Social organization and movements of desert rodents during population “booms” and “busts” in central Australia

Making the most of mortalities: Novel host-parasite records in a sandy inland mouse (Pseudomys hermannsburgensis)

From 2020 to 2022, systematic investigation of wildlife mortalities on Dirk Hartog Island, Western Australia was initiated to inform wildlife disease risk analyses for translocation purposes. As part of this monitoring, in November 2020, a sandy inland mouse (Pseudomys hermannsburgensis) was found deceased with multiple comorbidities. Gross necropsy, histopathology and ancillary molecular testing identified several novel host-parasite associations. Sarcoptes scabiei was identified via molecular methods in association with consistent cutaneous pathology, representing the first known detection of this parasite in an Australian native rodent. A putative novel virus belonging to the subfamily Gammaherpesvirinae was also identified, representing the first known detection of a herpesvirus (Orthoherpesviridae) from this species, although it was not clearly associated with other disease processes. A heavy burden of the cestode Hymenolepis microstoma was also present in the gastrointestinal tract, representing a new host record for this species, whilst a pancreatic adenocarcinoma was also found. Beyond the novelty of these host records, these findings contribute to important health baselines of rodent populations on Dirk Hartog Island and highlight the value of investigating mortalities and implementing health surveillance as part of ecological monitoring and wildlife translocation projects.

Experimentally testing animal responses to prescribed fire size and severity

Deserts are often highly biodiverse and provide important habitats for many threatened species. Fire is a dominant disturbance in deserts, and prescribed burning is increasingly being used by conservation managers and Indigenous peoples to mitigate the damaging effects of climate change, invasive plants, and land-use change. The size, severity, and patchiness of fires can affect how animals respond to fire. However, there are almost no studies examining such burn characteristics in desert environments, which precludes the use of such information in conservation planning. Using a before-after control-impact approach with 20 sampling sites, we studied the outcomes of 10 prescribed burns of varying size (5-267 ha), severity, and patchiness to identify which variables best predicted changes in small mammal and reptile species richness and abundance. Three of the 13 species showed a clear response to fire. Captures increased for 2 species (1 mammal, 1 reptile) and decreased for 1 species (a reptile) as the proportional area burned around traps increased. Two other mammal species showed weaker positive responses to fire. Total burn size and burn patchiness were not influential predictors for any species. Changes in capture rates occurred only at sites with the largest and most severe burns. No fire-related changes in capture rates were observed where fires were small and very patchy. Our results suggest that there may be thresholds of fire size or fire severity that trigger responses to fire, which has consequences for management programs underpinned by the patch mosaic burning paradigm. The prescribed burns we studied, which are typical in scale and intensity across many desert regions, facilitated the presence of some taxa and are unlikely to have widespread or persistent negative impacts on small mammal or reptile communities in this ecosystem provided that long unburned habitat harboring threatened species is protected.

Boom-bust population dynamics drive rapid genetic change

Increasing environmental threats and more extreme environmental perturbations place species at risk of population declines, with associated loss of genetic diversity and evolutionary potential. While theory shows that rapid population declines can cause loss of genetic diversity, populations in some environments, like Australia's arid zone, are repeatedly subject to major population fluctuations yet persist and appear able to maintain genetic diversity. Here, we use repeated population sampling over 13 y and genotype-by-sequencing of 1903 individuals to investigate the genetic consequences of repeated population fluctuations in two small mammals in the Australian arid zone. The sandy inland mouse (Pseudomys hermannsburgensis) experiences marked boom-bust population dynamics in response to the highly variable desert environment. We show that heterozygosity levels declined, and population differentiation (FST) increased, during bust periods when populations became small and isolated, but that heterozygosity was rapidly restored during episodic population booms. In contrast, the lesser hairy-footed dunnart (Sminthopsis youngsoni), a desert marsupial that maintains relatively stable population sizes, showed no linear declines in heterozygosity. These results reveal two contrasting ways in which genetic diversity is maintained in highly variable environments. In one species, diversity is conserved through the maintenance of stable population sizes across time. In the other species, diversity is conserved through rapid genetic mixing during population booms that restores heterozygosity lost during population busts.

Long-term livestock exclusion increases plant richness and reproductive capacity in arid woodlands

Herbivore exclusion is implemented globally to recover ecosystems from grazing by introduced and native herbivores, but evidence for large-scale biodiversity benefits is inconsistent in arid ecosystems. We examined the effects of livestock exclusion on dryland plant richness and reproductive capacity. We collected data on plant species richness and seeding (reproductive capacity), rainfall, vegetation productivity and cover, soil strength and herbivore grazing intensity from 68 sites across 6500 km2 of arid Georgina gidgee (Acacia georginae) woodlands in central Australia between 2018 and 2020. Sites were on an actively grazed cattle station and two destocked conservation reserves. We used structural equation modeling to examine indirect (via soil or vegetation modification) versus direct (herbivory) effects of grazing intensity by two introduced herbivores (cattle, camels) and a native herbivore (red kangaroo), on seasonal plant species richness and seeding of all plants, and the richness and seeding of four plant groups (native grasses, forbs, annual chenopod shrubs, and palatable perennial shrubs). Non-native herbivores had a strong indirect effect on plant richness and seeding by reducing vegetative ground cover, resulting in decreased richness and seeding of native grasses and forbs. Herbivores also had small but negative direct impacts on plant richness and seeding. This direct effect was explained by reductions in annual chenopod and palatable perennial shrub richness under grazing activity. Responses to grazing were herbivore-dependent; introduced herbivore grazing reduced native plant richness and seeding, while native herbivore grazing had no significant effect on richness or seeding of different plant functional groups. Soil strength decreased under grazing by cattle but not camels or kangaroos. Cattle had direct effects on palatable perennial shrub richness and seeding, whereas camels had indirect effects, reducing richness and seeding by reducing the abundance of shrubs. We show that considering indirect pathways improves evaluations of the effects of disturbances on biodiversity, as focusing only on direct effects can mask critical mechanisms of change. Our results indicate substantial biodiversity benefits from excluding livestock and controlling camels in drylands. Reducing introduced herbivore impacts will improve soil and vegetation condition, ensure reproduction and seasonal persistence of species, and protect native plant diversity.

Foraging and Food Selection in a Desert Rodent: Diet Shifts of the Sandy Inland Mouse between Population Booms and Busts

Seeds are commonly viewed as the mainstay of the diet of desert rodents. We describe the diet of a common Australian desert rodent, the sandy inland mouse Pseudomys hermannsburgensis, using direct observations of free-living animals and analysis of the stomach contents of preserved specimens. Direct observations showed that animals forage mostly on the ground surface and eat seeds from a wide range of plant species, as well as invertebrates and occasional green plant material. Stomach content analysis revealed no differences in the presence or absence of these three major food groups between seasons or the sexes. However, invertebrates were more prominent in the diet of mice during prolonged, dry, population 'bust' periods compared with post-rain population 'boom' periods, with this dietary shift probably reflecting a scarcity of seeds during the busts. The results confirm that seed is an important component of the diet of P. hermannsburgensis, with 92% of stomachs containing seed. The results also support the classification of the species as omnivorous rather than granivorous, with 70% of stomachs containing invertebrates and over half the specimens analysed containing both seeds and invertebrates. We suggest that dietary flexibility is important for rodent persistence in Australia's climatically unpredictable arid regions.

Odour-mediated Interactions Between an Apex Reptilian Predator and its Mammalian Prey

An important but understudied modality for eavesdropping between predators and prey is olfaction, especially between non-mammalian vertebrate predators and their prey. Here we test three olfactory eavesdropping predictions involving an apex reptilian predator, the sand goanna Varanus gouldii, and several species of its small mammalian prey in arid central Australia: 1) small mammals will recognize and avoid the odour of V. gouldii; 2) V. gouldii will be attracted to the odour of small mammals, especially of species that maximize its energetic returns; and 3) small mammals will be less mobile and will show higher burrow fidelity where V. gouldii is absent compared with where it is present. As expected, we found that small mammals recognized and avoided faecal odour of this goanna, feeding less intensively at food patches where the odour of V. gouldii was present than at patches with no odour or a pungency control odour. Varanus gouldii also was attracted to the odour of small mammals in artificial burrows and dug more frequently at burrows containing the odour of species that were energetically profitable than at those of species likely to yield diminishing returns. Our third prediction received mixed support. Rates of movement of three species of small mammals were no different where V. gouldii was present or absent, but burrow fidelity in two of these species increased as expected where V. gouldii had been removed. We conclude that olfaction plays a key role in the dynamic interaction between V. gouldii and its mammalian prey, with the interactants using olfaction to balance their respective costs of foraging and reducing predation risk. We speculate that the risk of predation from this apex reptilian predator drives the highly unusual burrow-shifting behaviour that characterizes many of Australia's small desert mammals.

Timing outweighs magnitude of rainfall in shaping population dynamics of a small mammal species in steppe grassland

Disentangling the effects of rainfall timing and magnitude on animal and plant populations is essential to reveal the biological consequence of diverse climate change scenarios around the world. We conducted a 10-y, large-scale, manipulative experiment to examine the bottom-up effects of changes in rainfall regime on the population dynamics of Brandt’s voles in the steppe grassland of Inner Mongolia, China. We found that a moderate rainfall increase during the early growing season could produce marked increases in vole population size by increasing the biomass of preferred plant species, whereas large increases in rainfall produced no additional increase in vole population growth. Our study highlights the importance of rainfall magnitude and timing on the nonlinear population dynamics of herbivores.

Climate change–induced shifts in species phenology differ widely across trophic levels, which may lead to consumer–resource mismatches with cascading population and ecosystem consequences. Here, we examined the effects of different rainfall patterns (i.e., timing and amount) on the phenological asynchrony of population of a generalist herbivore and their food sources in semiarid steppe grassland in Inner Mongolia. We conducted a 10-y (2010 to 2019) rainfall manipulation experiment in 12 0.48-ha field enclosures and found that moderate rainfall increases during the early rather than late growing season advanced the timing of peak reproduction and drove marked increases in population size through increasing the biomass of preferred plant species. By contrast, greatly increased rainfall produced no further increases in vole population growth due to the potential negative effect of the flooding of burrows. The increases in vole population size were more coupled with increased reproduction of overwintered voles and increased body mass of young-of-year than with better survival. Our results provide experimental evidence for the fitness consequences of phenological mismatches at the population level and highlight the importance of rainfall timing on the population dynamics of small herbivores in the steppe grassland environment.

Declines in rodent abundance and diversity track regional climate variability in North American drylands

Regional long-term monitoring can enhance the detection of biodiversity declines associated with climate change, improving future projections by reducing reliance on space-for-time substitution and increasing scalability. Rodents are diverse and important consumers in drylands, regions defined by the scarcity of water that cover 45% of Earth's land surface and face increasingly drier and more variable climates. We analyzed abundance data for 22 rodent species across grassland, shrubland, ecotone, and woodland ecosystems in the southwestern USA. Two time series (1995-2006 and 2004-2013) coincided with phases of the Pacific Decadal Oscillation (PDO), which influences drought in southwestern North America. Regionally, rodent species diversity declined 20%-35%, with greater losses during the later time period. Abundance also declined regionally, but only during 2004-2013, with losses of 5% of animals captured. During the first time series (wetter climate), plant productivity outranked climate variables as the best regional predictor of rodent abundance for 70% of taxa, whereas during the second period (drier climate), climate best explained variation in abundance for 60% of taxa. Temporal dynamics in diversity and abundance differed spatially among ecosystems, with the largest declines in woodlands and shrublands of central New Mexico and Colorado. Which species were winners or losers under increasing drought and amplified interannual variability in drought depended on ecosystem type and the phase of the PDO. Fewer taxa were significant winners (18%) than losers (30%) under drought, but the identities of winners and losers differed among ecosystems for 70% of taxa. Our results suggest that the sensitivities of rodent species to climate contributed to regional declines in diversity and abundance during 1995-2013. Whether these changes portend future declines in drought-sensitive consumers in the southwestern USA will depend on the climate during the next major PDO cycle.

Plague transforms positive effects of precipitation on prairie dogs to negative effects

Rodents characteristically benefit from increased precipitation, especially in typically dry habitats; "good years" of high precipitation improve their forage and water balance. However, Yersinia pestis (plague), a flea-borne pathogen of mammals that was introduced to western North America, has the greatest negative impact on at least some species of rodents during years of above-average precipitation. In the absence of plague mitigation, negative effects of plague in wet years might overwhelm the otherwise beneficial effects of increased moisture. In Montana and Utah, USA, where plague now occurs enzootically, we investigated the influence of precipitation on finite rates of annual population change (2000-2005) for 3 species of prairie dogs (Cynomys spp.) in replicated plots treated with deltamethrin dust and in non-treated plots for paired comparisons. There was a significant interaction between precipitation and treatment. When we reduced plague vector fleas, prairie dog visual counts tended to increase with increasing precipitation. Simultaneously, there was a negative relationship between counts and precipitation on paired plots where plague was not managed, suggesting that plague transformed and reversed the otherwise beneficial effect of increased precipitation. Are the good years gone for prairie dogs? Even if the good years are not gone, they are perhaps relatively scarce compared to historic times prior to the invasion of plague. This scenario might apply to other ecosystems and may pose broad conservation challenges in western North America.

Night of the hunter: using cameras to quantify nocturnal activity in desert spiders

Invertebrates dominate the animal world in terms of abundance, diversity and biomass, and play critical roles in maintaining ecosystem function. Despite their obvious importance, disproportionate research attention remains focused on vertebrates, with knowledge and understanding of invertebrate ecology still lacking. Due to their inherent advantages, usage of camera traps in ecology has risen dramatically over the last three decades, especially for research on mammals. However, few studies have used cameras to reliably detect fauna such as invertebrates or used cameras to examine specific aspects of invertebrate ecology. Previous research investigating the interaction between wolf spiders (Lycosidae: Lycosa spp.) and the lesser hairy-footed dunnart (Sminthopsis youngsoni) found that camera traps provide a viable method for examining temporal activity patterns and interactions between these species. Here, we re-examine lycosid activity to determine whether these patterns vary with different environmental conditions, specifically between burned and unburned habitats and the crests and bases of sand dunes, and whether cameras are able to detect other invertebrate fauna. Twenty-four cameras were deployed over a 3-month period in an arid region in central Australia, capturing 2,356 confirmed images of seven invertebrate taxa, including 155 time-lapse images of lycosids. Overall, there was no clear difference in temporal activity with respect to dune position or fire history, but twice as many lycosids were detected in unburned compared to burned areas. Despite some limitations, camera traps appear to have considerable utility as a tool for determining the diel activity patterns and habitat use of larger arthropods such as wolf spiders, and we recommend greater uptake in their usage in future.

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.

Patterns of decline of small mammal assemblages in vegetation communities of coastal south-east Australia: identification of habitat refuges

Since European settlement Australian native mammals have experienced significant extinctions and severe declines in the range and abundance of populations. Longitudinal studies are required to identify declines and activate timely management. Population studies of native small mammal communities were conducted across the eastern Otway Ranges during 1975–2007; however, their subsequent status was unknown. We aimed to: compare the current occurrence and abundance of species and communities (2013–18) to those in previous decades across major vegetation communities (heathy woodland, low forest, sand heathland, headland scrub, coastal dunes and estuarine wetland), and identify change characteristics and management priorities. Live trapping was employed to assess mammals at 30 sites across seven vegetation communities. In total, 67% of sites exhibited large to severe decreases in abundance and only 3% of sites had more than four species compared to 27% in earlier decades. Declines occurred following wildfire and drought, with drivers likely to be multifactorial. While regional declines were significant, higher mammal abundance (two- to six-fold) and native species richness were recorded at coastal dune sites, indicating that this community provides important mammal refuges. Identification of refuges across the landscape and their protection from inappropriate fire and predators should be management priorities.

Local effects of global climate on a small rodent Necromys lasiurus

Global climate drivers often have strong effects on the carrying capacity of animal populations, but little is known about how effects differ between regional and local scales. In this paper we evaluated how climate variables were correlated with regional and local fluctuations of a small rodent, Necromys lasiurus, in an Amazonian savanna. Between 2000 and 2019, we evaluated the temporal variation in abundance of N. lasiurus in eight 4.0-ha plots separated by 0.8 – 10.6 km. Using generalized linear mixed models, we found that, at a regional scale, the abundance of rodents captured was positively associated with the abundance in the prior year, but had little relationship with the Southern Oscillation Index (SOI), which had been shown to affect rats in a single plot in a previous study. However, variation in densities among years was coordinated among some plots, leading to patchiness in population dynamics. Based on the patterns of density fluctuations, the plots formed three clusters. Analyses based on these clusters indicated that only one was strongly affected by SOI, as in the previous study. The differences in the effects of global climate drivers on populations of a single species in relatively homogeneous habitat indicate that predictions about the effects of climate change should be based on simultaneous studies in a variety of sites or they may lead to spurious relationships.

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.

What can we deduce about the reproductive condition of spinifex hopping mice (Notomys alexis) from external examination?

Field studies often use external examination of the vagina or the swelling of the scrotum to make deductions about the reproductive condition of rodents. In this study we sought to determine what information on reproductive condition could be gained from external examination of the reproductive anatomy of spinifex hopping mice (Notomys alexis) using individuals from a captive colony. Female N. alexis with perforate vaginae had a significantly larger mean uterine mass and larger mean maximum ovarian follicle diameter than non-perforate females. Corpora lutea were recorded in two perforate animals but were not present in females with a ‘pinhole’-size perforate or non-perforate vagina. In male hopping mice scrotal bulge size was unrelated to testes mass, ventral prostate mass or presence/absence of sperm in the cauda epididymides. Males with dark scrotal pigmentation had a significantly smaller mean testes mass than males with light or no pigmentation. However, there was no relationship between scrotal pigmentation and ventral prostate mass or sperm presence in the cauda epididymides. Our study suggests that vaginal perforation is an acceptable indicator of sexual maturity in female hopping mice, but scrotal bulge size and scrotal pigmentation should not be used to predict reproductive condition of males.

Range-wide genetic structure of a cooperative mouse in a semi-arid zone: Evidence for panmixia

Landscape topography and the mobility of individuals will have fundamental impacts on a species' population structure, for example by enhancing or reducing gene flow and therefore influencing the effective size and genetic diversity of the population. However, social organization will also influence population genetic structure. For example, species that live and breed in cooperative groups may experience high levels of inbreeding and strong genetic drift. The western pebble-mound mouse (Pseudomys chapmani), which occupies a highly heterogeneous, semi-arid landscape in Australia, is an enigmatic social mammal that has the intriguing behaviour of working cooperatively in groups to build permanent pebble mounds above a subterranean burrow system. Here, we used both nuclear (microsatellite) and mitochondrial (mtDNA) markers to analyse the range-wide population structure of western pebble-mound mice sourced from multiple social groups. We observed high levels of genetic diversity at the broad scale, very weak genetic differentiation at a finer scale and low levels of inbreeding. Our genetic analyses suggest that the western pebble-mound mouse population is both panmictic and highly viable. We conclude that high genetic connectivity across the complex landscape is a consequence of the species' ability to permeate their environment, which may be enhanced by "boom-bust" population dynamics driven by the semi-arid climate. More broadly, our results highlight the importance of sampling strategies to infer social structure and demonstrate that sociality is an important component of population genetic structure.

Interactive effects of severe drought and grazing on the life history cycle of a bioindicator species

We used the lesser prairie-chicken (Tympanuchus pallidicinctus), an iconic grouse species that exhibits a boom-bust life history strategy, on the Southern High Plains, USA, as a bioindicator of main and interactive effects of severe drought and grazing. This region experienced the worst drought on record in 2011. We surveyed lesser prairie-chicken leks (i.e., communal breeding grounds) across 12 years that represented 7 years before the 2011 drought (predrought) and 4 years during and following the 2011 drought (postdrought). Grazing was annually managed with the objective of achieving ≤50% utilization of aboveground vegetation biomass. We used lek (n = 49) count data and covariates of weather and managed grazing to: (a) estimate long-term lesser prairie-chicken abundance and compare abundance predrought and postdrought; (b) examine the influence of annual and seasonal drought (modified Palmer drought index), temperature, and precipitation on long-term lesser prairie-chicken survival and recruitment; and (c) assess and compare the influence of grazing on lesser prairie-chicken population predrought and postdrought. Lesser prairie-chicken abundance was nearly seven times greater predrought than postdrought, and population declines were attributed to decreased survival and recruitment. The number of days with temperature >90th percentile had the greatest effect, particularly on recruitment. The population exhibited a substantial bust during 2011 and 2012 without a boom to recover in four postdrought years. Adaptive grazing positively influenced the population predrought, but had no effects postdrought. Results suggest that the severe drought in 2011 may have been beyond the range of environmental conditions to which lesser prairie-chickens, and likely other species, have adapted. Land management practices, such as grazing, should remain adaptive to ensure potential negative influences to all species are avoided. Increasing habitat quantity and quality by reducing habitat loss and fragmentation likely will increase resiliency of the ecosystem and individual species.

Assessing the potential for intraguild predation among taxonomically disparate micro-carnivores: marsupials and arthropods

Interspecific competition may occur when resources are limited, and is often most intense between animals in the same ecological guild. Intraguild predation (IGP) is a distinctive form of interference competition, where a dominant predator selectively kills subordinate rivals to gain increased access to resources. However, before IGP can be identified, organisms must be confirmed as members of the same guild and occur together in space and time. The lesser hairy-footed dunnart (Sminthopsis youngsoni, Dasyuridae) is a generalist marsupial insectivore in arid Australia, but consumes wolf spiders (Lycosa spp., Lycosidae) disproportionately often relative to their availability. Here, we test the hypothesis that this disproportionate predation is a product of frequent encounter rates between the interactants due to high overlap in their diets and use of space and time. Diet and prey availability were determined using direct observations and invertebrate pitfall trapping, microhabitat use by tracking individuals of both species-groups, and temporal activity using spotlighting and camera traps. Major overlap (greater than 75% similarity) was found in diet and temporal activity, and weaker overlap in microhabitat use. Taken together, these findings suggest reasonable potential, for the first time, for competition and intraguild predation to occur between taxa as disparate as marsupials and spiders.

Unpredictability of escape trajectory explains predator evasion ability and microhabitat preference of desert rodents

Mechanistically linking movement behaviors and ecology is key to understanding the adaptive evolution of locomotion. Predator evasion, a behavior that enhances fitness, may depend upon short bursts or complex patterns of locomotion. However, such movements are poorly characterized by existing biomechanical metrics. We present methods based on the entropy measure of randomness from Information Theory to quantitatively characterize the unpredictability of non-steady-state locomotion. We then apply the method by examining sympatric rodent species whose escape trajectories differ in dimensionality. Unlike the speed-regulated gait use of cursorial animals to enhance locomotor economy, bipedal jerboa (family Dipodidae) gait transitions likely enhance maneuverability. In field-based observations, jerboa trajectories are significantly less predictable than those of quadrupedal rodents, likely increasing predator evasion ability. Consistent with this hypothesis, jerboas exhibit lower anxiety in open fields than quadrupedal rodents, a behavior that varies inversely with predator evasion ability. Our unpredictability metric expands the scope of quantitative biomechanical studies to include non-steady-state locomotion in a variety of evolutionary and ecologically significant contexts.Biomechanical understanding of animal gait and maneuverability has primarily been limited to species with more predictable, steady-state movement patterns. Here, the authors develop a method to quantify movement predictability, and apply the method to study escape-related movement in several species of desert rodents.

Greater bilby burrows: important structures for a range of species in an arid environment

Greater bilbies (Macrotis lagotis) have been described as ecosystem engineers and their burrows are significant structures across an often featureless and harsh arid landscape. Remote cameras were deployed at bilby burrows to determine whether bilby burrows were important structures for other species. Cameras detected two mammal species, brush-tailed mulgara (Dasycercus blythi) and spinifex hopping mice (Notomys alexis), permanently occupying bilby burrows, and a further two species, short-beaked echidnas (Tachyglossus aculeatus acanthion) and sand goannas (Varanus gouldii), regularly using bilby burrows for shelter. An additional suite of 16 mammal, bird, reptile, amphibian and invertebrate species were detected interacting with bilby burrows. There was no difference in the number of species using disused or occupied bilby burrows, indicating that even disused bilby burrows are important structures for other species. We show that bilby burrows are used by a range of species and are analogous to the traditional, mostly North American, and commonly provided text book examples of the gopher tortoise and kangaroo rat. The disappearance of bilbies across at least 80% of their former range and thus the disappearance of their burrows as important structural resources in a harsh, arid environment may have had important consequences for a range of species.

The efficacy of monitoring techniques for detecting small mammals and reptiles in arid environments

Context Accurate surveying and monitoring of biodiversity provides essential baseline data for developing and implementing effective environmental management strategies. Land managers in arid zones face the challenge of managing vast, remote landscapes that support numerous cryptic species that are difficult to detect and monitor. Although researchers and land managers are using an increasingly wider variety of monitoring techniques to detect and monitor species, little is known of the relative effectiveness and comparative costs of these techniques. Aims The present study simultaneously assessed the efficacy of three popular monitoring techniques utilised in the spinifex sand plains of arid Australia, namely, live trapping, sign surveys and passive infrared (PIR)-camera trapping. Methods We explored variations in capture rates and species richness for each technique and compared initial and on-going costs of the techniques over time. Key results Sign surveys detected the greatest number of species and groups overall. Detectability of small mammals and reptiles, as a target group, was greater using PIR cameras, although the probability of detection by each technique varied among specific species. PIR cameras were initially the most expensive technique; however, the low ongoing costs of maintaining cameras in the field meant that they became the most cost effective after eight survey periods. Conclusions Each of the techniques tested here showed biases towards the detection of specific groups or species in the spinifex sand-plain habitat of Australia. Regardless, PIR cameras performed better at detecting the greatest diversity of target species and financially over time. Implications To accurately survey species across vast areas and climate variations, studies often extend over long time periods. Many long-term studies would be likely to benefit financially from the increased deployment of PIR cameras alongside or in place of live trapping surveys, with little impact on the ability to monitor the presence of most species in the region.

Changes in abundance and reproductive activity of small arid-zone murid rodents on an active cattle station in central Australia

Context Boom and bust population cycles are characteristic of many arid-zone rodents, but it is unknown to what extent these dynamics might be influenced by the presence of invasive rodents, such as the house mouse (Mus musculus) in Australia. Aim To determine whether the presence of M. musculus can have negative consequences on the population abundance and reproduction of two old Australian endemic rodents (the spinifex hopping mouse, Notomys alexis, and sandy inland mouse, Pseudomys hermannsburgensis). Methods The study took place on the sand dunes of a cattle station in central Australia. Population abundance was estimated as the number of individuals caught in small mammal traps, and female reproductive condition by external examination and, in a few cases, euthanasia and inspection of the reproductive tract. Key results Two synchronous periods of high abundance of N. alexis and M. musculus occurred several months after significant rainfall events, whereas the abundance of P. hermannsburgensis was consistently low. No reproduction took place in N. alexis or M. musculus when populations had reached high abundance. During low-rainfall periods, M. musculus was not detected on the sand dunes, and the two endemic species were sparsely distributed, with reproduction occasionally being evident. Conclusions During dry periods, M. musculus contracted back to refuges around the homestead and, after significant rainfall, it expanded onto the sand dunes and became abundant at the same time as did N. alexis. In contrast, and unlike in areas where M. musculus was generally rare, P. hermannsburgensis always remained at a low abundance. These patterns suggest that in areas of the natural environment close to human-modified sites, populations of at least one species of an old endemic rodent are supressed by the presence of M. musculus. Reproduction did not occur in the old endemics at times of high M. musculus abundance, but did take place in spring/early summer, even in some dry years. Implications The spread of M. musculus into the Australian arid zone may have had negative impacts on the population dynamics of P. hermannsburgensis. These findings suggest that the presence of human settlements has resulted in refuges for house mice, which periodically spread out into the natural environment during ‘boom’ times and adversely affect the natural population cycle of ecologically similar species such as P. hermannsburgensis.

Persistence of the plains mouse, Pseudomys australis, with cattle grazing is facilitated by a diet dominated by disturbance-tolerant plants

A suite of dryland mammals rely on refuges for long-term persistence during alternating cycles of low and high resource availability. Refuges are small, discrete areas into which populations contract during the lengthy dry periods that characterize dryland environments. Little is known about the characteristics of a location that make it functional as a refuge. Similarly, no information exists on how grazing-facilitated landscape modification affects small mammal refuges. To examine these questions, we assessed diet at refuge sites across the low phase (“bust”) of the population cycle of the plains mouse (Pseudomys australis), a threatened, refuge-using rodent coexisting with extensive cattle production in Australia’s drylands. The species has a varied diet dominated by species of grasses and forbs (mostly seeds) with a small proportion of invertebrates. Most of the plants consumed are shallow-rooted and short-lived species that should germinate in response to small rainfall events. Coexistence with cattle production is likely to be possible because grazing-tolerant plants are a dominant component of the diet. Our findings provide a plausible explanation for the persistence of P. australis with cattle production in dryland Australia, which should be further investigated to develop management strategies that will enable continued coexistence. This investigation should be extended to consider other refuge-using species of small mammal in pastoral systems.

Role of seasonality on predator-prey-subsidy population dynamics

The role of seasonality on predator-prey interactions in the presence of a resource subsidy is examined using a system of non-autonomous ordinary differential equations (ODEs). The problem is motivated by the Arctic, inhabited by the ecological system of arctic foxes (predator), lemmings (prey), and seal carrion (subsidy). We construct two nonlinear, nonautonomous systems of ODEs named the Primary Model, and the n-Patch Model. The Primary Model considers spatial factors implicitly, and the n-Patch Model considers space explicitly as a "Stepping Stone" system. We establish the boundedness of the dynamics, as well as the necessity of sufficiently nutritional food for the survival of the predator. We investigate the importance of including the resource subsidy explicitly in the model, and the importance of accounting for predator mortality during migration. We find a variety of non-equilibrium dynamics for both systems, obtaining both limit cycles and chaotic oscillations. We were then able to discuss relevant implications for biologically interesting predator-prey systems including subsidy under seasonal effects. Notably, we can observe the extinction or persistence of a species when the corresponding autonomous system might predict the opposite.

Ecology and conservation of the northern hopping-mouse (Notomys aquilo)

The northern hopping-mouse (Notomys aquilo) is a cryptic and enigmatic rodent endemic to Australia’s monsoonal tropics. Focusing on the insular population on Groote Eylandt, Northern Territory, we present the first study to successfully use live traps, camera traps and radio-tracking to document the ecology of N. aquilo. Searches for signs of the species, camera trapping, pitfall trapping and spotlighting were conducted across the island during 2012–15. These methods detected the species in three of the 32 locations surveyed. Pitfall traps captured 39 individuals over 7917 trap-nights. Females were significantly longer and heavier, and had better body condition, than males. Breeding occurred throughout the year; however, the greatest influx of juveniles into the population occurred early in the dry season in June and July. Nine individuals radio-tracked in woodland habitat utilised discrete home ranges of 0.39–23.95 ha. All individuals used open microhabitat proportionally more than was available, and there was a strong preference for eucalypt woodland on sandy substrate rather than for adjacent sandstone woodland or acacia shrubland. Camera trapping was more effective than live trapping at estimating abundance and, with the lower effort required to employ this technique, it is recommended for future sampling of the species. Groote Eylandt possibly contains the last populations of N. aquilo, but even there its abundance and distribution have decreased dramatically in surveys over the last several decades. Therefore, we recommend that the species’ conservation status under the Environment Protection and Biodiversity Conservation Act 1999 be changed from ‘vulnerable’ to ‘endangered’.

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.

Diversity and Community Composition of Vertebrates in Desert River Habitats

Animal species are seldom distributed evenly at either local or larger spatial scales, and instead tend to aggregate in sites that meet their resource requirements and maximise fitness. This tendency is likely to be especially marked in arid regions where species could be expected to concentrate at resource-rich oases. In this study, we first test the hypothesis that productive riparian sites in arid Australia support higher vertebrate diversity than other desert habitats, and then elucidate the habitats selected by different species. We addressed the first aim by examining the diversity and composition of vertebrate assemblages inhabiting the Field River and adjacent sand dunes in the Simpson Desert, western Queensland, over a period of two and a half years. The second aim was addressed by examining species composition in riparian and sand dune habitats in dry and wet years. Vertebrate species richness was estimated to be highest (54 species) in the riverine habitats and lowest on the surrounding dune habitats (45 species). The riverine habitats had different species pools compared to the dune habitats. Several species, including the agamid Gowidon longirostris and tree frog Litoria rubella, inhabited the riverine habitats exclusively, while others such as the skinks Ctenotus ariadnae and C. dux were captured only in the dune habitats. The results suggest that, on a local scale, diversity is higher along riparian corridors and that riparian woodland is important for tree-dependent species. Further, the distribution of some species, such as Mus musculus, may be governed by environmental variables (e.g. soil moisture) associated with riparian corridors that are not available in the surrounding desert environment. We conclude that inland river systems may be often of high conservation value, and that management should be initiated where possible to alleviate threats to their continued functioning.

Ecology of the rare but irruptive Pilliga mouse, Pseudomys pilligaensis. IV. Habitat ecology

We determined preferences of the Pilliga mouse, Pseudomys pilligaensis, for habitat attributes (ground and vegetation cover) through phases of a population irruption, and characterised refuge sites used when environmental conditions were unfavourable. In general, P. pilligaensis preferred areas with substrate dominated by sand and shrubs rather than rock or litter. However, its habitat selection changed with phases of the irruption. In the Increase phase, it showed no strong habitat preferences, perhaps because the abundance of food (seeds) overrode preferences for more stable habitat values. Its sensitivity to habitat variables increased in the Peak phase. In the Low phase, mice preferred ground cover with higher proportions of sand and shrubs, and lower proportions of rock and litter. Regression analyses suggested that sandy substrate is the most important factor for the refuge habitat of P. pilligaensis, perhaps because a sandy surface can support more understorey shrubs which provide seeds and protection from predators, and provides sites for burrows. Judging from areas where P. pilligaensis was caught during the Low phase, water run-on areas could also characterise refuge habitats. However, further studies are needed to define the species’ refuge habitats fully.

Divergent foraging behaviour of a desert rodent, Notomys fuscus, in covered and open microhabitats revealed using giving up densities and video analysis

We used a combination of giving up densities (GUD) and behavioural analysis from video footage to test the response of an Australian desert rodent, Notomys fuscus, to the experimental provision of cover microhabitat in the Strzelecki Desert, Australia. In many ecosystems, cover microhabitats are considered to be safe foraging locations for rodents. The response of bipedal desert rodents to cover microhabitats is less certain, with varied findings, due to their use of open habitats for fast travel. Notomys fuscus returned lower GUDs in cover than in open microhabitats and moved slowly for a greater amount of time under cover than in the open. These results suggest that N. fuscus has a preference for foraging under cover, where predation risk is lower, and under these conditions took longer to assess the cover microhabitat before foraging. This was distinctly different to the ‘get in, get out’ behaviour associated with foraging in open habitats. We advocate for the combined measurement of GUD and behavioural analysis using video footage as a way to improve understanding of rodents’ foraging behaviour.

Anthropogenic stressors influence small mammal communities in tropical East African savanna at multiple spatial scales

Context Protection of natural ecosystems undoubtedly safeguards ecological communities, with positive benefits for ecosystem processes and function. However, ecosystems are under threat from anthropogenic stressors that reduce the resilience both of component species and the system as a whole. Aims To determine how anthropogenic stressors (land use and climate change) could impact the diversity and resilience of a small mammal community in the greater Serengeti ecosystem, an East African savanna comprising Serengeti National Park (SNP) and adjacent agro-ecosystems, at local (SNP) and Africa-wide geographic scales. Methods We recorded small mammal species in 10 habitats in the greater Serengeti ecosystem, including the agro-ecosystem, over 48 years (1962–2010). We calculated richness and diversity for each habitat type, and used an index of similarity to quantify differences in the community among habitats. Species accumulation curves were also generated for each habitat type. Key results We recorded 40 species of small mammals in the greater Serengeti ecosystem. At the local scale, restricted habitat types in SNP (each <1% of the total area) made a disproportionately large contribution to diversity. Agro-ecosystems had lower richness and were less likely to contain specialist species. At regional and Africa-wide scales, local endemics were less likely to be recorded in the agro-ecosystem (57% species loss) compared with those with regional (33% loss) or Africa-wide (31%) geographic distributions. Conclusions At the local scale, the variety of habitats in SNP contributed to overall diversity. However, the ability to maintain this diversity in the adjacent agro-ecosystem was compromised for localised endemics compared with species with Africa-wide ranges. Land use intensification adjacent to SNP and projected changes in rainfall patterns for East Africa under global climate scenarios may compromise the future resilience of the small mammal community in this tropical savanna ecosystem. Implications The loss of rare or specialised species from protected areas and human-modified ecosystems could be mitigated by: (1) increasing habitat complexity and maintaining specialist habitats in the agro-ecosystem; and (2) creating buffers at the boundary of protected natural ecosystems that accommodate regime shifts in response to climatic change. These measures would increase the resilience of this coupled human–natural savanna ecosystem.