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Information on how the trophic ecology of predators shapes their movement patterns and space-use is fundamental to understanding ecological processes across organisational levels. Despite this, studies combining spatial and trophic ecology to determine how prey preference and/or resource availability shape space use are lacking in marine predators as these can occur at low density and are often difficult to track over extended periods. Furthermore, many exhibit behavioural variability within species and among closely related, sympatric species adding further complexity. We applied a context-focused, multimethod approach to the understudied great hammerhead shark (Sphyrna mokarran) to test if movement and home ranges relate to prey preference and availability. Movement data from satellite and acoustic telemetry in Queensland, Australia, were combined with stable-isotope analysis, drone surveys, and videos of hunting behaviour. Limited dispersal, and small home ranges in S. mokarran were linked to trophic specialisation on stingray prey. Drone surveys and videos showed predation events on stingrays and demonstrated high, year-round availability of this prey in shallow, inshore habitats, which may allow the majority of S. mokarran to remain resident. This affinity for inshore habitats suggests that critical life-history requirements are performed over local or regional scales, although some larger movements were evident. These results were interpreted in comparison to the well-studied bull shark (Carcharhinus leucas), which showed reliance on pelagic food webs. Carcharhinus leucas had high individual variability in movement, with both large-scale migrations and residency. This could indicate that only some individuals are locally sustained on dynamic, pelagic food webs, while others undergo large-scale excursions over distant habitats. The specialised foraging of S. mokarran indicates they play an apex predator role in shallow, inshore habitats, potentially shaping space-use, and foraging behaviour of batoids. As inshore habitats are disproportionately affected by anthropogenic stressors, S. mokarran's trophic specialisation and limited demographic connectivity may make the species particularly vulnerable to anthropogenic threats. [ABSTRACT FROM AUTHOR]

Australia's mammals are facing devastating effects from introduced predators such as cats and foxes. It is hypothesised that this may be because Australian mammals do not recognise some predators and are naïve to the threat they pose. We tested how wild-caught northern brown bandicoots (Isoodon macrourus) reacted to a variety of predators and their cues in captivity. These cues were live predators, taxidermied predators and predator faeces. Bandicoots spent less time feeding and took longer to begin feeding in the presence of a live dog. However, they did not display a significant difference in behaviours in the presence of any other predator cue when compared with the baseline. This suggests that bandicoots may perceive live dogs as a threat, and that the use of taxidermied predators and predator faeces may not elicit avoidance behaviours in bandicoots. Bandicoots may need to be trained to recognise and respond appropriately to some predator cues to maximise their chance of survival. [ABSTRACT FROM AUTHOR]

Information on how the trophic ecology of predators shapes their movement patterns and space-use is fundamental to understanding ecological processes across organisational levels. Despite this, studies combining spatial and trophic ecology to determine how prey preference and/or resource availability shape space use are lacking in marine predators as these can occur at low density and are often difficult to track over extended periods. Furthermore, many exhibit behavioural variability within species and among closely related, sympatric species adding further complexity. We applied a context-focused, multi-method approach to the understudied great hammerhead shark (Sphyrna mokarran) to test if movement and home ranges relate to prey preference and availability. Movement data from satellite and acoustic telemetry in Queensland, Australia, were combined with stable-isotope analysis, drone surveys, and videos of hunting behaviour. Limited dispersal, and small home ranges in S. mokarran were linked to trophic specialisation on stingray prey. Drone surveys and videos showed predation events on stingrays and demonstrated high, year-round availability of this prey in shallow, inshore habitats, which may allow the majority of S. mokarran to remain resident. This affinity for inshore habitats suggests that critical life-history requirements are performed over local or regional scales, although some larger movements were evident. These results were interpreted in comparison to the well-studied bull shark (Carcharhinus leucas), which showed reliance on pelagic food webs. Carcharhinus leucas had high individual variability in movement, with both large-scale migrations and residency. This could indicate that only some individuals are locally sustained on dynamic, pelagic food webs, while others undergo large-scale excursions over distant habitats. The specialised foraging of S. mokarran indicates they play an apex predator role in shallow, inshore habitats, potentially shaping space-use, and foraging behaviour of batoids. As inshore habitats are disproportionately affected by anthropogenic stressors, S. mokarran’s trophic specialisation and limited demographic connectivity may make the species particularly vulnerable to anthropogenic threats. [ABSTRACT FROM AUTHOR]

Toads of the amphibian family Bufonidae possess toxins that can be lethal to monitor lizards (family Varanidae) when ingested. In Australia, populations of several species of monitors (Varanus spp.) have been heavily impacted via direct poisoning by invasive cane toads (Rhinella marina). It has been suggested that the invasion of Asian black-spined toads (Duttaphrynus melanostictus) through the Indonesian archipelago could have equally devastating effects on other monitors, especially the iconic Komodo dragon, Varanus komodoensis. We review published information to evaluate the risk posed by invasive toads to varanids worldwide, and identify critical gaps in knowledge (e.g., specific varanid lineages not yet tested for the genetic signature of toxin resistance; mechanisms that buffer toad impacts even on physiologically susceptible predators; toxicity of D. melanostictus). We conclude that population-level impacts of invasive toads are unlikely to be significant for most yet-to-be-affected species of monitors, including V. komodoensis. Nonetheless, the likely spread of D. melanostictus through southern Australia may affect monitors (e.g., heath monitor V. rosenbergi) that are not currently imperiled by cane toads and, more generally, wildlife managers need to evaluate potential impacts of these toxic invaders on vulnerable native predators. [ABSTRACT FROM AUTHOR]

Understanding the determinants and consequences of predation effort, success and prey responses is important since these factors affect the fitness of predators and prey. When predators are also invasive species, the impacts on prey can be particularly far‐reaching with ultimate ecosystem‐level consequences. However, predators are typically viewed as behaviourally fixed within this interaction and it is unclear how variation in predator social dynamics affects predator–prey interactions. Using the invasive eastern mosquitofish Gambusia holbrooki and a native glass shrimp Paratya australiensis in Australia, we investigated how varying levels of social conflict within predator groups influences predator–prey interactions. By experimentally manipulating group stability of G. holbrooki, we show that rates of social conflict were lower in groups with large size differences, but that routine metabolic rates were higher in groups with large size differences. Predation effort and success did not vary depending on group stability, but in stable groups predation effort by aggressive dominants was greater than subordinates. The anti‐predator responses of prey to the stability of predator groups were mixed. While more prey utilized shelters when exposed to stable compared to unstable groups of predators, a greater proportion were sedentary when predator groups were unstable. Overall, this study demonstrates predator group stability is modulated by differences in body size and can influence prey responses. Further, it reveals a hidden metabolic cost of living in stable groups despite reduced overt social conflict. For invasive species management, it is therefore important to consider the behavioural and physiological plasticity of the invasive predators, whose complex social interactions and metabolic demands can modulate patterns of predator–prey interactions. [ABSTRACT FROM AUTHOR]

Few landscape-scale experiments test the effects of predators on the abundance and distribution of prey across habitat gradients. We use the assisted colonization of a top predator, the Tasmanian devil ( Sarcophilus harrisii ), to test the impacts of predation on the abundance, habitat use and temporal activity of a widespread prey species, the omnivorous common brushtail possum ( Trichosurus vulpecula ). Before introduction of devils to Maria Island, Tasmania, Australia, in 2012, possums were abundant in open grasslands as well as forests. Predation by devils caused high mortality of possums in grasslands, but individuals with access to trees had a higher survival probability. Possum abundance declined across the whole island from 2012-2016, as possums disappeared almost completely from grasslands and declined in drier forests with more open understorey. Abundance remained stable in wet forests, which are not preferred habitat for possums but provide better refuge from devils. Abundance and habitat use of possums remained unchanged at a control site on the adjacent Tasmanian mainland, where the devil population was low and stable. This study demonstrates how spatial variation in predator-caused mortality can limit both abundance and habitat breadth in generalist prey species, excluding them entirely from certain habitats.

Commonly, invaders have different impacts in different places. The spread of cane toads ( Rhinella marina: Bufonidae) has been devastating for native fauna in tropical Australia, but the toads' impact remains unstudied in temperate-zone Australia. We surveyed habitat characteristics and fauna in campgrounds along the central eastern coast of Australia, in eight sites that have been colonized by cane toads and another eight that have not. The presence of cane toads was associated with lower faunal abundance and species richness, and a difference in species composition. Populations of three species of large lizards (land mullets Bellatorias major, eastern water dragons Intellagama lesueurii, and lace monitors Varanus varius) and a snake (red-bellied blacksnake Pseudechis porphyriacus) were lower (by 84 to 100%) in areas with toads. The scarcity of scavenging lace monitors in toad-invaded areas translated into a 52% decrease in rates of carrion removal (based on camera traps at bait stations) and an increase (by 61%) in numbers of brush turkeys ( Alectura lathami). The invasion of cane toads through temperate-zone Australia appears to have reduced populations of at least four anurophagous predators, facilitated other taxa, and decreased rates of scavenging. Our data identify a paradox: The impacts of cane toads are at least as devastating in southern Australia as in the tropics, yet we know far more about toad invasion in the sparsely populated wilderness areas of tropical Australia than in the densely populated southeastern seaboard. [ABSTRACT FROM AUTHOR]

Predicting the ecological impacts of invasive species on native fauna is a formidable challenge for conservation biologists. One way to deal with that challenge is to stage encounters between the invader and native species in the laboratory, to illuminate likely outcomes of encounters in the wild. The invasion of the highly toxic cane toad Rhinella marina across tropical Australia threatens many frog-eating predators, including freshwater crocodiles (Crocodylus johnstoni). To predict the impact of cane toads on crocodiles, we need to know whether crocodiles will attack cane toads, and whether predators that survive the toads' poisons will learn to avoid toads. We quantified these traits under laboratory conditions in hatchling freshwater crocodiles from Lake Argyle in Western Australia. All toad-naïve hatchling crocodiles attacked toads during their first encounter, and none showed signs of overt illness after consuming toads. However, crocodiles rapidly learnt to avoid toads as prey, and only four out of the 10 crocodiles attacked toads during subsequent encounters. Compared to control (toadnaïve) conspecifics, toad-smart crocodiles inflicted fewer bites on toads, held toads in their mouths for shorter time periods, and were more likely to reject toads as prey. In the field, toads were consumed more rarely than native frogs. Our results show that hatchling freshwater crocodiles can rapidly learn to avoid cane toads as prey. Hence, even if toads cause mortality of larger crocodiles (as happens in some areas), populations may recover via hatchling recruitment. [ABSTRACT FROM AUTHOR]

Predicting which species will be affected by an invasive taxon is critical to developing conservation priorities, but this is a difficult task. A previous study on the impact of invasive cane toads (Bufo marinus) on Australian snakes attempted to predict vulnerability a priori based on the assumptions that any snake species that eats frogs, and is vulnerable to toad toxins, may be at risk from the toad invasion. We used time-series analyses to evaluate the accuracy of that prediction, based on >3600 standardized nocturnal surveys over a 138- month period on 12 species of snakes and lizards on a floodplain in the Australian wet-dry tropics, bracketing the arrival of cane toads at this site. Contrary to prediction, encounter rates with most species were unaffected by toad arrival, and some taxa predicted to be vulnerable to toads increased rather than declined (e.g., death adder Acanthophis praelongus; Children's python Antaresia childreni). Indirect positive effects of toad invasion (perhaps mediated by toad-induced mortality of predatory varanid lizards) and stochastic weather events outweighed effects of toad invasion for most snake species. Our study casts doubt on the ability of a priori desktop studies, or short-term field surveys, to predict or document the ecological impact of invasive species. [ABSTRACT FROM AUTHOR]

Although invasive species are viewed as major threats to ecosystems worldwide, few such species have been studied in enough detail to identify the pathways, magnitudes, and timescales of their impact on native fauna. One of the most intensively studied invasive taxa in this respect is the cane toad (Bufo marinus), which was introduced to Australia in 1935. A review of these studies suggests that a single pathway--lethal toxic ingestion of toads by frog-eating predators--is the major mechanism of impact, but that the magnitude of impact varies dramatically among predator taxa, as well as through space and time. Populations of large predators (e.g., varanid and scincid lizards, elapid snakes, freshwater crocodiles, and dasyurid marsupials) may be imperilled by toad invasion, but impacts vary spatially even within the same predator species. Some of the taxa severely impacted by toad invasion recover within a few decades, via aversion learning and longer-term adaptive changes. No native species have gone extinct as a result of toad invasion, and many native taxa widely, imagined to be at risk are not affected, largely as a result of their physiological ability to tolerate toad toxins (e.g., as found in many birds and rodents), as well as the reluctance of many native anuran-eating predators to consume toads, either innately or as a learned response. Indirect effects of cane toads as mediated through trophic webs are likely as important as direct effects, but they are more difficult to study. Overall, some Australian native species (mostly large predators) have declined due to cane toads; others, especially species formerly consumed by those predators, have benefited. For yet others, effects have been minor or have been mediated indirectly rather than through direct interactions with the invasive toads. Factors that increase a predator's vulnerability to toad invasion include habitat overlap with toads, anurophagy, large body size, inability to develop rapid behavioral aversion to toads as prey items, and physiological vulnerability to bufotoxins as a result of a lack of coevolutionaty history of exposure to other bufonid taxa. [ABSTRACT FROM AUTHOR]

Experimental evidence on the determinants of prey vulnerability is scarce, especially for vertebrates in the field. Invasive species offer robust opportunities to explore prey vulnerability, because the intensity of predation on or by such animals has not been eroded by coevolution. Around waterbodies in tropical Australia, native meat ants ( Iridomyrmex reburrus) consume many metamorph cane toads ( Bufo marinus, an invasive anuran). We document the determinants of toad vulnerability, especially the roles of toad body size and ant density. Larger metamorphs were attacked sooner (because they attracted more ants), but escaped more often. Overall, smaller toads were more likely to be killed. Ant densities influenced toad responses, as well as attack rate and success. Data on the immediate outcomes of attacks underestimate mortality: more than 73% of apparent ‘escapees’ died within 24 h. Because mortality during this period was independent of toad size, predation was less size selective than suggested by immediate outcomes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 738–751. [ABSTRACT FROM AUTHOR]

• The introduction of European rabbit fleas enhanced myxomatosis impact. • It is argued that flea-borne myxomatosis increases vulnerability to predation. • If fleas are present. fox abundance closely reflects rabbit productivity. • Rabbits increase and foxes decrease in absence of rabbit flea vectors. On introduction to Australia, European rabbit fleas spread myxomatosis among young wild rabbits during winter; recruitment into the adult rabbit population was strongly reduced. Nonetheless, the reasons behind the high efficacy of flea-borne myxomatosis remain poorly understood. A 17-year data set from Witchitie, a semi-arid site in South Australia, was reviewed to ask whether red foxes, specialist rabbit predators, could have enhanced mortality by preying on disease-debilitated rabbits. Advantage was taken of a natural experiment where, after initial establishment of fleas, drought greatly reduced their abundance, providing two periods for comparison, one where fleas actively spread myxoma virus, followed by another where fleas were no longer effective vectors and myxomatosis reverted to former mosquito-vectored summer outbreaks. The hypothesis that foxes contributed to the efficacy of flea-borne myxomatosis was not rejected. Instead, the study showed that when myxomatosis was being actively spread by fleas, foxes were not only abundant enough to have eaten most of the young rabbits produced each year, but fox population dynamics were also strongly associated with rabbit productivity. Related studies support the likelihood that predators significantly enhance disease-related mortality and indicate that further experimental study of an interaction between flea-borne myxomatosis and predation would be worthwhile. [ABSTRACT FROM AUTHOR]