14 research outputs found

    Climate-driven variation in food availability between the core and range edge of the endangered northern bettong (Bettongia tropica)

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    The endangered northern bettong (Bettongia tropica) occurs in four disjunct populations in far north Queensland, Australia, at a high density only in its range core (RC). A recent study suggested that B. tropica populations are sparse at the northern and southern range edges (SRE) due to more severe droughts and variable climatic conditions causing fluctuations in the availability of their principal food resource, truffle-like fungi. Truffle availability in the Australian tropics is affected by climate, specifically seasonality of precipitation. We aimed to determine whether the differences in weather patterns between the RC and SRE could be translated to actual differences in truffle availability. Truffle density was consistently lower on the SRE although biomass was slightly higher there due to dominance by drought-tolerant truffle taxa that produce few but large truffles. Lower densities of truffles on the SRE could explain why B. tropica is also less abundant there and why they may be less resilient to competition from the more generalist rufous bettong (Aepyprymnus rufescens). Increasing temperatures and, more importantly, harsher droughts predicted for this region as a result of climate change, may have further detrimental impacts on truffle availability and thus population densities of B. tropica and other mycophagous species

    The influences of climate, habitat and fire on the distribution of cockatoo grass (Alloteropsis semialata) (Poaceae) in the Wet Tropics of northern Australia

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    Cockatoo grass [Alloteropsis semialata (R.Br.) A. Hitchc.] is considered a keystone species in northern Australian ecosystems as it provides a food resource for many species, including several endangered vertebrates. This study examined both local and regional environmental factors influencing cockatoo grass distribution and abundance in the Wet Tropics of north Queensland, Australia. Local distribution and abundance were investigated in the sclerophyll ecotone between open woodland and tall open forest, because little is known about cockatoo grass distribution within this habitat; also, the endangered northern bettong (Bettongia tropica) is restricted to this habitat and depends on cockatoo grass for its survival. Regional-scale modelling of distribution was undertaken to examine the climatic tolerances of cockatoo grass in Queensland. Density of cockatoo grass was negatively related to litter cover, soil moisture, and the presence of two dominant grass species, Themeda triandra [Forssk.(R.Br.) Stapf] and Cleistochloa subjuncea (C.E.Hubb.). Soil nutrients (N, C, S, and C : N ratio) were positively related to density of cockatoo grass. A late dry season experimental burn demonstrated that cockatoo grass had high survival to fire, with increased density and flowering in response to fire. Regional-scale modelling using climate variables indicated that cockatoo grass is more suited to the drier end of the sclerophyll habitat range. Cockatoo grass in the woodland-forest ecotone in the Wet Tropics appears to be influenced by several environmental features associated with the ground layer. The species benefits from the reduction in litter cover and competing grass species that result from management actions such as prescribed burning. Understanding of the factors limiting this species, both at a local and regional scale, can be used to guide management of this ecotone habitat for both cockatoo grass and the survival of other species that depend on it

    Block-Based Distributed File Systems

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    Distributed file systems have become popular because they allow information to be shared be between computers in a natural way. A distributed file system often forms a central building block in a distributed system. Currently most distributed file systems are built using a communications interface that transfers messages about files between machines. This thesis proposes a different, lower level, communications interface. This `block-based' interface exchanges information about the blocks that make up the file but not about the files themselves. No other distributed file system is built this way. By demonstrating that a distributed file system can be implemented in a block-based manner, this thesis opens the way for many advances in distributed file systems. These include a reduction of the processing required at the server, uniformity in managing file blocks and fine-grained placement and replication of data. The simple communications model also lends itself to efficient implementation both at the server and in the communications protocols that support the interface. These advantages come at the cost of a more complex client implementation and the need for a lower level consistency mechanism. A block-based distributed file system (BB-NFS) has been implemented. BB-NFS provides the Unix file system interface and demonstrates the feasibility and implementability of the block-based approach. Experience with the implementation lead to the development of a lock cache mechanism which gives a large improvement in the performance of the prototype. Although it has not been directly measured it is plausible that the prototype will perform better than the file based approach. The block-based approach has much to offer future distributed file system developers. This thesis introduces the approach and its advantages, demonstrates its feasibility and shows that it can be implemented in a way that performs well

    How not to get scar(r)ed: pointers to the correct diagnosis in patients with suspected primary cicatricial alopecia

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    Primary cicatricial alopecias (PCAs) are a rare, but important, group of disorders that cause irreversible damage to hair follicles resulting in scarring and permanent hair loss. They may also signify an underlying systemic disease. Thus, it is of paramount importance that clinicians who manage patients with hair loss are able to diagnose these disorders accurately. Unfortunately, PCAs are notoriously difficult conditions to diagnose and treat. The aim of this review is to present a rational and pragmatic guide to help clinicians in the professional assessment, investigation and diagnosis of patients with PCA. Illustrating typical clinical and histopathological presentations of key PCA entities we show how dermatoscopy can be profitably used for clinical diagnosis. Further, we advocate the search for loss of follicular ostia as a clinical hallmark of PCA, and suggest pragmatic strategies that allow rapid formulation of a working diagnosis