Prey Naivete Research Articles

Phenotypic and Transcriptomic Analysis Revealed a Lack of Risk Perception by Native Tadpoles Toward Novel Non-Native Fish.

The introduction of alien species poses a serious threat to native biodiversity, and mountain lake systems in the southwest of China are particularly vulnerable to the introduction of non-native fish. The prey naivety hypothesis states that native species may not be able to recognize novel introduced species due to a lack of common evolutionary background and therefore become easy targets, so the impacts of non-native fish on mountain endemic amphibians need to be urgently assessed. In an ex-situ experiment, we exposed the tadpoles of the Chaochiao Brown Frog (Rana chaochiaoensis), endemic to western China, to kairomones of both native and translocated fish species, and their phenotypic and genetic response patterns were compared. The results revealed significant phenotypic plasticity responses in total length (TOL), tail length (TL), and tail muscle width (TW) of tadpoles induced by native fish kairomone, while tadpoles exposed to translocated fish kairomone exhibited weaker phenotypic changes. At the transcriptional level, the number of differently expressed genes (DEGs) in the native fish treatment was 3.1-fold (liver) and 52.6-fold (tail muscle) higher than in the translocated fish treatment, respectively. There were more unique DEGs in the native fish treatment, primarily enriched in terms and pathways related to stress response, energy metabolism, and muscle development. The study revealed a lack of risk perception by native tadpoles toward novel non-native fish, providing new evidence for the prey naivety hypothesis from both phenotypic and molecular perspectives. Future conservation efforts should prioritize assessing the impacts of non-native fish on alpine and subalpine threatened and narrowly distributed amphibians. Additionally, prevention, early warning, monitoring, and removal of non-native fish should be carried out as soon as possible.

Whose scat is that? Determining recognition of predator scat by Australian mammals

Introduced predators have been implicated in the extinction or range reduction of many Australian species, potentially due to native wildlife exhibiting prey naivety. We used traps with predator faeces present, monitored by camera traps, to determine if Australian mammals responded to native and introduced predator faeces. The presence of either faeces did not influence the trap or camera captures of any species.

Rapid change in anti‐predator behaviour of a threatened marsupial after thousands of years of isolation from predators

AbstractPrey naivety occurs when an animal does not recognize or is unable to respond effectively to the threat of a predator. Many animals lose their anti‐predator responses if they become isolated from predators, becoming vulnerable to increased predation rates if released into areas where native or introduced predators are present. In situ exposure to introduced predators is a technique that has been shown to improve anti‐predator traits in burrowing bettongs (Bettongia lesueur) and greater bilbies (Macrotis lagotis) and is associated with greater survival in bilbies. However, little is known about how in situ exposure to native predators can address the issue of prey naivety. This study investigated whether Shark Bay bandicoots (Perameles bougainville) from a remnant island population isolated from all mammalian predators for several thousand years could improve their anti‐predator behaviour after living with a native predator, the western quoll (Dasyurus geoffroii). We compared the vigilance and wariness behaviour, and nest site attributes of bandicoot populations living with and without native quolls at the Arid Recovery Reserve in South Australia. We found that after 6 years of quoll exposure, quoll‐exposed bandicoots had significantly larger flight initiation distances and spent more time engaged in vigilance behaviours at feed trays compared to control bandicoots. Quoll‐exposed bandicoots also selected nests with increased vegetation cover, preferring nests with both understory and overstory shrub cover present. The results of this study indicate that in situ exposure to native predators can improve vigilance and wariness behaviours in Shark Bay bandicoots over relatively short time frames. Exposing threatened species to native predators may assist with preparing them for life outside fenced safe havens.

Prey responses to foxes are not determined by nativeness

Introduced predators are thought to be responsible for the decline and extinction of their native prey. The prey naivety hypothesis provides a mechanism for these declines, suggesting that native prey are vulnerable to introduced predators as their coevolutionary history is insufficiently long for antipredator behaviours to fully develop. The prey naivety hypothesis thus predicts that prey will be less responsive to introduced predators than to native predators. Australia's endemic small mammals are thought to be vulnerable to predation by red foxes because they are less responsive to – or naive of – a predator with whom they have only co‐occurred since the 19th century. To test whether nativeness determines antipredator behaviours we compared small mammal behavioural responses to fox scent outside (Australia) and inside the foxes' native range (North America and Israel). We conducted giving‐up density experiments in the deserts of these three regions and evaluated small mammal antipredator responses to fox scent. To place these results in a broader context, we then integrated our results into a global meta‐analysis of studies assessing prey responsiveness to fox scent. All small mammals similarly increased their vigilance in response to fox scent, regardless of their coevolutionary history with foxes. Australian small mammals responded with greater wariness to fox scent, by decreasing time at food patches in response to fox scent more than Israeli and American small mammals did. However, we found no evidence that this behaviour influenced foraging as nut consumption was unaffected. Our meta‐analysis revealed that globally, small mammals respond with similar wariness to fox scent regardless of whether foxes are their native predator. We found no evidence that Australian small mammals respond in a maladaptive manner, compared to the foxes' native prey. Our results suggest that animals can develop antipredator behaviours to introduced predators to the same magnitude as native prey.

Anti-predatory responses of two native gastropods to an invasive predator

As native prey species lack a co-evolutionary history with invasive predators, they often have limited capacity to identify and respond to the threat of predation. This phenomenon has led to the prey naivety hypothesis. Invasive predators can have devastating impacts on native prey populations. Thus, there is a need to better understand the ability of native species to respond to invasive predators. Here, laboratory behavioural experiments tested the anti-predatory responses of two gastropods, Cominella lineolata and Dicathais orbita, against an invasive predator, Asterias amurensis, and a native predator, Coscinasterias muricata. There was no chemical exudate released by any D. orbita to either species of seastar or a wax seastar control. Only a small percentage of D. orbita individuals fled from the invasive (12.5%) and native (17%) seastars. The overall separation distance between D. orbita and the two seastars was recorded for a further three minutes. While the measured distance between the invasive seastar and D. orbita was greater (61 ± 7 mm) than the distance between the native seastar (39 ± 10 mm), this was not statistically significant. In contrast, C. lineolata exhibited strong responses to the native seastar, but less strongly to the invasive seastar. Only 50% of snails fled and 15% released an exudate in response to A. amurensis, compared to 80% of snails fleeing and releasing an exudate to the native seastar. In contrast to expectations, C. lineolata collected from naïve populations tended to respond less frequently (25% of snails) by fleeing from the invasive seastar than snails collected from exposed (50% of snails), however this was not significant. This same trend was observed for C. muricata with 70% and 90% of snails fleeing from exposed and naïve populations, respectively. After recording the behavioural responses of both seastars and snails for three minutes, the release of exudate resulted in an increased separation distance between C. lineolata and C. muricata of 122 mm (± 31 mm) compared with just 28 mm (± 16 mm) when the snails failed to release the exudate, whereas the separation distances between C. lineolata and A. amurensis was 143 mm (± 31 mm) and 87 mm (± 10 mm) with and without exudate release, respectively. This latter result indicates that while the exudate appears to be an effective anti-predatory mechanism against the native seastar, it appears less effective against the invasive seastar.

Addressing prey naivety in native mammals by accelerating selection for antipredator traits.

Harnessing natural selection to improve conservation outcomes is a recent concept in ecology and evolutionary biology and a potentially powerful tool in species conservation. One possible application is the use of natural selection to improve antipredator responses of mammal species that are threatened by predation from novel predators. We investigated whether long-term exposure of an evolutionary naïve prey species to a novel predator would lead to phenotypic changes in a suite of physical and behavioral traits. We exposed a founder population of 353 burrowing bettongs (Bettongia lesueur) to feral cats (Felis catus) over 5 years and compared the physical and behavioral traits of this population (including offspring) to a control (non-predator exposed) population. We used selection analysis to investigate whether changes in the traits of bettongs were likely due to phenotypic plasticity or natural selection. We also quantified selection in both populations before and during major population crashes caused by drought (control) and high predation pressure (predator-exposed). Results showed that predator-exposed bettongs had longer flight initiation distances, larger hind feet, and larger heads than control bettongs. Trait divergence began soon after exposure and continued to intensify over time for flight initiation distance and hind foot length relative to control bettongs. Selection analysis found indicators of selection for larger hind feet and longer head length in predator-exposed populations. Results of a common garden experiment showed that the progeny of predator-exposed bettongs had larger feet than control bettongs. Results suggest that long-term, low-level exposure of naïve prey to novel predators can drive phenotypic changes that may assist with future conservation efforts.

Savviness of prey to introduced predators.

The prey naivety hypothesis posits that prey are vulnerable to introduced predators because many generations in slow gradual coevolution are needed for appropriate avoidance responses to develop. It predicts that prey will be more responsive to native than introduced predators and less responsive to introduced predators that differ substantially from native predators and from those newly established. To test these predictions, we conducted a global meta-analysis of studies that measured the wariness responses of small mammals to the scent of sympatric mammalian mesopredators. We identified 26 studies that met our selection criteria. These studies comprised 134 experiments reporting on the responses of 36 small mammal species to the scent of six introduced mesopredators and 12 native mesopredators. For each introduced mesopredator, we measured their phylogenetic and functional distance to local native mesopredators and the number of years sympatric with their prey. We used predator and prey body mass as a measure of predation risk. Globally, small mammals were similarly wary of the scent of native and introduced mesopredators; phylogenetic and functional distance between introduced mesopredators and closest native mesopredators had no effect on wariness; and wariness was unrelated to the number of prey generations, or years, since first contact with introduced mesopredators. Small mammal wariness was associated with predator-prey body mass ratio, regardless of the nativity. The one thing animals do not seem to recognize is whether their predators are native.

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

AbstractPredator 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.

They do not fear the unknown: Ancylus fluviatilis (Mollusca, Planorbidae) shows no predator avoidance behavior towards a novel invasive predator

Biological invasion is a strong threat to native biodiversity, with limnic systems being especially vulnerable due to historical separation and resulting prey naivety. The prey naivety hypothesis states that native species may not be able to recognize novel predators due to a lack of common evolutionary background and, therefore, become easy targets. In a laboratory experiment, we added cues of native European bullhead (Cottus gobio Linnaeus, 1758) and invasive round goby [Neogobius melanostomus (Pallas, 1814)] to Ancylus fluviatilis Müller, 1774 originating from two different populations within the same river (one naive, one experienced towards round goby) and compared their predator avoidance behavior. Individuals from both populations recognized cues from the known predator C. gobio and reduced their locomotive activity. To round goby cues, however, naive individuals did not respond, thereby supporting the prey naivety hypothesis. Experienced individuals, in contrast, reduced their activity, suggesting a learning effect due to the co-occurrence of invasive predator and prey. At fast moving invasion fronts of highly invasive species like N. melanostomus, prey naivety can, hence, enhance their negative impact on ecosystems. Behavioral adaptation of native species resulting in predator avoidance reactions could, therefore, play an important role in ecosystem resilience and temporal invasion dynamics.

Sniffing out danger: rapid antipredator training of an endangered marsupial

Globally, predator aversion training has assisted naive prey species to learn to evade introduced predators, improving translocation success. Eastern barred bandicoots (Perameles gunnii; hereafter ‘bandicoot’) are extinct on mainland Australia due to habitat loss and introduced predators, and are the focus of a long-term captive breeding and reintroduction program. Our trials showed that captive bandicoots failed to recognise cat (Felis catus) scents as belonging to a predator, suggesting prey naivety towards cats. We trialled five stimuli to elicit short-term fear behaviour in bandicoots. An automatic compressed air spray and automatic bin lid were most effective. We coupled these stimuli with cat urine during predator aversion training and presented them to bandicoots on three occasions. Bandicoots learnt to avoid the area containing cat urine, suggesting bandicoots are capable of learning new behaviours rapidly. Six trained and five untrained captive bandicoots where released onto Summerland Peninsular, Phillip Island (with cat densities at 1.1 cats/km2). Both had high survival and recapture rates 7 months after release. Training endangered species to avoid introduced predators could assist with long-term species recovery.

Not so naïve: endangered mammal responds to olfactory cues of an introduced predator after less than 150 years of coexistence

Inability to recognise and/or express effective anti-predator behaviour against novel predators as a result of ontogenetic and/or evolutionary isolation is known as ‘prey naivete’. Natural selection favours prey species that are able to successfully detect, identify and appropriately respond to predators prior to their attack, increasing their probability of escape and/or avoidance of a predator. However, for many prey species, learning and experience are necessary to develop and perform appropriate anti-predator behaviours. Here, we investigate how a remnant population of bilbies (Macrotis lagotis) in south-west Queensland responded to the scents of two predators, native dingoes (Canis familiaris) and introduced feral cats (Felis catus); a procedural control (rabbits; Oryctolagus cuniculus); and an experimental control (no scent). Bilbies in Queensland have shared more than 8000 years of co-evolutionary history with dingoes and less than 140 years with feral cats and less than 130 years with rabbits. Bilbies spent the greatest proportion of time investigating and the least amount of time digging when cat and dingo/dog faeces were present. Our results show that wild-living bilbies displayed anti-predator responses towards the olfactory cues of both a long-term predator (dingoes) and an evolutionary novel predator (cats). Our findings suggest that native species can develop anti-predator responses towards introduced predators, providing support for the idea that predator naivete can be overcome through learning and natural selection as a result of exposure to introduced predators. Not so naive—As a result of lifetime and/or evolutionary isolation from predators, some prey species appear to be naive towards introduced predators. This is particularly the case in Australia, where native mammalian species appear to be naive towards recently introduced predators such as the feral cat and European red fox. In a study of wild-living bilbies, we found that 150 years of co-evolutionary experience is enough to develop predator recognition.

Testing the prey naiveté hypothesis: Can native prey (Astyanax ruberrimus) recognize an introduced top predator, Cichla monoculus?

The prey naivete hypothesis (PNH) posits that prey will often fail to recognize and respond to introduced predators with whom they do not share a co-evolutionary history. We tested this hypothesis by examining anti-predator behaviour in the native characid fish Astyanax ruberrimus in response to its main native (Hoplias microlepis) and introduced (Cichla monoculus) fish predators in Panama. We observed the behaviour of wild-caught A. ruberrimus from an invaded and uninvaded site following exposure to chemical stimuli from: (1) injured conspecifics, (2) the native predator, and (3) the introduced predator. We found, first, that A. ruberrimus consistently responded to cues from injured conspecifics, suggesting that this species possesses an alarm signaling mechanism similar to that observed across Ostariophysan fishes. Second, A. ruberrimus responded to cues from their native predator, but only in one population, suggesting responses may be threat-sensitive. Third, A. ruberrimus lacking prior exposure to C. monoculus did not respond to cues from this predator, consistent with the PNH. In contrast, A. ruberrimus that have co-occurred with C. monoculus for several decades did respond to cues from this predator, suggesting that prior exposure to C. monoculus has led (either via local adaptation or learning) to acquired predator recognition. Overall, our findings are consistent with the PNH, although we cannot conclusively rule out alternate explanations for the observed differences between populations. Our work represents a first step towards understanding the role that behavioural naivete may have played in the initial stages of this important tropical freshwater introduction.

A trial reintroduction of the western quoll to a fenced conservation reserve: implications of returning native predators

While fenced reserves provide sanctuary for many threatened prey species, few projects have reintroduced native threatened predators, despite their potential role in regulating prey, addressing prey naivety, trophic regulation, and predator conservation. We aimed to investigate a set of issues unique to predator reintroduction into fenced reserves: how to contain predators that are naturally wide roaming, how to estimate carrying capacity, and will native predators impact resident threatened species? We conducted a trial reintroduction of four western quolls (Dasyurus geoffroii) (two males, two females) into a fenced reserve where four threatened prey species had been reintroduced and feral cats and foxes excluded. We monitored quoll survival, diet, movement and reproduction. Nocturnal foraging ranges measured over a fortnight were 3–17km2, favouring burrows in dune habitat for shelter. Dietary analysis indicated a preference for reintroduced bettongs and western barred bandicoots, and resident hopping mice. Successful breeding was recorded but the two male quolls eventually escaped the reserve by climbing over the external fence and did not return. Results suggest that quoll reintroductions to fenced reserves will require fence designs that enable quolls to climb back into the reserve, threat management outside the reserve, and close monitoring of prey species.

Looking through the predator’s eyes: another perspective in naïveté theory

The topic of biological invasion has adopted the concepts of neophobia and dietary conservatism to explain why some species are reluctant to include nonnative species in their diets, with prey naivete predicting that prey would not be able to recognize novel predators in the environment. This is particularly true for fish, for which studies are rare, mainly in natural environments. Here, the existence of feeding selectivity in terms of prey origin was investigated in nature by quantifying the contribution of nonnative prey to the diets of native and nonnative predators. Three distinct rivers in the upper Parana River basin (Brazil) and 13 piscivores were used to test the hypothesis. Out of the 650 possible trait combinations, only prey body shape (sagittiform) and predator relative body height were found to be correlated. Even though native and nonnative prey presented similar functional traits, very strong selectivity by prey origin was observed, with native predators positively selecting native prey. Native predators possibly do not recognize nonnative prey or lack the necessary ability to prey upon nonnative prey. Such findings show that, for several predators, prey origin does matter. There are many implications of “predator naivete”, as an increasing number of nonnative species are being introduced worldwide, with advances in such area enabling a better understanding of several limitations in biological invasions. Perhaps looking through the predator’s eyes might bring some novel perspective and help to understand some as yet unexplainable paradigms in biological invasions.

Homing decisions reveal lack of risk perception by Caribbean damselfish of invasive lionfish

Prey naivete, or the failure of prey to recognize non-native predators due to a lack of co-evolutionary history, is thought to underpin the large impact of invasive Indo-Pacific lionfish (Pterois sp.) on coral reef fish populations in the western Atlantic. Most previous studies of lionfish recognition have taken place in experimental tanks that did not mimic natural conditions or used bottle or cage field designs that constrained natural behaviour. To alleviate these issues, we compared the homing patterns of experimentally translocated Caribbean bicolor damselfish (Stegastes partitus) in the presence and absence of standardized models of a lionfish, of an ecologically similar native piscivore (black grouper; Mycteroperca bonaci), and of a native non-piscivore (French grunt, Haemulon flavolineatum) in the field. The native grouper model elicited a strong predator avoidance response: translocated damselfish became unlikely to home when released beyond ~ 2 m from their territory and took longer to do so. In contrast, damselfish facing a lionfish model exhibited similar homing behaviours to those of damselfish in the presence of a non-piscivorous grunt and in the absence of any model. Fish length and translocation distance also influenced homing: damselfish stopped homing when released more than 5.6 m away from their territory and larger individuals crossed wider sand gaps. Overall, our findings are consistent with the idea that bicolor damselfish are naive to the threat of predation presented by lionfish, but also with the notion that damselfish might be assessing, but deeming to be low, the threat of a stalking predator hunting over open sand. Both mechanisms point to inaccurate risk perception in relation to invasive lionfish. More broadly, we highlight a novel experimental translocation approach to evaluate behavioural responses of native prey species to novel predators under realistic field conditions.

Differential effects of native vs. invasive predators on a common Caribbean reef fish

Predators may have consumptive (lethal) and non-consumptive (sub-lethal) effects on prey. Non-consumptive effects include altered behavior and reduced growth and fecundity. Native prey may not recognize non-native predators as a threat, and therefore may suffer pronounced effects. Additionally, non-native predators may elicit different behavioral responses from prey compared to native predators. Theory predicts that consumptive effects should be greater for non-native predators (due to prey naivete), and non-consumptive effects should be greater for native predators (due to predator recognition). To test these hypotheses, I monitored bicolor damselfish (Stegastes partitus) in the presence of invasive predatory Pacific lionfish (Pterois spp.), a native predator (graysby, Cephalopholis cruentata), and an egg predator (bluehead wrasse, Thalassoma bifasciatum). Body size and location of lionfish and graysby were monitored on reefs in the Bahamas. Bicolor fecundity was measured as the number and size of egg-masses that individual fish laid. Bicolor fecundity was negatively correlated with lionfish density but not graysby or bluehead density. Neither predator had a detectable effect on bicolor body size, but lionfish density was negatively correlated with the size of mature adult damselfish. I observed behavioral responses of bicolors to the two piscivores, to bluehead wrasse, and to two herbivorous fishes (Acanthurus coeruleus, Scarus spp.) as non-aggressive controls. Bicolors changed behavior (feeding and aggression) in the presence of all native fishes, but not in the presence of lionfish. Thus, differential effects exist between native and non-native predators, and invasive lionfish pose a non-consumptive threat to bicolor damselfish via reduced growth and fecundity.

Success criteria not met, but valuable information gained: monitoring a reintroduction of the tammar wallaby

Context Fauna translocations are a tool for improving the conservation status of threatened species. Reviews of translocations undertaken in Australia and globally have reported that many fail because of predation by exotic predators. The outcome of ~40% of translocations was unknown, often owing to inadequate post-release monitoring. Monitoring methods such as global positioning system data-loggers can provide valuable information on survival, habitat use and sociality, and can be particularly useful for cryptic species. Aims The present study used global positioning system (GPS) data-loggers and VHF radio-transmitters to evaluate the success of a reintroduction of the tammar wallaby and measured survival, short-term home-range, habitat use and proximity between reintroduced individuals (as a proxy for association). Methods Sixty-nine tammar wallabies of captive and wild stock were reintroduced to Kalbarri National Park (KNP) following long-term and broad-scale fox control, with nine receiving GPS data-loggers, and 16 receiving VHF radio-transmitters. Wallabies were intensively monitored for up to 11 months post-release. Mortalities were investigated using DNA identification and field necropsies. Key results In total, 16 of the 25 collared wallabies died within 11–319 days of release. Ten of the sixteen deaths were from predation. Home-range areas were larger than those reported elsewhere. Wallabies utilised long-undisturbed vegetation with a dense canopy cover during crepuscular periods. These areas were likely sought as refuge from predation and thermal extremes. During the main feeding period, a mosaic of recently burnt (i.e. ~1 year) and >10 years since last disturbance was important. Conclusions The reintroduction was not considered successful because two-thirds of the collared wallabies died within 1 year of release and, therefore, the success criteria were not met. Implications Despite long-term fox control in KNP, the majority of collared wallaby deaths were a result of fox predation. This highlights the inherent difficulty of establishing populations of some species in the presence of introduced predators. Additional research could assist in determining appropriate control levels for introduced predators, to help ensure the success of future translocations of this species. Consideration should be given to the prey naivety of source animals, prey-switching by introduced predators, and short-term supplementary feeding to assist population establishment.

Novel predators emit novel cues: a mechanism for prey naivety towards alien predators

Detecting enemies is crucial for survival and a trait that develops over an evolutionary timeframe. Introduced species disrupt coevolved systems of communication and detection in their new ranges, often leading to devastating impacts. The classic example is prey naivety towards alien predators, whereby prey fail to recognise a new predator. Yet exactly why native prey fail to recognise alien predators remains puzzling. Naivety theory predicts that it is because novel predators emit novel cues. Distantly related animals have distinct evolutionary histories, physiologies and ecologies, predicting they will emit different cues. Yet it also possible that all predators emit similar cues because they are carnivorous. We investigate whether odour cues differ between placental and marsupial carnivores in Australia, where native prey experienced only marsupial mammal predation until ~4000 years ago. We compared volatile chemical profiles of urine, scats and bedding from four placental and three marsupial predators. Chemical profiles showed little overlap between placental and marsupial carnivores across all odour types, suggesting that cue novelty is a plausible mechanism for prey naivety towards alien predators. Our results also suggest a role for olfactory cues to complement visual appearance and vocalisations as biologically meaningful ways to differentiate species.

Spatial variation in the importance of different prey types in the diet of red foxes

Invasive predators are identified as an important threatening process implicated in native species decline and extinction in Australia. This study aimed at developing our understanding of landscape-level spatial patterns in the red fox diet. We established prey importance based on dietary composition of red fox scats, and related this information to landscape structure. The relationship between scat composition and the frequency of detection and spatial patterns of occurrence of small mammals based on survey data from the same region was also evaluated using ordination analyses. We found that native vertebrates, dominated by Sminthopsinae, were the most important prey. However, Mus musculus were detected significantly more than Sminthopsinae across the region. Sminthopsinae were detected most frequently in traps in grazing landscapes; however, red fox scats from grazing landscapes were dominated by invertebrates. We propose these patterns may be partially driven by M. musculus abundance attracting predation pressure to the landscape and Sminthopsinae exhibiting prey naivety resulting in their disproportional representation in red fox scats.

Prey naiveté to invasive lionfish Pterois volitans on Caribbean coral reefs

Native prey can be particularly vulnerable to consumption by exotic predators. Prey naivete, the failure to recognize a novel predator due to lack of recent co-evolutionary history, likely facilitates the disproportionate impact that some exotic predators exert on prey populations. Lionfish Pterois volitans, exotic predators from the Pacific, have invaded coral reefs and other coastal habitats along the western Atlantic. Prey naivete towards novel lionfish was tested in field experiments and with observations using closest approach distance as the anti-predator response. We quantified the distance of prey fishes to exotic lionfish in both the Atlantic and Pacific (invasive and native ranges of lionfish) as well as to native predators in the Atlantic. In the Atlantic, exper- iments indicated that Haemulon plumierii, prey of lionfish, generally display a closer approach distance to exotic than to native predators, and field observations of free-ranging fish revealed that at least 5 other species of small fishes (Halichoeres bivitattus, Halichoeres garnoti, Scarus tae- niopterus, Stegastes leucostictus and Thalassoma bifasciatum) also might exhibit limited predator- avoidance behaviour towards invasive lionfish. We also found that 3 families of small fish (Labri- dae, Pomacentridae and Scaridae) maintained greater distances from lionfish in the Pacific compared with the Atlantic in both experimental and field observations. These results suggest prey naivete to exotic lionfish by at least 8 species of fish (Abudefduf saxatilis, H. plumierii, H. bivitattus, H. garnoti, S. taeniopterus, Sparisoma aurofrenatum, S. leucostictus and T. bifasciatum) in the Atlantic, which could be contributing to the rapid expansion of this invasive species by enhancing its fitness and reproductive output through high predation efficiency.