The Multipredator Hypothesis and the Evolutionary Persistence of Antipredator Behavior

Acoustic recognition of predators by mantled howler monkeys (Alouatta palliata): A playback experiment with naïve and experienced subjects

OBJECTIVES

When the production of antipredator behaviors is costly, prey is expected to stop displaying such behaviors and lose the ability to recognize extirpated predators. However, the loss or maintenance of predator recognition abilities is conditional on the eco-evolutionary context of prey. Here, we examined the behavioral responses of naïve and experienced mantled howler monkeys (Alouatta palliata) to simulated acoustic cues from natural predators.

METHODS

We studied experienced individuals in the Uxpanapa Valley and naïve individuals in Los Tuxtlas (Veracruz, México). Jaguars (Panthera onca) and harpy eagles (Harpia harpyja), the main predators of howler monkeys, are extant in the Uxpanapa Valley but have been extirpated in Los Tuxtlas for approximately 70 and 45 years, respectively. We exposed six naïve and six experienced groups to playbacks of acoustic stimuli from the two predators and a non-predator control species (plain chachalacas, Ortalis vetula), and recorded the latency, frequency, and duration of antipredation behaviors (n = 127 trials).

RESULTS

In contrast with experienced mantled howler monkeys, naïve subjects did not respond to trials from harpy eagles. However, response patterns were generally similar between naïve and experienced individuals when exposed to jaguar stimuli.

DISCUSSION

Our findings suggest that naïve mantled howler monkeys do not recognize harpy eagle calls, but they respond to jaguar calls in a manner consistent with experienced individuals. These results illustrate how different mechanisms for the recognition of extirpated predators operate within a single species according to evolutionary and ecological experience.

Sustained predation pressure may prevent the loss of anti-predator traits from havened populations

Conservation havens free of invasive predators are increasingly relied upon for fauna conservation, although havened populations can lose anti-predator traits, likely making them less suitable for life 'beyond the fence'. Sustaining low levels of mammalian predator pressure inside havens may prevent the loss of anti-predator traits from havened populations. We opportunistically compared behavioural and morphological anti-predator traits between four woylie (Bettongia penicillata ogilbyi) populations- one haven isolated from all mammalian predators, one haven containing a native mammalian predator (chuditch; Dasyurus geoffroii), and their respective non-havened counterparts (each containing both chuditch and invasive predators). Havened woylies existing without mammalian predators were smaller (shorter hindfeet, smaller body weight) and less reactive (consumed more food from fox-treated and control feeding stations, less agitated during human handling) than a non-havened reference population. However, in the haven containing chuditch, we found no difference in behaviour or morphology compared to the adjacent non-havened population. Across populations, anti-predator responses tended to appear stronger at sites with higher predator activity, suggestive of an adaptive response across a gradient of predation pressure. Our findings suggest that maintaining mammalian predation pressure in conservation havens could be effective for preventing or slowing the loss of anti-predator traits from these populations.

Keep the ball rolling: sexual differences in conglobation behavior of a terrestrial isopod under different degrees of perceived predation pressure

Background

Antipredator behaviors are theoretically subjected to a balance by which their display should be minimized when their benefits do not outweigh their costs. Such costs may be not only energetic, but also entail a reduction in the time available for other fitness-enhancing behaviors. However, these behaviors are only beneficial under predation risk. Therefore, antipredator behaviors are predicted to be maximized under strong predation risk. Moreover, predation pressure can differ among individuals according to traits such as sex or body size, if these traits increase vulnerability. Antipredator behaviors are expected to be maximized in individuals whose traits make them more conspicuous to predators. However, how sex, body size and antipredator behaviors interact is not always understood.

Methods

In this work, I tested the interaction between sex, body size and antipredator behavior in the common pill woodlouse (Armadillidium vulgare), which conglobate (i.e., they roll up their bodies almost conforming a sphere that conceals their appendages) in response to predator attacks. Specifically, I tested whether latency to unroll after a standardized mechanical induction was greater in animals exposed to predator chemical cues (toad feces) than in conspecifics exposed to cues of non-predatory animals (rabbits) or no chemical cues whatsoever (distilled water), incorporating sex and body mass in the analyses.

Results

In agreement with my prediction, latency to unroll was greater in individuals exposed to predator chemical cues. In other words, these animals engage in conglobation for longer under perceived predator vicinity. However, this result was only true for males. This sexual dimorphism in antipredator behavior could result from males being under greater predation risk than females, thus having evolved more refined antipredator strategies. Indeed, males of this species are known to actively search for females, which makes them more prone to superficial ground mobility, and likely to being detected by predators. Body size was unrelated to latency to unroll. As a whole, these results support the hypothesis that antipredator behavior is tuned to predator cues in a way consistent with a balance between costs and benefits, which might differ between the sexes.

Overcoming the phantoms of the past: Influence of predatory stimuli on the antipredator behavior of island pitvipers

The reduction of predation is a potentially important factor for the evolution of the traits of an island animal species. By relaxed selection, insular animals tend to lose their antipredator behaviors. A monophyletic group of pitvipers (genus Bothrops) in southeastern Brazil, which have high genetic affinity and dwell on the mainland and adjacent islands, provide an appropriate setting to study the evolution of antipredator behavior and how different predatory stimuli can influence this behavior. The mainland Bothrops jararaca has several terrestrial and aerial predators, whereas B. insularis and B. alcatraz, restricted to two small islands, Queimada Grande and Alcatrazes, respectively, have a smaller range of aerial predators. Terrestrial predators are absent on Queimada Grande, but one potential snake predator occurs on Alcatrazes. We observed that the defensive repertoire of island snakes has not been lost, but they display different frequencies of some antipredator behaviors. The type of predatory stimuli (terrestrial and aerial) influenced the defensive response. Bothrops insularis most often used the escape strategies, especially against terrestrial predatory stimuli. Bothrops alcatraz displayed the highest rate of strike for both terrestrial and aerial stimuli. Our results indicate that even though relaxed selection may occur in island environments as compared to mainland environments, these pitvipers still retain their antipredator behaviors but with different response degrees to the two predator types.

Are vipers prototypic fear-evoking snakes? A cross-cultural comparison of Somalis and Czechs

Snakes are known as highly fear-evoking animals, eliciting preferential attention and fast detection in humans. We examined the human fear response to snakes in the context of both current and evolutionary experiences, conducting our research in the cradle of humankind, the Horn of Africa. This region is characterized by the frequent occurrence of various snake species, including deadly venomous viperids (adders) and elapids (cobras and mambas). We conducted experiments in Somaliland and compared the results with data from Czech respondents to address the still unresolved questions: To which extent is human fear of snakes affected by evolutionary or current experience and local culture? Can people of both nationalities recognize venomous snakes as a category, or are they only afraid of certain species that are most dangerous in a given area? Are respondents of both nationalities equally afraid of deadly snakes from both families (Viperidae, Elapidae)? We employed a well-established picture-sorting approach, consisting of 48 snake species belonging to four distinct groups. Our results revealed significant agreement among Somali as well as Czech respondents. We found a highly significant effect of the stimulus on perceived fear in both populations. Vipers appeared to be the most salient stimuli in both populations, as they occupied the highest positions according to the reported level of subjectively perceived fear. The position of vipers strongly contrasts with the fear ranking of deadly venomous elapids, which were in lower positions. Fear scores of vipers were significantly higher in both populations, and their best predictor was the body width of the snake. The evolutionary, cultural, and cognitive aspects of this phenomenon are discussed.

The social microbiome: gut microbiome diversity and abundance are negatively associated with sociality in a wild mammal

The gut microbiome has a well-documented relationship with host fitness. Greater microbial diversity and abundance of specific microbes have been associated with improved fitness outcomes. Intestinal microbes also may be associated with patterns of social behaviour. However, these associations have been largely studied in captive animal models; we know less about microbiome composition as a potential driver of individual social behaviour and position in the wild. We used linear mixed models to quantify the relationship between fecal microbial composition, diversity and social network traits in a wild population of yellow-bellied marmots (Marmota flaviventer). We focused our analyses on microbes previously linked to sociability and neurobehavioural alterations in captive rodents, primates and humans. Using 5 years of data, we found microbial diversity (Shannon-Wiener and Faith's phylogenetic diversity) has a modest yet statistically significant negative relationship with the number of social interactions an individual engaged in. We also found a negative relationship between Streptococcus spp. relative abundance and two social network measures (clustering coefficient and embeddedness) that quantify an individual's position relative to others in their social group. These findings highlight a potentially consequential relationship between microbial composition and social behaviour in a wild social mammal.

Rhythm of relationships in a social fish over the course of a full year in the wild

BACKGROUND

Animals are expected to adjust their social behaviour to cope with challenges in their environment. Therefore, for fish populations in temperate regions with seasonal and daily environmental oscillations, characteristic rhythms of social relationships should be pronounced. To date, most research concerning fish social networks and biorhythms has occurred in artificial laboratory environments or over confined temporal scales of days to weeks. Little is known about the social networks of wild, freely roaming fish, including how seasonal and diurnal rhythms modulate social networks over the course of a full year. The advent of high-resolution acoustic telemetry enables us to quantify detailed social interactions in the wild over time-scales sufficient to examine seasonal rhythms at whole-ecosystems scales. Our objective was to explore the rhythms of social interactions in a social fish population at various time-scales over one full year in the wild by examining high-resolution snapshots of a dynamic social network.

METHODS

To that end, we tracked the behaviour of 36 adult common carp, Cyprinus carpio, in a 25 ha lake and constructed temporal social networks among individuals across various time-scales, where social interactions were defined by proximity. We compared the network structure to a temporally shuffled null model to examine the importance of social attraction, and checked for persistent characteristic groups over time.

RESULTS

The clustering within the carp social network tended to be more pronounced during daytime than nighttime throughout the year. Social attraction, particularly during daytime, was a key driver for interactions. Shoaling behavior substantially increased during daytime in the wintertime, whereas in summer carp interacted less frequently, but the interaction duration increased. Therefore, smaller, characteristic groups were more common in the summer months and during nighttime, where the social memory of carp lasted up to two weeks.

CONCLUSIONS

We conclude that social relationships of carp change diurnally and seasonally. These patterns were likely driven by predator avoidance, seasonal shifts in lake temperature, visibility, forage availability and the presence of anoxic zones. The techniques we employed can be applied generally to high-resolution biotelemetry data to reveal social structures across other fish species at ecologically realistic scales.

Integrating sensory ecology and predator-prey theory to understand animal responses to fire

Fire regimes are changing dramatically worldwide due to climate change, habitat conversion, and the suppression of Indigenous landscape management. Although there has been extensive work on plant responses to fire, including their adaptations to withstand fire and long-term effects of fire on plant communities, less is known about animal responses to fire. Ecologists lack a conceptual framework for understanding behavioural responses to fire, which can hinder wildlife conservation and management. Here, we integrate cue-response sensory ecology and predator-prey theory to predict and explain variation in if, when and how animals react to approaching fire. Inspired by the literature on prey responses to predation risk, this framework considers both fire-naïve and fire-adapted animals and follows three key steps: vigilance, cue detection and response. We draw from theory on vigilance tradeoffs, signal detection, speed-accuracy tradeoffs, fear generalization, neophobia and adaptive dispersal. We discuss how evolutionary history with fire, but also other selective pressures, such as predation risk, should influence animal behavioural responses to fire. We conclude by providing guidance for empiricists and outlining potential conservation applications.

Behavioural differences in predator aware and predator naïve Wellington tree wētā, Hemideina crassidens

Insects have evolved a wide range of behavioural traits to avoid predation, with anti-predator behaviours emerging as important adaptive responses to the specific strategies employed by predators. These responses may become ineffective, however, when a species is introduced to a novel predator type. When individuals cannot recognise an introduced predator for instance, they may respond in ways that mean they fail to avoid, escape, or neutralize a predator encounter. New Zealand's endemic insect fauna evolved in the absence of terrestrial mammalian predators for millions of years, resulting in the evolution of unique fauna like the large, flightless Orthopteran, the wētā. Here we investigate how experience with introduced mammalian predators might influence anti-predator behaviours by comparing behaviours in a group of Wellington tree wētā (Hemideina crassidens) living in an ecosanctuary, Zealandia, protected from non-native mammalian predators, and a group living in adjacent sites without mammalian predator control. We used behavioural phenotyping assays with both groups to examine rates of activity and defensive aggression shortly after capture, and again after a period of acclimation. We found that wētā living in protected areas were more active shortly after capture than wētā in non-protected habitats where mammalian predators were present. Male wētā living in non-protected areas tended to be less aggressive than any other group. These results suggest that lifetime experience with differing predator arrays may influence the expression of antipredator behaviour in tree wētā. Disentangling innate and experiential drivers of these behavioural responses further will have important implications for insect populations in rapidly changing environments.

Fear generalization and behavioral responses to multiple dangers

Animals often exhibit consistent-individual differences (CIDs) in boldness/fearfulness, typically studied in the context of predation risk. We focus here on fear generalization, where fear of one danger (e.g., predators) is correlated with fear of other dangers (e.g., humans, pathogens, moving vehicles, or fire). We discuss why fear generalization should be ecologically important, and why we expect fear to correlate across disparate dangers. CIDs in fear are well studied for some dangers in some taxa (e.g., human fear of pathogens), but not well studied for most dangers. Fear of some dangers has been found to correlate with general fearfulness, but some cases where we might expect correlated fears (e.g., between fear of humans, familiar predators, and exotic predators) are surprisingly understudied.

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.

Can native predators be used as a stepping stone to reduce prey naivety to novel predators?

Predator naivety negatively affects reintroduction success, and this threat is exacerbated when prey encounters predators with which they have had no evolutionary experience. While methods have been developed to inculcate fear into such predator-naïve individuals, none have been uniformly successful. Exposing ontogenetically- and evolutionary-naïve individuals first to native predators may be an effective stepping stone to improved responses to evolutionarily novel predators. We focused on greater bilbies (Macrotis lagotis) and capitalized on a multi-year mammalian recovery experiment whereby western quolls (Dasyurus geoffroii) were reintroduced into parts of a large fenced reserve that contained a population of naïve bilbies. We quantified a suite of anti-predator behaviors and measures of general wariness across quoll-exposed and quoll-naive bilby populations. We then translocated both quoll-exposed and quoll-naïve individuals into a large enclosure that contained feral cats (Felis catus) and monitored several behaviors. We found that bilbies can respond appropriately to quolls but found only limited support that experience with quolls better-prepared bilbies to respond to cats. Both populations of bilbies rapidly modified their behavior in a similar manner after their reintroduction to a novel environment. These results may have emerged due to insufficient prior exposure to quolls, inappropriate behavioral tests, or insufficient predation risk during cat exposure. Alternatively, quolls and cats are only distantly related and may not share sufficient similarities in their predatory cues or behavior to support such a learning transfer. Testing this stepping stone hypothesis with more closely related predator species and under higher predation risk would be informative.

Impact of predator model presentation paradigms on titi monkey alarm sequences

Abstract

Predator presentation experiments are widely used to investigate animal alarm vocalizations. They usually involve presentations of predator models or playbacks of predator calls, but it remains unclear whether the two paradigms provide similar results, a major limitation when investigating animal syntactic and semantic capacities. Here, we investigate whether visual and acoustic predator cues elicit different vocal reactions in black-fronted titi monkeys (Callicebus nigrifrons). We exposed six groups of wild titi monkeys to visual models or playbacks of vocalizations of raptor or felid. We characterized each group’s vocal reactions using sequence parameters known to reliably encode predatory events in this species. We found that titi monkeys’ vocal reactions varied with the predator species but also with the experimental paradigm: while vocal reactions to raptor vocalizations and models were similar, felid vocalizations elicited heterogeneous, different reactions from that given to felid models. We argue that subjects are not familiar with felid vocalizations, because of a lack of learning opportunities due to the silent behaviour of felids. We discuss the implication of these findings for the semantic capacities of titi monkeys. We finally recommend that playbacks of predator vocalizations should not be used in isolation but in combination with visual model presentations, to allow fine-grained analyses of the communication system of prey species.

Significance statement

It is common to present prey species with predator models or predator calls to study their vocal reactions. The two paradigms are often used independently, but it remains unclear whether they provide similar results. Here, we studied the vocal reactions of titi monkeys to calls and models of raptors and felids. We show that titi monkeys seem to recognize the vocalizations of raptors but not those of felids. The study of the vocal reactions emitted when titi monkeys cannot clearly identify the threat allows us to draw accurate hypotheses about the meaning of titi monkeys’ alarm utterances. We argue that playbacks of predator calls should be used in conjunction with model presentations, which can allow us to better investigate the information and the structure of the alarm systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00265-022-03250-1.

Geographical variation in nest defense among cinereous tit populations in China

Behavioral divergence among populations is common across taxonomic groups, still we know very little about anti-predator behaviors. Animal exposure to predation risk is variable in different ecological contexts. In addition, reproduction value of animals in different geographical regions usually varies. In this study, we tested whether cinereous tits Parus cinereus in different populations exhibited nest defense behaviors similar to those of nest or adult predators and whether their nest defense behaviors showed geographical variation. By using field dummy experiments, we observed tits’ nest defense behavior in nest predator common chipmunk Tamias sibiricus and red squirrel Sciurus vulgaris, adult predator Eurasian sparrowhawk Accipiter nisus and nonthreatening species Oriental turtle dove Streptopelia orientalis in the ZJ (44° N), DLS (18° N) and DZ (31° N) populations, respectively. The response scores varied significantly across the four dummies in ZJ-tits and DLS-tits but did not in DZ-tits. When facing the chipmunk, ZJ-tits showed the highest response score, and DZ-tits showed the lowest response score. When facing the squirrel, ZJ-tits showed a higher response score than tits in the other two populations. However, tits among the three populations responded similarly to a sparrowhawk or dove with slight response behaviors. In addition, response scores to nest predators were positively correlated with brood size across the three populations, but no trend was found for sparrowhawks or doves. Our results indicated that the nest defense behaviors of cinereous tits have evolved in response to large-scale geographical variation in ecological contexts and reproduction value.

The persistence and evolutionary consequences of vestigial behaviours

Behavioural traits are often noted to persist after relaxation or removal of associated selection pressure, whereas it has been observed that morphological traits under similar conditions appear to decay more rapidly. Despite this, persistent non‐adaptive, ‘vestigial’ behavioural variation has received little research scrutiny. Here we review published examples of vestigial behavioural traits, highlighting their surprising prevalence, and argue that their further study can reveal insights about the widely debated role of behaviour in evolution. Some vestigial behaviours incur fitness costs, so may act as a drag on adaptive evolution when that adaptation occurs via trait loss or reversal. In other cases, vestigial behaviours can contribute to future evolutionary trajectories, for example by preserving genetic and phenotypic variation which is later co‐opted by selection during adaptive evolution or diversification, or through re‐emergence after ancestral selection pressures are restored. We explore why vestigial behaviours appear prone to persistence. Behavioural lag may be a general phenomenon arising from relatively high levels of non‐genetic variation in behavioural expression, and pleiotropic constraint. Long‐term persistence of non‐adaptive behavioural traits could also result when their expression is associated with morphological features which might be more rapidly lost or reduced. We propose that vestigial behaviours could provide a substrate for co‐option by novel selective forces, and advocate further study of the fate of behavioural traits following relaxed and reversed selection. Vestigial behaviours have been relatively well studied in the context of antipredator behaviours, but they are far from restricted to this ecological context, and so deserve broader consideration. They also have practical importance, with mixed evidence, for example, as to whether predator/parasite‐avoidance behaviours are rapidly lost in wildlife refuges and captivity. We identify important areas for future research to help determine whether vestigial behaviours essentially represent a form of evolutionary lag, or whether they have more meaningful evolutionary consequences distinct from those of other vestigial and behavioural traits.

The Habituation Process in Two Groups of Wild Moor Macaques (Macaca maura)

When studying animal behavior in the wild, some behaviors may require observation from a relatively short distance. In these cases, habituation is commonly used to ensure that animals do not perceive researchers as a direct threat and do not alter their behavior in their presence. However, habituation can have significant effects on the welfare and conservation of the animals. Studying how nonhuman primates react to the process of habituation can help to identify the factors that affect habituation and implement habituation protocols that allow other researchers to speed up the process while maintaining high standards of health and safety for both animals and researchers. In this study, we systematically described the habituation of two groups of wild moor macaques (Macaca maura), an Endangered endemic species of Sulawesi Island (Indonesia), to assess the factors that facilitate habituation and reduce impact on animal behavior during this process. During 7 months, we conducted behavioral observations for more than 7,872 encounters and an average of 120 days to monitor how macaque behavior toward researchers changed through time in the two groups under different conditions. We found that both study groups (N = 56, N = 41) became more tolerant to the presence of researchers during the course of the habituation, with occurrence of neutral group responses increasing, and minimum distance to researchers and occurrence of fearful group responses decreasing through time. These changes in behavior were predominant when macaques were in trees, with better visibility conditions, when researchers maintained a longer minimum distance to macaques and, unexpectedly, by the presence of more than one researcher. By identifying these factors, we contribute to designing habituation protocols that decrease the likelihood of fearful responses and might reduce the stress experienced during this process.

When ancestry haunts – can evolutionary links to ancestors affect vulnerability of Australian prey to introduced predators? A preliminary study

The high extinction risk of Australian marsupials has been attributed to their failure to recognise novel predators, the application of inappropriate antipredator responses, and advanced hunting strategies of novel predators. This study is a preliminary attempt to explore whether the Lumholtz’ tree-kangaroo (Dendrolagus lumholtzi) (a) is able to recognise odour cues from different predators as threats, and (b) possesses predator-archetype specific antipredator responses. A small number of available captive tree-kangaroos were exposed to faecal odours from two extant predators of different archetypes (python, dingo), a regionally extinct predator which closely matches past terrestrial predators (Tasmanian devil), and a novel predator (domestic dog). Lavender oil was used as non-predator novel odour and water as control. Results suggest that all subjects associated the presented odours with a threat, albeit to different degrees, but did not display predator-archetype specific responses. It appears that this species applies an ancestral antipredator response of flight-on-the ground when encountering predators, including novel predators. Although the results need to be confirmed with more animals, further studies on the vulnerability of Australian prey to novel predators should take the ancestral history of Australian prey species into account.

Naive poison frog tadpoles use bi-modal cues to avoid insect predators but not heterospecific predatory tadpoles

For animals to survive until reproduction, it is crucial that juveniles successfully detect potential predators and respond with appropriate behavior. The recognition of cues originating from predators can be innate or learned. Cues of various modalities might be used alone or in multi-modal combinations to detect and distinguish predators but studies investigating multi-modal integration in predator avoidance are scarce. Here, we used wild, naive tadpoles of the Neotropical poison frog Allobates femoralis ( Boulenger, 1884) to test their reaction to cues with two modalities from two different sympatrically occurring potential predators: heterospecific predatory Dendrobates tinctorius tadpoles and dragonfly larvae. We presented A. femoralis tadpoles with olfactory or visual cues, or a combination of the two, and compared their reaction to a water control in a between-individual design. In our trials, A. femoralis tadpoles reacted to multi-modal stimuli (a combination of visual and chemical information) originating from dragonfly larvae with avoidance but showed no reaction to uni-modal cues or cues from heterospecific tadpoles. In addition, visual cues from conspecifics increased swimming activity while cues from predators had no effect on tadpole activity. Our results show that A. femoralis tadpoles can innately recognize some predators and probably need both visual and chemical information to effectively avoid them. This is the first study looking at anti-predator behavior in poison frog tadpoles. We discuss how parental care might influence the expression of predator avoidance responses in tadpoles.

The influence of maternal glucocorticoids on offspring phenotype in high- and low-risk environments

Elevated maternal glucocorticoid levels during gestation can lead to phenotypic changes in offspring via maternal effects. Although such effects have traditionally been considered maladaptive, maternally derived glucocorticoids may adaptively prepare offspring for their future environment depending upon the correlation between maternal and offspring environments. Nevertheless, relatively few studies test the effects of prenatal glucocorticoid exposure across multiple environments. We tested the potential for ecologically relevant increases in maternal glucocorticoids in the eastern fence lizard (Sceloporus undulatus) to induce adaptive phenotypic changes in offspring exposed to high or low densities of an invasive fire ant predator. Maternal treatment had limited effects on offspring morphology and behavior at hatching, but by 10 days of age, we found maternal treatment interacted with offspring environment to alter anti-predator behaviors. We did not detect differences in early-life survival based on maternal treatment or offspring environment. Opposing selection on anti-predator behaviors from historic and novel invasive predators may confound the potential of maternal glucocorticoids to adaptively influence offspring behavior. Our test of the phenotypic outcomes of transgenerational glucocorticoid effects across risk environments provides important insight into the context-specific nature of this phenomenon and the importance of understanding both current and historic evolutionary pressures.

History of canids in Chile and impacts on prey adaptations

Artiodactyl prey species of Chile, especially guanacos (Lama guanicoe), are reported to be very susceptible to predation by pack-hunting feral dogs. It has been previously suggested that guanacos and endemic South American deer may have evolved in the absence of pack-hunting cursorial predators. However, the paleoecology of canid presence in southern South America and Chile is unclear. Here, we review the literature on South American and Chilean canids, their distributions, ecologies, and hunting behavior. We consider both wild and domestic canids, including Canis familiaris breeds. We establish two known antipredator defense behaviors of guanacos: predator inspection of ambush predators, for example, Puma concolor, and rushing at and kicking smaller cursorial predators, for example, Lycalopex culpaeus. We propose that since the late Pleistocene extinction of hypercarnivorous group-hunting canids east of the Andes, there were no native species creating group-hunting predation pressures on guanacos. Endemic deer of Chile may have never experienced group-hunting selection pressure from native predators. Even hunting dogs (or other canids) used by indigenous groups in the far north and extreme south of Chile (and presumably the center as well) appear to have been used primarily within ambush hunting strategies. This may account for the susceptibility of guanacos and other prey species to feral dog attacks. We detail seven separate hypotheses that require further investigation in order to assess how best to respond to the threat posed by feral dogs to the conservation of native deer and camelids in Chile and other parts of South America.

Effects of environmental factors on the behaviour and nest group sizes of Smith's bush squirrels, Paraxerus cepapi, in a Zambezian bioregion

The responses of wildlife to environmental factors are of conservation importance. However, the absence of relevant information due to inadequate studies, and lack of understanding of the influences of environmental factors on wildlife, particularly in the Zambezian bioregion, remain a conservation concern. For instance, there is a shortage of knowledge on the relationship between fixed effects of environmental factors and behaviour as well as nest group sizes of Smith’s bush squirrels, Paraxerus cepapi Smith, 1836. Our study examined the relationship between fixed effects of several environmental factors (i.e., with focus on ecological factors) and the behaviour as well as nest group sizes of the bush squirrels in and around Zambia’s Chembe Bird Sanctuary (CBS). Flight initiation distances (FIDs) as an index of bush squirrel behaviour, and nest group sizes were simultaneously surveyed to understand the drivers of biological and population responses, respectively. The results revealed that higher tree height (m) and larger canopy coverage (%) could increase FIDs for bush squirrels. The nest group sizes of bush squirrels could also increase with canopy coverage (%) and presence of termite mounds. By focusing on the two different squirrels' responses, the results of this study highlight the most important environmental factors to consider in minimizing the impacts of human activities on bush squirrels, especially in conservation planning and management by taking into consideration the bush squirrels’ natural history, habitat protection and safe distance between humans and bush squirrels.

Vigilance in reindeer (Rangifer tarandus); evolutionary history, predation and human interference

To elucidate genetic variability in vigilance behaviour for reindeer with historical differences in their interactions with predators and humans, we measured vigilance frequency and duration for grazing reindeer in Southern Norway (Rondane and Norefjell-Reinsjøfjell), Svalbard (Edgeøya and Nordenskiöld Land) and Barf/Royal Bay and Busen in the southern Hemisphere (South Georgia). Averaged for all areas, frequency and duration of vigilance bouts were less than 0.5 and 2.5 s, respectively. Frequency was insignificantly 1.3 times higher in Rondane than Edgeøya, and significantly 2.0, 3.5, 5.2 and 12.4 times higher than Norefjell, Nordenskiöld Land, Barf/Royal Bay and Busen, respectively. Duration per vigilance bout was not different amongst the areas. Thus, while frequency varied considerably, duration remained constant, supporting a hard-wired adaptation to, among other suggestions, an open landscape. Plasticity in frequency allows for flexible behavioral responses to environmental factors with predation, domestication and hunting key drivers for reindeer. Other factors include (1) the open, treeless alpine/Arctic environment inhabited by Rangifer subspecies allowing warning time, (2) grouping behaviour, (3) relative low density of predators and (4) the anatomy and physiology of ungulate vision.

Mismatch Between Risk and Response May Amplify Lethal and Non-lethal Effects of Humans on Wild Animal Populations

Human activity has rapidly transformed the planet, leading to declines of animal populations around the world through a range of direct and indirect pathways. Humans have strong numerical effects on wild animal populations, as highly efficient hunters and through unintentional impacts of human activity and development. Human disturbance also induces costly non-lethal effects by changing the behavior of risk-averse animals. Here, we suggest that the unique strength of these lethal and non-lethal effects is amplified by mismatches between the nature of risk associated with anthropogenic stimuli and the corresponding response by wild animals. We discuss the unique characteristics of cues associated with anthropogenic stimuli in the context of animal ecology and evolutionary history to explore why and when animals fail to appropriately (a) detect, (b) assess, and (c) respond to both benign and lethal stimuli. We then explore the costs of over-response to a benign stimulus (Type I error) and under-response to a lethal stimulus (Type II error), which can scale up to affect individual fitness and ultimately drive population dynamics and shape ecological interactions. Finally, we highlight avenues for future research and discuss conservation measures that can better align animal perception and response with risk to mitigate unintended consequences of human disturbance.

Comparison of native and non-native predator consumption rates and prey avoidance behavior in North America and Europe

Novel predator-prey interactions can contribute to the invasion success of non-native predators. For example, native prey can fail to recognize and avoid non-native predators due to a lack of co-evolutionary history and cue dissimilarity with native predators. This might result in a competitive advantage for non-native predators. Numerous lady beetle species were globally redistributed as biological control agents against aphids, resulting in novel predator-prey interactions. Here, we investigated the strength of avoidance behavior of the pea aphid (Acyrthosiphon pisum) toward chemical cues of native lady beetles and non-native Asian Harmonia axyridis and European Coccinella septempunctata and Hippodamia variegata in North America, hypothesizing that cues of non-native lady beetles induce weaker avoidance behavior than cues of co-evolved native lady beetles. Additionally, we compared aphid consumption of lady beetles, examining potential predation advantages of non-native lady beetles. Finally, we compared cue avoidance behavior between North American and European pea aphid populations and aphid consumption of native and non-native lady beetles in North America and Europe. In North America, pea aphids avoided chemical cues of all ladybeetle species tested, regardless of their origin. In contrast to pea aphids in North America, European pea aphids did not avoid cues of the non-native H. axyridis. The non-native H. axyridis and C. septempunctata were among the largest and most voracious lady beetle species tested, on both continents. Consequently, in North America non-native lady beetle species might have a competitive advantage on shared food resources due to their relatively large body size, compared to several native American lady beetle species. In Europe, however, non-native H. axyridis might benefit from missing aphid cue avoidance as well as a large body size. The co-evolutionary time gap between the European and North American invasion of H. axyridis likely explains the intercontinental differences in cue avoidance behavior and might indicate evolution in aphids toward non-native predators.

Bugs scaring bugs: enemy-risk effects in biological control systems

Enemy-risk effects, often referred to as non-consumptive effects (NCEs), are an important feature of predator-prey ecology, but their significance has had little impact on the conceptual underpinning or practice of biological control. We provide an overview of enemy-risk effects in predator-prey interactions, discuss ways in which risk effects may impact biocontrol programs and suggest avenues for further integration of natural enemy ecology and integrated pest management. Enemy-risk effects can have important influences on different stages of biological control programs, including natural enemy selection, efficacy testing and quantification of non-target impacts. Enemy-risk effects can also shape the interactions of biological control with other pest management practices. Biocontrol systems also provide community ecologists with some of the richest examples of behaviourally mediated trophic cascades and demonstrations of how enemy-risk effects play out among species with no shared evolutionary history, important topics for invasion biology and conservation. We conclude that the longstanding use of ecological theory by biocontrol practitioners should be expanded to incorporate enemy-risk effects, and that community ecologists will find many opportunities to study enemy-risk effects in biocontrol settings.

Predators as Agents of Selection and Diversification

Predation is ubiquitous in nature and can be an important component of both ecological and evolutionary interactions. One of the most striking features of predators is how often they cause evolutionary diversification in natural systems. Here, we review several ways that this can occur, exploring empirical evidence and suggesting promising areas for future work. We also introduce several papers recently accepted in Diversity that demonstrate just how important and varied predation can be as an agent of natural selection. We conclude that there is still much to be done in this field, especially in areas where multiple predator species prey upon common prey, in certain taxonomic groups where we still know very little, and in an overall effort to actually quantify mortality rates and the strength of natural selection in the wild.

Global determinants of prey naiveté to exotic predators

Prey naiveté-the failure of prey to recognize novel predators as threats-is thought to exacerbate the impact that exotic predators exert on prey populations. Prey naiveté varies under the influence of eco-evolutionary mediating factors, such as biogeographic isolation and prey adaptation, although an overall quantification of their influence is lacking. We conducted a global meta-analysis to test the effects of several hypothesized mediating factors on the expression of prey naiveté. Prey were overall naive towards exotic predators in marine and freshwater systems but not in terrestrial systems. Prey naiveté was most pronounced towards exotic predators that did not have native congeneric relatives in the recipient community. Time since introduction was relevant, as prey naiveté declined with the number of generations since introduction; on average, around 200 generations may be required to erode naiveté sufficiently for prey to display antipredator behaviour towards exotic predators. Given that exotic predators are a major cause of extinction, the global predictors and trends of prey naiveté presented here can inform efforts to meet conservation targets.

Relaxed predation theory: size, sex and brains matter

Australia's wildlife is being considerably impacted by introduced mammalian predators such as cats (Felis catus), dogs (Canis lupus familiaris), and foxes (Vulpes vulpes). This is often attributed to native wildlife being naïve to these introduced predators. A systematic review of the literature reveals that native metatherians (body mass range 0.02-25 kg) do not recognise, and show relaxed antipredator behaviours towards, native and some introduced mammalian predators. Native eutherians (all with body mass < 2 kg), however, do appear to recognise and exhibit antipredator behaviours towards both native and introduced predators. Based on our findings, we propose a novel theory, the 'Relaxed Predation Theory'. Our new theory is based on the absence of large mammalian predators leading to reduced predation pressure in Australia during the past 40000-50000 years, and on three key differences between Australian metatherians and eutherians: size, sex, and brains. In light of this Relaxed Predation Theory, we make a number of recommendations for the conservation of Australian wildlife: (i) predator avoidance training of suitable species; (ii) exclusion fencing to exclude some, but not all, predators to facilitate the development of antipredator behaviours; (iii) captive breeding programs to prevent the extinction of some species; and (iv) reintroduction of Australia's larger predators, potentially to compete with and displace introduced predators. A more detailed understanding of the responses of Australian mammals to predators will hopefully contribute to the improved conservation of susceptible species.

Fears from the past? The innate ability of dogs to detect predator scents

Throughout the animal kingdom, antipredator mechanisms are an evolutionary driving force to enable the survival of species classified as prey. Information regarding a predator's location can be determined through chemosensory cues from urine, faeces, visual and/or acoustic signals and anal gland secretions; and in several lab and field-based studies it has been seen that these cues mediate behavioural changes within prey species. These behaviours are often linked to fear and avoidance, which will in turn increase the prey's survival rate. In many studies dogs (Canis lupus familiaris) have been used as a predator species, however, no research has addressed a dog's innate ability to detect predator scents, hence the rationale behind this study. We assessed the innate ability of the untrained domestic dog to detect faecal scents of wild Eurasian brown bear (Ursus arctos arctos) and European lynx (Lynx lynx). The study monitored 82 domestic dogs across the UK and Norway. The dogs were exposed to the two predator faecal scents from Eurasian brown bear and European lynx, a herbivore faecal scent of Eurasian beaver (Castor fiber) and water control. Measurements were taken upon the time spent within a 40 cm radius of each scent and changes in the dog's heart rate when within this 40 cm radius. We found dogs spent a decreased length of time around the predator scents and had an increased heart rate in relation to their basal heart rate. We conclude that dogs can innately sense predator scents of brown bear and lynx and elicit fear towards these odours, as shown through behavioural and physiological changes.

Mixed-species herding levels the landscape of fear

Prey anti-predator behaviours are influenced by perceived predation risk in a landscape and social information gleaned from herd mates regarding predation risk. It is well documented that high-quality social information about risk can come from heterospecific herd mates. Here, we integrate social information with the landscape of fear to quantify how these landscapes are modified by mixed-species herding. To do this, we investigated zebra vigilance in single- and mixed-species herds across different levels of predation risk (lion versus no lion), and assessed how they manage herd size and the competition-information trade-off associated with grouping behaviour. Overall, zebra performed higher vigilance in high-risk areas. However, mixed-species herding reduced vigilance levels. We estimate that zebra in single-species herds would have to feed for approximately 35 min more per day in low-risk areas and approximately 51 min more in high-risk areas to compensate for the cost of higher vigilance. Furthermore, zebra benefitted from the competition-information trade-off by increasing the number of heterospecifics while keeping the number of zebra in a herd constant. Ultimately, we show that mixed-species herding reduces the effects of predation risk, whereby zebra in mixed-species herds, under high predation risk, perform similar levels of vigilance compared with zebra in low-risk scenarios.

Responses to terrestrial nest predators by endemic and introduced Hawaiian birds

Birds free from nest predators for long periods may either lose the ability to recognize and respond to predators or retain antipredator responses if they are not too costly. How these alternate scenarios play out has rarely been investigated in an avian community whose members have different evolutionary histories. We presented models of two nest predators (rat and snake) and a negative control (tree branch) to birds on Hawai'i Island. Endemic Hawaiian birds evolved in the absence of terrestrial predators until rats were introduced approximately 1,000 years ago. Introduced birds evolved with diverse predator communities including mammals and snakes, but since their introduction onto the island approximately one century ago have been free from snake predation. We found that (a) endemic and introduced birds had higher agitation scores toward the rat model compared with the branch, and (b) none of the endemic birds reacted to the snake model, while one introduced bird, the Red-billed Leiothrix (Leiothrix lutea), reacted as strongly to the snake as to the rat. Overall, endemic and introduced birds differ in their response to predators, but some endemic birds have the capacity to recognize and respond to introduced rats, and one introduced bird species retained recognition of snake predators from which they had been free for nearly a century, while another apparently lost that ability. Our results indicate that the retention or loss of predator recognition by introduced and endemic island birds is variable, shaped by each species' unique history, ecology, and the potential interplay of genetic drift, and that endemic Hawaiian birds could be especially vulnerable to introduced snake predators.

Recognition of reptile predator scent is innate in an endangered lizard species

Chemical cues can alert prey to the presence of predators before the predator is within visual proximity. Recognition of a predator’s scent is therefore an important component of predator awareness. We presented predator and control scents to wild, wild-born captive, and predator-naive captive-born pygmy bluetongue lizards to determine (1) whether lizards respond to reptile chemical cues differently from controls, (2) whether captive lizards respond more strongly to a known predator than to other predatory reptiles, (3) whether captive-born lizards recognise predators innately, whether captive-born lizards have reduced predator recognition compared with wild lizards and whether time spent in captivity reduces responses to predators, and (4) whether the avoidance response to predator detection differs between naive and experienced lizards. There was no significant difference in the number of tongue flicks to predator scent among wild, wild-born and captive-born lizards, suggesting that predator detection is innate in the pygmy bluetongue lizard and time in captivity did not reduce predator recognition. The number of tongue flicks directed towards brown snake scent was significantly higher than that to the novel and water controls for all lizard origins. Lizards of all origins continued to bask in the presence of predator scents, suggesting that chemical cues alone may be insufficient to instigate an avoidance response and other cues may be required.

Captive-born collared peccaries learning about their predators: Lessons learnt but not remembered

Captive-born animals frequently lose their anti-predatory abilities due to the absence of encounters with their predators, but these abilities can be regained through specific training. Anti-predator training can, thus, enhance the success of reintroduction programs with predator naïve animals. In addition, a good memory is important to guarantee the effects of the anti-predator training and increase survival rate after release into the wild. In the present study, anti-predator training sessions were applied to 11 captive-born collared peccaries (Pecari tajacu), followed by memory tests at 30, 60 and 90 days after the end of the training sessions. The collared peccaries responded appropriately to training against predators, showing alert, escape and predator avoidance behaviors after anti-predator training; however, the animals maintained these acquired behaviors for only 30 days after the end of the anti-predator training. After 60 days, peccaries responded to the predator in a 'relaxed' manner, exhibiting no anti-predator behaviors. For the trained collared peccaries to be released into the wild, reinforcement in the anti-predator training would be required at least 30 days prior to release.

Behavioral response of naïve and non-naïve deer to wolf urine

Large carnivores are recolonizing many regions in Europe, where their ungulate prey have lived without them for >150 years. Whether the returning large carnivores will modify ungulate behavior and indirectly affect lower trophic levels, depends on the ability of ungulates to recognize risk based on past encounters and cues indicating carnivore presence. In two case studies, we tested, by means of camera trapping, the behavioral response of deer to wolf urine. The first case study was in the Netherlands where deer (still) live in absence of wolves, and the second in Poland with long-term wolf presence. As controls we used water (no scent) and all-purpose soap (unfamiliar scent). Deer vigilance level on control plots was 20% in both case studies indicating that wolf occupancy per se does not lead to a consistent difference in behavior. Placing wolf urine did not significantly affect deer behavior in either the wolf-absent or the wolf-present area. More intense cues, or a combination of cues, are likely needed to affect deer behavior. Moreover, we found an unexpected reaction of deer towards all-purpose soap of reduced foraging (and tendency for increased vigilance) in the wolf-present area, whereas it did not affect deer behavior in the wolf-absent area. We hypothesize that deer associate all-purpose soap with human presence, causing no response in human-dominated landscapes (the Netherlands), but triggering a behavioral reaction in more remote areas (Poland). This illustrates attention should be paid to controls used in scent experiments as they may be associated differently than intended.

Human influences on antipredator behaviour in Darwin's finches

Humans exert dramatic influences upon the environment, creating novel selective pressures to which organisms must adapt. On the Galapagos, humans have established a permanent presence and have altered selective pressures through influences such as invasive predators and urbanization, affecting iconic species such as Darwin's finches. Here, I ask two key questions: (a) Does antipredator behaviour (e.g., flight initiation distance - FID) change depending on whether invasive predators are historically absent, present, or eradicated? and (b) To what degree does urbanization affect antipredator behaviour? This study is one of the first to quantify antipredator behaviour in endemic species after the eradication of invasive predators. This will help to understand the consequences of invasive predator eradication and inform conservation measures. I quantified FID, an antipredator behaviour, in the small ground finch, across multiple islands in the Galapagos that varied in the presence, absence, or successful eradication of invasive predators. On islands with human populations, I quantified FID in urban and non-urban populations of finches. FID was higher on islands with invasive predators compared to islands with no predators. On islands from which invasive predators were eradicated ~11 years previously, FID was also higher than on islands with no invasive predators. Within islands that had both urban and non-urban populations of finches, FID was lower in urban finch populations, but only above a threshold human population size. FID in larger urban areas on islands with invasive predators was similar to or lower than FID on islands with no history of invasive predators. Overall, these results suggest that invasive predators can have a lasting effect on antipredator behaviour, even after eradication. Furthermore, the effect of urbanization can strongly oppose the effect of invasive predators, reducing antipredator behaviour to levels lower than found on pristine islands with no human influences. These results improve our understanding of human influences on antipredator behaviour which can help inform future conservation and management efforts on islands.

Chemosensory deficiency may render island-dwelling lizards more vulnerable to invasive predators

Newly introduced predators constitute a major threat to prey populations worldwide. Insular prey animals in particular often do not succeed in overcoming their naivety towards alien predators, making them specifically vulnerable. Why this is the case remains incompletely understood. Here, we investigate how the ability to detect and respond to predator chemical cues varies among populations of the Dalmatian wall lizard, Podarcis melisellensis. Lizards were sampled from five locations in south-eastern Croatia (one mainland location and four islands) that varied in the composition of their predator community. We observed the lizards’ behaviour in response to chemical cues of native saurophagous snakes (the Balkan whip snake, Hierophis gemonensis, and eastern Montpellier snake, Malpolon insignitus) and an introduced mammalian predator (the small Indian mongoose, Herpestes auropunctatus – a species held responsible for the loss of numerous insular reptile populations worldwide). Mainland lizards showed elevated tongue-flick rates (indicative of scent detection) as well as behaviours associated with distress in response to scents of both native and introduced predators. In sharp contrast, island lizards did not alter their behaviour when confronted with any of the predator cues. Alarmingly, even lizards from islands with native predators (both snakes and mammals) and from an island on which mongooses were introduced during the 1920s were non-responsive. This suggests that insular populations are chemosensorily deprived. As failure at the predator-detection level is often seen as the most damaging form of naivety, these results provide further insight into the mechanisms that render insular-living animals vulnerable to invasive species.