Do Australian small mammals respond to native and introduced predator odours?

Abstract Coevolution is thought to have led to many small mammal species avoiding the scent marks of their main mammalian predators, as they provide a reliable cue to predation risk. Most support for this hypothesis comes from northern hemisphere predator/prey systems, however, it is unclear whether this avoidance of predator faecal odour occurs in Australia's mammalian fauna, which has evolved in relative isolation from the rest of the world, and is dominated by marsupials rather than placentals. We tested this theory for an Australian system with marsupial and placental predators and prey, that share a long‐term (>1 million years) or short‐term (<150 years) exposure to each other. The predators were the native marsupial tiger quoll Dasyurus maculatus and the introduced placental red fox Vulpes vulpes. The potential prey were three native rodent species, the bush rat Rattus fuscipes, the swamp rat Rattus lutreolus, the eastern chestnut mouse Pseudomys gracilicaudatus, and the marsupial brown antechinus Antechinus stuartii. Small mammals were captured in Elliott traps with 1/3 of traps treated with fox faeces, 1/3 treated with quoll faeces and the remainder left untreated. The native rodent species all showed avoidance of both tiger quoll and red fox odours whereas the marsupial antechinus showed no responses to either odour. Either predator odour avoidance has not evolved in this marsupial or their reaction to predator odours may be exhibited in ways which are not recognizable through trapping. The avoidance by the rodents of fox odour as well as quoll odour indicates this response may either be due to common components in fox and quoll odour, or it may be a recently evolved response.     

Variation of prey responses to cues from a mesopredator and an apex predator

Detection and avoidance of predator cues can be costly, so it is important for prey to balance the benefits of gaining food against the costs of avoiding predators. Balancing these factors becomes more complicated when prey are threatened by more than one type of predator. Hence, the ability to recognize species‐specific predator odours and prioritize behaviours according to the level of risk is essential for survival. We investigated how rock rats, Zyzomys spp. modify their foraging behaviour and giving‐up density (GUD) in the presence of an apex predator, the dingo Canis dingo, a mesopredator, the northern quoll Dasyurus hallucatus, a herbivore, the rock wallaby Petrogale brachyotis as a pungency control and water as a procedural control. Both dingoes and quolls consume rock rats, but because quolls can enter small crevices inhabited by rock rats, they pose a greater threat to rock rats than dingoes. Rock rats demonstrated a stronger avoidance to quoll odour than dingo odour, and no avoidance of the pungency control (rock wallaby) and the procedural control (water). GUD values declined significantly over the duration of the study, but did not differ between odour treatments. Our results support the hypothesis that prey vary behaviour according to perceived predator threat, and show stronger responses to potentially more dangerous predators.     

Know thy enemy: Behavioural response of a native mammal (Rattus lutreolus velutinus) to predators of different coexistence histories

Abstract Predation is recognized as a major selective pressure influencing population dynamics and evolutionary processes. Prey species have developed a variety of predator avoidance strategies, not least of which is olfactory recognition. However, within Australia, European settlement has brought with it a number of introduced predators, perhaps most notably the red fox (Vulpes vulpes) and domestic cat (Felis catus), which native prey species may be unable to recognize and thus avoid due to a lack of coexistence history. This study examined the response of native Tasmanian swamp rats (Rattus lutreolus velutinus) to predators of different coexistence history (native predator‐ spotted‐tail quoll (Dasyurus maculatus), domestic cats and the recently introduced red fox). We used an aggregate behavioural response of R. l. velutinus to predator integumental odour in order to assess an overall behavioural response to predation risk. Rattus lutreolus velutinus recognized the integumental odour of the native quoll (compared with control odours) but did not respond to either cat or fox scent (compared with control odur). In contrast, analyses of singular behaviours resulted in the conclusion that rats did not respond differentially to either native or introduced predators, as other studies have concluded. Therefore, measuring risk assessment behaviours at the level of overall aggregate response may be more beneficial in understanding and analysing complex behavioural patterns such as predator detection and recognition. These results suggest that fox and cat introductions (and their interactive effects) may have detrimental impacts upon small native Tasmanian mammals due to lack of recognition and thus appropriate responses.     

The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

Do house mice modify their foraging behaviour in response to predator odours and habitat?

Predator odours and habitat structure are thought to influence the behaviour of small mammalian prey, which use them as cues to reduce risks of predation. We tested this general hypothesis for house mice, Mus domesticus, by manipulating fox odour density via addition of fox scats and habitat via patchy mowing of vegetation, for populations in 15 × 15-m field enclosures. Using giving-up densities (GUDs), the density of food remaining when an animal quits harvesting a patch, we measured foraging behaviours in response to these treatments. Mice consistently avoided open areas, leaving GUDs two to four times greater in these areas than in densely vegetated patches. However, mouse GUDs did not change in response to the addition of fox scats, even immediately after fresh scats were added. There was no interaction between fox odour and habitat use. We then tested whether habituation to fox odours had occurred, by comparing the individual responses to scats of eight mice born into enclosures with fox scats to those of eight mice born into scat-free enclosures and five wild mice. In smaller enclosures, GUDs of trays with scats did not differ from GUDs of trays without scats for any treatment. We conclude that exposure to high levels of fox odours did not alter the foraging behaviour of mice, but that mice did reduce foraging in areas where habitat was removed, perceiving predation risk to be greater in these areas than controls. We suggest further that studies using the ‘scat-at-trap’ technique, which have shown avoidance of predator odours by mice and other small mammals, may overestimate the general avoidance of predator odours by free-living prey, which must forage with a constant background of predator odours.     

Fox Odour Increases Vigilance in European Rabbits: A Study under Semi-Natural Conditions

The recognition of predator odours is a well‐known mechanism in many prey species which may lead to various behavioural and physiological responses. This has been shown for many mammal species under laboratory conditions, but efforts to validate the results in the field often have led to inconclusive results. We investigated the behavioural reactions and the physiological stress response of European rabbits (Oryctolagus cuniculus) to the odour of a mammalian predator (red fox, Vulpes vulpes) under semi‐natural conditions. The study was conducted on a rabbit population living in an outdoor enclosure of 2 ha. We compared the rates of vigilance and exploration, the time allocated to self‐directed behaviours, the home range sizes and the physiological responses of an experimental and a control group. Only animals from the experimental group were confronted with fox faeces. These animals increased their vigilance rate whereas the control animals did not respond. The increase did not differ between adult and subadult individuals. Furthermore, the experimental animals frequently approached the odour of the predator which might indicate an increase in investigative behaviour. Home‐range size, feeding and other self‐directed behaviours did not change in response to fox odour. Moreover, the animals of the experimental and the control group did not differ in serum corticosterone concentrations (measured after adrenocorticotrophic hormone challenge) that we determined in the beginning and in the end of the experiment. We suggest that the observed behavioural responses represent a low‐cost strategy for lowering the individual risk of predation.     

Does a top-predator provide an endangered rodent with refuge from an invasive mesopredator?

In arid environments, ecological refuges are often conceptualised as places where animal species can persist through drought owing to the localised persistence of moisture and nutrients. The mesopredator release hypothesis (MRH) predicts that reduced abundance of top-order predators results in an increase in the abundance of smaller predators (mesopredators) and consequently has detrimental impacts on the prey of the smaller predators. Thus according to the MRH, the existence of larger predators may provide prey with refuge from predation. In this study, we investigated how the abundance of an endangered rodent Notomys fuscus is affected by Australia's largest predator, the dingo Canis lupus dingo , introduced mesopredators, introduced herbivores, kangaroos and rainfall. Our surveys showed that N. fuscus was more abundant where dingoes occurred. Generalised linear modelling showed that N. fuscus abundance was associated positively with dingo activity and long-term annual rainfall and negatively with red fox Vulpes vulpes activity. Our results were consistent with the hypothesis that areas with higher rainfall and dingoes provide N. fuscus with refuge from drought and predation by invasive red foxes, respectively. Top-order predators, such as dingoes, could have an important functional role in broad-scale biodiversity conservation programmes by reducing the impacts of mesopredators.     

Habitat but not group size or recent predator activity affect corvid collective vigilance at carcasses

Vigilance is an important anti-predator behaviour that can be an indicator of the predation risk faced by potential prey animals. Here, we assess the collective vigilance, or the vigilance level of an entire group, of corvids (Family: Corvidae) at experimentally placed carcasses in a desert environment in Australia. Specifically, we explore the relationship between collective vigilance levels and the habitat in which the carcass was placed, the time since a potential predator (dingo Canis dingo, wedge-tailed eagle Aquila audax or red fox Vulpes vulpes) was present at a carcass, and the group size of corvids around the carcass. We found that corvids are more vigilant in open habitat, but that group size and the recent presence of a potential predator does not affect the collective vigilance behaviour of corvids. The results demonstrate the important link between habitat and vigilance, and that animals may adopt anti-predator behaviours irrespective of the size of the group in which they occur or the recent presence of a potential predator.     

Does a top predator reduce the predatory impact of an invasive mesopredator on an endangered rodent?

The mesopredator release hypothesis (MRH) predicts that reduced abundance of top‐order predators results in an increase in the abundance of smaller predators (mesopredators) due to a reduction in intra‐guild predation and competition. The irruption of mesopredators that follows the removal of top‐order predators can have detrimental impacts on the prey of the mesopredators. Here we investigated the mechanisms via which the presence of a top‐order predator can benefit prey species. We tested predictions made according to the MRH and foraging theory by contrasting the abundances of an invasive mesopredator (red fox Vulpes vulpes) and an endangered prey species (dusky hopping mouse Notomys fuscus), predator diets, and N. fuscus foraging behaviour in the presence and absence of a top‐predator (dingo Canis lupus dingo). As predicted by the MRH, foxes were more abundant where dingoes were absent. Dietary overlap between sympatric dingoes and foxes was extensive, and fox was recorded in 1 dingo scat possibly indicating intra‐guild predation. Notomys fuscus were more likely to occur in fox scats than dingo scats and as predicted by the MRH N. fuscus were less abundant in the absence of dingoes. The population increase of N. fuscus following rainfall was dampened in the absence of dingoes suggesting that mesopredator release can attenuate bottom‐up effects, although it remains conceivable that differences in grazing regimes associated with dingo exclusion could have also influenced N. fuscus abundance. Notomys fuscus exhibited lower giving‐up densities in the presence of dingoes, consistent with the prediction that their perceived risk of predation would be lower and foraging efficiency greater in the presence of a top‐predator. Our results suggest that mesopredator suppression by a top predator can create a safer environment for prey species where the frequency of fatal encounters between predators and prey is reduced and the non‐consumptive effects of predators are lower.     

Rarity of a top predator triggers continent-wide collapse of mammal prey: dingoes and marsupials in Australia

Top predators in terrestrial ecosystems may limit populations of smaller predators that could otherwise become over abundant and cause declines and extinctions of some prey. It is therefore possible that top predators indirectly protect many species of prey from excessive predation. This effect has been demonstrated in some small-scale studies, but it is not known how general or important it is in maintaining prey biodiversity. During the last 150 years, Australia has suffered the world's highest rate of mammal decline and extinction, and most evidence points to introduced mid-sized predators (the red fox and the feral cat) as the cause. Here, we test the idea that the decline of Australia's largest native predator, the dingo, played a role in these extinctions. Dingoes were persecuted from the beginning of European settlement in Australia and have been eliminated or made rare over large parts of the continent. We show a strong positive relationship between the survival of marsupials and the geographical overlap with high-density dingo populations. Our results suggest that the rarity of dingoes was a critical factor which allowed smaller predators to overwhelm marsupial prey, triggering extinction over much of the continent. This is evidence of a crucial role of top predators in maintaining prey biodiversity at large scales in terrestrial ecosystems and suggests that many remaining Australian mammals would benefit from the positive management of dingoes.     

Does a top predator suppress the abundance of an invasive mesopredator at a continental scale?

Aim We examined evidence for the mesopredator release hypothesis at a subcontinental scale by investigating the relationship between indices of abundance of the dingo Canis lupus dingo (top‐order predator) and the invasive red fox Vulpes vulpes (mesopredator) in three large regions across mainland Australia. The red fox is known to be one of the major threats to the persistence of small and medium‐sized native vertebrates across the continent. Location Australia. Methods Indices of abundance were calculated from three independently collected datasets derived from bounty returns and field surveys. Data were analysed using univariate parametric, semi‐parametric and nonparametric techniques. Results Predator abundance indices did not conform to a normal distribution and the relationships between dingo and fox abundance indices were not well described by linear functions. Semi‐parametric and nonparametric techniques revealed consistently negative associations between indices of dingo and fox abundance. Main conclusions The results provide evidence that mesopredator suppression by a top predator can be exerted at very large geographical scales and suggest that relationships between the abundances of top predators and mesopredators are not linear. Our results have broad implications for the management of canid predators. First, they suggest that dingoes function ecologically to reduce the activity or abundance of red foxes and thus are likely to dampen the predatory impacts of foxes. More generally, they provide support for the notion that the mesopredator‐suppressive effects of top predators could be incorporated into broad‐scale biodiversity conservation programmes in many parts of the world by actively maintaining populations of top predators or restoring them in areas where they are now rare. Determining the population densities at which the interactions of top predators become ecologically effective will be a critical goal for conservation managers who aim to maintain or restore ecosystems using the ecological interactions of top predators.     

Overcoming prey naiveté: Free‐living marsupials develop recognition and effective behavioral responses to alien predators in Australia

Naiveté in prey arises from novel ecological mismatches in cue recognition systems and antipredator responses following the arrival of alien predators. The multilevel naiveté framework suggests that animals can progress through levels of naiveté toward predator awareness. Alternatively, native prey may be preadapted to recognize novel predators via common constituents in predator odors or familiar predator archetypes. We tested predictions of these competing hypotheses on the mechanisms driving behavioral responses of native species to alien predators by measuring responses of native free‐living northern brown bandicoots (Isoodon macrourus) to alien red fox (Vulpes vulpes) odor. We compared multiple bandicoot populations either sympatric or allopatric with foxes. Bandicoots sympatric with foxes showed recognition and appropriate antipredator behavior toward fox odor via avoidance. On the few occasions bandicoots did visit, their vigilance significantly increased, and their foraging decreased. In contrast, bandicoots allopatric with foxes showed no recognition of this predator cue. Our results suggest that vulnerable Australian mammals were likely naïve to foxes when they first arrived, which explains why so many native mammals declined soon after fox arrival. Our results also suggest such naiveté can be overcome within a relatively short time frame, driven by experience with predators, thus supporting the multilevel naiveté framework.     

Damage released prey alarm substances or predator odours? Risk assessment by an aquatic oligochaete

Although the abilities of prey to detect and respond to chemical substances associated with a predator have been widely reported, the factors promoting the evolution of responses to prey alarm cues vs. predator odours are still vague. In this article, we combined field research with laboratory experiments to explore which chemical substance associated with predator activity (predator odour, conspecific or heterospecific alarm substances) induces defence responses in the aquatic oligochaete Stylaria lacustris, which is vulnerable to common littoral predators. The field results indicated that predators injure the oligochaetes and a great proportion, up to 45% of individuals in the population, were found to be damaged. The results of the laboratory experiments revealed that chemical odours from damselfly larvae feeding on S. lacustris did not induce the defence response in the oligochaetes. On the contrary, oligochaetes detected and responded to alarm substances from damaged conspecifics alone and substances from damaged cladoceran Daphnia magna. We discussed conditions favouring the responses to damage released prey alarm cues instead of predator odours in Stylaria lacustris. Our data suggest that the selection of responses to alarm cues from damaged prey vs. predator odours may be dependent on three factors: (1) non-species-specific predation, (2) divergence of food niche of the different stages of the predator and (3) complex food web with multiple predators. Handling editor: S. Declerk     

Are dingoes a trophic regulator in arid Australia? A comparison of mammal communities on either side of the dingo fence

The direct and indirect interactions that large mammalian carnivores have with other species can have far‐reaching effects on ecosystems. In recent years there has been growing interest in the role that Australia's largest terrestrial predator, the dingo, may have in structuring ecosystems. In this study we investigate the effect of dingo exclusion on mammal communities, by comparing mammal assemblages where dingoes were present and absent. The study was replicated at three locations spanning 300 km in the Strzelecki Desert. We hypothesized that larger species of mammal subject to direct interactions with dingoes should increase in abundance in the absence of dingoes while smaller species subject to predation by mesopredators should decrease in abundance because of increased mesopredator impact. There were stark differences in mammal assemblages on either side of the dingo fence and the effect of dingoes appeared to scale with body size. Kangaroos and red foxes were more abundant in the absence of dingoes while Rabbits and the Dusky Hopping‐mouse Notomys fuscus were less abundant where dingoes were absent, suggesting that they may benefit from lower red fox numbers in the presence of dingoes. Feral cats and dunnarts (Sminthopsis spp.) did not respond to dingo exclusion. Our study provides evidence that dingoes do structure mammal communities in arid Australia; however, dingo exclusion is also associated with a suite of land use factors, including sheep grazing and kangaroo harvesting that may also be expected to influence kangaroo and red fox populations. Maintaining or restoring populations of dingoes may be useful strategies to mitigate the impacts of mesopredators and overgrazing by herbivores.     

Population and behavioural responses of native prey to alien predation

The introduction of invasive alien predators often has catastrophic effects on populations of naïve native prey, but in situations where prey survive the initial impact a predator may act as a strong selective agent for prey that can discriminate and avoid it. Using two common species of Australian small mammals that have persisted in the presence of an alien predator, the European red fox Vulpes vulpes, for over a century, we hypothesised that populations of both would perform better where the activity of the predator was low than where it was high and that prey individuals would avoid signs of the predator’s presence. We found no difference in prey abundance in sites with high and low fox activity, but survival of one species—the bush rat Rattus fuscipes—was almost twofold higher where fox activity was low. Juvenile, but not adult rats, avoided fox odour on traps, as did individuals of the second prey species, the brown antechinus, Antechinus stuartii. Both species also showed reduced activity at foraging trays bearing fox odour in giving-up density (GUD) experiments, although GUDs and avoidance of fox odour declined over time. Young rats avoided fox odour more strongly where fox activity was high than where it was low, but neither adult R. fuscipes nor A. stuartii responded differently to different levels of fox activity. Conservation managers often attempt to eliminate alien predators or to protect predator-naïve prey in protected reserves. Our results suggest that, if predator pressure can be reduced, otherwise susceptible prey may survive the initial impact of an alien predator, and experience selection to discriminate cues to its presence and avoid it over the longer term. Although predator reduction is often feasible, identifying the level of reduction that will conserve prey and allow selection for avoidance remains an important challenge.     

Habitat and introduced predators influence the occupancy of small threatened macropods in subtropical Australia

Australia has had the highest rate of mammal extinctions in the past two centuries when compared to other continents. Frequently cited threats include habitat loss and fragmentation, changed fire regimes and the impact of introduced predators, namely the red fox (Vulpes vulpes) and the feral cat (Felis catus). Recent studies suggest that Australia's top predator, the dingo (Canis dingo), may have a suppressive effect on fox populations but not on cat populations. The landscape of fear hypothesis proposes that habitat used by prey species comprises high to low risk patches for foraging as determined by the presence and ubiquity of predators within the ecosystem. This results in a landscape of risky versus safe areas for prey species. We investigated the influence of habitat and its interaction with predatory mammals on the occupancy of medium‐sized mammals with a focus on threatened macropodid marsupials (the long‐nosed potoroo [Potorous tridactylous] and red‐legged pademelon [Thylogale stigmatica]). We assumed that differential use of habitats would reflect trade‐offs between food and safety. We predicted that medium‐sized mammals would prefer habitats for foraging that reduce the risk of predation but that predators would have a positive relationship with medium‐sized mammals. We variously used data from 298 camera trap sites across nine conservation reserves in subtropical Australia. Both dingoes and feral cats were broadly distributed, whilst the red fox was rare. Long‐nosed potoroos had a strong positive association with dense ground cover, consistent with using habitat complexity to escape predation. Red‐legged pademelons showed a preference for open ground cover, consistent with a reliance on rapid bounding to escape predation. Dingoes preferred areas of open ground cover whereas feral cats showed no specific habitat preference. Dingoes were positively associated with long‐nosed potoroos whilst feral cats were positively associated with red‐legged pademelons. Our study highlights the importance of habitat structure to these threatened mammals and also the need for more detailed study of their interactions with their predators.     

Effects of multiple disturbance processes on arboreal vertebrates in eastern Australia: implications for management

Habitat loss and invasive predators increasingly threaten global biodiversity. Here we use a landscape‐scale experimental approach to explore the individual and synergistic effects of logging and an invasive predator, the red fox Vulpes vulpes on two common native arboreal vertebrates (a predator and prey species) in south‐eastern Australia. We used site occupancy methods to evaluate different models evaluating the effects of site specific forest logging disturbance, lethal fox baiting and forest structural elements for explaining variation in site occupancy of a large monitor lizard Varanus varius, and a marsupial prey, the common ringtail possum Pseudocheirus peregrinus across a complex forest landscape. Site occupancy of ringtail possum was influenced by habitat resources and the structural complexity of forest, which indirectly mediated predation risk. Presence of fox baiting had no direct effect on the ringtail site occupancy. In contrast, access to prey resources and fox baiting appeared to best explain site occupancy variation in monitor lizards across the landscape. While these species are affected primarily by separate disturbances, synergistic interactions between the processes may intensify their effects. Our results demonstrate that species susceptibility to disturbance processes are highly idiosyncratic. This approach makes efficient use of integrated modelling to aid conservation management at both local and landscape levels.     

Responses of naïve and experienced European rabbits to predator odour

The response of prey species to predator scent has been investigated in many mammalian species; however, there is little information about the responses of European wild rabbits at the population level. Therefore, we conducted a simple experiment to investigate the behavioural response of a rabbit population to native predator cues in the wild. We compared the response to the scent of a predator (red fox) in a wild rabbit population bred in semi-natural conditions and naïve to terrestrial predators with the response of a population in a similar environment where terrestrial predators were present. The response to predators was based on rabbit abundance, inferred from pellet counts and measured by the defecation rate per day (DRD). Our results indicate that rabbits responded to the odour of fox faeces in the treatment warrens, resulting in a lower DRD. The main anti-predator behaviour observed was spatial avoidance (warren abandonment), which seemed to be more accentuated for rabbits who had not previously had contact with foxes in the plot where terrestrial predators were excluded. In both the fenced and the unfenced plot, the differences in the effect of the predator odour between the control and treatment warrens disappeared after cessation of treatment, suggesting a flexible and adaptive behaviour of rabbits to predator cues.

     

Olfactory response of the predator <Emphasis Type="Italic">Zetzellia mali</Emphasis> to a prey patch occupied by a conspecific predator

While searching for food, predators may use volatiles associated with their prey, but also with their competitors for prey. This was tested for the case of Zetzellia mali (Ewing) (Acari: Stigmaeidae), an important predator of the hawthorn spider mite, Amphitetranychus viennensis (Zacher) (Acari: Tetranychidae), in black-cherry orchards in Baraghan, Iran. Using a Y-tube olfactometer, the response of this predatory mite was tested to odour from black-cherry leaves with a conspecific female predatory mite, either with or without a female of the hawthorn spider mite when the alternative odour came from black-cherry leaves with the hawthorn spider mite only. Female predators avoided odours from leaves with both a hawthorn spider mite and a conspecific predator, as well as leaves with a conspecific predator only. We discuss whether avoidance emerges in response to cues from the competitor/predator, the herbivore/prey or the herbivore-damaged plant.     

Bottom-up and top-down processes interact to modify intraguild interactions in resource-pulse environments

Top predators are declining globally, in turn allowing populations of smaller predators, or mesopredators, to increase and potentially have negative effects on biodiversity. However, detection of interactions among sympatric predators can be complicated by fluctuations in the background availability of resources in the environment, which may modify both the numbers of predators and the strengths of their interactions. Here, we first present a conceptual framework that predicts how top-down and bottom-up interactions may regulate sympatric predator populations in environments that experience resource pulses. We then test it using 2 years of remote-camera trapping data to uncover spatial and temporal interactions between a top predator, the dingo Canis dingo, and the mesopredatory European red fox Vulpes vulpes and feral cat Felis catus, during population booms, declines and busts in numbers of their prey in a model desert system. We found that dingoes predictably suppress abundances of the mesopredators and that the effects are strongest during declines and busts in prey numbers. Given that resource pulses are usually driven by large yet infrequent rains, we conclude that top predators like the dingo provide net benefits to prey populations by suppressing mesopredators during prolonged bust periods when prey populations are low and potentially vulnerable.