Behavioural Response of Bats to Perceived Predation Risk While Foraging

The ability to detect and respond to predation risk while foraging may have important fitness consequences for prey organisms. Anti‐predator behaviours may reduce the probability of mortality because of predation, but they may also be associated with reduced foraging efficiency. Several behaviours of bats have been suggested to serve as anti‐predator responses, and there is evidence that predation, particularly by avian predators such as owls, may be an important cause of bat mortality. Previous studies have attempted to determine whether predator presence affects bat behaviour when emerging from roost sites, but few have examined effects of predator presence on bat behaviour while foraging. In this study, we investigated whether foraging bats respond to predator cues by presenting bats with an acoustic cue simulating the presence of an owl. Within matched trials, which were conducted at different locations each of 18 nights, significantly fewer bat detections were recorded at owl playback stations than at control stations (no auditory cue), suggesting an avoidance response by bats. An acoustic control (i.e. station playing woodpecker calls), however, did not have significantly more detections than the stations playing the owl calls, suggesting that bats may simply be avoiding noise and more detailed investigation is warranted. Although evidence for owl predation on bats is minimal in North America, results of this study may indicate that the perceived presence of owls may represent a factor influencing the behaviour of bats while foraging.     

Behavioural Responses of European Roe Deer to Temporal Variation in Predation Risk

In natural environments, predation risk varies over time. The risk allocation hypothesis predicts that prey is expected to adjust key anti‐predator behaviours such as vigilance to temporal variation in risk. We tested the predictions of the risk allocation hypothesis in a natural environment where both a species‐rich natural predator community and human hunters are abundant and where the differences in seasonal and circadian activity between natural and anthropogenic predators provided a unique opportunity to quantify the contributions of different predator classes to anti‐predator behaviour. Whereas natural predators were expected to show similar levels of activity throughout the seasons, hunter activity was high during the daytime during a clearly defined hunting season. According to the risk allocation hypothesis, vigilance should then be higher during the hunting season and during daytime hours than during the non‐hunting season and night‐time hours. Roe deer (Capreolus capreolus) on the edge of Bia?owie?a Primeval Forest in Eastern Poland displayed vigilance behaviour consistent with these predictions. The behavioural response of roe deer to temporarily varying predation risks emphasises the behavioural plasticity of this species and suggests that future studies of anti‐predator behaviour need to incorporate circadian variation in predation pressure as well as risk gradients of both natural and anthropogenic predators.     

Response to Predation Risk in Urban and Rural House Sparrows

Habitat urbanization may change the density of predators, and it is often assumed that such changes lead to altered predation risk for urban populations of their prey. Although it is difficult to study predation hazard directly, behavior responses of prey species may be informative in inferring such habitat differences. In this study, we compared the risk‐taking behavior of urban and rural house sparrows (Passer domesticus) after simulated attacks by two of their important predators (sparrowhawk Accipiter nisus and domestic cat Felis catus). The birds were startled by moving dummies of these predators and respective control objects, and their risk taking was estimated as their latency to feed after the startle. We found that sparrows responded more strongly (had longer post‐startle feeding latencies) to sparrowhawk attacks than to the control object, and their responses differed between the habitats. First, risk taking of urban birds strongly decreased with age (older birds had longer latencies than young birds), while there was no such age difference in rural birds. Second, young urban birds responded less strongly, while older urban birds responded more strongly to the sparrowhawk than the same age groups of rural birds, respectively. We did not succeed in evoking antipredatory response by simulated cat attacks, because birds responded similarly to the dummy and the control object. Our results support that predation risk, posed at least by avian predators, is different in urban and rural habitats of house sparrows. The increased wariness of older, hence presumably more experienced, urban birds implies that sparrows may be more exposed to predation in cities.     

动物觅食行为对捕食风险的反应

动物进行任何活动时均面临被捕食的风险 ,分析捕食风险与猎物觅食行为的关系 ,有助于揭示捕食者与猎物的协同进化机制。捕食风险具有限制或调节猎物种群数量的功能。在进化时间内 ,对猎物形态和行为特征的进化是潜在的选择压力之一 ,可利用环境因子作为信息源估测食物可利用性和捕食风险大小的动物 ,具有更大的适合度。信息源可分为包括视觉的、听觉的和化学的。动物进行觅食活动时 ,依据信息源的变化确定环境中捕食风险的大小 ,并根据自身的质量在捕食风险的大小之间做出权衡 ,通过食物选择、活动格局和栖息地利用等行为的变化降低捕食风险     

Alcohol Impairs Predation Risk Response and Communication in Zebrafish

The effects of ethanol exposure on Danio rerio have been studied from the perspectives of developmental biology and behavior. However, little is known about the effects of ethanol on the prey-predator relationship and chemical communication of predation risk. Here, we showed that visual contact with a predator triggers stress axis activation in zebrafish. We also observed a typical stress response in zebrafish receiving water from these conspecifics, indicating that these fish chemically communicate predation risk. Our work is the first to demonstrate how alcohol effects this prey-predator interaction. We showed for the first time that alcohol exposure completely blocks stress axis activation in both fish seeing the predator and in fish that come in indirect contact with a predator by receiving water from these conspecifics. Together with other research results and with the translational relevance of this fish species, our data points to zebrafish as a promising animal model to study human alcoholism.     

Behavioral Plasticity in Response to Perceived Predation Risk in Breeding House Wrens

Predation is a significant cause of nest failure in passerine birds, and, thus, natural selection is expected to favor behavioral plasticity to allow birds to respond to perceived changes in predation risk. However, behavioral plasticity in response to perceived predation risk, and its potential fitness-related costs, are understudied. In a wild population of breeding house wrens (Troglodytes aedon), we tested the hypotheses that (1) birds show behavioral plasticity in response to perceived nest-predation risk to reduce self-risk or risk to offspring, but (2) this plasticity incurs fitness-related costs. We experimentally increased the perceived risk of nest predation by enlarging the diameter of the nestbox entrance from the standard 3.2 to 5.0 cm once incubation began. Unexpectedly, large-hole females spent significantly less time being vigilant than small-hole (control) females during late incubation. Both males and females also exhibited plasticity in their provisioning behavior. Large-hole males increased and large-hole females decreased provisioning visits with increasing brood size, whereas small-hole males and females behaved similarly and were unaffected by brood size. Females did not show plasticity in their incubation or brooding behavior. Notwithstanding this behavioral plasticity in response to increased perceived predation risk, treatment had no effect on hatching success or early hatchling survival, nor did it affect nestling body condition or fledging success. We conclude, therefore, that house wrens show behavioral plasticity in response to perceived nest-predation risk, but that any short-term fitness-related costs associated with this flexibility appear negligible.     

Effects of Exogenous Testosterone on Parental Care Behaviours in Male Bluegill Sunfish (Lepomis macrochirus)

Androgens are known to mediate aggressive and defensive behaviour in many vertebrate species. However, high concentrations of androgens might also conflict with the expression of nurturing behaviours and therefore a trade‐off can exist between aggressive and nurturing behaviours during parental care. We explored the role of testosterone in paternal care in bluegill sunfish (Lepomis macrochirus), where males provide both sole defence of the young from predators and sole nurturing behaviour such as fanning of the eggs. At the onset of parental care, we manipulated testosterone levels in males using testosterone propionate implants. We then observed the frequency of nurturing and aggressive behaviours displayed by the males over 6 d of parental care. Testosterone‐implanted fish were more aggressive when presented with a brood predator, performing more bites, opercular flares and lateral displays than control males. Testosterone‐implanted males, however, were not less nurturing than control fish, performing similar levels of fanning and nest‐cleaning behaviours. Thus, our results support a positive relationship between testosterone and paternal aggression but no testosterone‐mediated trade‐off between paternal nurturing and aggression.     

Agonistic Interactions in Juvenile Sticklebacks (Gasterosteus aculeatus) in Relation to Local Predation Risk

Size-matched groups of three-spined stickleback (Gasterosteus aculeatus) fry were established using fish from two sites, one with abundant piscivorous predators (the high-risk site) and the other with very few heterospecific predators (the low-risk site). Over a period of two months, social interactions within groups were monitored regularly and mean lengths and coefficients of variance in length were tracked. Agonistic behaviour was observed in 45% of observation periods, but was more common in the groups of fry from the low-risk site, where it was more likely to take the form of direct attack rather than displacement without contact. In both categories of fish, the great majority of agonistic acts were directed to fish of a similar size or smaller. Mean size increased rapidly in all groups. At the same time, the coefficient of variation also increased, approaching 15% after two months in both categories of fish, reflecting differing growth rates among individuals. After three months, the two largest and the two smallest fish from each group were observed individually during an encounter with a model predatory fish. Large and small fish from both sites behaved identically in this test, suggesting that in sticklebacks (unlike guppies, for example) early experience of aggressive attacks from conspecific companions may not influence the development of anti-predator responses. As has been reported previously, sticklebacks from the high-risk site responded much more strongly than low-risk fish.     

Transgenerational Behavioral Plasticity in a Parthenogenetic Insect in Response to Increased Predation Risk

Reliable cues of increased predation risk can induce phenotypic changes in an organism’s offspring (i.e. transgenerational phenotypic plasticity). While induction of defensive morphologies in naïve offspring in response to maternal predation risk is widespread, little is known about transgenerational changes in offspring behavior. Here we provide evidence for transgenerational behavioral plasticity in the pea aphid, Acyrthosiphon pisum. When pre-reproductive individuals of two genotypes (“pink” and “green”) were exposed to the alarm pheromone (E)-β-Farnesene (EBF), a reliable cue of increased predation risk, next-generation offspring altered their feeding site choices relative to the location of the maternal aphids. Offspring of EBF-treated aphids occupied “safer” feeding sites: green offspring occupied “safer” feeding sites in the natal colony, while pink offspring dispersed to occupy sites on neighboring plant leaves.     

Opportunistic Visitors: Long-Term Behavioural Response of Bull Sharks to Food Provisioning in Fiji

Shark-based tourism that uses bait to reliably attract certain species to specific sites so that divers can view them is a growing industry globally, but remains a controversial issue. We evaluate multi-year (2004–2011) underwater visual (n = 48 individuals) and acoustic tracking data (n = 82 transmitters; array of up to 16 receivers) of bull sharks Carcharhinus leucas from a long-term shark feeding site at the Shark Reef Marine Reserve and reefs along the Beqa Channel on the southern coast of Viti Levu, Fiji. Individual C. leucas showed varying degrees of site fidelity. Determined from acoustic tagging, the majority of C. leucas had site fidelity indexes >0.5 for the marine reserve (including the feeding site) and neighbouring reefs. However, during the time of the day (09:00–12:00) when feeding takes place, sharks mainly had site fidelity indexes <0.5 for the feeding site, regardless of feeding or non-feeding days. Site fidelity indexes determined by direct diver observation of sharks at the feeding site were lower compared to such values determined by acoustic tagging. The overall pattern for C. leucas is that, if present in the area, they are attracted to the feeding site regardless of whether feeding or non-feeding days, but they remain for longer periods of time (consecutive hours) on feeding days. The overall diel patterns in movement are for C. leucas to use the area around the feeding site in the morning before spreading out over Shark Reef throughout the day and dispersing over the entire array at night. Both focal observation and acoustic monitoring show that C. leucas intermittently leave the area for a few consecutive days throughout the year, and for longer time periods (weeks to months) at the end of the calendar year before returning to the feeding site.     

Antipredatory Response and Food Intake in Wood Mice (Apodemus sylvaticus) under Simulated Predation Risk by Resident and Novel Carnivorous Predators

Chemical signals left by predators are a potential source of information about the risk of predation, and small mammals are known to take them into account when making decisions. We investigated whether wood mice (Apodemus sylvaticus) are more likely to avoid the faeces of resident predators (red fox Vulpes vulpes and common genet Genetta genetta) vs. a novel predator (European pine marten Martes martes). Odour recognition would increase perceived predation risk and reduce food intake by individual mice. Wood mice response to predators was analysed by live‐trapping using two untreated controls (baited/non‐baited) and traps experimentally manipulated with three predator treatments (faeces of red fox, common genet or pine marten). Traps were baited with 4 g of toasted corn, and food intake by wood mice was determined as the amount of bait remaining in each trap. We found that traps treated with faeces of resident predators were the most avoided, and the number of captures in traps treated with pine marten faeces was similar to the control‐baited traps. The variation found in food intake was explained by the interaction between the types of treatment and breeding condition. Food intake was similar in control‐baited traps and in traps with faeces of pine marten, but when predation risk by resident predators (red fox and common genet) was simulated, breeders reduced food intake significantly as compared to non‐breeders. These results indicate that predator recognition and feeding behaviour under predation risk depend on individual factors and the balance of costs‐benefits in each particular predation risk situation at a given place and time.     

Wall Lizards Modulate Refuge Use through Continuous Assessment of Predation Risk Level

Prey species might use several possible ways to assess predation risk when encountering a predator. Animals may consider the risk level estimated in a first encounter to remain unchanged across subsequent encounters (fixed risk response), or they may update and change their responses across encounters in accordance with short‐term changes in risk levels (flexible risk response). We examined in the field how wall lizards assess risk level by analyzing time spent in refuges after simulated predator attacks. We first examined how risk was assessed when multiple consecutive sources of risk were present simultaneously. The results suggest that wall lizards assess risk based on multiple cues, such as approach speed, directness, and persistence (measured as the distance of the predator to their refuge after an attack). When risk was high lizards remained longer in their refuges. The first decision to appear partly from the refuge depended on both approach speed and persistence, whereas the decision to emerge completely depended only on persistence and not on approach speed. This suggests that wall lizards update information on predator threat and adjusted their emergence accordingly. In a second experiment, we analyzed how short‐term changes in risk level of successive attacks affected refuge use. Successive emergence times varied as a function of current risk level of each repeated attack, independently of the risk level of previous attacks. This indicated that lizards could track short‐term changes in risk level through time and modify their initial responses when required. Fine adjustments of refuge use may help lizards to minimize costs of refuge use in unfavorable and variable environments where antipredatory responses are costly.     

Field Assessment of the Predation Risk - Food Availability Trade-Off in Crab Megalopae Settlement

Settlement is a key process for meroplanktonic organisms as it determines distribution of adult populations. Starvation and predation are two of the main mortality causes during this period; therefore, settlement tends to be optimized in microhabitats with high food availability and low predator density. Furthermore, brachyuran megalopae actively select favorable habitats for settlement, via chemical, visual and/or tactile cues. The main objective in this study was to assess the settlement of Metacarcinus edwardsii and Cancer plebejus under different combinations of food availability levels and predator presence. We determined, in the field, which factor is of greater relative importance when choosing a suitable microhabitat for settling. Passive larval collectors were deployed, crossing different scenarios of food availability and predator presence. We also explore if megalopae actively choose predator-free substrates in response to visual and/or chemical cues. We tested the response to combined visual and chemical cues and to each individually. Data was tested using a two-way factorial design ANOVA. In both species, food did not cause significant effect on settlement success, but predator presence did, therefore there was not trade-off in this case and megalopae respond strongly to predation risk by active aversion. Larvae of M. edwardsii responded to chemical and visual cues simultaneously, but there was no response to either cue by itself. Statistically, C. plebejus did not exhibit a differential response to cues, but reacted with a strong similar tendency as M. edwardsii. We concluded that crab megalopae actively select predator-free microhabitat, independently of food availability, using chemical and visual cues combined. The findings in this study highlight the great relevance of predation on the settlement process and recruitment of marine invertebrates with complex life cycles.     

Sex‐Specific Parental Care in Response to Predation Risk in the European Roller,Coracias garrulus

Sublethal effects of predation constitute an important part of predation effects, which may modulate prey population and community dynamics. In birds, the risk of nest predation may cause a reduction in parental activity in the care of offspring to reduce the chance of being detected by predators. In addition, parents may modify their parental food allocation preferences within the brood in response to predation risk. Our aim in this study was to evaluate the effects of risk of nest predation on parental care and within‐nest food allocation in the European Roller (Coracias garrulus), an asynchronously hatching bird. We manipulated brood predation risk by placing a snake model near the nests that simulates the most common nest predator in the Mediterranean region. Our results show that males but not females increased their provisioning rate when they were exposed to the model and that despite this, nestlings’ body mass decreased in response to this temporary increase in predation risk. We did not find evidence that parents changed their food allocation strategy towards senior or junior nestlings in their nests in response to predation risk. These results show that the European roller modifies parental care in response to their perception of predation risk in the nest and a sex‐specific sensitivity to the threat, which suggests a different perception of offspring reproductive value by parents. Finally, our results show that changes in parental behaviour in response to nest predation risk might have consequences for nestling fitness prospects.     

Predation Risk Perception,Food Density and Conspecific Cues Shape Foraging Decisions in a Tropical Lizard

When foraging, animals can maximize their fitness if they are able to tailor their foraging decisions to current environmental conditions. When making foraging decisions, individuals need to assess the benefits of foraging while accounting for the potential risks of being captured by a predator. However, whether and how different factors interact to shape these decisions is not yet well understood, especially in individual foragers. Here we present a standardized set of manipulative field experiments in the form of foraging assays in the tropical lizard Anolis cristatellus in Puerto Rico. We presented male lizards with foraging opportunities to test how the presence of conspecifics, predation-risk perception, the abundance of food, and interactions among these factors determines the outcome of foraging decisions. In Experiment 1, anoles foraged faster when food was scarce and other conspecifics were present near the feeding tray, while they took longer to feed when food was abundant and when no conspecifics were present. These results suggest that foraging decisions in anoles are the result of a complex process in which individuals assess predation risk by using information from conspecific individuals while taking into account food abundance. In Experiment 2, a simulated increase in predation risk (i.e., distance to the feeding tray) confirmed the relevance of risk perception by showing that the use of available perches is strongly correlated with the latency to feed. We found Puerto Rican crested anoles integrate instantaneous ecological information about food abundance, conspecific activity and predation risk, and adjust their foraging behavior accordingly.     

Behavioral and Ecological Determinants of Home Range Size in Juvenile Pumpkinseed Sunfish (Lepomis gibbosus)

Numerous species of freshwater fish are known to be site specific, yet the ecological and behavioral factors influencing home range size have rarely been examined. In this study we examine aggression, predator avoidance and feeding rate in juvenile pumpkinseed sunfish as a function of location within their home range. We also compare the behavior of individuals within their home range with individuals that were displaced from their home range by being transplanted from one pond to another. Juvenile pumpkinseeds had a higher feeding rate in the center of their home range than on the periphery. Transplanted juveniles did not adopt a restricted home range over a 3-wk period and had a lower feeding rate than residents in the same pond. Aggression and predator avoidance do not appear to be important determinants of home range size in our study.     

Nature of Predation Risk Cues in Container Systems: Mosquito Responses to Solid Residues From Predation

In aquatic systems, prey animals associate predation risk with cues that originate either from the predator or from injured conspecifics. Sources and benefits of these cues have received considerable attention in river, lake, and pond ecosystems but are less well understood in small container ecosystems that can hold less than a liter of water. Mosquitoes Aedes triseriatus (Say) and Aedes albopictus (Skuse) encounter predatory Corethrella appendiculata (Grabham) and Toxorhynchites rutilus (Coquillett) in small containers and show antipredatory behavioral responses. We investigated the sources of the predation cues to which these prey larvae respond. We tested whether Ae. albopictus larvae show behavioral responses to cues emanating from the predator or from damage to prey caused by the act of predation. We also tested whether Ae. triseriatus respond to cues present in fluid or solid residues from predator activity. Ae. albopictus showed behavioral modifications only in response to waterborne cues from a feeding predator and not to cues from a starving predator, indicating that Ae. albopictus respond to cues created by the act of predation, which could include substances derived from damaged prey or substances in predator feces. Ae. triseriatus showed behavioral responses to solid residues from predation but not to fluid without those solids, indicating that the cues to which they respond originate in predator feces or uneaten prey body parts. Our results suggest that cues in this system may be primarily chemicals that are detected upon contact with solid residues that are products of the feeding processes of these predators.     

Predation Response of Vibrio fischeri Biofilms to Bacterivorus Protists

Vibrio fischeri proliferates in a sessile, stable community known as a biofilm, which is one alternative survival strategy of its life cycle. Although this survival strategy provides adequate protection from abiotic factors, marine biofilms are still susceptible to grazing by bacteria-consuming protozoa. Subsequently, grazing pressure can be controlled by certain defense mechanisms that confer higher biofilm antipredator fitness. In the present work, we hypothesized that V. fischeri exhibits an antipredator fitness behavior while forming biofilms. Different predators representing commonly found species in aquatic populations were examined, including the flagellates Rhynchomonas nasuta and Neobodo designis (early biofilm feeders) and the ciliate Tetrahymena pyriformis (late biofilm grazer). V. fischeri biofilms included isolates from both seawater and squid hosts (Euprymna and Sepiola species). Our results demonstrate inhibition of predation by biofilms, specifically, isolates from seawater. Additionally, antiprotozoan behavior was observed to be higher in late biofilms, particularly toward the ciliate T. pyriformis; however, inhibitory effects were found to be widespread among all isolates tested. These results provide an alternative explanation for the adaptive advantage and persistence of V. fischeri biofilms and provide an important contribution to the understanding of defensive mechanisms that exist in the out-of-host environment.