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

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Keystone effects of an alien top-predator stem extinctions of native mammals

Alien predators can have catastrophic effects on ecosystems and are thought to be much more harmful to biodiversity than their native counterparts. However, trophic cascade theory and the mesopredator release hypothesis predict that the removal of top predators will result in the reorganization of trophic webs and loss of biodiversity. Using field data collected throughout arid Australia, we provide evidence that removal of an alien top-predator, the dingo, has cascading effects through lower trophic levels. Dingo removal was linked to increased activity of herbivores and an invasive mesopredator, the red fox (Vulpes vulpes), and to the loss of grass cover and native species of small mammals. Using species distribution data, we predict that reintroducing or maintaining dingo populations would produce a net benefit for the conservation of threatened native mammals across greater than 2.42 × 10⁶ km² of Australia. Our study provides evidence that an alien top predator can assume a keystone role and be beneficial for biodiversity conservation, and also that mammalian carnivores more generally can generate strong trophic cascades in terrestrial ecosystems.     

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.     

Impact of Livestock Husbandry on Small- and Medium-Sized Carnivores in Kalahari Savannah Rangelands

ABSTRACT We analyzed relative sensitivities of small- and medium-sized carnivores to livestock husbandry (stocking rates and predator control) in Kalahari, South Africa, rangelands at a regional scale. We monitored small carnivores using track counts on 22 Kalahari farms across a land-use gradient ranging from low to high stocking rates and also interviewed each farm manager to identify farmers' perception of small carnivores as potential predators for livestock. We recorded 12 species of small- and medium-sized carnivores across 22 Kalahari farms. Stocking rate was the most important driving variable for local carnivore abundance. Abundance of all species was lowest on farms where stocking rate was high. Most farm managers perceived medium-sized carnivores, in particular, African wildcat (Felis silvestris lybica), black-backed jackal (Canis mesomelas), and caracal (Caracal caracal), as potential predators of livestock. Multiple regression analysis shows that black-backed jackal, African wildcat, and caracal were negatively affected by predator control measures, whereas bat-eared fox (Otocyon megalotis), cape fox (Vulpes chama), and small-spotted genet (Genetta genetta) were positively affected. Our results show a need for expanding research and conservation activities toward small- and medium-sized carnivores in southern African savannah rangelands. We, therefore, suggest developing a monitoring program combining passive tracking with indigenous knowledge of local Khoisan Bushmen to monitor carnivore populations, and we recommend additional predator removal experiments that manipulate predator densities.     

Functional responses of an apex predator and a mesopredator to an invading ungulate: Dingoes,red foxes and sambar deer in south‐east Australia

Biological invasions by large herbivores involve the establishment of novel interactions with the receiving mammalian carnivore community, but understanding these interactions is difficult due to the large spatiotemporal scales at which such dynamics would occur. We quantified the functional responses of a native apex predator (the dingo (Canis familiaris), which includes wild dogs and their hybrids) and a non‐native mesopredator (red fox; Vulpes vulpes) to an invading non‐native ungulate (sambar deer; Cervus unicolor) in Australia. We predicted that the apex predator would exhibit a stronger functional response to increasing sambar deer abundance than the mesopredator. We used a state–space model to link two 30‐year time series: (i) sambar deer abundance (hunter catch‐per‐unit‐effort); and (ii) percentages of sambar deer in dingo (N = 4531) and fox (N = 5002) scats. Sambar deer abundance increased over fourfold during 1984?2013. The percentages of sambar deer in dingo and fox scats increased during this 30‐year period, from nil in both species in 1984 to 8.2% in dingoes and 0.5% in foxes in 2013. Dingoes exhibited a much stronger functional response to increasing sambar deer abundance than foxes. The prediction that invading deer would be utilized more by the apex predator than by the mesopredator was therefore supported. The increasing abundance of sambar deer during the period 1984?2013 provided an increasingly important food source for dingoes. In contrast, the smaller red fox utilized sambar deer much less. Our study demonstrates that prey enrichment can be an important consequence of large herbivore invasions and that the effect varies predictably with the trophic position of the mammalian carnivores in the receiving community.     

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.     

Relationship Between Small-game Hunting and Carnivore Diversity in Central Spain

Small-game hunting plays an important economic role in central Spain and some game species are key food resources for threatened predators. Small carnivores may reduce numbers of important game species. To alleviate predation pressure on game populations, management is often focused on predator control. Control methods can be non-selective, and so could potentially have a negative impact on non-target carnivore species, affecting carnivore guild composition and diversity. Using data on carnivore diversity in 70 quadrants (5 × 5 km) in a large area of central Spain with two main land uses (small-game hunting and a mixture of big-game hunting and forestry), we assessed how game management was related to carnivore diversity. Carnivore species richness was significantly lower in those areas managed for small-game hunting than in areas where other land uses predominated. The apparently least affected species by predator control was the red fox (Vulpes vulpes), the main target species of predator control. Results suggested that low carnivore species richness was linked to small-game hunting activities, which was probably associated with non-selective predator control practices. Therefore, in order to reconcile carnivore conservation and economic goals it is imperative to develop and to evaluate selective predator control techniques.     

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.     

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.     

Assessing resource and predator effects on habitat use of tropical small carnivores

Habitat use of animals is influenced by a combination of factors including food abundance and interactions with other species. Animals typically must forage while simultaneously avoiding predation from multiple potential predators, but habitat use in tropical forest ecosystems that assesses effects of both predation risk and resources has rarely been conducted. We used camera traps and occupancy analyses to document small mammalian carnivore occurrence in relation to food abundance and interactions with large predators. We hypothesized that habitat use of six small mammalian carnivores (≤15 kg) would be influenced by (1) abundance of resources (fruit, rodents, and streams) and/or (2) large predators. Predictions regarding food and habitat resources were only supported for one species (crab-eating mongoose, Urva urva), which was positively associated with rodents and streams. Three small carnivores (masked palm civet Paguma larvata, common palm civet Paradoxurus hermaphroditus, yellow-throated marten Martes flavigula) were affected negatively by leopard and mesopredators as predicted. Counter to our predictions, two species (masked palm civet and yellow-throated marten) showed spatial avoidance of tiger suggesting that an apex predator might also pose predation risk to small carnivores. The focal small carnivores and large predators of this study appeared to have moderately to highly overlapping temporal activity indicating no temporal avoidance. In conclusion, food resources appeared to have minimal effects for six small carnivores in this ecosystem probably due to continuous resource availability. Predation risk appeared to affect some species in terms of spatial occupancy but not in temporal activity, indicating perhaps complex, but not entirely negative interactions between larger carnivores and this guild of small carnivores. The mechanisms which facilitate co-occurrence between small carnivores and large predators may, however, operate at finer spatiotemporal scales than we investigated here.     

Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

Emerging evidence increasingly illustrates the importance of a holistic, rather than taxon-specific, approach to the study of ecological communities. Considerable resources are expended to manage both introduced and native mammalian carnivores to improve conservation outcomes; however, management can result in unforeseen and sometimes catastrophic outcomes. Varanid lizards are likely to be apex- or mesopredators, but being reptiles are rarely considered by managers and researchers when investigating the impacts of mammalian carnivore management. Instances of mesopredator release have been described for Varanus gouldii as a result of fox and cat management in Australia, with cascading effects on faunal community structure. A meta-analysis showing extensive dietary niche overlap between varanids, foxes and cats plus a review of experimental and circumstantial evidence suggests mesopredator release of V. gouldii and about five other medium to large species of varanid lizard is likely in other regions. This highlights the need for managers to adopt a whole-of-community approach when attempting to manage predators for sustained fauna conservation, and that additional research is required to elucidate whether mesopredator release of varanids is a widespread consequence of carnivore management, altering the intended faunal responses.     

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.     

Interactions Between Carnivores in Madagascar and the Risk of Disease Transmission

Introduced carnivores exert considerable pressure on native predators through predation, competition and disease transmission. Recent research shows that exotic carnivores negatively affect the distribution and abundance of the native and endangered carnivores of Madagascar. In this study, we provide information about the frequency and distribution of interactions between exotic (dogs and cats) and native carnivores (Eupleridae) in the Betampona Natural Reserve (BNR), Madagascar, using noninvasive camera trap surveys. Domestic dogs (Canis familiaris) were the most frequently detected carnivore species within the BNR, and we found that indirect interactions between exotic and native carnivores were frequent (n = 236). Indirect interactions were more likely to occur near the research station (incidence rate ratio = 0.91), which may constitute a disease transmission hot spot for carnivores at BNR. The intervals between capture of native and exotic carnivores suggest that there is potential for pathogen transmission between species in BNR. These capture intervals were significantly shorter near the edge of the reserve (P = 0.04). These data could be used to implement biosecurity measures to monitor interactions and prevent disease transmission between species at the domestic animal and wildlife interface.     

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.     

Use of agroecosystem matrix habitats by mammalian carnivores (Carnivora): a global‐scale analysis

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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.     

Does removal of an alien predator from small islands in the Baltic Sea induce a trophic cascade?

Changes in carnivore abundance can alter the distribution and abundance of plants on a community wide basis, an effect known as a trophic cascade. Because alien predators can have a disproportionate impact, compared to native predators, on herbivore populations, they may induce stronger trophic cascades in plant communities than native predators. We studied the indirect effects of the removal of an alien predator, the American mink Mustela vison on plant communities on small islands in the Baltic Sea, SW Finland. Mink had been removed from a group of islands for 12 yr, while another group of islands with mink presence served as a control area. Field voles Microtus agrestis and bank voles Myodes glareolus exert strong grazing pressure on the island vegetation and are an important part of mink diet. On nine islands of the mink removal area and five islands of the control area we studied the vegetation in ten randomly chosen plots; five in herbaceous and five in woody (i.e. dwarf shrub) vegetation. We studied the cascading impacts of mink predation on grassy and woody vegetation using the Shannon diversity and equitability indices and comparing abundances of different species between mink removal and control islands. Diversity and equitability of plant communities were higher on mink removal islands. In grassy patches, abundances of several species differed between mink removal and control islands. Our results demonstrate, for the first time, that alien predator removal may induce a trophic cascade on small islands.     

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.     

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.     

Localised control of an introduced predator: creating problems for the future?

Introduced mammalian predators have had significant impacts on many native prey species. Although control of such predators for conservation management is becoming increasingly commonplace, it is often undertaken at a relatively small scale in relation to the overall predator population. Processes such as immigration mean that it remains difficult to determine the effectiveness of control measures. We investigated the impacts of feral ferret Mustela furo removal on the entire feral ferret population on Rathlin Island, UK. Removal of ferrets prior to breeding led to a substantial increase in the post-dispersal population through the enhanced survival of juveniles. Despite increased numbers, overwinter survival remained high, potentially aided by the reduced territoriality shown by this feral species compared to wild carnivores. The response of this ferret population to control is a further illustration of the complex ecological processes and outcomes arising from the anthropogenic disruption of wildlife populations. It highlights how partial or localised management may prove ineffective, and at worst might exacerbate the problems that management was designed to avert.