Urban rooftops near sports pitches provide a safe haven for a declining shorebird

Urbanisation has contributed to a severe decline in biodiversity worldwide. However, urban ecosystems can also play an important role in the conservation of threatened species, including ground-nesting birds such as the Eurasian Oystercatcher (Haematopus ostralegus). While the coastal populations of this shorebird have declined sharply, there is growing evidence that pairs nesting on urban flat roofs have high reproductive success. However, the reasons for rooftop nesting and the species' habitat use in urban areas remain poorly understood. In this study, we investigate the territory selection and foraging behaviour of the Eurasian Oystercatcher in the city of Münster (NW Germany). All nesting sites were located on flat roofs (N = 24), most of which were covered with gravel. Overall, reproductive success was high. This was mainly because the roofs provided protection from mammalian predators, leading to increased nest and chick survival. Moreover, breeding performance in the study area was favoured by the proximity of sports pitches. According to our observations, they provided a large amount of easily accessible prey throughout the breeding season. Overall, our study highlights that the reproductive success of the Eurasian Oystercatcher in urban environments is highly dependent on both safe nesting sites on flat roofs and the availability of suitable foraging habitats. Although our study suggests that breeding in urban areas can be beneficial for the model organism, the species' strong territory fidelity makes it very sensitive to the rapid environmental changes occurring in cities. The value of urban ecosystems for bird conservation should therefore be better integrated into urban planning and management.

Do domestic budgerigars perceive predation risk?

Predation risk may affect the foraging behavior of birds. However, there has been little research on the ability of domestic birds to perceive predation risk and thus adjust their feeding behavior. In this study, we tested whether domestic budgerigars (Melopsittacus undulatus) perceived predation risk after the presentation of specimens and sounds of sparrowhawks (Accipiter nisus), domestic cats (Felis catus), and humans, and whether this in turn influenced their feeding behavior. When exposed to visual or acoustic stimuli, budgerigars showed significantly longer latency to feed under sparrowhawk, domestic cat, and human treatments than with controls. Budgerigars responded more strongly to acoustic stimuli than visual stimuli, and they showed the longest latency to feed and the least number of feeding times in response to sparrowhawk calls. Moreover, budgerigars showed shorter latency to feed and greater numbers of feeding times in response to human voices than to sparrowhawk or domestic cat calls. Our results suggest that domestic budgerigars may identify predation risk through visual or acoustic signals and adjust their feeding behavior accordingly.

Spoilt for choice: Do female mosquitoes experience choice overload when deciding where to lay eggs?

Animals live in complex natural environments. Based on the effects of natural selection, theory on animal information use says that it is optimal for animals to make "rational" decisions, i.e., to choose alternatives which maximize fitness gains, irrespective of the number of alternatives presented to them. Yet, animals commonly make seemingly "irrational" choices in the face of complex and variable stimuli that challenge their cognitive machinery. Here, we test the choice overload hypothesis - decision-making is negatively affected when animals experience an overload of choice. Using simultaneous-choice trials that varied in choice repertoire size, we examined oviposition site selection behaviour in Aedes aegypti towards larval predators, the nymphs of Bradinopyga geminata. Based on the underlying fitness trade-offs of oviposition decision-making, we predicted that female oviposition preference would be weaker and variation in this response would be higher in complex, multiple-choice trials than in binary-choice trials. In partial support of our hypothesis, oviposition preference was weaker in the complex, multiple-choice trials, but the variation in response depended on predator density, and did not depend on choice repertoire size. We suggest that information overload can negatively affect certain aspects of animal decision-making, resulting in choices appearing as "irrational" if the complexity of the decision-making context is not incorporated. Information overload can potentially lead to alternative strategies, such as bet-hedging or decision-making with reduced discrimination.

Flock size increases with the diversity and abundance of local predators in an avian family

Group living has long been viewed as an adaptation to reduce predation risk. Earlier comparative analyses provided support for the hypothesis but typically ignored variation in group size at the local scale and included proxies of predation risk rather than more direct estimates. Here, we related variation in group size at the scale of a study site in various species with the diversity and abundance of local predators. If larger groups provide protection against predators, we expected larger groups to evolve in species facing locally more diverse and abundant predators. We examined this hypothesis in one avian family, the Paridae, which are small arboreal birds that include some of the better studied species in ecology. From the literature, we gathered 275 flock size estimates from 34 species. In a phylogenetic framework and controlling for the potential confounding effect of latitude, we found that flock size increased with predation risk but only in flocks that included more than one species. We suggest that competition sets an upper limit to the size of flocks including conspecifics only. Joining flocks with other species, thus, allows individuals to increase flock size in response to higher predation risk without a substantial increase in competition. Overall, our results based on more direct estimates of predation risk provide further comparative evidence for an association between predation and the evolution of flocking in birds.

Freshwater salinization reduces vertical movement rate and abundance of Daphnia: Interactions with predatory stress

Contaminants in human-dominated landscapes are changing ecological interactions. The global increase in freshwater salinity is likely to change predator-prey interactions due to the potential interactive effects between predatory stress and salt stress. We conducted two experiments to assess the interactions between the non-consumptive effects of predation and elevated salinity on the abundance and vertical movement rate of a common lake zooplankton species (Daphnia mendotae). Our results revealed an antagonism rather than a synergism between predatory stress and salinity on zooplankton abundance. Elevated salinity and predator cues triggered a >50% reduction in abundance at salt concentrations of 230 and 860 mg Cl^-/L, two thresholds designed to protect freshwater organisms from chronic and acute effects due to salt pollution. We found a masking effect between salinity and predation on vertical movement rate of zooplankton. Elevated salinity reduced zooplankton vertical movement rate by 22-47%. A longer exposure history only magnified the reduction in vertical movement rate when compared to naïve individuals (no prior salinity exposure). Downward movement rate under the influence of predatory stress in elevated salinity was similar to the control, which may enhance the energetic costs of predator avoidance in salinized ecosystems. Our results suggest antagonistic and masking effects between elevated salinity and predatory stress will have consequences for fish-zooplankton interactions in salinized lakes. Elevated salinity could impose additional energetic constraints on zooplankton predator avoidance behaviors and vertical migration, which may reduce zooplankton population size and community interactions supporting the functioning of lake ecosystems.

Prey species increase activity in refugia free of terrestrial predators

The decline of terrestrial predator populations across the globe is altering top-down pressures that drive predator-prey interactions. However, a knowledge gap remains in understanding how removing terrestrial predators affects prey behavior. Using a bifactorial playback experiment, we exposed fox squirrels to predator (red-tailed hawks, coyotes, dogs) and non-predator control (Carolina wren) calls inside terrestrial predator exclosures, accessible to avian predators, and in control areas subject to ambient predation risk. Fox squirrels increased their use of terrestrial predator exclosures, a pattern that corresponded with 3 years of camera trapping. Our findings suggest fox squirrels recognized that exclosures had predictably lower predation risk. However, exclosures had no effect on their immediate behavioral response towards any call, and fox squirrels responded most severely to hawk predator calls. This study shows that anthropogenically driven predator loss creates predictably safer areas (refugia) that prey respond to proactively with increased use. However, the persistence of a lethal avian predator is sufficient to retain a reactive antipredator response towards an immediate predation threat. Some prey may benefit from shifting predator-prey interactions by gaining refugia without sacrificing a sufficient response towards potential predators.

Performance of Daphnia simultaneously exposed to nitrite and predation risk: Reduced nitrite tolerance and aggravated predation-induced miniaturization

Nitrogenous pollutants derived from human activities not only pose direct risk on aquatic organisms but may also indirectly endanger the stability of interspecific relations. To date, the effects of the nitrogen-containing pollutants on the induced defense remain unclear. Here, we aim to investigate the induced defense of an aquatic keystone species, Daphnia pulex, which responds to predation risk under nitrite pollution at environmentally relevant concentrations and simultaneously evaluate the effects of their induced defenses on nitrite tolerance. Results showed that increasing nitrite significantly reduced the survival time of D. pulex and posed severe reproductive toxicity, consequently reducing the offspring and broods. In the morphological defensive responses, early nitrite exposure interfered with the spine elongation, but the relative spine length induced by the predation risk was unaffected by the nitrite concentrations with exposure time prolonged, although high-dose nitrite inhibited the spine elongation and the increase of the body size. The integration of biomarker response index analyses further indicated that the reproductive capacity was more seriously impaired than the morphology and the survival. Moreover, the sensitivity analyses of growth and reproduction indicated that predation risk significantly reduced Daphnia's tolerance to nitrite. Conclusively, these findings highlight that long-term nitrite exposure exacerbates the predator-induced miniaturization of zooplanktons, and predation risk also reduces their tolerance to nitrite, which provides new insights into the performance changes of zooplanktons exposed to pollutants under predation risk and the vulnerability of predator-prey interspecific relationships in polluted environments.

Exploring potential drivers of brain size variation in the electric fish Brachyhypopomus occidentalis

Characterizing the factors that shape variation in brain size in natural populations is crucial to understanding the evolution of brain size in animals. Here, we explore how relative brain size and brain allometry vary with drainage, predation risk and sex in natural populations of the electric knifefish Brachyhypopomus occidentalis. Fish were sampled from high and low predation risk sites within two independent river drainages in eastern and central Panamá. Overall, we observed low variation in brain-body size allometric slopes associated with drainage, predation risk and sex category. However, we observed significant differences in allometric intercepts between predation risk sites. We also found significant differences in relative brain mass associated with drainage, as well as significant differences in absolute brain mass associated with drainage, predation risk and sex category. Our results suggest potential constraints in brain-body allometry across populations of B. occidentalis. However, both drainage and predation risk may be playing a role in brain mass variation among populations. We suggest that variation in brain mass in electric fishes is affected by multiple extrinsic and intrinsic factors, including geography, environmental complexity, social interaction and developmental or functional constraints.

Predation risk affects the ecotoxicity evaluation of antibiotics: Population growth and antioxidase activity in the ciliate Paramecium jenningsi

Although predation risk exists under natural conditions, its role is usually ignored when evaluating the ecotoxicity of environmental contaminants, and the interaction between predation risk and antibiotic ecotoxicity is not yet clear. To investigate the nonconsumptive effects (NCEs) of predation on the ecotoxicity evaluation of antibiotics, the median lethal concentration (LC₅₀), relative population growth rate (RGR), and activities of three antioxidases were measured in the ciliate Paramecium jenningsi exposed to graded concentrations of the antibiotics nitrofurazone (NFZ) or erythromycin (ERY) in the presence or absence of a predator, i.e., the ciliate Didinium nasutum. The results showed that (1) NCEs significantly reduced the LC₅₀ of NFZ but had no effect on that of ERY; (2) predation pressure alone had no significant effect on the inhibitory rate of the P. jenningsi population, but the interaction with NFZ was synergistic, while that with CRY was additive; (3) the concentrationresponse (i.e., mortality) model for each antibiotic exposure with and without predation pressure differed significantly in the parameter slope; (4) RGRs were significantly reduced by antibiotic exposure or NCEs; only in NFZ-exposed groups did the RGRs decrease linearly with increasing exposure concentration; and (5) the activities of all three antioxidases significantly increased due to NCEs or following exposure to antibiotics. In brief, NCEs were detected in P. jenningsi, and these had additive or synergistic effects on antibiotic ecotoxicity, but their magnitude depended on the properties and exposure concentrations of the antibiotics. Our findings suggest that it is necessary to consider the roles of NCEs in the ecotoxicity evaluation of environmental contaminants.

Individual response in body mass and basal metabolism to the risks of predation and starvation in passerines

Wintering energy management in small passerines has focused on the adaptive regulation of the daily acquisition of energy reserves within a starvation-predation trade-off framework. However, the possibility that the energetic cost of living, i.e. basal metabolic rate (BMR), is being modulated as part of the management energy strategy has been largely neglected. Here, we addressed this possibility by experimentally exposing captive great tits (Parus major) during winter to two consecutive treatments of increased starvation and predation risk for each individual bird. Body mass and BMR were measured prior to and after each week-long treatment. We predicted that birds should be lighter but with a higher metabolic capacity (higher BMR) as a response to increased predation risk, and that birds should increase internal reserves while reducing their cost of living (lower BMR) when exposed to increased starvation risk. Wintering great tits kept a constant body mass independently of a week-long predation or starvation treatment. However, great tits reduced the cost of living (lower BMR) when exposed to the starvation treatment, while BMR remained unaffected by the predation treatment. Energy management in wintering small birds partly relies on BMR regulation, which challenges the current theoretical framework based on body mass regulation.

Predation stress experienced as immature mites extends their lifespan

The early-life experience is important in modulating the late-life performance of individuals. It has been predicted that there were trade-offs between early-life fitness and late-life success. Most of the studies on senescence have focused on the trade-offs between the reproduction and lifespan, and the influences of diet, mating, and other factors. Because the negative, non-consumptive effects of predators could also modulate the behaviour and underlying mechanisms of the prey, this study aimed to examine the different effects of predator-induced stress experienced in the early life compared with later life of the prey. The prey (Tyrophagus putrescentiae) was exposed to predation stress from the predator (Neoseiulus cucumeris) during different periods of its life (immature, oviposition period, and post-oviposition period). The results showed that the predation stress experienced during immature stages delayed development by 7.3% and prolonged lifespan by 9.7%, while predation stress experienced in the adult stage (both oviposition and post-oviposition periods) decreased lifespans of T. putrescentiae (by 24.8% and 28.7%, respectively). Predation stress experienced during immature stages also reduced female fecundity by 7.3%, whereas that experienced during the oviposition period reduced fecundity of the prey by 50.7%. This study demonstrated for the first time lifespan extension by exposure to predation stress when young and highlighted the importance of early-life experience to aging and lifespan.

Zebrafish embryos hatch early in response to chemical and mechanical indicators of predation risk, resulting in underdeveloped swimming ability of hatchling larvae

Plasticity in hatching time allows embryos to maximize fitness by balancing the benefits and costs of remaining bound within the chorion against the benefits and costs of emerging as a free-swimming larva. Here, in the first experiment, we exposed zebrafish (Danio rerio) embryos to either chemical cues from crushed embryos (simulating egg predation) or to blank water control. Embryos exposed to alarm cues hatched sooner, and had shorter body lengths and underdeveloped fins, relative to larvae from the water treatment. Burst swimming speed was significantly slower for larvae that hatched from the alarm cue treatment than for larvae from the water treatment. In a second 2×2 experiment, we exposed zebrafish embryos to either chemical alarm cues from conspecific embryos, mechanical disturbance (magnetic stir bar) to simulate a predator probing the substrate for developing embryos, both chemical and mechanical indicators of risk, or neither (control). We found similar effects in terms of earlier time to hatch at an earlier stage of development and poorer swimming performance of hatchling larvae. In the second experiment, these effects occurred in response to mechanical disturbance with or without the presence of chemical alarm cues. Alarm cues alone produced no effects in the second experiment. Taken together, these data indicate that zebrafish embryos demonstrate a facultative trade-off between risk of predation acting on two stages of their life history.

Level-dependent effects of predation stress on prey development, lifespan and reproduction in mites

In predator-prey interactions, non-consumptive effects of predators have been less studied than consumptive effects. However, non-consumptive effects may have significant influences on prey and can change different aspects of their life history such as development, reproduction and lifespan. The odour and other cues associated with a predator, without direct contact, could induce stress in prey, leading to phenotypic changes in life history traits. In this study, we investigate how mild and strong predator-induced stress could affect prey life history. The prey (Tyrophagus putrescentiae) was exposed, from hatching to death, to three different levels of predation stress from its predator (Neoseiulus cucumeris) (1, 3 or 5 predator adults in an adjacent cage separated by a mesh screen). Compared with the control, both males and females under predator-induced stress had longer developmental time and shorter lifespan when the level of predation stress increased, showing significant level-dependence. In addition, females had reduced fecundity under predation stress. Sex-specific response to predation stress was observed under a low level of predation stress: females had greater reduction in lifespan than males. Furthermore, the reduction in female lifespan was due more from the decrease in the post-oviposition period than the decrease in the oviposition period. Future studies applying even milder levels of predation press, such as exposure of prey to predator cues only during part of the prey lifespan, may provide additional insights.

Intersexual differences in the number of genes differentially expressed in wild mammals in response to predation risk

Predation is a psychological stressor in prey animals. Besides direct killing and consumption by predators, the perception of predation risk indirectly influence prey population behavior, dynamics and physiology. Few studies identified the transcriptomic response associated with predator presence/abundance in natural populations and uncontrolled settings. However, to our knowledge, intersexual differences in the number of genes whose expression change in response to high predation risk have not been previously reported in wild mammals. Here, by using publicly available gene expression data in wild yellow-bellied marmots (Marmota flaviventer), we found that the number of differentially expressed genes in response to predator stress is higher in female marmots (n = 516) than males (n = 387). Only a small percentage of these differentially expressed genes (n = 36) are shared between the sexes, and that the most of the differentially expressed genes are expressed in a sex-specific manner in response to predation stress. Overall, our results provide new insight into sex-specific variation in gene expression changes in wild mammals under high predation risk.

Perceived predation risk predicts glucocorticoid hormones, but not reproductive success in a colonial rodent

The Cort-Adaptation hypothesis suggests that elevated glucocorticoids (GCs) can facilitate an adaptive response to environmental and physiological challenges. Most previous studies have focused on avian species, which may limit their generalizability to mammals, where lactation is known to be a major physiological challenge. Furthermore, the effect of predation risk on GC levels has not been tested in the Cort-Adaptation hypothesis. We sought to test this hypothesis in a colonial prey species, black-tailed prairie dogs (Cynomys ludovicianus). We predicted that individuals located near fewer neighboring conspecifics would perceive an increased risk of predation and, in turn, have increased GCs (measured through hair cortisol concentration (HCC)) and reduced annual reproductive success compared to more centrally located individuals. We also investigated other putative influences on HCC: age, lactation status, body condition, and season of hair growth. Levels of vigilance behavior were higher for those with fewer neighboring conspecifics, suggesting variation in perceived risk of predation. Further, the risk of predation appeared to represent a chronic, detrimental stressor as evidenced by a significant increase in HCC for prairie dogs with fewer neighbors. Lactation status and season also influenced HCC. We found support for the Cort-Adaptation hypothesis where increased HCC during the reproductive season correlated with whether a female produced a litter, but not litter size, suggesting a minimum threshold of GCs is required for successful reproduction in this species. Our work illustrates that HCC may operate as an indicator of perceived predation risk, but care should be taken to consider the variety of factors influencing GC homeostasis, in particular lactation, when drawing conclusions using HCC as a marker of long-term stress.

Cat colonies and flight initiation distances of urban birds: Dealing with conflicting sources of citizen wellbeing

Feral cat colonies in cities improve the wellbeing of people who feed and care for them, but they can have negative effects on biodiversity due to the predatory behaviour of cats. We analyse the effect of the presence of the 1171 colonies of feral cats reported for the city of Madrid (Spain) on the flight escape distances (FIDs) of birds to approaching human observers under standardized conditions. Location of cat colonies was obtained from maps maintained by the city authorities. The FID is a behavioural trait that integrates effects on bird's fearfulness of exposure to predation, disturbance, and physiological and reproductive needs. Shorter flight distances are associated with less exposure to predators and disturbance and better access to food and mates. Shorter FIDs are also associated to higher abundances and more positive population trends, at least in Spain. Mean FIDs of 694 birds of 34 species measured in nine city areas in the spring of 2021 were 10% longer in zones with colonies of feral cats than in neighbouring paired zones without colonies but similar regarding other factors potentially affecting FIDs (i.e. urban landscape structure). Birds were 33% higher above ground in zones with colonies, with no significant effects of perching higher on bird fleeing behaviour. Cat colonies were therefore increasing the fearfulness of individual birds and, presumably, downgraded their population trends. Compromising bird conservation with wellness effects of cat colonies on citizens at the city scale will thus imply the maintenance of colony-free areas, especially for ground-foraging birds. In addition, provision of perches for its use as temporal refuges around colonies might reconcile positive and negative effects at local scales.

Variable stoichiometric and macronutrient responses to lizard predation in Ozark glade grasshopper communities

The General Stress Paradigm (GSP) predicts that prey body compositions should shift under chronic predation as prey increase body carbon and decrease body nitrogen content through dietary changes, heightened metabolism, reduced dietary efficiency, and the breakdown of nitrogen rich tissues to make labile carbohydrates available. In our study, we explored how the elemental and macronutrient content along with the morphology of three abundant Ozark glade grasshopper species differed between glades with and without predatory collared lizard (Crotaphytus collaris) populations. Our results indicated that lichen grasshoppers (Trimerotropis saxatilis) increased body C:N ratios in response to predators. Scudder's short-wing grasshoppers (Melanoplus scudderi) increased both body %C and %protein content, while the handsome grasshoppers (Syrbula admirabilis) did not significantly respond to the presence of collared lizards. None of the three grasshopper species showed morphological responses to predation. We also found that elemental and macronutrient content of grasshoppers was not always significantly correlated and was not associated with the same environmental factors, indicating a need to incorporate both perspectives in future research and utilize more accurate macromolecular assays. Overall, we found support for some aspects of the GSP in field-active animals and add to the growing body of evidence that predator-induced changes in prey body composition are more complex than predicted by the original GSP.

Disturbance cues function as a background risk cue but not as an associative learning cue in tadpoles

Chemical information has an important role in the sensory ecology of aquatic species. For aquatic prey, chemical cues are a vital source of information related to predator avoidance and risk assessment. For instance, alarm cues are released by prey that have been injured by predators. In addition to providing accurate information about current risk, repeated exposure to alarm cues can elicit a fear response to novel stimuli (neophobia) in prey. Another source of chemical information is disturbance cues, released by prey that have been disturbed or harassed (but not injured) by a predator. While disturbance cues have received much less attention than alarm cues, they appear to be useful as an early warning signal of predation risk and have the potential to be used as a priming cue for learning. In this study, we used wood frog (Lithobates sylvaticus) tadpoles to test whether repeated exposure to disturbance cues during the embryonic stage can induce neophobic behaviour. Three weeks following repeated exposure to disturbance cues, tadpoles showed reduced activity when exposed to a novel odour, but they no longer displayed an antipredator response to disturbance cues. In a second experiment, we found that tadpoles failed to learn that a novel odour was dangerous following a pairing with disturbance cues, whereas alarm cues facilitated such learning. Our results add to the growing body of information about disturbance cues and provide evidence of their function as an embryonic risk cue but not as an associative learning cue.

Risk Odors Deriving from Predator Abdominal Gland Secretions Mediate Non-Consumptive Effects on Prey

Prey can detect the presence of predators by predator-released cues and then flexibly alter their phenotypical traits to mitigate the risk, thus non-consumptive effects emerge. Non-consumptive effects have been widely studied in many ecosystems, however, the mechanisms underlying these effects are poorly understood, leaving questions as to the nature of the risk cues and how prey detect the predator. Here, we used a Y-tube olfactometer to examine whether small brown planthoppers, Laodelphax striatellus (Fallén), could detect the presence of rove beetles (Paederus fuscipes Curtis) via odor from rove beetle abdominal gland secretion. We further identified the chemicals of abdominal gland secretion by gas chromatography-mass spectrometry. Chemicals identified were exposed to a planthopper to test their effects on planthopper behavior. Female or male planthoppers could distinguish the predation risk odors of rove beetle or rove beetle abdominal gland secretion from odor without predation risks. Through gas chromatography-mass spectrometry, sixteen of the most abundant chemicals were found in female and male abdominal gland secretion. Five of them (n-undecane, n-pentadecane, n-hexadecane, n-eicosane, and n-heneicosane) individually or collectively reduced the activity level of planthoppers. These findings enhance our understanding of the role of abdominal gland secretion in mediating non-consumptive predator effects, with significant implications for pest management, and the evolution of chemical signals.

Surrounded by challenges: The simulated presence of competitors and predators modulates perianal secretion marking behaviour in the European mink (Mustela lutreola)

Animals face a variety of daily challenges to their reproduction and survival that can detect in time through to the environment cues. By using an individual focal sampling, we evaluated the variations in the time devoted to the perianal secretion marking behaviour (PSMB) of European mink when they were exposed to the simulated presence of conspecifics and two potential predators. Model results indicated that males and adult individuals dedicated more time to PSMB than females and subadults. The presence of conspecifics increased PSMB time only in adult and males, probably as an intrasexual territorial competence response. The heightened decrease in PSMB time in presence of a dog suggests an innate response due to the detection of volatile substances from faeces of carnivorous. In addition, simulated conspecific presence increased PSMB in absence of odours (control) and with owl faeces. However, when facing dog faeces, the simulated conspecific presence had no effects on PSMB. Thus, minks seem to prioritize the imminent risk of predation to avoid being detected. The stimulation of PSMB in captivity by simulated cues from conspecifics and potential predators could be useful to facilitate the reintroduction of individuals into nature, as well as their adaptation and survival.

Shade affects magnitude and tactics of juvenile Chinook salmon antipredator behavior in the migration corridor

Environmental conditions strongly affect antipredator behaviors; however, it is less known how migrating prey adjust antipredator behavior in migration corridors, in part, because active migrants are difficult to observe and study. Migrants are vulnerable and encounter many predators in the corridor, and their propensity to travel towards their destination ties antipredator behavior with movement. We evaluated how environmental risk cues in the migration corridor including in-water habitat structure (present, absent) and overhead shade (sun, shade), and salmon origin (hatchery, wild) affected how juvenile Chinook salmon (Oncorhynchus tshawytscha) reacted to a live predator. We measured how salmon react to predation risk as the difference in time to swim downstream through a 9.1-m long field enclosure with or without a live predatory largemouth bass (Micropterus salmoides). Shade significantly modified the reaction to the predator, and it did so in two ways. First, the magnitude of antipredator behavior was larger in shade compared to direct sun, which suggests salmon perceived shade to be a riskier environment than sun. Second, the escape tactic also varied; salmon slowed down to be cautious in shade and sped up in sun. Structure did not significantly affect behavior and hatchery and wild salmon behaved similarly. Our study suggests that environmental risk cues can shape the magnitude and tactics of how migrants react to predation risk and illustrates how these responses relate to movement with potential to scale up and affect migration patterns.

Habituation in anuran tadpoles and the role of risk uncertainty

The ability to learn in the context of predation allows prey to respond to threats by adjusting their behavior based on specific information acquired from their current environment. Habituation is a process that allows animals to adapt to environmental changes. Very little is known about habituation in wild animals in general and there are no studies on habituation in anuran tadpoles in particular. Here, we performed three experiments to investigate the behavioral response of predator naïve Pleurodema thaul tadpoles to repeated stimulation with two predation risk cues (injured conspecific and predator fed cues) which a priori provide different information regarding risk. Experiment 1 showed that P. thaul tadpoles habituate the antipredator response when undergo predation risk chemical cues from injured conspecific and that response is long term. Experiment 2 showed that P. thaul tadpoles did not habituate their antipredator response when exposed to cues derived from an event of nymph odonate preying on P. thaul tadpoles (predator fed cues). Experiment 3 specifically evaluated the risk imposed by each of the risk cues used in Experiment 1 and Experiment 2 and showed that the degree of perceived risk in tadpoles appear to be similar in a single experience with any risk stimuli. We suggest that the behavioral habituation of tadpoles in the context of predation could be modulated by the level of uncertainty associated with risk stimuli.

Responses to predation risk cues and alarm pheromones affect plant virus transmission by an aphid vector

Herbivores assess predation risk in their environment by identifying visual, chemical, and tactile predator cues. Detection of predator cues can induce risk-avoidance behaviors in herbivores that affect feeding, dispersal, and host selection in ways that minimize mortality and reproductive costs. For herbivores that transmit plant pathogens, including many aphids, changes in herbivore behavior in response to predator cues may also affect pathogen spread. However, few studies have assessed how aphid behavioral responses to different types of predator cues affect pathogen transmission. Here, we conducted greenhouse experiments to assess whether responses of pea aphids (Acyrthosiphon pisum) to predation risk and alarm pheromone (E-β-Farnesene), an aphid alarm signal released in response to predation risk, affected transmission of Pea enation mosaic virus (PEMV). We exposed A. pisum individuals to risk cues, and quantified viral titer in aphids and pea (Pisum sativum) host plants across several time periods. We also assessed how A. pisum responses to risk cues affected aphid nutrition, reproduction, and host selection. We show that exposure to predator cues and alarm pheromone significantly reduced PEMV acquisition and inoculation. Although vectors avoided hosts with predator cues, predator cues did not alter vector reproduction or reduce nutrient acquisition. Overall, these results suggest that non-consumptive effects of predators may indirectly decrease the spread of plant pathogens by altering vector behavior in ways that reduce vector competence and pathogen transmission efficiency.

The microbiome mediates the interaction between predation and heavy metals

Gut microbiota communities are fundamental ecological components in the aquatic food web. Their potential to mediate how organisms respond to multiple environmental stressors remains understudied. Here we explored how manipulations of the gut microbiome of Daphnia pulex, a keystone species in aquatic communities, influenced life history (size at maturity, age at maturity, somatic growth rate and clutch size), morphology (induced defence) and body condition (lipid status deposits) responses to combined anthropogenic (copper) and natural (predation risk) stress. Data from a factorial experiment revealed that the effect of predation risk on traits was often mediated by copper (predation risk and copper interact). These patterns align with theory linking predation risk and copper contamination via digestive physiology. We also found that each stressor, and their combination, was associated with the same community composition of the D. pulex microbiome. However, antibiotic manipulation of the microbiome reversed 7/12 the trait responses across life history, morphology and body condition. This was associated with dramatically different communities to control conditions, with clear and unique patterns of microbiome community composition for each stressor and their combination. Our study revealed that microbiome community composition is highly correlated with the response of organisms to multiple, simultaneous stressors.

Toxic Microcystis aeruginosa alters the resource allocation in Daphnia mitsukuri responding to fish predation cues

Many prey organisms adaptively respond to predation risk by inducible defenses with underlying tradeoffs in resource allocation. Cyanobacterial blooms expose zooplankton to poor food conditions, affecting the herbivores' fitness. Given the interferences on resources allocation and life history traits, poor-quality cyanobacteria are predicted to affect the adaptive predator-induced responses in zooplankton. Here, we exposed two clones (i.e., clones SH and ZJ) of the cladoceran Daphnia mitsukuri to different combinations of fish predation cues and diets containing toxic Microcystis aeruginosa (0%-30%). D. mitsukuri matured at a small size and had elongated relative tail spine as adaptive responses to fish cues. Despite the comparable tail spine defense, fish cue-induced changes in growth and reproduction in the clone SH were more pronounced than those in the clone ZJ under no M. aeruginosa. Animals accumulated microcystin in the whole body with increasing abundance of M. aeruginosa. However, the inducible enhanced tail spine allometry was not affected, resulting in unchanged tail spine defense by Daphnia under all M. aeruginosa treatments. By contrast, M. aeruginosa remarkably decreased the adaptive maturation size and the offspring number in all animals. However, the inducible reproductive effort tended to increase or remain unchanged depending on clones associated with the constant or decreased responses of the somatic growth effort under increasing M. aeruginosa. Our results suggested that toxic M. aeruginosa did not alter the resource allocation to antipredator morphological defense but affected the somatic growth and reproduction in D. mitsukuri under fish cues. The present study highlights the different effects of toxic cyanobacteria on adaptive predator-induced responses in zooplankton, promoting the understanding for the morphological defense-mediated predator-prey interactions in eutrophic environments.

Fall supplemental feeding increases population growth rate of an endangered caribou herd

Most woodland caribou (Rangifer tarandus caribou) populations are declining primarily because of unsustainable predation resulting from habitat-mediated apparent competition. Wolf (Canis lupus) reduction is an effective recovery option because it addresses the direct effect of predation. We considered the possibility that the indirect effects of predation might also affect caribou population dynamics by adversely affecting summer foraging behaviour. If spring and/or summer nutrition was inadequate, then supplemental feeding in fall might compensate for that limitation and contribute to population growth. Improved nutrition and therefore body condition going into winter could increase adult survival and lead to improved reproductive success the next spring. To test that hypothesis, we fed high-quality food pellets to free-ranging caribou in the Kennedy Siding caribou herd each fall for six years, starting in 2014, to see if population growth rate increased. Beginning in winter 2015–16, the Province of British Columbia began a concurrent annual program to promote caribou population increase by attempting to remove most wolves within the Kennedy Siding and the adjacent caribou herds’ ranges. To evaluate the impact of feeding, we compared lambdas before and after feeding began, and to the population trend in the adjacent Quintette herd over the subsequent four years. Supplemental feeding appeared to have an incremental effect on population growth. Population growth of the Kennedy Siding herd was higher in the year after feeding began (λ = 1.06) compared to previous years (λ = 0.91) and to the untreated Quintette herd (λ = 0.95). Average annual growth rate of the Kennedy Siding herd over the subsequent four years, where both feeding and wolf reduction occurred concurrently, was higher than in the Quintette herd where the only management action in those years was wolf reduction (λ = 1.16 vs. λ = 1.08). The higher growth rate of the Kennedy Siding herd was due to higher female survival (96.2%/yr vs. 88.9%/yr). Many caribou were in relatively poor condition in the fall. Consumption of supplemental food probably improved their nutritional status which ultimately led to population growth. Further feeding experiments on other caribou herds using an adaptive management approach would verify the effect of feeding as a population recovery tool. Our results support the recommendation that multiple management actions should be implemented to improve recovery prospects for caribou.

--Effect of multimodal cues from a predatory fish on refuge use and foraging on an amphidromous shrimp

Background

Prey can alter their behavior when detecting predator cues. Little is known about which sensory channel, number of channels, or the interaction among channels that shrimp species use to evaluate the threat from predators. The amphidromous shrimp Xiphocaris elongata has an induced defense, an elongated rostrum, where predatory fishes are present. We sought to test if kairomones or visual cues when presented singly from fish either eating flakes or shrimp, had more effect on altering the temporal feeding and refuge use patterns of long-rostrum (LR) X. elongata. We were also interested in elucidating potential interactions among cues when presented simultaneously in different combinations (kairomones + visual + mechanosensory, kairomones + alarm + visual, kairomones + alarm, kairomones + visual) on the same response variables. We expected that when presented alone kairomones will significantly increase refuge use and decrease foraging, particularly late at night, in comparison to visual cues alone, and that multiple cues when presented simultaneously will further increase refuge use and decrease foraging at night.

Methods

We exposed shrimp to individual or multiple cues from the predatory fish mountain mullet, Augonostomus monticola. We examined shrimp behavior with respect to refuge use and foraging activity during four time periods (after sunset, nighttime, sunrise, and sunset) in a 24-hour period.

Results

Shrimp presented fish visual and chemical cues singly did not differ from one another but differed from control shrimp (no cues) with respect to refuge use or foraging. The number of shrimp using refuge in the treatment with most cues (KVM: kairomones+ visual + mechanosensory) was higher than in all the treatments with less cues. A significant decline in foraging was observed when multiple cues were presented simultaneously. The highest number of shrimp foraged one hour after sunset and at nighttime. A significant interaction was observed between cue treatments and time periods, with shrimp in the KVM treatment foraging less and using more refuge late at night and at sunrise than shrimp in other treatments or time periods.

Conclusions

The observation that fish chemical and visual cues when presented singly produced similar refuge use and foraging patterns was contrary to expectation and suggests that visual and chemical cues, when presented alone, provide redundant information to X. elongata with regards to predation threat. The significant increase in refuge use and reduction in foraging observed in the KVM treatment suggest multimodal signal enhancement in the perception of threat. This makes evolutionary sense in “noisy” environments, such as streams, where detection, localization, and intention of predators is much improved when cues are received through multiple sensory channels.

Prey and habitat distribution are not enough to explain predator habitat selection: addressing intraspecific interactions, behavioural state and time

BACKGROUND

Movements and habitat selection of predators shape ecological communities by determining the spatiotemporal distribution of predation risk. Although intraspecific interactions associated to territoriality and parental care are involved in predator habitat selection, few studies have addressed their effects simultaneously with those of prey and habitat distribution. Moreover, individuals require behavioural and temporal flexibility in their movement decisions to meet various motivations in a heterogeneous environment. To untangle the relative importance of ecological determinants of predator fine-scale habitat selection, we studied simultaneously several spatial, temporal, and behavioural predictors of habitat selection in territorial arctic foxes (Vulpes lagopus) living within a Greater snow goose (Anser caerulescens atlantica) colony during the reproductive season.

METHODS

Using GPS locations collected at 4-min intervals and behavioural state classification (active and resting), we quantified how foxes modulate state-specific habitat selection in response to territory edges, den proximity, prey distribution, and habitats. We also assessed whether foxes varied their habitat selection in response to an important phenological transition marked by decreasing prey availability (goose egg hatching) and decreasing den dependency (emancipation of cubs).

RESULTS

Multiple factors simultaneously played a key role in driving habitat selection, and their relative strength differed with respect to the behavioural state and study period. Foxes avoided territory edges, and reproductive individuals selected den proximity before the phenological transition. Higher goose nest density was selected when foxes were active but avoided when resting, and was less selected after egg hatching. Selection for tundra habitats also varied through the summer, but effects were not consistent.

CONCLUSIONS

We conclude that constraints imposed by intraspecific interactions can play, relative to prey distribution and habitat characteristics, an important role in the habitat selection of a keystone predator. Our results highlight the benefits of considering behavioural state and seasonal phenology when assessing the flexibility of predator habitat selection. Our findings indicate that considering intraspecific interactions is essential to understand predator space use, and suggest that using predator habitat selection to advance community ecology requires an explicit assessment of the social context in which movements occur.

Behaviorally-mediated trophic cascade attenuated by prey use of risky places at safe times

The mere threat of predation may incite behavioral changes in prey that lead to community-wide impacts on productivity, biodiversity, and nutrient cycling. The paucity of experimental manipulations, however, has contributed to controversy over the strength of this pathway in wide-ranging vertebrate systems. We investigated whether simulated gray wolf (Canis lupus) presence can induce behaviorally-mediated trophic cascades, specifically, whether the 'fear' of wolf olfactory cues alone can change deer foraging behavior in ways that affect plants and soils. Wolves were recently removed from the Cedar Creek Ecosystem Science Reserve (Minnesota, USA), such that consumptively mediated predator effects were negligible. At 32 experimental plots, we crossed two nested treatments: wolf urine application and herbivore exclosures. We deployed camera traps to quantify how white-tailed deer (Odocoileus virginianus) adjusted their spatiotemporal habitat use, foraging, and vigilance in response to wolf cues and how these behavioral changes affected plant productivity, plant communities, and soil nutrients. Weekly applications of wolf urine significantly altered deer behavior, but deer responses did not cascade to affect plant or soil properties. Deer substantially reduced crepuscular activity at wolf-simulated sites compared to control locations. As wolves in this area predominantly hunted during mornings and evenings, this response potentially allows deer to maximize landscape use by accessing dangerous areas when temporal threat is low. Our experiment suggests that prey may be sensitive to 'dynamic' predation risk that is structured across both space and time and, consequentially, prey use of risky areas during safe times may attenuate behaviorally-mediated trophic cascades at the predator-prey interface.

Does global warming intensify cost of antipredator reaction? A case study of freshwater amphipods

Global warming is a worldwide phenomenon affecting the functioning of diverse ecosystems, including fresh waters. Temperature increase affects physiology and behaviour of ectotherms due to growing energetic demands necessary to sustain increased metabolic rate. Anti-predator responses may resemble temperature-induced changes in organisms, suggesting synergism between these factors. To check how temperature shapes physiological and behavioural responses of ectotherms to predation risk, we exposed amphipods: Dikerogammarus villosus and Gammarus jazdzewskii to fish kairomones at 10, 17 or 24 °C. Animals were placed in tanks where temperature was gradually adjusted to the desired test temperature and acclimated under such conditions for 3 subsequent days. Then they were exposed to the predator cue (the Eurasian perch kairomone) for 35 min to test their acute responses. We measured metabolic rate (as respiration), antioxidant defence (CAT: catalase activity, TAS: total antioxidant status), oxidative molecules (TOS: total oxidative status), oxidative damage (TBARS: thiobarbituric acid reactive substances) and behaviour (locomotor activity). Amphipods increased respiration with raising temperature and when exposed to predation risk (all temperatures). Only G. jazdzewskii exhibited increased TOS when exposed to 24 °C or to predation risk at all temperatures. Antioxidant defence increased with raising temperature (CAT, TAS) and decreased under predation risk (CAT). Cellular damage increased in G. jazdzewskii under predation risk at 10 and 24 °C, but raised temperature itself did not generate any damage. Amphipods reduced locomotor activity at 24 °C. Thus, at elevated temperatures, amphipods minimized their cellular damage at the cost of increased antioxidant defence and lower locomotor activity (potentially disadvantageous under higher energetic demands). Under predation risk, the performance of antioxidant systems was reduced, probably due to energy allocation into anti-predatory mechanisms, leading to increased cellular damage at suboptimum temperatures. Thus, negative consequences of elevated temperature for organisms may be amplified by changes in behaviour (compromising food acquisition) and non-consumptive predator effects.

Among-individual differences in foraging modulate resource exploitation under perceived predation risk

Foraging is risky and involves balancing the benefits of resource acquisition with costs of predation. Optimal foraging theory predicts where, when and how long to forage in a given spatiotemporal distribution of risks and resources. However, significant variation in foraging behaviour and resource exploitation remain unexplained. Using single foragers in artificial landscapes of perceived risks and resources with diminishing returns, we aimed to test whether foraging behaviour and resource exploitation are adjusted to risk level, vary with risk during different components of foraging, and (co)vary among individuals. We quantified foraging behaviour and resource exploitation for 21 common voles (Microtus arvalis). By manipulating ground cover, we created simple landscapes of two food patches varying in perceived risk during feeding in a patch and/or while travelling between patches. Foraging of individuals was variable and adjusted to risk level and type. High risk during feeding reduced feeding duration and food consumption more strongly than risk while travelling. Risk during travelling modified the risk effects of feeding for changes between patches and resulting evenness of resource exploitation. Across risk conditions individuals differed consistently in when and how long they exploited resources and exposed themselves to risk. These among-individual differences in foraging behaviour were associated with consistent patterns of resource exploitation. Thus, different strategies in foraging-under-risk ultimately lead to unequal payoffs and might affect lower trophic levels in food webs. Inter-individual differences in foraging behaviour, i.e. foraging personalities, are an integral part of foraging behaviour and need to be fully integrated into optimal foraging theory.

Effect of nest age and habitat variables on nest survival in Marsh Harrier (Circus aeruginosus) in a fishpond habitat

Background

One important anti-predator strategy adopted by birds involves nest site selection and timing of breeding. Nest-site selection by marsh-nesting birds often involves nest concealment and water depth as key features influencing nest survival. Marsh Harrier (Circus aeruginosus) is an obligate ground nester, which sets it apart from other raptors. The aim of the present study was to identify for the first time possible temporal and habitat factors affecting nest survival in Marsh Harrier. Understanding features which affect nest survival are essential for assessing relevant conservation strategies.

Methods

To understand the relative contributions of different temporal and habitat variables to brood losses, it is useful to determine the daily survival rate (DSR). We examined 82 Marsh Harrier nests located on fishponds in eastern Poland, where predation is the main cause of nest loss. Six habitat variables were measured for each active nest. DSR was calculated using known-fate models with the RMark package.

Results

The best-supported model predicted that DSR decreased with nest age and was positively affected by the water depth and the diameter of reed stems, but not by the height or density of vegetation at the nest site. The distances of nests to the fishpond dyke and to open water received no support in the models. The chances of nest survival were lower if a neighbouring nest had been depredated. This result suggests that the Marsh Harrier is more susceptible to mammalian than avian predation and confirms the high level of predator pressure in fishpond habitats.

Bigger doesn't mean bolder: behavioral variation of four wild rodent species to novelty and predation risk following a fast-slow continuum

Background

Understanding how wild species respond to novel situations with associated risk can provide valuable insights for inter-specific behavioral variation and associations with pace-of-life (POL). Rodents, a globally distributed and diverse taxonomic group, have been the subjects of countless studies emulating risky situations. Controlled laboratory experiments with a focus on wild-caught species provide the opportunity to test fine-scale behavioral responses to contexts of risk with ecological implications. For example, assessing the importance of predator cues eliciting antipredator responses, as well as whether wild rodents embody behavioral plasticity and repertoires, illustrated by habituation and variation in behavioral traits, respectively.

Results

In this comparative study, we examined multiple behavioral responses of four rodent species in eastern Taiwan (three native species Mus caroli, Apodemus agrarius, Rattus losea, and one invasive, Rattus exulans) exposed to an unfamiliar microenvironment and novel cue from an allopatric predator, the leopard cat (Prionailurus bengalensis). All wild-caught animals were subjected to two consecutive nights of experimental trials in a laboratory setting. Behavioral responses to a novel situation during the first trial differed between species; smaller species investing more time in non-defensive behaviors compared to the larger species. More specifically, the smaller species M. caroli and A. agrarius allocated more time to exploration and foraging, whereas the larger rat species R. exulans and R. losea spent more time motionless or concealing. During the second trial, the addition of leopard cat cues did not elicit antipredator behaviors, but rather, rodents were found to exhibit increased non-defensive behaviors, specifically foraging efforts.

Conclusions

Our results suggest that these four species do largely follow a behavioral fast-slow continuum with the two smaller mice species demonstrating increased boldness in a novel context compared to the larger rat species. Also, the wild populations of rodents in eastern Taiwan may be naïve to leopard cats. Finally, the rodents in our study demonstrated habituation to the microenvironment, indicating they possess adaptive capacity.

Shifts in foraging behaviour of heterospecific flocking birds in a lowland Malaysian rainforest

Mixed-species flocks (MSFs) serve important roles in bird communities, especially in tropical forests. Although structure of mixed-species bird flocks and its benefits has been intensively studied globally, the foraging plasticity of a species when joining MSFs has rarely been evaluated. The present study examines foraging strategies of the Rufous-crowned Babbler (Malacopteron magnum), Chestnut-winged Babbler (Cyanoderma erythropterum) and Black-naped Monarch (Hypothymis azurea) when participating in MSFs in the Krau Wildlife Reserve, central Peninsular Malaysia. These species exhibit active foraging shifts in utilisation of vertical strata, foraging substrate, attack manoeuvres and foliage density, when foraging in MSFs, compared to when foraging outside MSFs. While the Rufous-crowned Babbler and Chestnut-winged Babbler commonly used gleaning and stretching (to completely extend the legs or neck to reach the food items) manoeuvres when foraging outside MSFs, respectively, they adopted probing manoeuvre and frequently used higher strata upon joining MSFs. The Chestnut-winged Babbler tended to forage on the underside of leaves and the Black-naped Monarch frequently utilised branches when joining MSFs, while they exclusively used aerial leaf litter and live green leaves, respectively, when foraging with conspecifics. The monarch also adopted the hovering manoeuvre and frequently foraged within denser foliage cover when joining MSFs. This study demonstrated that flock members exhibits foraging plasticity either through an expansion or active shift in foraging niches when participating in MSFs, thus suggesting the occurrence of possible foraging improvement and/or reductions in predation risk.

For emergency only: terrestrial feeding in Coimbra-Filho's titis reflects seasonal arboreal resource availability

Terrestriality in Platyrrhine primates is primarily associated with low arboreal resource availability, low predation risk when on the ground and increased contact time with human observers. To test the relationship between these variables and ground use frequency, we studied a group of endangered Coimbra-Filho's titi monkeys (Callicebus coimbrai) in a 14-ha forest fragment in north-eastern Brazil. Terrestriality data were collected on a monthly basis (33 months) using scan sampling procedures from July 2008 to July 2012. Overall, Coimbra-Filho's titi monkeys were recorded during 0.6% of observation time (113 out of 18,164 scans) on the ground. Most of the time on the ground was spent feeding on young leaves (71 records) and the least amount of time on fruits (14 records). Availability of arboreal foods, rainfall, and time of contact with human observers did not influence overall terrestrial behaviour (ground use). However, the timing and nature of the monkeys' terrestrial feeding was strongly related to the absence of arboreal fruit (β-estimate = -3.078) and young leaf (β-estimate = -3.515) food resources. We suggest that terrestrial feeding by Coimbra-Filho's titi monkeys could be an adaptation to low arboreal fruit availability and the exploitation of alternative food resources.

Chronic exposure to a pervasive pharmaceutical pollutant erodes among-individual phenotypic variation in a fish

Pharmaceutical pollution is now recognised as a major emerging agent of global change. Increasingly, pharmaceutical pollutants are documented to disrupt ecologically important physiological and behavioural traits in exposed wildlife. However, little is known about potential impacts of pharmaceutical exposure on among-individual variation in these traits, despite phenotypic diversity being critical for population resilience to environmental change. Furthermore, although wildlife commonly experience multiple stressors contemporaneously, potential interactive effects between pharmaceuticals and biological stressors-such as predation threat-remain poorly understood. To redress this, we investigated the impacts of long-term exposure to the pervasive pharmaceutical pollutant fluoxetine (Prozac®) on among-individual variation in metabolic and behavioural traits, and the combined impacts of fluoxetine exposure and predation threat on mean metabolic and behavioural traits in a freshwater fish, the guppy (Poecilia reticulata). Using a mesocosm system, guppy populations were exposed for 15 months to one of two field-realistic levels of fluoxetine (nominal concentrations: 30 and 300 ng/L) or a solvent control. Fish from these populations were then tested for metabolic rate (oxygen uptake) and behaviour (activity), both before and after experiencing one of three levels of a predation treatment: an empty tank, a non-predatory fish (Melanotaenia splendida) or a predatory fish (Leiopotherapon unicolor). Guppies from both fluoxetine treatments had ∼70% lower among-individual variation in their activity levels, compared to unexposed fish. Similarly, fluoxetine exposure at the higher dosage was associated with a significant (26%) reduction in individual-level variation in oxygen uptake relative to unexposed fish. In addition, mean baseline metabolic rate was disrupted in low-fluoxetine exposed fish, although mean metabolic and behavioural responses to predation threat were not affected. Overall, our study demonstrates that long-term exposure to a pervasive pharmaceutical pollutant alters ecologically relevant traits in fish and erodes among-individual variability, which may be detrimental to the stability of contaminated populations globally.

Effects of artificial light at night on foraging behavior and vigilance in a nocturnal rodent

Artificial light at night has greatly changed the physical environment for many organisms on a global scale. As an energy efficient light resource, light emitting diodes (LEDs) have been widely used in recent years. As LEDs often have a broad spectrum, many biological processes may be potentially affected. In this study, we conducted manipulated experiments in rat-proof enclosures to explore the effects of LED night lighting on behavior of a nocturnal rodent, the Mongolian five-toed jerboa (Allactaga sibirica). We adopted the giving-up density (GUD) method and camera video trapping to study behavioral responses in terms of patch use, searching efficiency and vigilance. With the presence of white LED lighting, jerboas spent less time in patches, foraged less intensively (with higher GUDs) and became vigilant more frequently, while their searching efficiency was higher than under dark treatment. Although both positive and negative effects of LEDs on foraging were detected, the net effect of LEDs on jerboas is negative, which may further translate into changes in population dynamics, inter-specific interaction and community structure. To our knowledge, this is the first field study to explore how LED lighting affect foraging behavior and searching efficiency in rodents. Our results may have potential implications for practices such as pest control.

Proportional fitness loss and the timing of defensive investment: a cohesive framework across animals and plants

The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer-resource interactions (e.g., enemy-victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dilemma of uncertainty of attack, can gather information from the environment to predict future attacks and alter their defensive investment accordingly. Here, we present a novel, unifying framework based on the way an organism's ability to defend itself during an attack can shape their pre-attack investment in defense. This framework provides a useful perspective on the nature of information use and variation in defensive investment across the sequence of attack-related events, both within and among species. It predicts that organisms with greater proportional fitness loss if attacked will gather and respond to risk information earlier in the attack sequence, while those that have lower proportional fitness loss may wait until attack is underway. This framework offers a common platform to compare and discuss consumer effects and provides novel insights into the way risk information can propagate through populations, communities, and ecosystems.

The effect of ecological factors on eye morphology in the western rainbowfish, Melanotaenia australis

Ecological factors such as spatial habitat complexity and diet can explain variation in visual morphology, but few studies have sought to determine whether visual specialisation can occur among populations of the same species. We used a small Australian freshwater fish (the western rainbowfish, Melanotaenia australis) to determine whether populations showed variation in eye size and eye position, and whether this variation could be explained by environmental (light availability, turbidity) and ecological (predation risk, habitat complexity, invertebrate abundance) variables. We investigated three aspects of eye morphology - (1) eye size relative to body size, (2) pupil size relative to eye size and (3) eye position in the head - for fish collected from 14 sites in a major river catchment in northwest Western Australia. We found significant variation among populations in all three measures of eye morphology, but no effect of sex on eye size or eye position. Variation in eye diameter and eye position was best explained by the level of habitat complexity. Specifically, fish occurring in habitats with low complexity (i.e. open water) tended to have smaller, more dorsally located eyes than those occurring in more complex habitats (i.e. vegetation present). The size of the pupil relative to the size of the eye was most influenced by the presence of surrounding rock formations; fish living in gorge habitats had significantly smaller pupils (relative to eye size) than those occupying semi-gorge sites or open habitats. Our findings reveal that different ecological and environmental factors contribute to habitat-specific visual specialisations within a species.

Increased terrestriality in a Neotropical primate living on islands with reduced predation risk

An arboreal lifestyle is thought to be central to primate origins, and most extant primate species still live in the trees. Nonetheless, terrestrial locomotion is a widespread adaptation that has arisen repeatedly within the primate lineage. The absence of terrestriality among the New World monkeys (Platyrrhini) is thus notable and raises questions about the ecological pressures that constrain the expansion of platyrrhines into terrestrial niches. Here, we report the results of a natural experiment, comparing patterns of terrestrial behavior in white-faced capuchin monkeys (Cebus capucinus imitator) living on two islands off the Pacific coast of Panama that lack mammalian predators (island sites) with the behavior of capuchins at three sites in central Panama with more intact predator communities (mainland sites). Surveys with camera traps revealed increased terrestriality in island vs. mainland sites. Capuchin detection rates were higher, the range of party sizes observed was larger, and individuals engaged in a wider range of terrestrial behaviors on the islands lacking mammalian predators. Furthermore, females carrying infants were frequently photographed on the ground at the island sites, but never at the mainland sites. These findings support the long-standing hypothesis that predators constrain the exploitation of terrestrial niches by primates. These results are also consistent with the hypothesis that arboreal locomotion imposes costs that primates will avoid by walking on the ground when predation risk is low.

Design and development of a robotic predator as a stimulus in conditioned place aversion for the study of the effect of ethanol and citalopram in zebrafish

Zebrafish are becoming a species of choice in psychopharmacology, laying a promising path to refined pharmacological manipulations and high-throughput behavioral phenotyping. The field of robotics has the potential to accelerate progress along this path, by offering unprecedented means for the design and development of accurate and reliable experimental stimuli. In this work, we demonstrate, for the first time, the integration of robotic predators in place conditioning experiments. We hypothesized zebrafish to be capable of forming a spatial association under a simulated predation risk. We repeatedly exposed experimental subjects to a robotic heron impacting the water surface and then evaluated their spatial avoidance within the experimental tank in a subsequent predator-free test session. To pharmacologically validate the paradigm, we tested zebrafish in drug-free conditions (control groups) or in response to three different concentrations of citalopram (30, 50, and 100 mg/L) and ethanol (0.25, 0.50, and 1.00%). Experimental data indicate that, when tested in the absence of the conditioning stimulus, zebrafish displayed a marked preference for the bottom of the test tank, that is, the farthest location from the simulated attacks by the robotic heron. This conditioned geotaxis was reduced by the administration of citalopram in a linear dose-response curve and ethanol at the low concentration. Ultimately, our data demonstrate that robotic stimuli may represent valid conditioning tools and, thereby, aid the field of zebrafish psychopharmacology.

Vigilance behaviour in Siberian ibex (Capra sibirica): Effect of group size, group type, sex and age

Gregarious prey species modify their behaviours in response to predation risk in two ways: by increasing vigilance level or enlarging herd size. However, individuals of various sex and age have different responses to the same danger, and even the same individuals react differently depending on their status during biological events or within group types. But how these factors influence the interactions between vigilance level and group size is still poorly understood. Therefore, we studied this phenomenon by observing and analyzing the behaviours of the Siberian ibex (Capra sibirica) in the Eastern Tian-Shan Mountains (China). We found that similar to many other gregarious ungulates, Siberian ibex demonstrated a decrease in vigilance level with an increase in group size, since staying in larger groups increased the probability of predator detection and reduced the possibility of being captured. In general, males were more vigilant than females during the rut due to the sharp increase in their social alertness to achieve greater success in reproduction. In contrast, females were more vigilant than males out of rutting time, particularly significantly following parturition, since mothers spent a lot of their energy in maternal care, which coupled with having small and unexperienced newborns, made them more vulnerable to predation than other conspecifics. Siberian ibex had the same vigilance level in summer and winter, because of seasonally opposite trade-offs between feeding duration and vigilance level based on seasonal changes in food availability. Individuals in mixed-sex and female groups were more often targeted by predators, prompting individuals from these groups to be more vigilant than in male groups. The vigilance level in males decreased with age likely because of their increased body size and enhanced vigilance experience, which reduced their risk of predation. Our study confirmed that the Siberian ibex' vigilance level inversely correlated with group size, but other various factors, such as forage biomass/quality, sex, biological cycle, group types and age, had significant impacts on their interrelationship.

Dynamic rodent behavioral response to predation risk: implications for disease ecology

Prey modify their behavior in response to variation in predation risk, and such modifications can affect trophic processes such as disease transmission. However, variation in predation risk is complex, arising from direct risk from the predator itself and indirect risk due to the environment. Moreover, direct risk typically stems from multiple predators and varies over timescales (e.g., a predator nearby vs. its seasonal activities). We implemented a field-based experiment to disentangle these sources of risk and relate them to antipredator behavior in rodents. We modeled rodent occurrence and activity as a function of short- and long-term risk from a primary predator, red foxes (Vulpes vulpes), long-term risk from a second predator, coyotes (Canis latrans), and environmental variables. We found that long-term red fox activity strongly reduced rodent occurrence and that cues of nearby red fox presence decreased rodent activity by > 50%. In addition, this activity reduction was dynamic in that varied according to the background level of long-term red fox activity. Importantly, rodents did not respond to environmental variables (moonlight, temperature, and habitat) or long-term coyote activity. These results bear upon recent work that suggests predators can alter tick-borne disease dynamics via induced antipredator behavior of rodents, which are hosts for pathogens and ticks. Specifically, our study corroborates the hypothesis that red foxes act as important proximal agents in regulating tick-borne diseases by reducing rodent activity. More generally, this study highlights the need to consider the dynamic nature of prey antipredator response across landscapes with variable long-term predation risk.

Differential antipredatory responses in the tuco-tuco (Ctenomys talarum) in relation to endogenous and exogenous changes in glucocorticoids

Glucocorticoids participate in the behavioral and physiological responses generated under stressful circumstances coming from different sources-physical and/or psychological. In mammals, the increases of these hormones are mediated by the activation of the hypothalamic-pituitary-adrenal axis. This response occurs after exposure to novel and unpredictable situations that lead to the loss of homeostasis, for example, a direct encounter with predators or their cues. However, the relationship between the physiological and behavioral responses is still a complex issue in vertebrates. We evaluate the effects of an experimental manipulation of glucocorticoid levels on the generation of the behavioral and physiological response to stress by predation in the subterranean rodent C. talarum. We found that when tuco-tucos encountered predator cues-fur odor, and largely, immobilization-they responded physiologically by secreting cortisol. This response was accompanied by an associated behavioral response. However, when the increase in plasma cortisol originated exogenously by the injection of cortisol, a behavioral response was not observed. Finally, inhibition of glucocorticoids' synthesis was effective in weakening the behavioral effects produced by immobilization. In conclusion, in tuco-tucos, predator cues act as stress factors that trigger differential increases in plasma cortisol and a behavioral response associated with the appearance of anxiety states.

Gimme shelter: The effect of rocks and moonlight on occupancy and activity pattern of an endangered rodent, the garden dormouse Eliomys quercinus

Information on spatial behaviour and temporal activity patterns is paramount for the conservation of animal species. This is particularly true for endangered taxa that are threatened by ongoing climatic and environmental changes. The garden dormouse Eliomys quercinus is a native European rodent (family Gliridae), whose populations are declining throughout the Continent. Notwithstanding this, neither International nor National laws explicitly require mandatory monitoring of populations. As a result, compelling information on the spatiotemporal behaviour of dormouse is lacking. We aimed to fill this gap by investigating occupancy patterns in relation to environmental features and activity rhythms in relation to moonlit nights in an Alpine population of dormouse within the Stelvio National Park, northern Italy. Data were collected between May and October 2015. Twenty camera-traps were deployed in a 500 ha coniferous forest, using a random tessellation approach; camera trap data were analyzed with occupancy models and kernel smoothers. Camera-traps provided a reliable assessment of the presence of the garden dormouse, with only 1 % of false absence and a high detection probability (68 %). The occurrence of the garden dormouse was positively influenced by the percentage of rock coverage on the ground. The species showed a strictly nocturnal behaviour, with an activity peak before midnight, negatively related to moonlit nights. The use of rocky areas for nesting, shelter site and thigmotactic movements and moonlight avoidance may represent adaptations of the garden dormouse to avoid predation risk. Our results shed some light on the habitat requirement of a poorly known, near-threatened species, and provide baseline information for future monitoring and conservation activities.

nov) is higher in forest-edge microhabitats

How rodents perceive predation risk may alter their seed foraging behaviour and therefore potentially influence the recruitment of tree species. In this study we used two methods to investigate the effect of predation risk on habitat use by the African giant pouched rat (Cricetomys sp. nov) in Ngel Nyaki forest reserve, Nigeria. The first method was 'giving up density' (GUD), an index of perceived risk of predation at an artificial food patch, and the second was the 'spool-and-line' approach, whereby unravelling spools attached to rodent bodies are used to trace their tracks. For our GUD experiment, we chose four major sites in the forest; two representative of core habitat and two at the forest edge. Additionally, three characteristic microsites were used in the GUD experiment: dense understory, open understory and near-burrows. We hypothesised that GUDs would be lower on every succeeding observation day as rats learn to use the food patches, higher GUDs would be observed in the forest edges and open microsites, and rats would show preference for the microhabitats with least exposure to potential predators. In support of our first hypothesis, we found that GUDs were highest on the first experimental nights of every session. We also found that GUDs in the forest edges were higher than GUDs in the forest core. Lower GUDs were observed close to the rat burrows and in dense understory microsites, even though these differences were not statistically significant. Tracking of rat movements using the spool-and-line method overall revealed an even use across microhabitats, with a weak preference for those with logs, dense understory or exposed ground. Overall, our results suggest that vegetation density on a microhabitat scale has little or no effect on the perception of predation risk by African giant pouched rats.

Behaviour and cardiac response to stress in signal crayfish exposed to environmental concentrations of tramadol

Evidence of the ecological and biological impact of pharmaceuticals in surface waters on aquatic organisms is increasing. Tramadol is a synthetic opioid analgesic used to treat chronic and acute pain. To investigate its long-term effects at environmentally relevant levels, we evaluated heart rate (HR) and locomotion of signal crayfish Pacifastacus leniusculus during a 21-day exposure to 1 μg L-1 tramadol followed by 14 days depuration. Locomotion and HR were recorded over a period 30 min before and 30 min after exposure to physiological fluids of an injured conspecific, a natural stressor, four times during the tramadol exposure and four times during depuration. A significant increase in HR following stress induction was found in the majority of tramadol-exposed and control crayfish, as well as significant group-specific HR changes between both groups. Locomotor activity during tramadol treatment differed from that during depuration, in general showing less time spent in locomotion and lower distance moved. The tramadol exposed crayfish exhibited higher velocity during depuration than during the exposure period. Results may suggest a potential shift in prey-predator relationships.

Are there different vigilance strategies between types of social units in Lama guanicoe?

Group vigilance is a cooperative behaviour in social species that reduces individual risk of predation. Lama guanicoe is a social species of camelid performing cooperative vigilance, but little is known about the vigilance behaviour of different social units. We analysed the vigilance behaviour in different types of social units of L. guanicoe, to better understand the complexity of this behaviour. The best supported models for both the frequency of vigilance and the proportion of time vigilant included the type and size of social units as the most important predictors that affect the vigilance behaviour. Solitary males devoted proportionally more time in vigilance behaviour than family, mixed or bachelor groups, whereas females in female groups spent more time vigilant than guanacos in mixed groups. Frequency of vigilance was higher in family individuals and solitary males than in bachelor or mixed groups. It is likely that that in family and females groups, the presence of offspring would increase the vigilance behaviour to detect possible predators. Topography and habitat characteristics that determine the predation risk, affected vigilance behaviour of mixed groups and solitary males. Our results suggest that vigilance behaviour should not be generalized for this species, since there are differences between the types of social units, probably related to intrinsic characteristics of each one and the perception of risk.

Behavioral adjustments to prior predation experience and food deprivation of a common cyprinid fish species vary between singletons and a group

Fish often undergo predation stress and food shortages in nature, and living in groups may provide the ecological benefits of decreased predator risk but the costs of increased food competition. The main aim of the present study was to test whether the behavioral response of qingbo (Spinibarbus sinensis) to predators and/or starvation differed between a singleton and a group. We measured the locomotor activity and distance to a predator and/or food item of prior predator-experienced, starved, double-treated and control qingbo; the qingbo were tested both as singletons and in a group (five individuals). Fish from all groups showed increased activity when tested collectively compared to individually. The predator-experienced fish showed decreased locomotor activity to predators as an antipredator strategy when tested as singletons; however, increased locomotor activity occurred when tested in a group, which might be partially due to the decreased predator risk when living in a group and thus higher levels of boldness. As expected, starvation elicited increased activity indicating increased foraging willingness when tested in a group; however, the difference between starved and normal-fed fish was no longer significant when they were tested as singletons, possibly due to the increased predation risk and decreased food competition when living individually and higher behavioral variation among individual fish than among those in a shoal. Compared with the control fish, the double-treated fish showed no difference in activity when tested both individually and collectively (except a slower speed when tested in a group). The reason for the results from the singletons might be an offset of the effect of predator exposure and starvation. The reason for this difference in the group might be due to the impaired body condition indicated by a slower swimming speed as a consequence of severe stress. The present study demonstrated that behavioral adjustment was closely related to the size of the group, which might be due to differences in the predation risk and food competition.

Chemically induced plasticity in early life history of Palaemon argentinus: are chemical alarm cues conserved within palaemonid shrimps?

Most aquatic animals use infochemicals from both conspecifics and heterospecifics to assess local predation risks and enhance predator detection. Released substances from injured conspecifics and other species (chemical alarm cues) are reliable cues to indicate an imminent danger in a specific habitat and often mediate the development of inducible defenses. Amphibian and fish embryos have been shown to acquire this information while at the embryonic stage of development, in relation to the developing nervous system and sensory development. With the exception of Daphnia, there is no information on chemically mediated responses to alarm cues in embryos of any crustacean groups. Therefore, we tested whether embryo exposure to chemical cues simulating predation on conspecifics or heterospecifics (closely related, non-coexisting species), or a mixture of both, alters embryonic developmental time, size and morphology of the first larval instar in Palaemon argentinus (Crustacea: Decapoda). Embryonic exposure to chemical alarm cues from conspecifics shortened the embryonic developmental time and elicited larger larvae with a longer rostrum. Rostrum length of the first larval instar changed independently of their size, thus elongated rostra can be considered a defensive feature. Embryonic developmental time was not altered by chemical alarm cues from either heterospecifics or the mixed cues treatment; however, exposure to these cues resulted in larger larvae compared with the control group. Chemically induced morphological plasticity in larvae in response to alarm cues from con- and heterospecifics suggests that such cues are conserved in palaemonids shrimps, providing embryos with an innate recognition of heterospecific alarm cues as predicted by the phylogenetic relatedness hypothesis.