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Ecological consequences of the bold-shy continuum: The effect of predator boldness on prey risk

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Although the existence of different personality traits within and between animal populations has been relatively well established, the ecological implications of this variation remain neglected. In this study we tested whether differences in the boldness of pairs of three-spined sticklebacks led to differential predation risk in their prey, Chironomidae larvae. Bolder pairs, those that left a refuge and crossed the tank mid-line sooner, ate a greater proportion of prey in 10 min than less bold fish (therefore prey were at a greater per capita risk). Fish crossed the mid-line more rapidly when a larger number of prey were presented, suggesting they accepted greater risk in return for a larger foraging reward. Perception of predation risk also affected the differences between fish in boldness, as larger fish crossed the mid-line sooner after leaving the refuge (larger fish are less at risk from predation). Hence, an interesting trophic interaction occurs, where the risk experienced by the chironomid larvae is determined by the risk perceived by their predators. Through the variation generated by boldness, a form of behaviourally mediated trophic cascade can occur within (as well as between) communities.
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... This concept has been reviewed in Niemela et al. (2012). This selective benefit of boldness is seen in three-spined sticklebacks Gasterosteus aculeatus, in which bolder individuals consume more chironomid prey than shyer conspecifics, and thus gained higher fitness, though no predators were present in this experiment (Ioannou et al., 2008). However, the expression of a personality within a population of animals is dependent upon the interaction of predation rates and resource distributions as well as other factors, thus personality and fitness trade-offs are context dependent (Dingemanse & Reale, 2005). ...
... Crayfish were ran in a behavioural trial once per day in order to allow crayfish to recover from trials (Edwards et al., 2018). The three behavioural assays used to determine personality included latency to emerge with exposure to alarm cue (Ioannou et al., 2008;Reisinger et al., 2015;Steele & Moore, 2019), foraging choice (Edwards et al., 2018) and exploration (Edwards et al., 2018). The nine behavioural trials were conducted in a haphazard order to avoid any potential habituation or learning. ...
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The expression of an individual animal’s behaviour can be placed along many different personality spectra. Parasite load can alter animal behaviour and, thus, fitness. The personality traits of rusty crayfish, Faxonius rusticus , were analysed in three different behavioural contexts: foraging, exploration, and threatened. Each crayfish was tested in each context 3 times, giving a total of 9 assays per crayfish. After assays were completed, crayfish were dissected, and the hepatopancreas of each crayfish was photo analysed to determine the parasite load of the trematode, Microphallus spp. A composite personality score for each assay and parasite load was loaded into a PCA. The PCA model showed that as parasite load increased, crayfish became bolder in threatening contexts and less exploratory in novel environments, whether or not a food stimulus was present. Thus, parasite load alters the placement of crayfish on different personality spectra, but this change is context specific.
... Goal-orientedness was also shown to have a positive impact on leadership in fish, however only when balanced with moderate levels of social tendency, as fish which were highly goaloriented would split from the group, reducing their influence [75]. As goal-orientedness is thought to represent a trade-off between propensity to risk isolation and the safety of the group [76], such a behaviour may correlate with individual differences in boldness [76,77]. Indeed boldness has been found to predict leadership propensity in fish [77] and pigeons [74]. ...
... Goal-orientedness was also shown to have a positive impact on leadership in fish, however only when balanced with moderate levels of social tendency, as fish which were highly goaloriented would split from the group, reducing their influence [75]. As goal-orientedness is thought to represent a trade-off between propensity to risk isolation and the safety of the group [76], such a behaviour may correlate with individual differences in boldness [76,77]. Indeed boldness has been found to predict leadership propensity in fish [77] and pigeons [74]. ...
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Animals are characterised, in part, by their use of voluntary movement, which is used to explore and exploit resources from their surrounding environment. Movement can therefore benefit animals, but will cost them their energetic reserves. Thus, adaptations for faster movements with negligible increases in energy expenditure will likely evolve via natural selection. Individual and social-level mechanisms have been shown to optimise this speed/energetic trade-off. Nevertheless, studies of social-level traits typically ignore individual variation, which is a cornerstone principle in evolutionary ecology. Furthermore, how individual phenotype interacts with the phenotypic composition of the group to govern the cost of transport may have been entirely overlooked. We investigate speed and the energetic consequences of individual-level phenotypic differences using body mass (both natural and artificially manipulated with additional weights) of homing pigeons (Columba livia) (N =16 birds; N = 193 useable flight trajectories). We then turn to social level phenomena, and manipulate the composition of pigeon groups by body mass (N= 12 birds in four treatments; N = 192 useable flight trajectories) and leadership rank (N = 30 birds in three groups, N = 286 useable flight trajectories) following earlier leadership identification flights (N = 33 birds, N = 306 useable flight trajectories). Natural body mass was predictive of flying speed in solo flights, but not in groups of greater mass by composition; artificial mass loading had no impact on speed in solo fliers, and was not tested in groups. Groups of leader phenotypes, showed faster speeds, and greater cohesion than follower phenotype groups, both in terms of flock spread, but also in consistency of positioning within the flock (flock stasis) across the flight. Flock stasis was further analysed across all other group flights. Its positive impact on speed was found to be consistent across all experimental treatments. Therefore, predicting flock stasis may be critical to understanding optimal phenotypic compositions of birds, and thus the social evolution of birds which fly together. We provide evidence that greater stasis may be driven by phenotypic compositions (i.e. groups of leaders, and homogeneous mass groups) and also discuss the implications of stasis for different flocking structures (e.g. V-formations) and human crowd control.
... Regarding predator-prey interactions, several studies have shown that individual differences in predator behavior can influence hunting (Pettorelli et al., 2011). For example, in several predator fish species, bolder individuals have a markedly higher predation rate compared with shyer ones (Ioannou et al., 2008;Rhoades et al., 2019). In their review of the drivers of hunting behavior in domestic cats, Cecchetti et al. (2021a) speculated that cats with certain personality traits, particularly those with high levels of boldness and extraversion, could potentially be more motivated to hunt wild prey. ...
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The domestic cat, Felis catus, is one of the most popular and widespread domestic animals. Because domestic cats can reach high population densities and retain at least some tendency to hunt, their overall impact on wildlife can be severe. Domestic cats have highly variable predation rates depending on the availability of prey in their environment, their owners’ practices, and individual cat characteristics. Among these characteristics, cat personality has recently been hypothesized to be an important factor contributing to variations in the hunting activity of cats. In this study, we used surveys of 2,508 cat owners living in France to collect information about cat personalities using the Feline Five personality model and about the frequency with which the cats bring home prey. For both birds and rodents, cats with high levels of extraversion or low levels of neuroticism had significantly higher frequencies of prey return. Owners whose cats had low levels of agreeableness or high levels dominance reported a significantly lower frequency of bird return. Personality differences therefore seem to contribute to the high variability in predation rates between domestic cats. We also found that the owner-reported prey return frequencies were significantly higher for cats spending more time outdoors, for non-pedigree cats, and for owners living in rural or suburban areas as opposed to urban areas. By contrast, we did not detect an effect of cat sex or age on their reported prey return rates.
... Of course, the degree of boldness demonstrated during the novel object test will have been determined by perception of costs by individuals of both species. While the specific drivers of the behaviour of both species are beyond the scope of this study, goldfish are larger than the white cloud mountain minnows, and greater size has been shown to facilitate greater risk taking, due to lower likelihood of predation (Ioannou et al. 2008). However, goldfish also have to balance this against colouration that makes them more visible to potential visual predators (their ability to change the turbidity of water bodies is deemed a survival benefit for this reason: Richardson et al. 1995). ...
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Invasive alien species (IAS) are major drivers of global biodiversity loss, and the poorly regulated international pet trade is a source of emerging and future invaders. Predictions of the likely ecological impacts and risks of such IAS have been significantly enhanced in recent years with new metrics, which require application to many more actual and potential IAS. Hence, this study assesses the potential ecological impacts and risks of two readily available pet trade species: goldfish, Carassius auratus, a species with non-native populations worldwide; and white cloud mountain minnow, Tanichthys albonubes, a species with a limited invasion history to date. First, we compared the per capita feeding rates of these non-native species with two European trophically analogous natives-the stone loach, Barbatula barbatula, and the common minnow, Phoxinus phoxinus-using the Comparative Functional Response method. Second, we used foraging experiments in conspecific pairs to determine synergistic, neutral or antagonistic intraspecific interactions. Third, we performed novel object experiments using the two pet trade species to assess boldness , a known "dispersal enhancing trait". Goldfish had the highest maximum feeding rates of the four species, while white cloud mountain minnows had the lowest. Neutral interactions were observed for all four species in the paired foraging experiments, with goldfish having the highest consumption and white cloud mountain minnows having the lowest. Goldfish demonstrated greater boldness, being more active during the experimental trials and more likely to approach a novel object than white cloud mountain minnows. Further, combining maximum feeding rates, boldness and species availabilities from our survey of pet shops, we assessed the relative invasion risks (RIR) of the two non-natives. This highlighted goldfish as the higher risk and most worthy of management prioritisation, mirroring its more extensive invasion history. We propose that such metrics have potential to direct future IAS policy decisions and management towards the ever-increasing rates of biological invasions worldwide.
... Boldness is known to influence invasion success (Chapple et al., 2012), and behavioural differences along this axis are known to influence foraging ability (Mittelbach et al., 2014;Réale et al., 2007;Sih et al., 2004;Wilson et al., 1994), with bolder individuals using prey patches faster than shy individuals (Ioannou et al., 2008) and consuming prey at faster rates than both heterospecific and shy conspecific competitors (Webster et al., 2009). Therefore, there is a timely need to study the role that personality plays in governing competitive interactions in N. melanostomus, as it might have important implications for the invasion dynamics of bold-biased invasions fronts such as those noted in Myles-Gonzalez et al. (2015). ...
... These decisions can have enormous impacts on ecological communities owing to their effects on predation risk, predator-prey dynamics and trophic interactions (Sih et al. 1988;Orrock et al. 2013;Belgrad and Griffen 2016). In three-spined sticklebacks (Gasterosteus aculeatus), refuge use behaviour is known to vary consistently between individuals (Bevan et al. 2018;Szopa-Comley et al. 2020) and is a measure of an individual's willingness to accept potential risk traded off for greater access to resources, also known as boldness (Ioannou et al. 2008;Harcourt et al. 2009;McDonald et al. 2016). In this study, we presented three-spined sticklebacks with either a foraging context (feeding treatment) or a control trial with no food (control treatment) on alternate days for four consecutive days to experimentally test whether the opportunity to forage affected inter-individual consistency in refuge use behaviour between trials at the start compared to the end of trials. ...
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Consistent inter-individual variation in behaviour within a population, widely referred to as personality variation, can be affected by environmental context. Feedbacks between an individual’s behaviour and state can strengthen (positive feedback) or weaken (negative feedback) individual differences when experiences such as predator encounters or winning contests are dependent on behavioural type. We examined the influence of foraging on individual-level consistency in refuge use (a measure of risk-taking, i.e. boldness) in three-spined sticklebacks, Gasterosteus aculeatus , and particularly whether changes in refuge use depended on boldness measured under control conditions. In the control treatment trials with no food, individuals were repeatable in refuge use across repeated trials, and this behavioural consistency did not differ between the start and end of these trials. In contrast, when food was available, individuals showed a higher degree of consistency in refuge use at the start of the trials versus controls but this consistency significantly reduced by the end of the trials. The effect of the opportunity to forage was dependent on behavioural type, with bolder fish varying more in their refuge use between the start and the end of the feeding trials than shyer fish, and boldness positively predicted the likelihood of feeding at the start but not at the end of the trials. This suggests a state-behaviour feedback, but there was no overall trend in how bolder individuals changed their behaviour. Our study shows that personality variation can be suppressed in foraging contexts and a potential but unpredictable role of feedbacks between state and behaviour. Significance statement In this experimental study, we examined how foraging influences consistency in risk-taking in individual three-spined sticklebacks. We show that bolder individuals become less consistent in their risk-taking behaviour than shyer individuals during foraging. Some bolder individuals reinforce their risk-taking behaviour, suggesting a positive feedback between state and behaviour, while others converge on the behaviour of shyer individuals, suggesting a negative feedback. In support of a role of satiation in driving negative feedback effects, we found that bolder individuals were more likely to feed at the start but not at the end of the trials. Overall, our findings suggest that foraging can influence personality variation in risk-taking behaviour; however, the role of feedbacks may be unpredictable.
... Boldness can be defined as an animal's propensity to engage in risky behavior (Reale et al., 2007;Putman et al., 2020) and hence can be measured as the strength of an individual's response to potential threats (Reale et al., 2007). Bolder individuals may be better able to compete for territory or mates (Reaney & Backwell, 2007), or exploit foraging opportunities in open habitats (Ioannou et al., 2008;Short & Petren, 2008). Hence, boldness may confer strong fitness advantages (Smith & Blumstein, 2008), including higher reproductive success (Ariyomo & Watt, 2012;Reale et al., 2009) and survival (Sinn et al., 2014). ...
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Anthropogenic activities often create distinctive but discontinuously distributed habitat patches with abundant food but high risk of predation. Such sites can be most effectively utilized by individuals with specific behaviors and morphologies. Thus, a widespread species that contains a diversity of sizes and behavioral types may be pre‐adapted to exploiting such hotspots. In eastern Australia, the giant (to >2 m) lizard Varanus varius (lace monitor) utilizes both disturbed (campground) and undisturbed (bushland) habitats. Our surveys of 27 sites show that lizards found in campgrounds tended to be larger and bolder than those in adjacent bushland. This divergence became even more marked after the arrival of a toxic invasive species (the cane toad, Rhinella marina) caused high mortality in larger and bolder lizards. Some of the behavioral divergences between campground and bushland lizards may be secondary consequences of differences in body size, but other habitat‐associated divergences in behavior are due to habituation and/or nonrandom mortality. Lace monitors (Varanus varius) are keen exploiters of anthropogenically disturbed habitat; however, only a subset of morphological and behavioral phenotypes in this species favor these artificial environments (i.e., large, bold individuals). The arrival of a toxic invader (Rhinella marina) may further exacerbate phenotypic divergences.
... Boldness is known to influence invasion success (Chapple et al., 2012), and behavioural differences along this axis are known to influence foraging ability (Mittelbach et al., 2014;Réale et al., 2007;Sih et al., 2004;Wilson et al., 1994), with bolder individuals using prey patches faster than shy individuals (Ioannou et al., 2008) and consuming prey at faster rates than both heterospecific and shy conspecific competitors (Webster et al., 2009). Therefore, there is a timely need to study the role that personality plays in governing competitive interactions in N. melanostomus, as it might have important implications for the invasion dynamics of bold-biased invasions fronts such as those noted in Myles-Gonzalez et al. (2015). ...
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This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as “bold”, fish that took more time to resume movement were categorized as “shy”, and those who fell in between these two categories were determined to have “intermediate” boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Hence, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus, however results also show that competition is also governed by other mechanisms which require further study. This article is protected by copyright. All rights reserved.
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In farmed animals, individuality have demonstrated links to performance traits, health and disease susceptibility, and animal welfare. This research aimed at exploring whether there are differences in the secretion of hormones in the caudal neurosecretory system of different individuailty, and investigating whether it is related to physiological behaviors. In the experiment we selected through multiple behavioral tests two types of olive flounders, bold individuals (BI) and shy individuals (SI), and found that they differed in behavior and physiology. The standard metabolic rate, maximum metabolic rate, and absolute aerobic scope of BI were markedly higher than those of SI. Additionally, the swimming speed of BI was also higher than that of SI in the natural photoperiod. BI and SI showed distinct coping styles to deal with acute stress. Overall, the number of Dahlgren cells secreting UI, the relative UI and CRH mRNA expression in the caudal neurosecretory system (CNSS) of SI was relatively higher than that in BI. By contrast, the number of Dahlgren cells secreting UII and the mRNA expression of UII is lower than that of BI. Through the correlation analysis, it was found that there are some differences in hormone secretion among different individuality groups, which indicates individuality affects hormone production and the number of secretion cells and existed correlation with respiratory metabolism, spontaneous behavior, appetite. It means differences in the regulation mechanism of the flounders in BI and SI.
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Theory predicts that staying in a refuge has benefits in terms of predator avoidance and costs in terms of lost feeding opportunities. In this study, we investigated how the relative importance of these costs and benefits changes with increasing body length. This is of particular interest in animals such as fish, which show continuous growth throughout their lives. Our results suggest that larger fish are subject to lower predation risks and are less affected by food deprivation than small fish, with fish decreasing their responses to food-deprivation treatments more strongly with increasing body length than to predation treatments. This may explain our observation that large fish emerged later from a refuge than small ones and spent shorter times outside the refuge. The key role of differential responses to food deprivation was further illustrated by the finding that the relative weight loss of individual fish was strongly correlated with a reduction in hiding time even in the absence of body length differences. The importance of inter-individual differences in metabolic rates for the decision-making behaviour of animals is discussed.
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