Recent Submissions

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    Fire and life history affect the distribution of plant species in a biodiversity hotspot
    (Wiley, 2019-07) Magadzire, N; De Klerk, Helen; Esler, KJ; Slingsby, JA; Syphard, A
    Aim: Species distribution models (SDMs) provide valuable insights into species–environment relationships and potential climate change impacts on diversity. Most SDMs do not account for the role of natural disturbance regimes such as fire in determining current and future species distributions, or how species traits mediate their response to these stressors. Here, we investigate the importance of fire in determining the distributions of species in fire-prone fynbos vegetation, and how this varies in relation to different life history traits (growth form and fire-response strategy). Location: Cape Floristic Region, South Africa. Methods: We modelled the distribution of 104 plant species with different life history traits, using Maxent. The model included five climatic variables, one edaphic and one fire variable. Post hoc analyses of model output and permutation procedures were conducted to assess variable importance across different life history traits. We accounted for phylogenetic autocorrelation using sister species comparisons. Results: Permutation importance scores identified fire return interval as a major determinant of fynbos species’ distributions. Linear mixed effect analyses revealed that seeder species were significantly more sensitive to fire than resprouters. Coefficients from the (linear) response curves of the different predictors indicated that the occurrence of species across all life histories was negatively associated with longer fire return intervals. Main conclusions: Fire and life history traits governing species’ response to fire are key factors determining species distributions in our study system. SDMs that ignore the role of fire in driving species distributions, and how this varies across different life history types, compromise our ability to understand species–environment relationships in fire-prone ecosystems. There is great need for better spatial data describing historical, current and future fire regimes and for models that can incorporate different responses based on species life histories, to improve vulnerability assessments for fire-prone ecosystems.
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    Drought and endophyte impact African black beetle feeding on perennial ryegrass
    (New Zealand Grassland Association, 2024-05-28) Hewitt, KG; Phillips, CB; Hofmann, RW; Ball, OJ; Luo, D; Popay, AJ
    Water is essential to plant growth, driving interactions between plants, herbivorous insects and fungal Epichloë endophytes. However, water availability fluctuates, a phenomenon intensified by climate change, challenging the success of New Zealand’s pastoral industry. The impacts of climatic changes, such as intensifying drought, on pastoral insect pests have received little attention. In a no-choice bioassay, African black beetle (ABB) were fed semi-synthetic diets containing freeze-dried foliage material from drought-exposed and well-watered perennial ryegrass containing endophyte strains AR37 or NZCT, or with material free of endophyte (Nil). Diet consumption, beetle weight change, fungal alkaloid concentrations, phytohormones, and NRI (nitrogen reflectance index) concentrations were measured and compared. Except for AR37, ABB consumed more diets containing drought-exposed rather than well-watered material, with a 61% increase in Nil and a 50% increase in diets containing NZCT, though these effects were not accompanied by corresponding ABB weight changes. Here, we discuss the implications of these results on ABB damage in New Zealand pastures in the context of increasing drought and illustrate how spatial patterns of ABB damage could change over the next 75 years. Areas that do not currently have high populations of ABB such as Manawatū-Whanganui, Wairarapa and Marlborough will become increasingly vulnerable to damage.
  • ItemOpen Access
    An analysis of the recent fire regimes in the Angolan catchment of the Okavango Delta, Central Africa
    (SpringerOpen, 2022) van Wilgen, B. W.; De Klerk, Helen M.; Stellmes, M,; Archibald, S,
    Background: This paper presents an analysis of fire regimes in the poorly studied Angolan catchment of the Okavango Delta in Botswana. We used MODIS data to examine the frequency and seasonality of fires over 20 years (from 2000 to 2020) in three dominant vegetation types (miombo woodlands, open woodlands and grasslands, and short closed to open bushlands), and in areas where people were present, and where they were absent. Results: The median fire return intervals for both open woodlands and grasslands and short bushlands were relatively short (1.9 and 2.2 years respectively). In miombo woodlands, fires were less frequent (median return periods of 4.5 years). Human population density had no discernible effect on the fire return intervals, but about 14% of the miombo woodlands experienced no fires over 20 years. Ongoing shifting cultivation within miombo woodlands has led to structural changes and the introduction of fire into this vegetation type where fires were rare or absent in the past. About 12% of the miombo did not burn during the period examined where people were present, whereas close to 20% of the sites remained unburnt where people were absent. This suggests that people did not change the fire return interval in any of the vegetation types studied, but that they altered the amount of the landscape that is flammable in miombo vegetation. Fires occurred between June and September, with a peak in the late dry season (August and September). Conclusions: Historical research indicates that late dry-season fires are detrimental to miombo woodlands, and our analysis suggests that degradation in parts of the catchment has led to the introduction of fire to this previously fire-free and fire-sensitive vegetation type. Deforestation of miombo woodlands, and the consequent introduction of fire, is a cause for concern with respect to the ecological stability of the Okavango Delta. Managers should therefore aim to protect the remaining closed-canopy miombo stands from further clearing and to attempt to shift the timing of burns to the early dry season to reduce their intensity.
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    Generating mock skeletons for lightweight web-service testing
    (IEEE, 2019) Bhagya, T; Dietrich, J; Guesgen, H
    Modern application development allows applications to be composed using lightweight HTTP services. Testing such an application requires the availability of services that the application makes requests to. However, access to dependent services during testing may be restrained. Simulating the behaviour of such services is, therefore, useful to address their absence and move on application testing. This paper examines the appropriateness of Symbolic Machine Learning algorithms to automatically synthesise HTTP services' mock skeletons from network traffic recordings. These skeletons can then be customised to create mocks that can generate service responses suitable for testing. The mock skeletons have human-readable logic for key aspects of service responses, such as headers and status codes, and are highly accurate.
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    GHTraffic: A dataset for reproducible research in service-oriented computing
    (IEEE, 2018) Bhagya, T; Dietrich, J; Guesgen, H; Versteeg, S
    We present GHTraffic, a dataset of significant size comprising HTTP transactions extracted from GitHub data and augmented with synthetic transaction data. The dataset facilitates reproducible research on many aspects of service-oriented computing. This paper discusses use cases for such a dataset and extracts a set of requirements from these use cases. We then discuss the design of GHTraffic, and the methods and tool used to construct it. We conclude our contribution with some selective metrics that characterise GHTraffic.