Risk Allocation Hypothesis Research Articles

Intensive hunting changes human-wildlife relationships.

Wildlife alter their behaviors in a trade-off between consuming food and fear of becoming food themselves. The risk allocation hypothesis posits that variation in the scale, intensity and longevity of predation threats can influence the magnitude of antipredator behavioral responses. Hunting by humans represents a threat thought to be perceived by wildlife similar to how they perceive a top predator, although hunting intensity and duration varys widely around the world. Here we evaluate the effects of hunting pressure on wildlife by comparing how two communities of mammals under different management schemes differ in their relative abundance and response to humans. Using camera traps to survey wildlife across disturbance levels (yards, farms, forests) in similar landscapes in southern Germany and southeastern USA, we tested the prediction of the risk allocation hypothesis: that the higher intensity and longevity of hunting in Germany (year round vs 3 months, 4x higher harvest/km2/year) would reduce relative abundance of hunted species and result in a larger fear-based response to humans (i.e., more spatial and temporal avoidance). We further evaluated how changes in animal abundance and behavior would result in potential changes to ecological impacts (i.e., herbivory and predation). We found that hunted species were relatively less abundant in Germany and less associated with humans on the landscape (i.e., yards and urban areas), but did not avoid humans temporally in hunted areas while hunted species in the USA showed the opposite pattern. These results are consistent with the risk allocation hypothesis where we would expect more spatial avoidance in response to threats of longer duration (i.e., year-round hunting in Germany vs. 3-month duration in USA) and less spatial avoidance but more temporal avoidance for threats of shorter duration. The expected ecological impacts of mammals in all three habitats were quite different between countries, most strikingly due to the decreases in the relative abundance of hunted species in Germany, particularly deer, with no proportional increase in unhunted species, resulting in American yards facing the potential for 25x more herbivory than German yards. Our results suggest that the duration and intensity of managed hunting can have strong and predictable effects on animal abundance and behavior, with the potential for corresponding changes in the ecological impacts of wildlife. Hunting can be an effective tool for reducing wildlife conflict due to overabundance but may require more intensive harvest than is seen in much of North America.

A tale of two fishes: depth preference of migrating Atlantic salmon smolt and predatory brown trout in a Norwegian lake

To understand the predator–prey interactions during this transitional migration, we tracked 22 Atlantic salmon ( Salmo salar) smolts and their most prevalent predator, brown trout ( Salmo trutta) ( N = 21), and recorded their depth use in a basin of Lake Evanger, Norway, with acoustic telemetry during May 2020. Both salmon smolts (mean ± SD: 3.8 ± 3.3 m) and trout (2.9 ± 1.7 m) were distributed relatively shallow in the lake despite depths in the area largely exceeding 30 m. Both species were deeper at midday and smolts tended to be deeper in the water earlier in the migration, overlapping less with trout early in May, but as daily daylight increased and water temperature warmed vertical distribution of smolts and trout increasingly overlapped. Based on depth traces from the tags, only seven were detected at the end of the lake and confirmed to make it through. Despite the behaviour of the salmon smolts mostly matching with predictions of the risk allocation hypothesis, it seems a large share of the tagged smolts succumbed to predation.

Individual snowshoe hares manage risk differently: integrating stoichiometric distribution models and foraging ecology

Abstract Herbivores making space use decisions must consider the trade-off between perceived predation risk and forage quality. Herbivores, specifically snowshoe hares (Lepus americanus), must constantly navigate landscapes that vary in predation risk and food quality, providing researchers with the opportunity to explore the factors that govern their foraging decisions. Herein, we tested predictions that intersect the risk allocation hypothesis (RAH) and optimal foraging theory (OFT) in a spatially explicit ecological stoichiometry framework to assess the trade-off between predation risk and forage quality. We used individual and population estimates of snowshoe hare (n = 29) space use derived from biotelemetry across three summers. We evaluated resource forage quality for lowbush blueberry (Vaccinium angustifolium), a common and readily available forage species within our system, using carbon:nitrogen and carbon:phosphorus ratios. We used habitat complexity to proxy perceived predation risk. We analyzed how forage quality of blueberry, perceived predation risk, and their interaction impact the intensity of herbivore space use. We used generalized mixed effects models, structured to enable us to make inferences at the population and individual home range level. We did not find support for RAH and OFT. However, variation in the individual-level reactions norms in our models showed that individual hares have unique responses to forage quality and perceived predation risk. Our finding of individual-level responses indicates that there is fine-scale decision-making by hares, although we did not identify the mechanism. Our approach illustrates spatially explicit empirical support for individual behavioral responses to the food quality–predation risk trade-off.

Paternal care effects outweigh gamete-mediated and personal environment effects during the transgenerational estimation of risk in fathead minnows

BackgroundIndividuals can estimate risk by integrating prenatal with postnatal and personal information, but the relative importance of different information sources during the transgenerational response is unclear. The estimated level of risk can be tested using the cognitive rule of risk allocation, which postulates that under consistent high-risk, antipredator efforts should decrease so that individual metabolic requirements can be satisfied. Here we conduct a comprehensive study on transgenerational risk transmission by testing whether risk allocation occurs across 12 treatments that consist of different maternal, paternal, parental care (including cross-fostering) and offspring risk environment combinations in the fathead minnow Pimephales promelas, a small cyprinid fish with alloparental care. In each risk environment, we manipulated perceived risk by continuously exposing individuals from birth onwards to conspecific alarm cues or a control water treatment. Using 2810 1-month old individuals, we then estimated shoaling behaviour prior to and subsequent to a novel mechanical predator disturbance.ResultsOverall, shoals estimating risk to be high were denser during the prestimulus period, and, following the risk allocation hypothesis, resumed normal shoaling densities faster following the disturbance. Treatments involving parental care consistently induced densest shoals and greatest levels of risk allocation. Although prenatal risk environments did not relate to paternal care intensity, greater care intensity induced more risk allocation when parents provided care for their own offspring as opposed to those that cross-fostered fry. In the absence of care, parental effects on shoaling density were relatively weak and personal environments modulated risk allocation only when parental risk was low.ConclusionsOur study highlights the high relative importance of parental care as opposed to other information sources, and its function as a mechanism underlying transgenerational risk transmission.

Short-term predation risk and habitat complexity influence cheetah antipredator behaviours

Animals can reduce predation risk by increasing antipredator behaviours in areas of high long-term risk (risky places hypothesis), escalating antipredator behaviours when exposed to immediate risks (risky times hypothesis), varying responses to short-term risk based on long-term risk (risky times and risky places hypothesis, or predation risk allocation hypothesis) or altering antipredator behaviours based on habitat characteristics (habitat complexity risk mediation hypothesis). Most research on responses to predation risk has come from studies on herbivore prey, whereas little research has focused on mesopredator behavioural responses to risk. We studied antipredator behaviours of mesopredator cheetahs, Acinonyx jubatus , exposed to top predator risk from lions, Panthera leo , and leopards, Panthera pardus , by using a playback experiment to manipulate short-term predation risk in areas of differing long-term risk. We did not find support for the risky places hypothesis; cheetah vigilance was not influenced by long-term risk. On the contrary, we found support for the risky times hypothesis; cheetahs were more vigilant and more likely to flee following lion and leopard playbacks. Additionally, we did not find support for the risky times and risky places hypothesis or the predation risk allocation hypothesis; cheetah antipredator behaviours following a predator playback were not associated with long-term predation risk. Finally, cheetahs had higher baseline vigilance in areas of open vegetation but were more likely to flee from lion sounds in areas of dense vegetation and from leopards in areas of open vegetation. We highlight the importance of understanding spatial and temporal factors that influence mesopredator risk perception and show that antipredator behaviours can differ among trophic levels. • Cheetahs vary antipredator behaviours based on short-term risk and habitat features. • Cheetahs increased vigilance and were likely to flee following predator playbacks. • Long-term risk of encountering top predators did not influence cheetah vigilance. • Cheetahs were more likely to flee from leopard playbacks in open habitats. • Cheetahs were more likely to flee from lion playbacks in dense vegetation.

Do pastoralist cattle fear African lions?

Fear of predators fundamentally shapes the ecology of prey species and drives both inter‐ and intra‐specific interactions. Extensive research has examined the consequences of predation risk from large carnivores on the behavior of wild ungulate prey species. However, many large carnivores not only hunt wild prey but also depredate domestic livestock, especially in pastoralist systems where livestock share land and resources with large carnivores. Northern Tanzania is a hotspot for human–carnivore conflict driven by livestock depredation and interactions are particularly severe between African lions Panthera leo and pastoralist cattle Bos taurus. In this ecosystem, we explored the degree to which pastoralist cattle exhibited anti‐predator behaviors during their daily grazing routines. Using focal animal sampling, we compared two typical anti‐predator behaviors, vigilance and grouping, among cattle in village rangelands with high and low background depredation rates. We found that cattle in high risk village rangelands formed 21.2% larger groups than cattle in low risk village rangelands. Interestingly, cattle in low risk village rangelands spent 68.4% more time vigilant than cattle in high risk village rangelands. These patterns were influenced significantly by the time of day: as sunset approached, cattle in low risk village rangelands spent more time vigilant and cattle in high risk village rangelands formed larger groups. These results suggest that pastoralist cattle exhibit anti‐predator strategies that vary both spatially and temporally, and that such strategies might help livestock optimally tradeoff the costs and benefits of anti‐predator behavior across timescales (i.e. the risk allocation hypothesis). We discuss the implications of our results for husbandry techniques that might reduce behavioral costs associated with cattle anti‐predator behaviors and help increase tolerance for lions and other large carnivores. These improvements are critical to human–carnivore coexistence given the prevalence of pastoralism globally and the rising potential for conflict with large carnivores such as lions.

Exposure to eagle owl feces induces anti-predator behavior, physiology, and hypothalamic gene responses in a subterranean rodent, the plateau zokor (Eospalax baileyi)

Predator odors are natural stressors that induce anti-predator defensive responses, which have developed under evolutionary pressures to maximize the fitness of an individual to avoid dangerous confrontations. In this study, we analyzed the defensive responses of a subterranean rodent species, the plateau zokor (Eospalax baileyi), to predation threat, and examined the trade-offs between defensive responses and foraging. Plateau zokors were exposed to 1, 3, and 6 g of eagle owl (Bubo bubo) feces, and the anti-predator behavioral, hormonal, and hypothalamic corticotropin-releasing factor and c-fos mRNA expression responses were analyzed and compared with the control (distilled water). Exposure of the animals to owl feces led to significant reductions in both duration of feeding and amount of food consumed, while some defensive behavioral responses (e.g., freezing and rearing) were more significant in the exposed animals than in the control. Serum levels of adrenocorticotropic hormone and corticosterone in plateau zokors exposed to owl feces were significantly higher compared with the control. The hypothalamic corticotropin-releasing factor and c-fos mRNA expression levels of plateau zokors exposed to 1, 3, and 6 g owl feces increased significantly, concomitant with the amount of eagle owl feces presented. Owl feces induced various behavioral, hormonal, and hypothalamic gene expression changes in plateau zokors exposed to them. Some behavioral and gene expression (but not hormonal) responses appeared to be threshold dependent. Predator odors supersede other signals and can provide comprehensive information to prey during life-threatening events. The plateau zokor is a typical subterranean rodent living in dark and enclosed subterranean habitats. Owing to this special habitat, zokors may be able to recognize ground predator odors and respond defensively. We investigated changes in behavior, hormones, and the hypothalamic corticotropin-releasing factor and c-fos mRNA expression levels of the plateau zokor when exposed to different amounts of eagle owl feces. We believe that our study makes a significant contribution to the literature because our results support the predation risk allocation hypothesis, showing that eagle owl feces inhibit foraging and induce various anti-predatory behavioral and neuroendocrine responses in plateau zokors.

Zooming in on mechanistic predator-prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions.

Camera trap technology has galvanized the study of predator-prey ecology in wild animal communities by expanding the scale and diversity of predator-prey interactions that can be analysed. While observational data from systematic camera arrays have informed inferences on the spatiotemporal outcomes of predator-prey interactions, the capacity for observational studies to identify mechanistic drivers of species interactions is limited. Experimental study designs that utilize camera traps uniquely allow for testing hypothesized mechanisms that drive predator and prey behaviour, incorporating environmental realism not possible in the laboratory while benefiting from the distinct capacity of camera traps to generate large datasets from multiple species with minimal observer interference. However, such pairings of camera traps with experimental methods remain underutilized. We review recent advances in the experimental application of camera traps to investigate fundamental mechanisms underlying predator-prey ecology and present a conceptual guide for designing experimental camera trap studies. Only 9% of camera trap studies on predator-prey ecology in our review use experimental methods, but the application of experimental approaches is increasing. To illustrate the utility of camera trap-based experiments using a case study, we propose a study design that integrates observational and experimental techniques to test a perennial question in predator-prey ecology: how prey balance foraging and safety, as formalized by the risk allocation hypothesis. We discuss applications of camera trap-based experiments to evaluate the diversity of anthropogenic influences on wildlife communities globally. Finally, we review challenges to conducting experimental camera trap studies. Experimental camera trap studies have already begun to play an important role in understanding the predator-prey ecology of free-living animals, and such methods will become increasingly critical to quantifying drivers of community interactions in a rapidly changing world. We recommend increased application of experimental methods in the study of predator and prey responses to humans, synanthropic and invasive species, and other anthropogenic disturbances.

Animal communication of fear and safety related to foraging behavior and fitness: An individual-based modeling approach

Animal communication impacts many kinds of behavior including mating and courtship, escaping from predators and foraging activity. In this article, our investigation focuses primarily on how alarm communication impacts foraging activity, using individual based computer simulations. We used this approach to help resolve a debate in the literature between the risk-allocation hypothesis, which predicts that over time, animals become habituated to alarm communication versus the hypothesis that alarm communication consistently decreases foraging activity to avoid predators. We found that in most cases, alarm communication did indeed decrease foraging activity whereas in other cases, alarm communication resulted in habituation and a gradual increase in foraging activity, suggesting that there is some truth to both hypotheses. Moreover, it is possible that a decrease in foraging as well as habituation in response to alarm communication both contribute to fitness, or more generally, that alarm communication contributes to fitness as opposed to non-communication. Among the communication runs, we found that although there were higher levels of fitness compared with non-communication runs, fitness was higher when communication results in decreased foraging activity vs. runs where communication results in increased foraging activity. Finally, we used a variational autoencoder based estimation of distribution algorithms in conjuction with C4.5 decision trees as a wrapper to discern the features that distinguish communication runs from non-communication runs. In general, communication runs tend to have relatively low population densities, whereas non-communication runs tend to have relatively high population densities, suggesting that the ability to communicate fear obviates the need for prey to stay in close proximity to one another in order to defend against predators. Also a high level of reproductive urgency was observed in individuals with communication ability when the level of fear of predators was low.

High background risk induces risk allocation rather than generalized neophobia in the fathead minnow

AbstractTo cope with the heterogeneous nature of predation and the trade-off between predator avoidance and foraging, prey animals have evolved several cognitive rules. One of these is the risk allocation hypothesis, which predicts that in environments with long periods of sustained high risk, individuals should decrease their antipredator effort to satisfy their metabolic requirements. The neophobia hypothesis, in turn, predicts increased avoidance of novel cues in high-risk habitats. Despite the recent interest in predator-induced neophobia across different sensory channels, tests of such generalized neophobia are restricted to a single fish taxon, the Cichlidae. Hence, we retested the generalized neophobia hypothesis in fathead minnows Pimephales promelas, a small schooling North American cyprinid fish. From hatching onward, minnows were exposed to conspecific alarm cues, which indicate predation risk, or distilled water in a split-clutch design. After 1 month, shoaling behavior was examined prior and subsequent to a mechanical predator disturbance. Fish previously exposed to elevated background risk formed compact shoals for a shorter time interval after the stimulus compared with controls. These results contrast previous studies of generalized neophobia but match the risk allocation hypothesis. Consequently, risk allocation and generalized neophobia are not ubiquitous cognitive rules but instead evolved adaptations of different taxa to their respective environments.

Temporal structuring of vigilance behaviour by female Thomson's gazelles with hidden fawns

Prey animals often face a trade-off between investing time in antipredator behaviour and performing self-maintenance activities, such as foraging. Parents face particularly high stakes as they must protect highly vulnerable offspring while also meeting elevated energetic demands. To optimize this trade-off, the risk allocation hypothesis predicts that prey should adjust their antipredator behaviour to reflect temporal fluctuations in risk. That is, they should invest more in antipredator behaviour when risk is high and prioritize other activities when risk is low. Here we investigate whether changes in risk level resulting from periodic fawn exposure drive maternal vigilance patterns in Thomson's gazelle, Eudorcas thomsonii. We find that maternal vigilance patterns match the predictions of the risk allocation hypothesis. Mothers are highly vigilant prior to fawn retrieval, when risk of fawn detection by predators is high. They exhibit low levels of vigilance after fawns resume hiding, when certainty of predator absence is high and, therefore, risk is low. We suggest that fawn active periods may function secondarily as a form of predator sampling and that mothers may adjust their vigilance levels in response to information yielded by this sampling.

Re-examining the Causes and Meaning of the Risk Allocation Hypothesis.

The risk allocation hypothesis has inspired numerous studies seeking to understand how temporal variation in predation risk affects prey foraging behavior, but there has been debate about its generality and causes. I examined how imperfect information affects its predictions and sought to clarify the causes of the predicted patterns. I first confirmed that my modeling approach-given a threshold or linear fitness function-produced the risk allocation prediction that prey increase their foraging efforts during low and high risk as the proportion of high-risk periods increases. However, the causes of this result and its robustness differed for the two fitness functions. When prey that had evolved to use perfect information received imperfect information, risk allocation was reduced. However, prey that evolved to use imperfect information in some cases reversed the risk allocation prediction. The model also showed that risk allocation occurs even when prey have no knowledge that the proportions of low- and high-risk periods have changed. I conclude that risk allocation is largely not driven by prey expectations about future states of the environment but rather by the prey's current energetic state and time remaining. I discuss the consequences for experimental design and explanations for empirical results.

Human risk induced behavioral shifts in refuge use by elk in an agricultural matrix

ABSTRACTScientists increasingly acknowledge the influence that nonlethal effects of predation have on structuring wildlife‐landscape interactions. In landscapes dominated by human activities, wildlife can respond to human disturbance in a similar fashion to the risk of predation. Further, the risk allocation hypothesis suggests that individuals respond most strongly to risk when it is spatially and temporally predictable. We predict that individuals in agriculturally dominated landscapes will respond to potential risk from humans during hunting season by shifting their behavior to avoid agricultural areas during the day, instead retreating to refuge habitat. We predict that this shift to more nocturnal behavior will be strongest for elk (Cervus elaphus) adult female–calf pairs and will be influenced by the level of moon illumination. Using motion‐sensing cameras, we studied the response of elk moving between the Wainwright Dunes Ecological Reserve (a hunting refuge) and surrounding agriculturally dominated landscape in east‐central Alberta, Canada, to human disturbance in relation to sunrise and sunset. Elk became increasingly nocturnal with the onset of hunting, leaving the refuge following sunset and returning to the refuge earlier before sunrise. Further, elk became increasingly nocturnal in response to greater levels of moon illumination. Lastly, we found that adult female–calf pairs perceived greater risks associated with diurnal activity and exhibited the most nocturnal behavior relative to other demographic classes. Our results suggest that ungulate management based on traditional hunting seasons and times may be problematic as it creates strong cues for resident elk, allowing them to minimize risk by avoiding risky places at risky times in accordance with the risk allocation hypothesis. © 2017 The Wildlife Society.

Risk Allocation Across the Enterprise: Evidence from the Insurance Industry

Financial researchers initially regarded hedging activities as a means to reduce total firm risk, which often is defined in terms of cash flow volatility. More recently, researchers have focused on the strategic allocation of risk. Direct tests of risk allocation have been problematic, however, because hedging data are rarely available and, when available, are only specific to a single operation of the firm, such as bank lending. In this study, we exploit unique data from the insurance industry that allows us to observe hedging proxies for both investment and insurance underwriting risks and test the risk allocation hypothesis developed in the finance literature. We also conduct separate examinations of life-health and property-casualty insurers, which reveal differences in the risks and hedging activities of these two types of insurers.

Derivatives-hedging, risk allocation and the cost of debt: Evidence from bank holding companies

We investigate the association between derivatives-hedging and the cost of debt in publicly-traded bank holding companies (BHCs) and test the risk-allocation effect of derivatives-hedging using the 2007–2009 financial crisis as a quasi-experiment. Consistent with Froot and Stein (1998) and Schrand and Unal (1998), we find evidence supporting the risk allocation hypothesis in BHCs. Banks reduce their exposure to tradable risk (e.g., interest rate and exchange rate risks) via derivatives-hedging and simultaneously extend more loans and take greater credit risk in lending (their main area of expertise) in order to earn higher economic rents. The risk allocation strategy is associated with an increase in overall bank risk, measured by the cost of debt, during the non-crisis periods but its dynamics breaks down during the financial crisis of 2007–2009, resulting in a negative relationship between derivatives-hedging and the cost of debt.

Living on the edge: how does environmental risk affect the behavioural and cognitive ecology of prey?

Prey show remarkable plasticity across a range of traits that allow them to adapt to changes in predation risk in their local environment. While we know much about behavioural, morphological, physiological and life-history responses, we know less about how background risk alters cognitive functioning related to risk assessment. Here, we exposed wood frog tadpoles, Lithobates sylvaticus, to high- or low-risk environments for 7 days. Following this, we exposed tadpoles to one of four treatments that either continued risk, ended risk, taught tadpoles to recognize a predator or provided a false predator learning control. Tadpoles were tested for responses to predator odour, alarm cues or water either 1 day or 11 days after conditioning ended. Comparisons between conditioning treatments and test odours allowed us to assess how background risk alters a range of cognitive functions relating to risk assessment. Tadpoles that experienced high background risk responded to alarm cues with a weaker response than low-risk tadpoles, as predicted by the risk allocation hypothesis. High-risk tadpoles also developed neophobic responses to novel odours, unlike low-risk tadpoles, but displayed similar responses to a learned predator as tadpoles from low risk. When tested again 11 days later, high- and low-risk tadpoles responded equally across all treatments with the exception of learned predator responses, where high-risk tadpoles still responded strongly to the predator odour, while low-risk tadpoles did not. Our results demonstrate that recent experience with risk induces short-term cognitive plasticity in a number of functions related to risk assessment.

Vigilance adjustments in relation to long- and short term risk in wild fallow deer (Dama dama)

The risk allocation hypothesis predicts that vigilance should be adjusted to the temporal variation in risk. We test this hypothesis in wild fallow deer exposed to short term (disturbance) and long term (presence of a fawn after parturition) changes in risk. We recorded the proportion, frequency and type of vigilance and size of used area before and after parturition, in GPS-collared wild female fallow deer. Vigilance was divided in two main groups: “non-grazing vigilance” and “grazing vigilance”. The latter group was divided into “grazing vigilance while chewing” and a “grazing vigilance when chewing was interrupted”. By recording external disturbance in form of passing cars, we were able to investigate if this altered the amount, and type of vigilance. We found that females increased the proportion and frequency of “grazing vigilance stop chewing” after parturition. The “grazing vigilance chewing” was unaffected, but “non-grazing vigilance” decreased. Disturbance increased the proportion “grazing vigilance stop chewing” to the same extent before and after parturition. We found a clear decrease in female home range size after parturition as a possible behavioural adjustment. The increase in “grazing vigilance stop chewing” after parturition is a rarely described but expected cost of reproduction.

Plastic response of fearful prey to the spatiotemporal dynamics of predator distribution.

Ecological theory predicts that the intensity of antipredator responses is dependent upon the spatiotemporal context of predation risk (the risk allocation hypothesis). However, most studies to date have been conducted over small spatial extents, and did not fully take into account gradual responses to predator proximity. We simultaneously collected spatially explicit data on predator and prey to investigate acute responses of a threatened forest ungulate, the boreal caribou (Rangifer tarandus), to the spatiotemporal dynamics of wolf (Canis lupus) distribution during spring. Movement analysis of GPS-collared individuals from both species revealed high plasticity in habitat-selection decisions of caribou. Female caribou avoided open areas and deciduous forests and moved relatively fast and toward foraging areas when wolves were closer than 2.5 km. Caribou also avoided food-rich areas only when wolves were within 1 km. Our results bridge the gap between long-term perceived risk and immediate flight responses by revealing dynamic antipredator tactics in response to predator proximity.

European Roe Deer Increase Vigilance When Faced with Immediate Predation Risk by Eurasian Lynx

AbstractPrey animals must balance antipredatory behaviour with foraging behaviour. According to the risk allocation hypothesis, prey increase antipredatory behaviour and reduce foraging activity during pulses of high risk, but with continuous risk, other activities must continue and antipredatory behaviour decreases despite the risk. We studied the impact of lynx presence on the vigilance behaviour of wild roe deer under conditions of (i) a pulsed elevated risk by experimentally spreading lynx urine as an olfactory cue, and (ii) continuous risk by comparing an area where lynx was eradicated 160 years ago to an area where lynx has been re‐introduced 30 years ago. Roe deer were extremely vigilant in response to the predator olfactory cue; however, roe deer vigilance did not differ measurably among areas with or without potential lynx presence. Deer were more vigilant before sunset than during the night at both study areas, probably due to long‐term adaptation of roe deer to human hunting during daytime. Vigilance decreased from August to September even though activity of lynx increases in autumn, which may be a result either of increased foraging due to decrease in food quality in autumn, or of changes in social organization of the deer. Our results suggested that the degree of vigilance depends on environmental cues. We found that roe deer respond to lynx urine despite a long absence of lynx in the ecosystem. Our results support the risk allocation hypothesis for responses to pulses of high risk but not for responses to continuous elevated levels of risk.

Strong food odours mask predation risk and affect evocation of defence behaviours in the tadpoles of Sphaerotheca breviceps

Tadpoles of Sphaerotheca breviceps detect food and predators using waterborne chemical cues (odours), which evoke appropriate behaviour. The present study aimed to determine whether they are capable of resolving the conflict between foraging choice and predator avoidance on encountering both food and predatory chemical cues together. Experiments were designed using an association choice apparatus in which prey tadpoles were given a choice to move themselves close to or away from a given stimulus (food or a predator). Food odours were either strong or weak. Tadpoles of Hoplobatrachus tigerinus (n = 4) were placed in an open-ended mesh cage wrapped in a cheese cloth that provided predator cues. The time spent by the test tadpoles in the predator’s zone or away from it and the time spent feeding were recorded for 10 min (n = 25 trials). When food odours were weak, the prey tadpoles avoided predators and spent significantly more time in the predator-free zone. In contrast, when food odours were strong, they foraged equally in the two zones of the test apparatus regardless of the presence or absence of predators. These findings confirm the inherent ability of S. breviceps tadpoles to distinguish between food and predators, and indicate that strong food odours mask predation risk. We suggest that foraging theory and the predation risk allocation hypothesis should include factors that mislead prey during predation risk assessment and the evocation of defence behaviours.