Desert small mammal responses to wildfire and predation in the aftermath of a La Nińa driven resource pulse

Diet and occurrences of the letter-winged kite in a predation refuge

Nomadism is an advantageous life history strategy for specialised predators because it enables the predator to respond rapidly to changes in prey populations. The letter-winged kite (Elanus scriptus) is a nomadic nocturnal bird of prey endemic to arid and semi-arid zones of Australia. Letter-winged kites prey almost exclusively on nocturnal rodents and are often associated with rodent irruptions, but little is known about the ecology of letter-winged kites inside their core range. The Strzelecki Desert contains a known dingo-mediated predation refuge for native rodents. In this manuscript, we compare kite sightings, predator activity, and small mammal populations across survey sites in the Strzelecki Desert where dingoes were common and where dingoes were rare and use publicly available data from the Atlas of Living Australia (ALA) to assess trends in the occurrence of kites in the region. Ninety-five percent of ALA observations occurred in areas where dingoes were common. Similarly, all our observations of kites occurred where dingoes were common and during an extended population irruption of Notomys fuscus. Notomys fuscus was the most frequent item in the letter-winged kite diet at our study sites. We suggest that there is significant evidence that these sites in the Strzelecki Desert form part of the core range for the letter-winged kite whose use of this area is facilitated by a predation refuge for rodents mediated by the dingo. We conclude that predation refuges mediated by dingoes could be a factor driving the distributions of letter-winged kites and other predators of rodents, particularly nomadic predators.

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.

Rodents' responses to manipulated plant litter and seed densities: implications for restoration

Rodent populations in arid grasslands do not always track seed production, possibly due to high levels of plant litter. When natural disturbances are suppressed, litter accumulates becoming physically complex, causing rodents to harvest fewer seeds per equivalent time foraging. It also alters security from predation. Restoring natural disturbances may be an important element in conserving rodent communities. The aim of this study was to assess the influence of two levels of plant litter cover and seed densities on nocturnal rodent population characteristics in a semiarid grassland. Specifically, I hypothesized that kangaroo rats, pocket mice, grasshopper mice, and total rodents would be higher in the sparse plant litter treatment than dense litter, whereas deer mice would be lower in sparse plots. I further hypothesized that kangaroo rats and deer mice would be higher in the seed augmented treatment compared to the unseeded treatment. A prescribed fire removed litter in four of eight plots prior to sowing native seeds 1 year postfire into two burned and two unburned plots. Rodents were live-trapped during spring and fall 1 year. Sparse litter treatment had higher total rodent abundance, biomass, and frequency of offspring compared to dense plots indicating use of stored seeds. Banner-tailed kangaroo rats had higher abundance, implying reduced predation risk. Pocket mice body mass was greater in dense plots. After winter, seeded plots had higher kangaroo rat body mass and grasshopper mice abundance than unseeded, reflecting the use of stored seeds. These short term results demonstrate litter's physical complexity may be equivalent to seed pulses on the responses of nocturnal rodents. Managers might positively influence grassland rodents by providing a mosaic of varying levels of plant litter.

Intercontinental test of constraint-breaking adaptations: Testing behavioural plasticity in the face of a predator with novel hunting strategies

Constraint-breaking adaptations are evolutionary tools that provide a mechanism for incumbent-replacement between species filling similar ecological roles. In common-garden experiments, we exposed populations of two desert rodents to two different viper species, testing their ability to adjust to novel predators that use different hunting strategies. We aimed to understand whether both predators and prey with constraint-breaking adaptations actually manifest comparative advantage over their counterparts. We used convergent species from desert dunes in the Mojave Desert in North America, Merriam's kangaroo rat Dipodomys merriami and the sidewinder rattlesnake Crotalus cerastes, and from the Negev Desert in the Middle East, the greater Egyptian gerbil Gerbillus pyramidum and the Saharan horned viper Cerastes cerastes. Both Mojave species hold constraint-breaking adaptations in relation to their counterparts from the Negev. The rattlesnakes have heat sensing organs (pits) and the kangaroo rats have fur-lined cheek pouches that allow for greater foraging efficiency and food preservation. Using patch-use theory, we evaluated the rodents' risk-assessment from each snake-separately, together and in combination with barn owls. Initially each rodent species foraged less in the presence of its familiar snake, but within a month both foraged less in the presence of the pit-viper (sidewinder). Our findings indicate a level of learning, and behavioural plasticity, in both rodents and ability to assess the risk from novel predators. The kangaroo rats were capable of harvesting far greater amounts of resources under the same conditions of elevated risk. However, the reason for their advantage may lie in bi-pedal agility and not only their ability collect food more efficiently.

On the landscape of fear: shelters affect foraging by dunnarts (Marsupialia, Sminthopsis spp.) in a sandridge desert environment

Disturbances such as fire reduce the structural complexity of terrestrial habitats, increasing the risk of predation for small prey species. The postfire effect of predation has especially deleterious effects in Australian habitats owing to the presence of invasive mammalian predators, the red fox (Vulpes vulpes) and feral cat (Felis catus), that rapidly exploit burned habitats. Here, we investigated whether the provision of artificial shelter could alleviate the risk of predation perceived by two species of small marsupial, the dunnarts Sminthopsis hirtipes and S. youngsoni, in open postfire habitat in the sandridge system of the Simpson Desert, central Australia. We installed artificial shelters constructed from wire mesh that allowed passage of the dunnarts but not of their predators at one site, and measured and compared the perceived risk of predation by the dunnarts there with those on a control site using optimal patch-use theory (giving-up densities, GUDs). GUDs were lower near artificial shelters than away from them, and near dune crests where dunnarts typically forage, suggesting that the shelters acted as corridors for dunnarts to move up to the crests from burrows in the swales. Foraging was lower near the crest in the control plot. Two-day foraging bouts were observed in dunnart activity, with recruitment to GUD stations occurring a day earlier in the augmented shelter plot. Despite these results, the effects of the shelters were localized and not evident at the landscape scale, with GUDs reduced also in proximity to sparse natural cover in the form of regenerating spinifex grass hummocks. Mapping dunnart habitat use using the landscape of fear (LOF) framework confirmed that animals perceived safety near shelter and risk away from it. We concluded that the LOF framework can usefully assess real-time behavioral responses of animals to management interventions in situations where demographic responses take longer to occur.

Predator responses to fire: A global systematic review and meta-analysis

Knowledge of how disturbances such as fire shape habitat structure and composition, and affect animal interactions, is fundamental to ecology and ecosystem management. Predators also exert strong effects on ecological communities, through top-down regulation of prey and competitors, which can result in trophic cascades. Despite their ubiquity, ecological importance and potential to interact with fire, our general understanding of how predators respond to fire remains poor, hampering ecosystem management. To address this important knowledge gap, we conducted a systematic review and meta-analysis of the effects of fire on terrestrial, vertebrate predators world-wide. We found 160 studies spanning 1978-2018. There were 36 studies with sufficient information for meta-analysis, from which we extracted 96 effect sizes (Hedges' g) for 67 predator species relating to changes in abundance indices, occupancy or resource selection in burned and unburned areas, or before and after fire. Studies spanned geographic locations, taxonomic families and study designs, but most were located in North America and Oceania (59% and 24%, respectively), and largely focussed on felids (24%) and canids (25%). Half (50%) of the studies reported responses to wildfire, and nearly one third concerned prescribed (management) fires. There were no clear, general responses of predators to fire, nor relationships with geographic area, biome or life-history traits (e.g. body mass, hunting strategy and diet). Responses varied considerably between species. Analysis of species for which at least three effect sizes had been reported in the literature revealed that red foxes Vulpes vulpes mostly responded positively to fire (e.g. higher abundance in burned compared to unburned areas) and eastern racers Coluber constrictor negatively, with variances overlapping zero only slightly for both species. Our systematic review and meta-analysis revealed strong variation in predator responses to fire, and major geographic and taxonomic knowledge gaps. Varied responses of predator species to fire likely depend on ecosystem context. Consistent reporting of ongoing monitoring and management experiments is required to improve understanding of the mechanisms driving predator responses to fire, and any broader effects (e.g. trophic interactions). The divergent responses of species in our study suggest that adaptive, context-specific management of predator-fire relationships is required.

The role of refuges in the persistence of Australian dryland mammals

Irruptive population dynamics are characteristic of a wide range of fauna in the world's arid (dryland) regions. Recent evidence indicates that regional persistence of irruptive species, particularly small mammals, during the extensive dry periods of unpredictable length that occur between resource pulses in drylands occurs as a result of the presence of refuge habitats or refuge patches into which populations contract during dry (bust) periods. These small dry-period populations act as a source of animals when recolonisation of the surrounding habitat occurs during and after subsequent resource pulses (booms). The refuges used by irruptive dryland fauna differ in temporal and spatial scale from the refugia to which species contract in response to changing climate. Refuges of dryland fauna operate over timescales of months and years, whereas refugia operate on timescales of millennia over which evolutionary divergence may occur. Protection and management of refuge patches and refuge habitats should be a priority for the conservation of dryland-dwelling fauna. This urgency is driven by recognition that disturbance to refuges can lead to the extinction of local populations and, if disturbance is widespread, entire species. Despite the apparent significance of dryland refuges for conservation management, these sites remain poorly understood ecologically. Here, we synthesise available information on the refuges of dryland-dwelling fauna, using Australian mammals as a case study to provide focus, and document a research agenda for increasing this knowledge base. We develop a typology of refuges that recognises two main types of refuge: fixed and shifting. We outline a suite of models of fixed refuges on the basis of stability in occupancy between and within successive bust phases of population cycles. To illustrate the breadth of refuge types we provide case studies of refuge use in three species of dryland mammal: plains mouse (Pseudomys australis), central rock-rat (Zyzomys pedunculatus), and spinifex hopping-mouse (Notomys alexis). We suggest that future research should focus on understanding the species-specific nature of refuge use and the spatial ecology of refuges with a focus on connectivity and potential metapopulation dynamics. Assessing refuge quality and understanding the threats to high-quality refuge patches and habitat should also be a priority. To facilitate this understanding we develop a three-step methodology for determining species-specific refuge location and habitat attributes. This review is necessarily focussed on dryland mammals in continental Australia where most refuge-based research has been undertaken. The applicability of the refuge concept and the importance of refuges for dryland fauna conservation elsewhere in the world should be investigated. We predict that refuge-using mammals will be widespread particularly among dryland areas with unpredictable rainfall patterns.

Correlates of Recent Declines of Rodents in Northern and Southern Australia: Habitat Structure Is Critical

Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south.

Historical resurveys reveal persistence of smoky mouse (Pseudomys fumeus) populations over the long-term and through the short-term impacts of fire

Context Range contractions are often the first indicator that a species is in decline. However, natural population fluctuations, characteristic of many Australian rodents, make differentiating between natural lows and unsustainable declines challenging. The endangered smoky mouse (Pseudomys fumeus) is a prime example. Surveys have failed to detect the species across much of its range over the past decade, but P. fumeus is known to experience fluctuations in abundance and periods of low detectability. Aims We compared past and current distributions of P. fumeus in the Victoria Range, Grampians–Gariwerd National Park (Victoria, Australia), to assess long-term population persistence over 40 years and short-term population persistence following a high-severity fire. Methods To evaluate the efficacy of surveys in detecting P. fumeus, we conducted analyses to explicitly model detectability using historical (1974, 2002) and modern (2013) survey data. We also tested the short-term impacts of fire on the presence of P. fumeus by surveying burned and unburned sites 3 months prior to, and 7 to 21 months following, a severe wildfire. Key results Our surveys detected P. fumeus at five new sites, confirmed presence at one historical site, and absence from two historical sites. The species persisted in situ through fire, and for at least 21 months following. We detected resident populations in burned and unburned wet drainage systems. Conclusions Despite periods of low density in which the species was undetected, P. fumeus persisted in an 8 km radius area of the eastern escarpment of Victoria Range of the Grampians–Gariwerd National Park for at least four decades through droughts, the presence of invasive predators, and the short-term impacts of wildfire. Implications Although P. fumeus persisted through a severe fire, factors influencing survival must be assessed before generalisations are made about the impacts of wildfire on the species. Management of P. fumeus should recognise that the species survives and breeds in wet drainage systems. Regular resurveys incorporating statistical estimates of detectability are necessary to identify and track distributional changes of threatened species, like P. fumeus, particularly in the context of natural, sustainable fluctuations.