Not all predators are equal: a continent‐scale analysis of the effects of predator control on Australian mammals

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The (Non)Effects of Lethal Population Control on the Diet of Australian Dingoes

Top-predators contribute to ecosystem resilience, yet individuals or populations are often subject to lethal control to protect livestock, managed game or humans from predation. Such management actions sometimes attract concern that lethal control might affect top-predator function in ways ultimately detrimental to biodiversity conservation. The primary function of a predator is predation, which is often investigated by assessing their diet. We therefore use data on prey remains found in 4,298 Australian dingo scats systematically collected from three arid sites over a four year period to experimentally assess the effects of repeated broad-scale poison-baiting programs on dingo diet. Indices of dingo dietary diversity and similarity were either identical or near-identical in baited and adjacent unbaited treatment areas in each case, demonstrating no control-induced change to dingo diets. Associated studies on dingoes'' movement behaviour and interactions with sympatric mesopredators were similarly unaffected by poison-baiting. These results indicate that mid-sized top-predators with flexible and generalist diets (such as dingoes) may be resilient to ongoing and moderate levels of population control without substantial alteration of their diets and other related aspects of their ecological function.     

Assessing predation risk to threatened fauna from their prevalence in predator scats: dingoes and rodents in arid Australia

The prevalence of threatened species in predator scats has often been used to gauge the risks that predators pose to threatened species, with the infrequent occurrence of a given species often considered indicative of negligible predation risks. In this study, data from 4087 dingo (Canis lupus dingo and hybrids) scats were assessed alongside additional information on predator and prey distribution, dingo control effort and predation rates to evaluate whether or not the observed frequency of threatened species in dingo scats warrants more detailed investigation of dingo predation risks to them. Three small rodents (dusky hopping-mice Notomys fuscus; fawn hopping-mice Notomys cervinus; plains mice Pseudomys australis) were the only threatened species detected in <8% of dingo scats from any given site, suggesting that dingoes might not threaten them. However, consideration of dingo control effort revealed that plains mice distribution has largely retracted to the area where dingoes have been most heavily subjected to lethal control. Assessing the hypothetical predation rates of dingoes on dusky hopping-mice revealed that dingo predation alone has the potential to depopulate local hopping-mice populations within a few months. It was concluded that the occurrence of a given prey species in predator scats may be indicative of what the predator ate under the prevailing conditions, but in isolation, such data can have a poor ability to inform predation risk assessments. Some populations of threatened fauna assumed to derive a benefit from the presence of dingoes may instead be susceptible to dingo-induced declines under certain conditions.     

Resolving the value of the dingo in ecological restoration

There is global interest in restoring populations of apex predators, both to conserve them and to harness their ecological services. In Australia, reintroduction of dingoes (Canis dingo) has been proposed to help restore degraded rangelands. This proposal is based on theories and the results of studies suggesting that dingoes can suppress populations of prey (especially medium‐ and large‐sized herbivores) and invasive predators such as red foxes (Vulpes vulpes) and feral cats (Felis catus) that prey on threatened native species. However, the idea of dingo reintroduction has met opposition, especially from scientists who query the dingo's positive effects for some species or in some environments. Here, we ask ‘what is a feasible experimental design for assessing the role of dingoes in ecological restoration?’ We outline and propose a dingo reintroduction experiment—one that draws upon the existing dingo‐proof fence—and identify an area suitable for this (Sturt National Park, western New South Wales). Although challenging, this initiative would test whether dingoes can help restore Australia's rangeland biodiversity, and potentially provide proof‐of‐concept for apex predator reintroductions globally.     

The virtuous circle: predator‐friendly farming and ecological restoration in Australia

In Australia, dingoes are widely regarded as enemies of livestock, and accordingly livestock producers commonly attempt to reduce or eradicate them by lethal control. This can have two forms of perverse outcomes: lethal control often does not succeed in reducing dingo populations and can even result in increased attacks on livestock; and the environmental benefits provided by dingoes, some of which are valuable to livestock production, are lost. We describe these outcomes and suggest mechanisms by which tolerance of dingoes could provide benefits to livestock enterprises, at the same time widening the scope of ecological restoration, and humane treatment of wildlife in Australia.     

Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study

Top‐order predators often have positive effects on biological diversity owing to their key functional roles in regulating trophic cascades and other ecological processes. Their loss has been identified as a major factor contributing to the decline of biodiversity in both aquatic and terrestrial systems. Consequently, restoring and maintaining the ecological function of top predators is a critical global imperative. Here we review studies of the ecological effects of the dingo Canis lupus dingo, Australia's largest land predator, using this as a case study to explore the influence of a top predator on biodiversity at a continental scale. The dingo was introduced to Australia by people at least 3500 years ago and has an ambiguous status owing to its brief history on the continent, its adverse impacts on livestock production and its role as an ecosystem architect. A large body of research now indicates that dingoes regulate ecological cascades, particularly in arid Australia, and that the removal of dingoes results in an increase in the abundances and impacts of herbivores and invasive mesopredators, most notably the red fox Vulpes vulpes. The loss of dingoes has been linked to widespread losses of small and medium‐sized native mammals, the depletion of plant biomass due to the effects of irrupting herbivore populations and increased predation rates by red foxes. We outline a suite of conceptual models to describe the effects of dingoes on vertebrate populations across different Australian environments. Finally, we discuss key issues that require consideration or warrant research before the ecological effects of dingoes can be incorporated formally into biodiversity conservation programs.     

Apex predator suppression is linked to restructuring of ecosystems via multiple ecological pathways

Removal of apex predators can drive ecological regime shifts owing to compensatory positive and negative population level responses by organisms at lower trophic levels. Despite evidence that apex predators can influence ecosystems though multiple ecological pathways, most studies investigating apex predators’ effects on ecosystems have considered just one pathway in isolation. Here, we provide evidence that lethal control of an apex predator, the dingo Canis dingo, drives shifts in the structure of Australia's tropical‐savannah ecosystems. We compared mammal assemblages and understorey structure at seven paired‐sites. Each site comprised an area where people poisoned dingoes and an area without dingo control. The effects of dingo control on mammals scaled with body size. Where dingoes were poisoned, we found greater activity of herbivorous macropods and feral cats, a mesopredator, but sparser understorey vegetation and lower abundances of native rodents. Our study suggests that ecological cascades arising from apex predators’ suppressive effects on herbivores and mesopredators occur simultaneously. Concordant effects of dingo removal across tropical‐savannah, forest and desert biomes suggest that dingoes once exerted ubiquitous top–down effects across Australia and provides support for calls that top–down forcing should be considered a fundamental process governing ecosystem structure.     

Ecologically functional landscapes and the role of dingoes as trophic regulators in south‐eastern Australia and other habitats

Large carnivores can play a pivotal role in maintaining healthy, balanced ecosystems. By suppressing the abundances and hence impacts of herbivores and smaller predators, top predators can indirectly benefit the species consumed by herbivores and smaller predators. Restoring and maintaining the ecosystem services that large carnivores provide has been identified as a critical step required to sustain biodiversity and maintain functional, resilient ecosystems. Recent research has shown that Australia's largest terrestrial predator, the Dingo (Canis lupus dingo), has strong effects on ecosystems in arid Australia and that these effects are beneficial for the conservation of small mammals and vegetation. Similarly, there is evidence from south‐eastern Australia that dingoes suppress the abundance of macropods and red Fox (Vulpes vulpes). It is likely that dingoes in south‐eastern Australia also generate strong indirect effects on the prey of foxes and macropods, as has been observed in the more arid parts of the continent. These direct and indirect effects of dingoes have the potential to be harnessed as passive tools to assist biodiversity conservation through the maintenance of ecologically functional dingo populations. However, research is required to better understand dingoes' indirect effects on ecosystems and the development of dingo management strategies that allow for both the preservation of dingoes and protection of livestock.     

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.     

More than Mere Numbers: The Impact of Lethal Control on the Social Stability of a Top-Order Predator

Population control of socially complex species may have profound ecological implications that remain largely invisible if only their abundance is considered. Here we discuss the effects of control on a socially complex top-order predator, the dingo (Canis lupus dingo). Since European occupation of Australia, dingoes have been controlled over much of the continent. Our aim was to investigate the effects of control on their abundance and social stability. We hypothesized that dingo abundance and social stability are not linearly related, and proposed a theoretical model in which dingo populations may fluctuate between three main states: (A) below carrying capacity and socially fractured, (B) above carrying capacity and socially fractured, or (C) at carrying capacity and socially stable. We predicted that lethal control would drive dingoes into the unstable states A or B, and that relaxation of control would allow recovery towards C. We tested our predictions by surveying relative abundance (track density) and indicators of social stability (scent-marking and howling) at seven sites in the arid zone subject to differing degrees of control. We also monitored changes in dingo abundance and social stability following relaxation and intensification of control. Sites where dingoes had been controlled within the previous two years were characterized by low scent-marking activity, but abundance was similar at sites with and without control. Signs of social stability steadily increased the longer an area was allowed to recover from control, but change in abundance did not follow a consistent path. Comparison of abundance and stability among all sites and years demonstrated that control severely fractures social groups, but that the effect of control on abundance was neither consistent nor predictable. Management decisions involving large social predators must therefore consider social stability to ensure their conservation and ecological functioning.     

Temporal and spatial trends in the abundances of an apex predator,introduced mesopredator and ground-nesting bird are consistent with the mesopredator release hypothesis

Apex predator extirpation has been identified as a key driver of biodiversity losses. The mesopredator release hypothesis (MRH) predicts that reduced abundance of apex predators results in an increase in the abundance and predatory impact of mesopredators. Here we test predictions made according to the MRH that an apex predator, the dingo (Canis dingo), benefits a small ground-nesting bird, the little button-quail (Turnix velox), by reducing the abundance of introduced mesopredators, the red fox (Vulpes vulpes) and feral cat (Felis catus). We also examined an alternative hypothesis that herbivore grazing negatively affects little button-quail abundance by reducing ground cover. To test our predictions we compared dingo, mesopredator, quail, herbivore and ground cover abundances and predator diets over a 25 month period and across a 10,000 km² region encompassing areas where dingoes were common and rare, pastoral properties, and conservation reserves. Little button-quails were primarily observed where dingoes were common and foxes rare. Cats were detected at low numbers throughout the sample area irrespective of the index abundance of little button-quails, dingoes or foxes. Birds occurred less frequently in dingo than fox or cat scats. Ground cover and herbivore grazing activity were poor correlates of little button-quail abundance. Our results are consistent with the hypothesis that apex predators’ mesopredator-suppressive effects translate to population-level benefits for a ground-nesting bird. Positive associations between the abundances of dingoes and small-prey species suggests that positive management of dingoes could be incorporated into broad-scale biodiversity conservation programs as a strategy to alleviate the predatory impacts of foxes.     

Minimizing animal welfare harms associated with predation management in agro‐ecosystems

The impacts of wild predators on livestock are a common source of human–wildlife conflict globally, and predators are subject to population control for this reason in many situations. Animal welfare is one of many important considerations affecting decisions about predation management. Recent studies discussing animal welfare in this context have presented arguments emphasizing the importance of avoiding intentional harm to predators, but they have not usually considered harms imposed by predators on livestock and other animals. Efforts to mitigate predation impacts (including ‘no control’ approaches) cause a variety of harms to predators, livestock and other wildlife. Successfully minimizing the overall frequency and magnitude of harms requires consideration of the direct, indirect, intentional and unintentional harms imposed on all animals inhabiting agricultural landscapes. We review the harms resulting from the management of dingoes and other wild dogs in the extensive beef cattle grazing systems of Australia to illustrate how these negative impacts can be minimized across both wild and domestic species present on a farm or in a free‐ranging livestock grazing context. Similar to many other predator–livestock conflicts, wild dogs impose intermittent harms on beef cattle (especially calves) including fatal predation, non‐fatal attack (mauling and biting), pathogen transmission, and fear‐ or stress‐related effects. Wild dog control tools and strategies impose harms on dingoes and other wildlife including stress, pain and death as a consequence of both lethal and non‐lethal control approaches. To balance these various sources of harm, we argue that the tactical use of lethal predator control approaches can result in harming the least number of individual animals, given certain conditions. This conclusion conflicts with both traditional (e.g. continuous or ongoing lethal control) and contemporary (e.g. predator‐friendly or no‐control) predation management approaches. The general and transferable issues, approaches and principles we describe have broad applicability to many other human–wildlife conflicts around the world.     

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.     

Conservation implications for dingoes from the maternal and paternal genome: Multiple populations,dog introgression,and demography

It is increasingly common for apex predators to face a multitude of complex conservation issues. In Australia, dingoes are the mainland apex predator and play an important role in ecological functioning. Currently, however, they are threatened by hybridization with modern domestic dogs in the wild. As a consequence, we explore how increasing our understanding of the evolutionary history of dingoes can inform management and conservation decisions. Previous research on whole mitochondrial genome and nuclear data from five geographical populations showed evidence of two distinct lineages of dingo. Here, we present data from a broader survey of dingoes around Australia using both mitochondrial and Y chromosome markers and investigate the timing of demographic expansions. Biogeographic data corroborate the presence of at least two geographically subdivided genetic populations, southeastern and northwestern. Demographic modeling suggests that dingoes have undergone population expansion in the last 5,000 years. It is not clear whether this stems from expansion into vacant niches after the extinction of thylacines on the mainland or indicates the arrival date of dingoes. Male dispersal is much more common than female, evidenced by more diffuse Y haplogroup distributions. There is also evidence of likely historical male biased introgression from domestic dogs into dingoes, predominately within southeastern Australia. These findings have critical practical implications for the management and conservation of dingoes in Australia; particularly a focus must be placed upon the threatened southeastern dingo population.     

Could direct killing by larger dingoes have caused the extinction of the thylacine from mainland Australia?

Invasive predators can impose strong selection pressure on species that evolved in their absence and drive species to extinction. Interactions between coexisting predators may be particularly strong, as larger predators frequently kill smaller predators and suppress their abundances. Until 3500 years ago the marsupial thylacine was Australia's largest predator. It became extinct from the mainland soon after the arrival of a morphologically convergent placental predator, the dingo, but persisted in the absence of dingoes on the island of Tasmania until the 20th century. As Tasmanian thylacines were larger than dingoes, it has been argued that dingoes were unlikely to have caused the extinction of mainland thylacines because larger predators are rarely killed by smaller predators. By comparing Holocene specimens from the same regions of mainland Australia, we show that dingoes were similarly sized to male thylacines but considerably larger than female thylacines. Female thylacines would have been vulnerable to killing by dingoes. Such killing could have depressed the reproductive output of thylacine populations. Our results support the hypothesis that direct killing by larger dingoes drove thylacines to extinction on mainland Australia. However, attributing the extinction of the thylacine to just one cause is problematic because the arrival of dingoes coincided with another the potential extinction driver, the intensification of the human economy.     

Do dingoes suppress the activity of feral cats in northern Australia?

Large predators can have profound impacts on community composition. Not only do they directly affect prey abundance, they also indirectly affect prey abundance through their direct effects on smaller predators. In Australia, dingoes fill the role of a large predator and, in southern Australia, have clear impacts on introduced foxes. Their effect on introduced cats, however, is less clear. Here we present data from multiple sites across northern Australia (where foxes are absent), which reveal a negative correlation between cat and dingo activity. This relationship could arise because cats avoid areas where dingoes are active, or because cats are less abundant in areas with high dingo densities, or a combination of both. At a subset of our study sites, we experimentally reduced dingo (but not cat) abundance by poison baiting. This resulted in a 55% drop in dingo activity within 4 weeks of baiting, but without a compensatory increase in cat activity. This suggests the negative correlation between cat and dingo activity is not a simple consequence of cats reactively avoiding areas with higher dingo traffic, but rather, that there are fewer cats in areas where dingoes are more active. This study is a rare demonstration of the potential for dingoes to affect the behaviour and potentially the population size of feral cats, and therefore reduce the impact of feral cats on vulnerable native prey species.     

Death by sex in an Australian icon: a continent‐wide survey reveals extensive hybridization between dingoes and domestic dogs

Hybridization between domesticated animals and their wild counterparts can disrupt adaptive gene combinations, reduce genetic diversity, extinguish wild populations and change ecosystem function. The dingo is a free‐ranging dog that is an iconic apex predator and distributed throughout most of mainland Australia. Dingoes readily hybridize with domestic dogs, and in many Australian jurisdictions, distinct management strategies are dictated by hybrid status. Yet, the magnitude and spatial extent of domestic dog–dingo hybridization is poorly characterized. To address this, we performed a continent‐wide analysis of hybridization throughout Australia based on 24 locus microsatellite DNA genotypes from 3637 free‐ranging dogs. Although 46% of all free‐ranging dogs were classified as pure dingoes, all regions exhibited some hybridization, and the magnitude varied substantially. The southeast of Australia was highly admixed, with 99% of animals being hybrids or feral domestic dogs, whereas only 13% of the animals from remote central Australia were hybrids. Almost all free‐ranging dogs had some dingo ancestry, indicating that domestic dogs could have poor survivorship in nonurban Australian environments. Overall, wild pure dingoes remain the dominant predator over most of Australia, but the speed and extent to which hybridization has occurred in the approximately 220 years since the first introduction of domestic dogs indicate that the process may soon threaten the persistence of pure dingoes.     

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.     

Lethal control of an apex predator has unintended cascading effects on forest mammal assemblages

Disruption to species-interaction networks caused by irruptions of herbivores and mesopredators following extirpation of apex predators is a global driver of ecosystem reorganization and biodiversity loss. Most studies of apex predators'' ecological roles focus on effects arising from their interactions with herbivores or mesopredators in isolation, but rarely consider how the effects of herbivores and mesopredators interact. Here, we provide evidence that multiple cascade pathways induced by lethal control of an apex predator, the dingo, drive unintended shifts in forest ecosystem structure. We compared mammal assemblages and understorey structure at seven sites in southern Australia. Each site comprised an area where dingoes were poisoned and an area without control. The effects of dingo control on mammals scaled with body size. Activity of herbivorous macropods, arboreal mammals and a mesopredator, the red fox, were greater, but understorey vegetation sparser and abundances of small mammals lower, where dingoes were controlled. Structural equation modelling suggested that both predation by foxes and depletion of understorey vegetation by macropods were related to small mammal decline at poisoned sites. Our study suggests that apex predators’ suppressive effects on herbivores and mesopredators occur simultaneously and should be considered in tandem in order to appreciate the extent of apex predators’ indirect effects.     

Exploitation ecosystems and trophic cascades in non‐equilibrium systems: pasture – red kangaroo – dingo interactions in arid Australia

The exploitation ecosystems hypothesis (EEH) proposes that 1) plant biomass reflects the primary productivity of an ecosystem modified by the regulating effect of herbivory, and 2) herbivore abundance reflects the productivity of plants modified by the regulating effect of predation. Primary productivity thus determines the number of trophic levels in an ecosystem and the extent to which bottom–up and top–down regulation influence the biomass ratios of adjacent and non‐adjacent trophic levels (i.e. trophic cascading). We constructed an interactive model of plant (pasture), herbivore (red kangaroo Macropus rufus) and predator (dingo Canis lupus dingo), a system in which trophic cascades have been suggested to occur, and used it to test the effects of increasing stochastic variation in primary productivity and dingo culling on predictions of the EEH. The model contained four feedback loops: the predator–herbivore and herbivore–plant feedback loops, and the predator and plant density‐dependent feedback loops. The equilibrium conditions along the primary productivity gradient reproduced the three zones of trophic dynamics predicted by the EEH, plus an additional zone at productivities above which the maximum density of a predator is achieved due to social regulation: that zone is characterized by increasing herbivore density and decreasing plant biomass. Culling dingoes produced trophic cascades that were strongly attenuated at primary productivities below which the maximum density of dingoes was attained. Results were robust to uncertainty in kangaroo off‐take by dingoes and to the efficacy of dingo culling, but prey switching by dingoes from red kangaroos to reptiles would weaken trophic cascades. We conclude that social regulation of carnivores has important implications for expression of the EEH and trophic cascades, and that attenuation of trophic cascades increases with increasing stochasticity in primary productivity. Our model also provides a framework for understanding the conditions in which dingo‐mediated trophic cascades might be expected to occur, and generates testable predictions about the effects of higher dingo densities (e.g. by stopping culling or reintroduction to former range) on kangaroo and pasture dynamics.