years has been demonstrated in many intact ecosystems. When disease causes mortality of seed-bearing trees in an ecosystem, the abundance of food sources may alter seed predator behavior and abundance, and the ecosystem services derived from mutualistic seed dispersers. We used the endangered limber pine (Pinus flexilis) to examine whether the benefits of interannual variation in cone production vary depending on the severity of white pine blister rust (Cronartium ribicola) infections, the abundance of seed predator populations, and stand characteristics. We compared infection level, cone production, cone predation, and abundance of red squirrels (Tamiasciurus hudsonicus) in 17 stands over two mast years and two nonmast years. Stands were selected from a southern and northern ecosystem within Alberta's montane ecoregion, with varying forest composition and history of blister rust infection. Considerable variability in interannual cone production, and proportionately greater cone escape (those remaining in stands) in the 2010 mast year led to 10 times greater cone escape overall in the mast year than in nonmast years. Model selection using Akaike's information criterion (AIC) suggests that both cone escape and proportion cone escape from seed predators depended primarily on temporal variability in cone production among mast vs. nonmast years, basal area of canopy trees within stands, squirrel abundance, and ecosystem differences. Several two-way and three-way interactions between masting, ecosystems, and predator abundance were selected by AIC for inclusion into the best model of the a priori candidate set for both the cone escape model and proportion cone escape model. Our study suggests that masting confers temporal resiliency in seed escape in declining limber pine ecosystems, even under varying disease and seed predator threats. These findings also suggest that evolved seed escape strategies may be resilient to a variety of ecological conditions, including low reproductive capacity. Nonetheless, proximate ecological conditions may determine the fate of declining species, as predator behavior differed between ecosystems, and greater net cone escape in favorable stands may be necessary to attract mutualistic seed dispersers. [ABSTRACT FROM AUTHOR]

Predator avoidance and prey capture are among the most vital of animal behaviors. They require fast reactions controlled by comparatively straightforward neural circuits often containing giant neurons, which facilitates their study with electrophysiological techniques. Naturally occurring avoidance behaviors, in particular, can be easily and reliably evoked in the laboratory, enabling their neurophysiological investigation. Studies in the laboratory alone, however, can lead to a biased interpretation of an animal's behavior in its natural environment. In this Review, we describe current knowledge - acquired through both laboratory and field studies - on the visually guided escape behavior of the crab Neohelice granulata. Analyses of the behavioral responses to visual stimuli in the laboratory have revealed the main characteristics of the crab's performance, such as the continuous regulation of the speed and direction of the escape run, or the enduring changes in the strength of escape induced by learning and memory. This work, in combination with neuroanatomical and electrophysiological studies, has allowed the identification of various giant neurons, the activity of which reflects most essential aspects of the crabs' avoidance performance. In addition, behavioral analyses performed in the natural environment reveal a more complex picture: crabs make use of much more information than is usually available in laboratory studies. Moreover, field studies have led to the discovery of a robust visually guided chasing behavior in Neohelice. Here, we describe similarities and differences in the results obtained between the field and the laboratory, discuss the sources of any differences and highlight the importance of combining the two approaches. [ABSTRACT FROM AUTHOR]

Animal display behaviors are used to convey specific messages to other animals, including potential mates, rivals, and predators. However, because these different types of interactions can be mediated by a single behavioral display, or conversely, multiple signals can be used to convey one specific message, interpretation of any particular behavioral display can be difficult. Leiocephalus lizards (i.e., curly tails) provide an excellent opportunity to study the use of display behaviors across multiple contexts. Previous research has demonstrated that the use of tail curling in these lizards is associated with predation risk, but less is known regarding the use of this behavior in social interactions with conspecifics. The goal of this study was to determine the extent to which tail curling display behavior is used to mediate both social and predatory interactions in two species, Leiocephalus barahonensis and L. carinatus. We found that in lizards of both species, tail curling was used in interactions with both conspecifics and potential (human) predators. However, tail curl intensity did not differ between lizards involved in social encounters and solitary lizards, although L. barahonensis lizards performed more headbobs during social than non-social observations. Further, L. carinatus lizards exhibited greater intensity of tail curling upon fleeing from a human predator than during observations in which individuals interacted with conspecifics, and lizards that exhibited tighter tail curls fled from predators for a longer distance. Finally, tail curl intensity was not correlated with headbob displays in either species, suggesting that these two components of display communicate different information. Our results suggest that tail curling displays, while consistently a component of interactions with potential predators, are not a necessary component of social interactions. These data contribute to a more complete understanding of how and why visual signals evolve for use in communication across multiple contexts. [ABSTRACT FROM AUTHOR]

The Japanese lacertid lizard Takydromus tachydromoides and the praying mantis Tenodera aridifolia are sympatric generalist predators feeding on similar prey. To confirm reciprocal predation between them, we observed the behavioural interactions between the lizards and the mantises of different sizes in a laboratory condition. The lizards caught small mantises (from first to fifth instars), but sometimes escaped from large mantises (from sixth instar to adult). Large mantises occasionally showed catch responses to the lizards. The lizards sometimes caught the mantis without a tongue-flick response (sampling of chemical cues), and they sometimes did not catch the small mantises showing immobile or cryptic responses that prevent visual detection. These results suggested the primary role of vision on recognition of the mantis as a prey. The lizards spent a longer time to approach larger mantises. The time from orienting to catch was longer when the lizards showed tongue-flick responses. The lizard also spent a longer time before deciding to escape from the mantis than to catch it. Biological significance of these differences in timing was discussed. [ABSTRACT FROM AUTHOR]

Escape maneuvers are essential to the survival and fitness of many animals. Escapes are frequently initiated when an animal is already in motion. This may introduce constraints that alter the escape performance. In fish, escape maneuvers and steady, body caudal fin (BCF) swimming are driven by distinct patterns of curvature of the body axis. Pre-existing muscle activity may therefore delay or diminish a response. To quantify the performance consequences of escaping in flow, escape behavior was examined in bluegill sunfish ( Lepomis macrochirus) in both still-water and during steady swimming. Escapes executed during swimming were kinematically less variable than those made in still-water. Swimming escapes also had increased response latencies and lower peak velocities and accelerations than those made in still-water. Performance was also lower for escapes made up rather than down-stream, and a preference for down-stream escapes may be associated with maximizing performance. The constraints imposed by pre-existing motion and flow, therefore, have the potential to shape predator-prey interactions under field conditions by shifting the optimal strategies for both predators and prey. [ABSTRACT FROM AUTHOR]

Interpopulation comparisons in species that show behavioural variations associated with particular ecological disparities offer good opportunities for assessing how environmental factors may foster specific functional adaptations in the brain. Yet, studies on the neural substrate that can account for interpopulation behavioural adaptations are scarce. Predation is one of the strongest driving forces for behavioural evolvability and, consequently, for shaping structural and functional brain adaptations. We analysed the escape response of crabs Neohelice granulata from two isolated populations exposed to different risks of avian predation. Individuals from the high-risk area proved to be more reactive to visual danger stimuli (VDS) than those from an area where predators are rare. Control experiments indicate that the response difference was specific for impending visual threats. Subsequently, we analysed the response to VDS of a group of giant brain neurons that are thought to play a main role in the visually guided escape response of the crab. Neurons from animals of the population with the stronger escape response were more responsive to VDS than neurons from animals of the less reactive population. Our results suggest a robust linkage between the pressure imposed by the predation risk, the response of identified neurons and the behavioural outcome. [ABSTRACT FROM AUTHOR]

Fast starts are crucial in the survival of aquatic swimmers to capture prey or avoid predators. Currently, it is widely accepted that during C-starts: (1) the caudal fin generates a considerable hydrodynamic force; and (2) anal/dorsal fins are erected to significantly increase the hydrodynamic force. In this work, the above hypotheses on the role of fins during C-starts are studied using experimentally guided numerical simulations of four bluegill sunfish, whose fins are removed or erected. The amount of force created by the body and fins at each time instant was not constant and varied during the C-start. Nevertheless, in agreement with hypothesis (1), up to 70% of the instantaneous hydrodynamic force was generated by the tail during Stage 2 of the C-start, when the sunfish rapidly bends out of the C-shape. Additionally, the contribution in Stage 1, when the sunfish bends into a C-shape, is less than 20% at each instant. Most of the force in Stage 1 was produced by the body of the sunfish. In contrast to hypothesis (2), the effect of erection/removal of the fins was less than 5% of the instantaneous force in both Stages 1 and 2, except for a short period of time (2 ms) just before Stage 2. However, it is known that the anal/dorsal fins are actively controlled during the C-start from muscle activity measurements. Based on the results presented here, it is suggested that the active control of the anal/dorsal fins can be related to retaining the stability of the sunfish against roll and pitch movements during the C-start. Furthermore, the erection of the fins increases the moment of inertia to make the roll and pitch movements more difficult. [ABSTRACT FROM AUTHOR]

Cost-benefit models of escape behaviour predict that flight initiation distance (FID. predator-prey distance when the prey starts to flee from an approaching predator) increases as the cost of not fleeing (risk) increases. This prediction has been verified for many risk factors and prey species. The same predictions may apply to other aspects of escape, but testing has been much less extensive. For the lizards Callisaurus draconoides and Sceloporus magister, we tested several such predictions and examined the effect of a previously unstudied risk factor, recent movement by prey. Starting distance (predator-prey distance when approach begins) was unrelated to FID in C. draconoides, as in previously studied ambush foragers. Because movement increases probability of being detected, we predicted that FID would be greater for prey that had moved immediately before being approached than those that had been immobile. FID and distance fled (DF) were longer for lizards that had moved recently. In C. draconoides DF and probability of entering refuge were greater for the second of two approaches, as predicted from greater threat posed by a persistent predator. Callisaurus draconoides had shorter FID and shorter DF, and fewer entered refuge where lizards were habituated than unhabituated to human presence. In S. magister FID increased as distance to refuge increased, FID and DF were longer for fast than slow approaches; probability of fleeing and FID were larger for direct than indirect approach. Effects of these risk factors on FID are consistent across studies, but approach speed has affected DF in only half of studies, perhaps due to constraints by refuge entry and variable distance to refuge. Similarities in effects of risk factors across escape variables, types of predator-prey encounters, and latency to emerge from refuge suggest that similar risk assessment mechanism are used for all variables and settings. [ABSTRACT FROM AUTHOR]

Predation risk may affect space use and foraging patterns of prey animals, with strong down-stream effects on diet composition and ecological interactions. Wild boar Sus scrofa is a notorious crop raider but also a popular game species, yet little is known about how risk perception of human hunting affects wild boar space use. We studied the effects of human hunting on the movement of GPS-collared female wild boar. We found that the hunting method affected whether the wild boar fled or hid. After fleeing into refuge ranges, wild boar moved less and preferred habitats that provided cover and forage such as mast or crops. This suggests that the wild boar tried to reduce the risk of being detected, and possibly also that they avoided competition with resident wild boar in the refuge by using forage that could not be monopolised. The type of hunting thus strongly affected the type of avoidance behaviour displayed by wild boar, with implications for their movement and space use. This suggests that adjusting hunting method to season could be an important management tool for minimising crop losses. [ABSTRACT FROM AUTHOR]

The invasive ctenophore Mnemiopsis leidyi, which now may be established in the NW Mediterranean, is a voracious predator of zooplankton and ichthyoplankton. Pelagia noctiluca, an abundant scyphomedusa there, eats other gelatinous species. We measured predation, digestion and escape when different sizes of medusae fed on ctenophores. Clearance rates increased with predator size and ingestion rates increased with prey concentration. Digestion times were longer when medusae were smaller than the ctenophores. All large ctenophores escaped from the medusae, but small ctenophores were ingested completely. Pelagia noctiluca is potentially an important predator of M. leidyi that may help control populations of this ctenophore. [ABSTRACT FROM AUTHOR]

One of the most important decisions animals have to make is how to respond to an attack from a potential predator.The response must be prompt and appropriate to ensure survival. Invertebrates have been important models in studying the underlying neurobiology of the escape response due to their accessible nervous systems and easily quantifiable behavioral output. Moreover, invertebrates provide opportunities for investigating these processes at a level of analysis not available in most other organisms. Recently, there has been a renewed focus in understanding how value-based calculations are made on the level of the nervous system, i.e., when decisions are made under conflicting circumstances, and the most desirable choice must be selected byweighing the costs and benefits for each behavioral choice. This article reviews samples from the current literature on anti-predator decision making in invertebrates, from single neurons to complex behaviors. Recent progress in understanding the mechanisms underlying value-based behavioral decisions is also discussed. [ABSTRACT FROM AUTHOR]

When a predator is immobile near an immobile prey, the probability that the predator will detect and attack increases over time. The prey’s cost of moving, thereby abandoning crypsis due to immobility, therefore decreases. Cost of not moving increases over time if movement is required for prey to conduct fitness-enhancing activities. We tested a cost-benefit model that predicts effects of factors that affect predation risk and cost of not moving on a prey’s latency to flee. Acting as simulated predators, we conducted experiments on the lizards Iberolacerta cyreni and Podarcis lilfordi. All predictions for 5 risk factors and a cost of moving factor were verified. Lizards fled sooner when the predator stood closer, approached rapidly rather than slowly before stopping, approached directly rather than indirectly, and gazed at the lizard rather than away from it, and after the second of 2 successive approaches. Latency to move was shorter in the presence than absence of a mealworm, suggesting the importance of opportunity cost of immobility. The effect of standing distance has 2 components, greater rate of detection by the predator and greater risk of being captured if detected at shorter distances. Escape theory has been highly successful in predicting how close a prey allows a predator to approach before fleeing. Our model extends an economic approach to study of escape decisions in response to an immobile predator that may be an ambush forager or an active forager that has stopped moving nearby. [ABSTRACT FROM PUBLISHER]

Escape success of copepod nauplii (N5–6) of the copepod Acartia tonsa was significantly lower than that of copepodites (C1–2) when exposed to a coral reef fish Acanthemblemaria paula, but no difference was observed when exposed to the seahorse Hippocampus zosterae. The addition of low level turbulence inhibited feeding by the seahorse but did not affect overall capture success in A. paula, although a shift in predator behavior occurred. This study highlights the importance of considering predatory mode and behavior in the context of planktonic predator–prey dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Predators can simultaneously have lethal (consumption) and non-lethal (modification of traits) effects on their prey. Prey escape or fleeing from potential predators is a common form of a non-lethal predator effect. The efficiency of this response depends on the prey''s ability to detect and correctly identify its predator far enough to increase the probability of successful escape, yet short enough to allow it to allocate time to other activities (e.g. foraging). In this study, we characterized the non-lethal effect of the sun star Heliaster helianthus on the black sea urchin Tetrapygus niger by assessing the nature of predator detection and the spatial scale involved both in predator detection and in the escape response. Through field and laboratory experiments we demonstrate that T. niger detects chemical cues released by H. helianthus. In the laboratory, these chemical signals can be detected at distances of up to about 50cm. In the field, the distance traveled by urchins when escaping, after recognition of the predation risk, was also restricted to about 40cm. Thus, considering the sizes of the predator and prey, the spatial scale of both detection and escape is comparatively small suggesting that non-lethal effects of H. helianthus (e.g. how it modifies the behavior of T. niger) should be important at local spatial scales and highly variable at the landscape scale. [Copyright &y& Elsevier]

Survivable injuries are a common yet costly experience. The ability to sense and respond to noxious stimuli is an almost universal trait, and prolonged behavioral alterations, including sensitization to touch and other stimuli, may function to ameliorate fitness costs associated with injury. Cephalopods can modify their behavior by learned association with noxious electric shock, but non-associative alterations of behavioral responses after tissue injury have not been studied. The aim of this study was to make the first systematic investigations in any cephalopod of behavioral responses and alterations elicited by explicit, minor injury. By testing responsiveness in the longfin squid, Loligo pealeii, to the approach and contact of an innocuous filament applied to different parts of the body both before and after injury to the distal third of one arm, we show that a cephalopod expresses behavioral alterations persisting for at least 2 days after injury. These alterations parallel forms of nociceptive plasticity in other animals, including general and site-specific sensitization to tactile stimuli. A novel finding is that hyper-responsiveness after injury extends to visual stimuli. Injured squid are more likely to employ crypsis than escape in response to an approaching visual stimulus shortly after injury, but initiate escape earlier and continue escape behaviors for longer when tested from 1 to 48 h after injury. Injury failed to elicit overt wound-directed behavior (e.g. grooming) or change hunting success. Our results show that long-lasting nociceptive sensitization occurs in cephalopods, and suggest that it may function to reduce predation risk after injury. [ABSTRACT FROM AUTHOR]

Economic theories of antipredatory behavior take into account expected fitness losses and gains to predict escape decisions. Prey at greater risk are predicted to have longer flight initiation distance (= distance from predator when escape begins), flee farther, be more likely to enter refuge, and have longer hiding time (= time between entering and exiting refuge). We simulated predators to study effects of risk factors in the lizard Sceloporus jarrovii. Flight initiation distance, distance fled and probability of entering refuge increased with approach speed. Flight initiation distance increased additively with increases in speed and directness of approach. Lizards habituated to human presence had shorter flight initiation distances than unhabituated lizards. As predicted from greater threat posed by a persistent predator, flight initiation distance and hiding time were longer after the second of two approaches. Fleeing was more likely when an investigator stood nearby and turned toward them than when farther way or turned away. These findings verify theoretical predictions of escape and refuge use for several risk factors and most are consistent with those for other lizards. However, speed and directness of approach had additive effects in S. jarrovii, but interacted in other species. Another novel finding was a small interaction between individual investigator and directness of approach. Although outcomes of tests of escape and refuge use theories consistently confirm qualitative predictions, quantitative comparisons between studies by different investigators may have limited value unless information is available about relative responses by prey to each investigator. [ABSTRACT FROM AUTHOR]

Flight initiation distance is the distance separating predator and prey when escape begins. The optimal flight initiation distance occurs where expected postencounter fitness is maximized, which depends on the prey's initial fitness, benefits obtainable by not fleeing, energetic escape costs, and expected fitness loss due to predation risk. In current optimal escape theory, prey die when contacted by a predator. We explore effects of variable lethality, L, the probability of being killed on contact. Optimal flight initiation distance increases as lethality increases, matching expectations that prey should not flee when contact entails no fitness loss but should be increasingly wary as expected fitness loss on contact increases. Addition of lethality improves the ability of optimal escape theory to predict effects of factors affecting escape ability. Autotomy, the voluntary shedding of tails or other expendable parts as a last-ditch defense to permit escape, provides an example. After autotomy, running speed decreases in many prey, lethality increases because autotomy cannot be used again until the lost part has regenerated, and ability to obtain benefits may decrease due to reduced social status and foraging ability. These changes favor longer flight initiation distance but lowered initial fitness after autotomy has the opposite effect. Optimal escape theory including a lethality term clarifies how autotomy may lead to increase or decrease in flight initiation distance depending on the balance of its multiple effects. Effects of additional factors that may alter multiple parameters of the model, including age, sex, reproductive condition, injury, disease, and parasitism are discussed. [ABSTRACT FROM PUBLISHER]

Escape theory predicts that a prey should start escaping (flight initiation distance = FID) from a predator when the costs of fleeing and the cost staying are equal or until future fitness is maximized. Consequently, prey escape performances and current reproductive asset can affect FID. We tested effects of body condition, morphology, and whether the tail was regenerated or original on FID in the Balearic lizard (Podarcis lilfordi) by ourselves simulating predators. Lizards with better body condition had longer FID and lizards with longer intact tails had shorter FID. Lizards with regenerated tail presented shorter FID than lizards with intact tails. These results suggest that impaired escape performance is counterbalanced by fitness costs of tail regeneration or by alteration of escape behaviour. The weak association between morphology, body condition and FID suggest that escape performances and asset protection have relatively small effect on P. lilfordi escape decisions. [ABSTRACT FROM AUTHOR]

Previous studies have shown that squamates (lizards and snakes) are capable of spatial learning, but only after extensive training. In nature, squamates'' capacity to learn may be better than that suggested by laboratory studies, because they have the opportunity to become familiar with the location of important landmarks and vital resources as they wander through their home range. I conducted three laboratory experiments to test the hypothesis that prior experience with a habitat improves spatial learning in little brown skinks. Individual lizards were subjected to a simulated predatory attack and tested for their ability to take refuge under one of two cardboard retreats (experiment 1) and to choose the ‘correct’ retreat without prior experience (experiment 2) and with 48h of prior experience (experiment 3) in the ‘habitat’. Although little brown skinks learned to take refuge under cardboard retreats (experiment 1), inexperienced lizards did not learn to take refuge under the ‘correct’ retreat (experiment 2). However, experienced lizards did learn to take refuge under the correct retreat (experiment 3) and did so after only a few trials. I discuss the influence of experience, the ecological relevance of stimuli used in learning experiments, and other methodological issues. [Copyright &y& Elsevier]

Escape theory predicts flight initiation distance (FID), distance between predator and prey when escape begins, for factors affecting costs of fleeing and not fleeing. Starting distance (SD), distance between predator and prey when approach begins, appears to affect FID for some species and risk levels, but not others. I predicted that in an active forager under low risk FID would appear to increase as SD increases due to (1) inclusion of SDs shorter than optimal FID and (2) spontaneous movements not motivated by escape. I predicted that FID and SD are unrelated at low risk when SDs shorter than optimal FID and spontaneous movements are excluded. When I approached the lizard Aspidoscelis exsanguis, an active forager, all predictions were confirmed. Effects of short SD and spontaneous movement might account for relationships between FID and SD in some birds and lizards. Nevertheless, as a predator approaches, costs of monitoring may increase, as may assessed risk and risk-averse errors due to shorter available assessment time. Risk-aversion might account for restriction of the relationship between FID and SD to high risk levels in an ambushing lizard species, for which spontaneous movements are far less frequent than for active foragers such as A. exsanguis. Although FID and SD are unrelated in A. exsanguis, SD and the related alert distance can provide valuable insights into risk assessment in other taxa having escape movements distinct from other movements. Present findings emphasize the importance of distinguishing between escape and other movements that may be initiated during approaches. A previously untested prediction of escape theory is that escape begins immediately when a prey detects an approaching predator closer than optimal FID, leading to the prediction of a slope of 1.0 between FID and SD. This prediction was confirmed for SDs less than 1.5 m. [ABSTRACT FROM AUTHOR]

Using grey mullet Mugil cephalus as a model species, the hypothesis that escape latency increases with body size was tested. Minimum escape latency was c. 10 ms (mean ±s.d. 18·1 ± 13·7 ms; range 8–72 ms) and was independent of body size. [ABSTRACT FROM AUTHOR]

The wind-sensitive cercal system, well-known for mediating terrestrial escape responses, may also mediate insect aerial bat-avoidance responses triggered by wind generated by the approaching bat. One crucial question is whether enough time exists between detection and capture for the insect to perform a successful evasive maneuver. A previous study estimated this time to be 16 ms, based on cockroach behavioral latencies and a prediction for the detection time derived from a simulated predator moving toward a simulated prey. However, the detection time may be underestimated since both the simulated predator and prey lacked certain characteristics present in the natural situation. In the present study, actual detection times are measured by recording from wind-sensitive interneurons of a tethered praying mantis that serves as the target for a flying, attacking bat. Furthermore, using hot-wire anemometry, we describe and quantify the wind generated by an attacking bat. Anemometer measurements revealed that the velocity of the bat-generated wind consistently peaks early with a high acceleration component (an important parameter for triggering wind-mediated terrestrial responses). The physiological recordings determined that the mantis cercal system detected an approaching bat 74 ms before contact, which would provide the insect with 36 ms to perform a maneuver before capture. This should be sufficient time for the mantis to respond. Although it probably would not have time for a full response that completely evades the bat, even a partial response might alter the mantid's trajectory enough to cause the bat to mishandle the insect, allowing it to escape. [ABSTRACT FROM AUTHOR]

Praying mantids perform evasive maneuvers that vary with the level of danger posed by their bat predators. The vocalization pattern of attacking bats provides cues that mantids can potentially use to decide how and when to respond. Using pulse trains simulating bat attack echolocation sequences, this study determines when in the attack sequence the mantis power dive (its response to high-level threat) occurs and predicts the parameters within the echolocation sequence that are important for eliciting the response. For sequences with a rapid transition from low to high pulse repetition rates (PRRs), the evasive response occurred close to the point during the simulated sequence when the bat would have contacted the mantis. However, the evasive response occurred earlier if the transition was gradual. Regardless of the transition type, the prediction data show that sequences trigger the response when PRRs reach 20–40 pulses s-1. These results suggest that a bat gradually increasing its PRR could ‘tip off’ the mantis, enabling it to escape. Attack sequences contain gradual transitions when bats engage in strobing behavior, an echolocation phenomenon that may help the bat perceive the auditory scene. Conversely, bat attack sequences that contain rapid increases in PRR close to the point of capture could circumvent the mantid's auditory defense. Based on these findings, mantids as well as other insects could benefit from having a back-up defense response to offset any advantage the bat gains by rapidly switching from low to high PRRs. [ABSTRACT FROM AUTHOR]

The effect of school size on capture success in three different piscivores, perch Perca fluviatilis, pikeperch Stizostedion lucioperca and pike Esox lucius, was investigated. Roach Rutilus rutilus were used as prey in a pool experiment where individual predators were presented prey at densities of one, two, four, eight and 16 prey, respectively. Treatments were replicated seven times for each predator species. Perch was at first virtually unable to capture a prey from a school and suffered a significant confusion effect with increasing prey density. The effect, however, was limited in the long run, as the perch was a very effective predator in its hunting strategy where it singled out and repeatedly attacked single prey irrespective of prey density or school size. Pikeperch and pike were able to attack and capture prey at any prey density equally successfully and thus did not suffer from a confusion effect. Neither did these predators receive any apparent advantages from increasing prey density. [ABSTRACT FROM AUTHOR]

The neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey—predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all three known types of escape tail-flips during the interactions with the dragonfly nymphs. Tail-flips generated by activity in the giant neurons were predominantly observed to trigger the initial escape responses to an attack, but non-giant mediated tail-flips were often generated to attempt escape after capture. Attacks to the front of the crayfish triggered tail-flips mediated either by the medial giant neuron or by non-giant circuitry, whereas attacks to the rear always elicited tail-flips mediated by the lateral giant neuron. Overall, tail flipping was found to be a successful behavior in preventing predation, and only a small percentage of crayfish were killed and consumed. [ABSTRACT FROM AUTHOR]

High body mass caused by fat storage during migration is believed to increase a bird's risk of predation by decreasing its ability to escape predators. We demonstrate the negative effect of wing loading (mass/wing area) on escape speed and angle of two migrating species of shorebird. We also show significant differences in escape performance between the species and genders. To help explain these differences, we test two potential proximate causes, wing shape and leg bone length. Wing shape is correlated with differences in escape performance between the species, but we found no correlation of wing shape or leg bone length with gender. Ultimately, greater predation risk due to habitat use or larger body size, for the species and genders respectively, may have resulted in evolution of enhanced escape ability. [ABSTRACT FROM AUTHOR]

Ciliates can form an important link between the microbial loop and higher trophic levels primarily through consumption by copepods. This high predation pressure has resulted in a number of ciliate species developing rapid escape swimming behaviour. Several species of these escaping ciliates also possess a long contractile tail for which the functionality remains unresolved. We use high-speed video, specialized optics and novel fluid visualization tools to evaluate the role of this contractile appendage in two free-swimming ciliates, Pseudotontonia sp. and Tontonia sp., and compare the performance to escape swimming behaviour of a non-tailed species, Strobilidium sp. Here, we show that 'tailed' species respond to hydrodynamic disturbances with extremely short response latencies (less than or equal to 0.89 ms) by rapidly contracting the tail which carries the cell body 2-4 cell diameters within a few milliseconds. This provides an advantage over non-tailed species during the critical first 10-30 ms of an escape. Two small, short-lived vortex rings are created during contraction of the tail. The flow imposed by the ciliate jumping can be described as two well-separated impulsive Stokeslets and the overall flow attenuates spatially as r−3. The high initial velocities and spatio-temporal arrangement of vortices created by tail contractions appear to provide a means for rapid escape as well as hydrodynamic 'camouflage' against fast striking, mechanoreceptive predators such as copepods. [ABSTRACT FROM AUTHOR]