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.
The ecology of the dusky hopping mouse (Notomys fuscus) was studied at Pelican Waterhole in southwest Queensland and Montecollina Bore in north-east South Australia over an eight-year period. Population parameters of N. fuscus differed markedly between the two study sites. Whilst the population at Montecollina Bore exhibited large fluctuations in size, captures at Pelican Waterhole were lower but more consistent. Recaptures between sessions at Montecollina Bore peaked at 60% but no individuals were recaptured at Pelican Waterhole. No evidence of seasonal breeding was recorded at either site. Male N. fuscus captured at Montecollina Bore were significantly heavier (average 31.4 g) than Pelican Waterhole animals (average 26.6 g). Over a 1-4-night period, the maximum linear distance moved by radio-collared individuals was 1.5 km (average 481 m) at Pelican Waterhole and 400 m (average 199 m) at Montecollina Bore. Differences in population dynamics between the two sites are ascribed to food availability and habitat quality. Whilst Pelican Waterhole may constitute a more stable, less degraded environment, Montecollina Bore appears to be defined by periods of either very high or very low resource availability depending on rainfall. The abundance of dingoes and low cat and fox activity may contribute to the persistence of N. fuscus at the two study sites.
The distribution, habitat and conservation status of Notomys fuscus were determined by collating past records of the species and conducting field investigations covering areas of historical distribution and similar habitats. Detailed population sampling was carried out in two geographically distinct locations where populations appeared to be extant. Evidence of N. fuscus was found throughout the Strzelecki Desert east and south of the Strzelecki Creek in South Australia and in an isolated group of dunes south-east of the Diamantina River in south-west Queensland. Populations were located in a variety of sand dune habitats (excepting those dominated by Triodia) throughout these areas, implying that the species is a habitat-generalist with a preference for a sandy substrate. Eight floristic groups were identified from the 66 sites sampled, three of which supported N. fuscus populations. These ranged from extremely degraded dune and sand plain systems in the southern Strzelecki Desert, supporting mostly ephemeral plants, to well-vegetated dunes covered by sandhill canegrass,Zygochloa paradoxa, in south-west Queensland. However, the results suggest that the presence of consolidated dunes and perennial vegetation are important for the maintenance of stable populations. Relatively dense populations of N. fuscus were recorded only in the vicinity of major drainage systems. It is hypothesised that the higher nutrient status of the soils surrounding such systems may be an important factor affecting the distribution of N. fuscus. The study reaffirmed the species’ decline since European settlement of Australia, and recommends that the present vulnerable status of the species (IUCN Species Survival Commission (SSC) Rodent Specialist Group) be maintained.
Two disparate populations of Pseudomys australis, in the southern and north-western Lake Eyre Basin of South Australia, were studied over a 3-year period using trapping and radio-tracking techniques. Various aspects of the species’ ecology were investigated. Past records of the species were almost always associated with population irruptions following exceptionally wet years. Aspects of population dynamics, fine-scale habitat use, activity ranges and burrows were studied and related to habitat condition during three dry seasons following a good season. Both areas were associated with floodout plains in a gibber desert environment but differed in soils and vegetation structure. The population dynamics and structure and home-range activity also differed. These differences appeared to relate to the availability and distribution of food and shelter in the respective locations. The differences between populations in the two areas are discussed with reference to the source/sink and refugia concepts.
Rangelands support many ecosystem services important to humans, including climate regulation. They also have a significant role to play in the mitigation of greenhouse gases. However, the capacity of any rangeland to do this depends foremost upon the condition of biodiversity, and the functioning of its ecosystems. Considerable research has been undertaken on rangeland condition but it has not yet included the assessment of biodiversity (plants, animals and microbes) as a primary focus. Rangeland managers have struggled to assess biodiversity condition because it is rarely defined, is everywhere (so what do you assess?), is always changing in response to natural and human disturbances (so how do you know when it has changed?) and what amount signals management action. Here we present a framework that addresses these issues, and apply it to select surrogates and indicators that are scientifically defensible in biological and planning terms for assessing biodiversity. An arid Australian rangeland region is used as a case study to develop and apply our approach. We were not able to illustrate interpretation of condition because of the absence of long-term monitoring data in Australian rangelands, but we do provide guiding principles about sampling design and analytical methods for interpretation that use raw data rather than multimetrics. We discovered that different management outcomes expected to be informed from assessing biodiversity condition affected surrogate and indicator choice, and that a number indicators were not robust when assessed on conceptual relevance, measurement qualities, feasibility of implementation and policy and management relevance for four different management outcomes. Our work highlights the importance of stating the expected outcomes of biodiversity condition assessments up front, so that indicators relevant to future management are chosen. It also shows that critical thought on the robustness of indicators is warranted, especially as condition assessments under climate change will require information on the functional traits of species. We conclude by assessing the strengths and weaknesses of our framework in relation to environmental planning.
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