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

Savviness of prey to introduced predators

The prey naivety hypothesis posits that prey are vulnerable to introduced predators because many generations in slow gradual coevolution are needed for appropriate avoidance responses to develop. It predicts that prey will be more responsive to native than introduced predators and less responsive to introduced predators that differ substantially from native predators and from those newly established. To test these predictions, we conducted a global meta-analysis of studies that measured the wariness responses of small mammals to the scent of sympatric mammalian mesopredators. We identified 26 studies that met our selection criteria. These studies comprised 134 experiments reporting on the responses of 36 small mammal species to the scent of six introduced mesopredators and 12 native mesopredators. For each introduced mesopredator, we measured their phylogenetic and functional distance to local native mesopredators and the number of years sympatric with their prey. We used predator and prey body mass as a measure of predation risk. Globally, small mammals were similarly wary of the scent of native and introduced mesopredators; phylogenetic and functional distance between introduced mesopredators and closest native mesopredators had no effect on wariness; and wariness was unrelated to the number of prey generations, or years, since first contact with introduced mesopredators. Small mammal wariness was associated with predator-prey body mass ratio, regardless of the nativity. The one thing animals do not seem to recognize is whether their predators are native.

Effect of scavenging on predation in a food web

Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes two facultative scavenger species, which we refer to as the predator or scavenger species according to their natural scavenging propensity, as well as live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics (exploitative competition) allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. One fundamental prediction is that scavengers most likely increase predator kill rates, especially if there are exploitative feedback effects on the prey or carrion resources like is normally observed in natural systems. Scavengers only have minimal effects on predator kill rate when predator, scavenger, and prey abundances are kept constant by management. In such controlled systems, interference competition can greatly affect the interactions in contrast to more natural systems, with an increase in interference competition leading to a decrease in predator kill rate. Our study adds to studies that show that the presence of predators affects scavenger behavior, vital rates, and food web structure, by showing that scavengers impact predator kill rates through multiple mechanisms, and therefore indicating that scavenging and predation patterns are tightly intertwined. We provide a road map to the different theoretical outcomes and their support from different empirical studies on vertebrate guilds to provide guidance in wildlife management.

Fire and Its Interactions With Other Drivers Shape a Distinctive, Semi-Arid ‘Mallee’ Ecosystem

Fire shapes ecosystems globally, including semi-arid ecosystems. In Australia, semi-arid ‘mallee’ ecosystems occur primarily across the southern part of the continent, forming an interface between the arid interior and temperate south. Mallee vegetation is characterized by short, multi-stemmed eucalypts that grow from a basal lignotuber. Fire shapes the structure and functioning of mallee ecosystems. Using the Murray Mallee region in south-eastern Australia as a case study, we examine the characteristics and role of fire, the consequences for biota, and the interaction of fire with other drivers. Wildfires in mallee ecosystems typically are large (1000s ha), burn with high severity, commonly cause top-kill of eucalypts, and create coarse-grained mosaics at a regional scale. Wildfires can occur in late spring and summer in both dry and wet years. Recovery of plant and animal communities is predictable and slow, with regeneration of eucalypts and many habitat components extending over decades. Time since the last fire strongly influences the distribution and abundance of many species and the structure of plant and animal communities. Animal species display a discrete set of generalized responses to time since fire. Systematic field studies and modeling are beginning to reveal how spatial variation in fire regimes (‘pyrodiversity’) at different scales shapes biodiversity. Pyrodiversity includes variation in the extent of post-fire habitats, the diversity of post-fire age-classes and their configuration. At regional scales, a desirable mix of fire histories for biodiversity conservation includes a combination of early, mid and late post-fire age-classes, weighted toward later seral stages that provide critical habitat for threatened species. Biodiversity is also influenced by interactions between fire and other drivers, including land clearing, rainfall, herbivory and predation. Extensive clearing for agriculture has altered the nature and impact of fire, and facilitated invasion by pest species that modify fuels, fire regimes and post-fire recovery. Given the natural and anthropogenic drivers of fire and the consequences of their interactions, we highlight opportunities for conserving mallee ecosystems. These include learning from and fostering Indigenous knowledge of fire, implementing actions that consider synergies between fire and other processes, and strategic monitoring of fire, biodiversity and other drivers to guide place-based, adaptive management under climate change.

Does aerial baiting for controlling feral cats in a heterogeneous landscape confer benefits to a threatened native meso-predator?

Introduced mammalian predators can have devastating impacts on recipient ecosystems and disrupt native predator–prey relationships. Feral cats (Felis catus) have been implicated in the decline and extinction of many Australian native species and developing effective and affordable methods to control them is a national priority. While there has been considerable progress in the lethal control of feral cats, effective management at landscape scales has proved challenging. Justification of the allocation of resources to feral cat control programs requires demonstration of the conservation benefit baiting provides to native species susceptible to cat predation. Here, we examined the effectiveness of a landscape-scale Eradicat® baiting program to protect threatened northern quolls (Dasyurus hallucatus) from feral cat predation in a heterogeneous rocky landscape in the Pilbara region of Western Australia. We used camera traps and GPS collars fitted to feral cats to monitor changes in activity patterns of feral cats and northern quolls at a baited treatment site and unbaited reference site over four years. Feral cat populations appeared to be naturally sparse in our study area, and camera trap monitoring showed no significant effect of baiting on cat detections. However, mortality rates of collared feral cats ranged from 18–33% after baiting, indicating that the program was reducing cat numbers. Our study demonstrated that feral cat baiting had a positive effect on northern quoll populations, with evidence of range expansion at the treatment site. We suggest that the rugged rocky habitat preferred by northern quolls in the Pilbara buffered them to some extent from feral cat predation, and baiting was sufficient to demonstrate a positive effect in this relatively short-term project. A more strategic approach to feral cat management is likely to be required in the longer-term to maximise the efficacy of control programs and thereby improve the conservation outlook for susceptible threatened fauna.

The canid pest ejector challenge: controlling urban foxes while keeping domestic dogs safe

Abstract ContextIt is widely recognised that red foxes (Vulpes vulpes) are abundant within urban areas; however, it is difficult to apply lethal control measures using poison baits in cities because of concerns about the safety of domestic pets, particularly dogs (Canis familiaris). AimsWe tested canid pest ejectors (CPEs) as a potential method of fox control by measuring visitation and activation behaviour of foxes and other wildlife while assessing non-target risk to domestic dogs. MethodsWe compared eight urban and eight peri-urban sites in Sydney, with half of the sites having restricted access for domestic dogs. We allocated five camera traps and ejectors per site. Through generalised linear mixed models, we compared the probability of ejector activation between foxes and dogs. We also assessed the relationship between dog visitation and distance to habitation and dog restrictions as measures of dog safety. Key resultsBoth species of canids were equally likely to pull the ejector (P=0.26). As expected, dog visitation was significantly lower in sites with dog restrictions (P<0.001). However, it was not related to distance from habitation. Only two non-canid species were recorded pulling the ejector, suggesting high target-specificity for canids. ConclusionsIn sites with dog restrictions, the risk of dog casualties from CPEs is minimal. However, distance from habitation does not increase dog safety, at least within 250m. The ejector is highly specific for canids. ImplicationsWe provide specific recommendations for the design of a potential fox control program using CPEs in urban and peri-urban areas. The ejector may be a safe method for fox control in cities when deployed at places without domestic dogs.

The influence of weather and moon phase on small mammal activity

Small mammals are commonly surveyed using live trapping but the influence of weather conditions on trap success is largely unknown. This information is required to design and implement more effective field surveys and monitoring. We tested the influence of weather and moon phase on capture rates of small mammals in the Murray Mallee region of semi-arid Australia. We used extensive pitfall trapping data collected at 267 sites, totalling 54492 trap-nights. We built regression models to explore the relationship between the capture rates of five species and daily meteorological conditions, and across families of mammals, including dasyurids, burramyids and rodents. A relationship common to several taxa was the positive influence of high winds (>20km h−1) on capture rates. We also identified differences between taxa, with warmer overnight temperatures increasing capture rates of mallee ningaui but decreasing those of Bolam’s mouse. This makes it difficult to determine a single set of ‘optimal’ meteorological conditions for surveying the entire community but points to conditions favourable to individual species and groups. We recommend that surveys undertaken in warmer months encompass a variety of meteorological conditions to increase capture rates and provide a representative sample of the small mammal community present in a landscape.

A framework of integrated research for managing introduced predators in the Pilbara bioregion, Western Australia

The effective control of wild dogs, feral cats and foxes is of primary interest to land managers, both for biodiversity conservation and for the protection of livestock. Control programs primarily target single species within the context of biodiversity conservation or livestock practices, but their effectiveness in depressing predator densities is unclear because monitoring is limited or not conducted. Here, we review and discuss the outcomes of a workshop to identify research priorities for managing predation on native fauna by introduced predators in the Pilbara bioregion in Western Australia. We suggest that the control of introduced predators will be most effective if it is implemented at a landscape-scale comprising integrated predator management that considers interspecific (predator) interactions combined with standardised monitoring to measure the effectiveness and benefits of control. Four research themes were identified: (1) collation and collection of baseline data, (2) effective monitoring of introduced predators, (3) understanding functional (ecological) roles of introduced predators within the different ecosystem contexts, and (4) identifying novel complementary approaches to protect threatened species. These themes collectively include research areas that invest in foundational, ecological and alternative biological parameters in research to close knowledge gaps related to the functional roles of introduced predators in the landscape. Addressing these research themes will assist land managers to achieve outcomes that address the needs of both biodiversity conservation and pastoral production. This framework is timely given the ongoing investment in offset funding being mobilised in the region.

Good times, bad times: Resource pulses influence mammal diversity in meridional Brazilian highlands

Understanding spatiotemporal patterns of species distributions and their determinants is paramount in ecology. Here, we explore the relationship between the diversity of surviving mammals and two of the main alimentary resources (araucaria seeds and feijoa fruits) across the Araucaria Forest (FOM) in South America. First, we investigated the influence of landscape and environment on the species distribution and pulse of forest productivity. Then, we evaluated how these spatiotemporal pulses in resource availability influence the mammalian diversity. We analyzed the data via diversity descriptors, Morisita index and multiple regressions. Our findings highlighted that climate, tree density, and other environmental variables explained the pulses of productivity. Mammalian diversity of first-order consumers mammals-all those immediately feeding on seeds and fruits-was partially related to resource pulses. Our results revealed that the pulses of forest resources can influence mammal diversity over the years, including delayed responses and asynchronous oscillations. The integrity of vegetal elements of the FOM is key to maintain several mammal-mediated ecological processes. Maintaining the viability of tree populations, encouraging the sustainable use of non-timber resources, and promoting the conservation of the mammalian fauna, which is undergoing an unprecedented diversity crisis worldwide, can help to preserve the remaining ecological processes.

Conserving Australia’s threatened native mammals in predator-invaded, fire-prone landscapes

Abstract Inappropriate fire regimes and predation by introduced species each pose a major threat to Australia’s native mammals. They also potentially interact, an issue that is likely to be contributing to the ongoing collapse of native mammal communities across Australia. In the present review, I first describe the mechanisms through which fire could create predation pinch points, exacerbating the impacts of predators, including red foxes, Vulpes vulpes, and feral cats, Felis catus, on their native mammalian prey. These mechanisms include a localised increase in predator activity (a numerically mediated pathway) and higher predator hunting success after fire (a functionally moderated pathway), which could both increase native mammal mortality and limit population recovery in fire-affected landscapes. Evidence for such interactions is growing, although largely based on unreplicated experiments. Improving native mammal resilience to fire in predator-invaded landscapes requires addressing two key questions: how can the impacts of introduced predators on native mammals in fire-affected areas be reduced; and, does a reduction in predation by introduced species result in higher native mammal survival and population recovery after fire? I then examine potential management options for reducing predator impacts post-fire. The most feasible are landscape-scale predator control and the manipulation of fire regimes to create patchy fire scars. However, robust field experiments with adequate statistical power are required to assess the effectiveness of these approaches and preclude null (e.g. compensatory mortality) or adverse (e.g. mesopredator or competitor release) outcomes. Ongoing predator management and prescribed burning programs provide an opportunity to learn through replicated natural experiments as well as experimental manipulations. Standardised reporting protocols and cross-jurisdiction monitoring programs would help achieve necessary spatial and environmental replication, while multi-trophic, spatially explicit simulation models could help synthesise findings from disparate study designs, predict management outcomes and generate new hypotheses. Such approaches will be key to improving management of the complex mechanisms that drive threatened native mammal populations in Australia’s predator-invaded, fire-prone landscapes.