School of BioSciences - Research Publications
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ItemA working guide to spatial mechanistic modelling in Julia(Wiley Open Access, 2022-05)Models that can predict the dynamics of larger scale ecological processes are increasingly important in a rapidly changing world. The Julia language gives a unique opportunity to produce new, generic tools to develop spatial mechanistic models, and to simultaneously increase their performance, resolution and predictive power. Here, we describe two new Julia software packages, DynamicGrids.jl and Dispersal.jl, that facilitate the development of spatial mechanistic models that are concise, extensible and performant, with several key attributes. First, they allow arbitrary spatially and temporally heterogeneous inputs (e.g. regional climatic data to drive population dynamics). Second, they apply rules to discrete spatial grids, including: (a) single grid cells (e.g. population growth, Allee effects, land‐use change), (b) neighborhoods (e.g. local dispersal); and (c) arbitrary locations (e.g. long‐distance wind dispersal, human‐mediated dispersal). Finally, they allow interactions between multiple grids (e.g. predator–prey models, management/environmental feedbacks). Through in‐line examples, we explore how these properties can be used to develop simple and complex grid‐based mechanistic models that run on both CPUs and GPUs. We demonstrate models of population growth, wind and self‐directed dispersal and host–parasitoid dynamics. We also demonstrate the ease by which custom rules can be combined with rules provided by packages, and the potential for use in other fields and interdisciplinary research. These Julia packages provide concise, extensible and performant tools for a wide range of grid‐based spatial models in ecology and beyond. More broadly, they highlight new opportunities for ecological modelling using the Julia language, with its combination of clear syntax, extensibility from its solution to the expression problem and its performance on CPUs and GPUs.
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ItemWarmer temperatures reduce chemical tolerance in the redlegged earth mite (Halotydeus destructor), an invasive winter-active pest(JOHN WILEY & SONS LTD, 2022-07)
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ItemClimate contributes to the evolution of pesticide resistance(WILEY, 2018-02)Abstract Aim The evolution of pesticide resistance through space and time is of great economic significance to modern agricultural production systems, and consequently, is often well documented. It can thus be used to dissect the evolutionary and ecological processes that underpin large‐scale evolutionary responses. There are now nearly 600 documented cases of pesticide resistance in arthropod pests. Although the evolution of resistance is often attributed to the persistent use of chemicals for pest suppression, the rate of development of resistance should also depend on other factors, including climatic conditions that influence population size and generation time. Here, we test whether climatic variables are linked to evolution of resistance by examining the spatial pattern of pyrethroid resistance in an important agricultural pest. Location Southern, agricultural regions of Australia. Time period 2007–2015. Major taxa studied The redlegged earth mite, Halotydeus destructor. Methods We quantified patterns of chemical usage based on paddock histories and collated long‐term climatic data. These data were then compared against presence–absence data on resistance using a boosted regression‐tree approach, applied here for the first time to the spatial categorization of pesticide resistance. Results Although chemical usage was a key driver of resistance, our analysis revealed climate‐based signals in the spatial distribution of resistance, linked to regional variation in aridity, temperature seasonality and precipitation patterns. Climatic regions supporting increased voltinism were positively correlated with resistance, in line with expectations that increased voltinism should accelerate evolutionary responses to selection pressures. Main conclusions Our findings suggest that the prediction of rapid evolutionary processes at continental scales, such as pesticide resistance, will be improved through methods that incorporate climate and ecology, in addition to more immediate selection pressures, such as chemical usage. Boosted regression trees present a powerful tool in the management of resistance issues that has hitherto not been used.
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ItemThe effect of egg size on hatch time and metabolic rate: theoretical and empirical insights on developing insect embryos(WILEY, 2017-01)Body size scaling relationships allow biologists to study ecological phenomena in terms of individual level metabolic processes. Recently, dynamic energy budget (DEB) theory has been shown to offer novel insights on the effect of body size on biological rates. We test whether DEB theory and its unique partitioning of biomass into reserve and structural components can explain the effect of egg size on hatch time and the time course of respiration in insect embryos. We find that without any parameterization (calibration), DEB theory is able to predict hatch time for eggs sizes spanning four orders of magnitude from fundamental biological processes. We find, however, that the standard DEB model poorly predicts the time course of respiration, particularly in early embryonic development where a strong effect of egg size is observed. Further, we show that other theoretical models also poorly predict early embryonic respiration. By modifying the assumption that a fresh egg is entirely reserve, we show that embryonic respiration and hatch time can be better predicted by the DEB model. Useful theories in metabolic ecology, such as DEB theory, can help explain universal scaling patterns in development times. However, simple theoretical models must be expanded if they are to capture the scaling of metabolic rate in insect eggs. A Lay Summary is available for this article.
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ItemEscalating insecticide resistance in Australian grain pests: contributing factors, industry trends and management opportunities(JOHN WILEY & SONS LTD, 2019-06)
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ItemRegional and seasonal activity predictions for fall armyworm in Australia.(Elsevier BV, 2021)Since 2016, the fall armyworm (FAW), Spodoptera frugiperda, has undergone a significant range expansion from its native range in the Americas, to continental Africa, Asia, and in February 2020, mainland Australia. The large dispersal potential of FAW adults, wide host range of immature feeding stages, and unique environmental conditions in its invasive range creates large uncertainties in the expected impact on Australian plant production industries. Here, using a spatial model of population growth and spread potential informed by existing biological and climatic data, we simulate seasonal population activity potential of FAW, with a focus on Australia's grain production regions. Our results show that, in Australia, the large spread potential of FAW will allow it to exploit temporarily favourable conditions for population growth across highly variable climatic conditions. It is estimated that FAW populations would be present in a wide range of grain growing regions at certain times of year, but importantly, the expected seasonal activity will vary markedly between regions and years depending on climatic conditions. The window of activity for FAW will be longer for growing regions further north, with some regions possessing conditions conducive to year-round population survival. Seasonal migrations from this permanent range into southern regions, where large areas of annual grain crops are grown annually, are predicted to commence from October, i.e. spring, with populations subsequently building up into summer. The early stage of the FAW incursion into Australia means our predictions of seasonal activity potential will need to be refined as more Australian-specific information is accumulated. This study has contributed to our early understanding of FAW movement and population dynamics in Australia. Importantly, the models established here provide a useful framework that will be available to other countries should FAW invade in the future. To increase the robustness of our model, field sampling to identify conditions under which population growth occurs, and the location of source populations for migration events is required. This will enable accurate forecasting and early warning to farmers, which should improve pest monitoring and control programs of FAW.
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ItemPredicting the global invasion of Drosophila suzukii to improve Australian biosecurity preparedness(WILEY, 2021-04)Predicting biological invasions remains a challenge to applied ecologists and limits pre‐emptive management of biosecurity threats. In the last decade, spotted‐wing drosophila Drosophila suzukii has emerged as an internationally significant agricultural pest as it rapidly spread across Europe and the Americas. However, the underlying drivers of its global invasion remain unstudied, while countries like Australia, presently free from D. suzukii, require robust estimates of spread and establishment potential to aid development of effective preparedness strategies. Here, we analysed the ecoclimatic and human‐mediated drivers of the global invasion of D. suzukii to understand historical spread patterns and improve forecasts of future spread potential. Using a modular approach, climate‐driven population dynamics were linked in space via dispersal processes to simulate spread at continental scales. Combined with biological parameters measured in laboratory studies, the spread model was parameterized and validated on international spread data. Model accuracy was high and was able to predict 83% of regional presence–absence through time in the United States and, without further model fitting, 78% of the variation in the Europe incursion. Omitting human‐assisted spread from the model reduced predictability by over 20%, highlighting the large anthropogenic influence in this modern biological invasion. Economic activity (GDP) rather than human population density was more strongly associated with human‐mediated spread. Simulations predicted that eastern Australian coastal regions, particularly those near major cities with high economic activity, will result in the fastest spread of D. suzukii. Synthesis and applications. Incursions of Drosophila suzukii into Australia will have significant consequences for horticultural industries with the predicted speed of spread making eradication programs extremely difficult. However, the identified areas of significant fruit production, and high environmental suitability and economic activity will form a logical means for prioritizing industry preparedness. In light of our findings, a key component of preparedness strategies will be the ability of fruit producers to rapidly transition to effective management of D. suzukii.
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ItemSusceptibility of the bird cherry-oat aphid, Rhopalosiphum padi (Hemiptera: Aphididae), to four insecticides(WILEY, 2020-11)Abstract The bird‐cherry oat aphid (Rhopalosiphum padi) is a global pest, attacking most cereal crops including barley, wheat, oats and triticale. The aphids cause yield losses through direct feeding damage and the transmission of plant viruses. In Australia, feeding injury can reduce cereal yields by 6%, with the damage caused by aphid‐vectored viruses reducing the yield of cereal crops by up to 30%. Aphid control in these crops is achieved almost exclusively with insecticides, and there is growing concern surrounding insecticide resistance evolution in multiple aphid species. In this study, nine field populations of R. padi were collected from localities representing the major grain growing regions of Australia. Toxicity data against four insecticides (dimethoate, alpha‐cypermethrin, pirimicarb and imidacloprid) was generated for each aphid population. This revealed little differences in population responses for three of these insecticides. For alpha‐cypermethrin, a widely used insecticide in Australia, there were significant differences between several populations. These data will be important for future monitoring of insecticide responses of R. padi and highlight the impending pest management challenges growers could encounter in Australia.