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It is widely assumed that organisms at low trophic levels, particularly microbes and plants, are essential to basic services in ecosystems, such as nutrient cycling. In theory, apex predators' effects on ecosystems could extend to nutrient cycling and the soil nutrient pool by influencing the intensity and spatial organization of herbivory. Here, we take advantage of a long-term manipulation of dingo abundance across Australia's dingo-proof fence in the Strzelecki Desert to investigate the effects that removal of an apex predator has on herbivore abundance, vegetation and the soil nutrient pool. Results showed that kangaroos were more abundant where dingoes were rare, and effects of kangaroo exclusion on vegetation, and total carbon, total nitrogen and available phosphorus in the soil were marked where dingoes were rare, but negligible where dingoes were common. By showing that a trophic cascade resulting from an apex predator's lethal effects on herbivores extends to the soil nutrient pool, we demonstrate a hitherto unappreciated pathway via which predators can influence nutrient dynamics. A key implication of our study is the vast spatial scale across which apex predators' effects on herbivore populations operate and, in turn, effects on the soil nutrient pool and ecosystem productivity could become manifest.

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 naiveté’. 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 antipredator 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 antipredator responses towards introduced predators, providing support for the idea that predator naiveté can be overcome through learning and natural selection as a result of exposure to introduced predators.

Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective.

In arid environments, shade provided by vegetation forms the crux of many facilitation pathways by providing other organisms with relief from high levels of solar radiation and extreme temperatures. Shade is an important determinant that structures arid ecosystem processes and functioning. While shade is considered an essential refuge for many organisms in arid environments, few studies have assessed how parasitic plants such as aerial mistletoes can influence the quality of shade provided by its host, and how this can subsequently influence species interactions. Here, we investigate how mistletoe influences the microclimate and daytime use of sub-canopy habitat by a large herbivore that seeks out shady micro-habitats to avoid daytime heat in Australia’s Strzelecki Desert. We experimentally removed the pale-leaved mistletoe (Amyema maidenii) from mulga trees (Acacia aneura) and monitored sub-canopy ambient temperatures and the daytime use of sub-canopy habitat by red kangaroos (Osphranter rufus). Results showed that average hourly temperature during the daytime and daily maximum temperature were cooler and that kangaroos were approximately three times more likely to shelter beneath trees where mistletoe was present (control) compared to where mistletoes had been removed (treatment). By showing that mistletoe can improve the quality of shade provided by their host trees, our study offers a novel insight into how mistletoes can facilitate the surrounding biota through modifying the abiotic environment beyond its physical structure. More broadly, the results of our study emphasise the prevalence of positive interactions within ecological communities and how they can occur in unexpected ways and indirectly between organisms that never come into direct contact.

1. Incorporating an understanding of animal behaviour into conservation programmes can influence conservation outcomes. Exotic predators can have devastating impacts on native prey species and thwart reintroduction efforts, in part due to prey naïveté caused by an absence of co-evolution between predators and prey. Attempts have been made to improve the anti-predator behaviours of reintroduced native prey by conducting laboratory-based predator recognition training but results have been varied and have rarely led to improved survival in reintroduction programmes. 2. We investigated whether in situ predator exposure could improve anti-predator responses of a predator-naïve mammal by exposing prey populations to low densities of introduced predators under controlled conditions. We reintroduced 352 burrowing bettongs to a 26-km² fenced exclosure at the Arid Recovery Reserve in South Australia and exposed them to feral cats (density 0.03-0.15 cats/km²) over an 18-month period. At the same time, we translocated a different group of bettongs into an exclosure free of introduced predators, as a control. We compared three behaviours (flight initiation distances, trap docility and behaviour at feeding trays) of cat-exposed and control bettongs before the translocations, then at 6, 12 and 18 months post-translocation. 3. Cat-exposed bettongs displayed changes in behaviour that suggested increased wariness, relative to control bettongs. At 18 months post-reintroduction, cat-exposed bettongs had greater flight initiation distances and approached feed trays more slowly than control bettongs. Cat-exposed bettongs also increased their trap docility over time. 4. Synthesis and applications. Translocation is recommended as a conservation tool for many threatened species yet success rates are generally low. We demonstrate that controlled levels of in situ predator exposure can increase wariness in the behaviour of naïve prey. Our findings provide support for the hypothesis that in situ predator exposure could be used as a method to improve the anti-predator responses of predator-naïve threatened species populations.

Large-bodied animals play essential roles in ecosystem structuring and stability through both indirect and direct trophic effects. In recent times, humans have disrupted this trophic structure through both habitat destruction and active extirpation of large predators, resulting in large declines in numbers and vast contractions in their geographic ranges. Ripple et al. ( 10.1126/science.1241484 ; see the Perspective by Roberts ) review the status, threats, and ecological importance of the 31 largest mammalian carnivores globally. These species are responsible for a suite of direct and indirect stabilizing effects in ecosystems. Current levels of decline are likely to result in ecologically ineffective population densities and can lead to ecosystem instability. The preservation of large carnivores can be challenging because of their need for large ranges and their potential for human conflict. However, the authors demonstrate that the preservation of large carnivores is ecologically important and that the need for conservation action is immediate, given the severity of the threats they face. Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth’s largest carnivores and all that depends upon them, including humans.

Invasive predators, land clearing and altered fire regimes have been implicated in species decline and extinction worldwide. Enhanced knowledge of how these factors interact and influence medium-sized mammals is warranted. We tested three hypotheses using occupancy data for a diverse mammal assemblage including three threatened species, five common species, two introduced mesopredators and an apex predator in eastern Australia. We hypothesised that occupancy of mammal species within the assemblage would be influenced by (i) the physical environment (rainfall, vegetation type and elevation), (ii) habitat disturbance (number of fires and habitat fragmentation) and (iii) mesopredator release, whereby occupancy and/or detection of medium-sized mammals are influenced by mesopredators, the feral cat ( Felis catus ) and the red fox ( Vulpes vulpes ), which are influenced by an apex predator, the dingo ( Canis familiaris ). We utilised camera-trapping data from 173 sites (692 camera locations) across a north–south gradient spanning ~ 1500 km in eastern Australia. Although hypotheses i (physical environment) and ii (habitat disturbance) are not mutually exclusive, we show that the variables considered in each were only weakly correlated. We conducted occupancy modelling to investigate the physical environment and habitat disturbance hypotheses. We conducted co-occurrence modelling to investigate interactions between species. The physical environment hypothesis best supported occupancy models for six mammal species: red-necked pademelon ( Thylogale thetis ), bandicoots ( Isoodon macrourus and Perameles nasuta ), swamp wallaby ( Wallabia bicolor ), red-necked wallaby ( Macropus rufogriseus ), eastern grey kangaroo ( Macropus giganteus ) and feral cat. The disturbance hypothesis best supported occupancy models for four mammal species: long-nosed potoroo ( Potorous tridactylus ), red-necked pademelon and both mesopredators. Support for the mesopredator release hypothesis was equivocal. Large macropods showed site avoidance towards the red fox. Four species showed higher detection at sites where mesopredators were not detected. The fox showed a negative detection interaction to the dingo and the cat did not. Our study highlights how factors such as rainfall, land clearing, elevation and number of fires influence the occupancy of species within a diverse mammal assemblage at the macroecological scale. Our findings have implications for the conservation of threatened species in managed landscapes and suggestions for further research following the recent 2019–2020 wildfires.

Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators’ ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss. Top predators can reduce local mesopredator abundance either through direct predation or behavioural changes. Here, Newsome and colleagues demonstrate at a landscape scale across three continents that mesopredator populations are suppressed at the core, but less so on the periphery, of top predators’ ranges.

The “life-dinner principle” posits that there is greater selection pressure on the species that have more to lose in an interaction. Thus, based on the asymmetry within predator-prey interactions, there is an advantage for prey to learn quickly, especially in response to novel, introduced predators. Here, we test the “learned recognition” hypothesis that posits that naïve prey species’ ability to recognise and respond to introduced predators can be induced through experience. We quantified the behavioural response of initially predator-naïve burrowing bettongs (Bettongia lesueur) that had been living in the presence (for 8–15 months) and absence of an introduced predator (feral cats—Felis catus) to models of cats, a herbivore (rabbit (Oryctolagus cuniculus)), novel object (plastic bucket) and no object (control). We expected that if bettongs recognised cats as a threat, they would be more wary in the presence of cat models than either rabbit models, buckets or the control. Bettongs living without predators did not modify their behaviour in response to the cat model, but spent more time cautiously approaching the rabbit model compared with the control. However, bettongs living with cats spent more time cautiously approaching the cat model compared with the rabbit, bucket and control. Our results are consistent with the learned recognition hypothesis which suggests that a predator-naïve prey species ability to recognise novel predators is inducible through experience. Our finding suggests that antipredator responses of reintroduced species could be improved prior to release by exposing them to predators under carefully controlled conditions.

We collated an environmental history for a 8580 km2 study area in the Simpson Desert, Australia. Quantitative and qualitative data on climate, land-use, fire history and ecosystem dynamics were used to construct a chronology of processes threatening terrestrial mammal species. Over the last 150 years there has been the transition in land tenure from a hunter–gatherer economy to pastoralism, the loss of 11 mammal species, the cessation of small scale burning by Aboriginal people and the introduction of the fox and cat. Annual rainfall was highly variable and was influenced by the phase of the El Niño Southern Oscillation (ENSO). Irruptions of rodents, marked increases in the populations of native and introduced predators and extensive wildfires were associated with the La Niña phase of ENSO and occurred when rain-year (July–June) rainfall approached or exceeded the 90th percentile of the historical rainfall distribution. Large rainfall events in arid Australia have been viewed traditionally as the ‘boom’ times that benefit wildlife and pastoral production. However, because of hyper-predation and the risk of wildfire, we show that the years including and immediately following flooding rains should be identified as critical, or ‘bust’ periods for wildlife and conservation management. ENSO related climatic forecasts appear to be useful cues which can be incorporated into fire and predator management strategies in arid Australia. Studies such as this, which utilise a broad range of data types across extensive areas, can identify the timing and potential of threatening process not possible using contemporary studies alone.