School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemTwo-step adaptive management for choosing between two management actions(Ecological Society of America, 2017-06-01)Adaptive management is widely advocated to improve environmental management. Derivations of optimal strategies for adaptive management, however, tend to be case specific and time consuming. In contrast, managers might seek relatively simple guidance, such as insight into when a new potential management action should be considered, and how much effort should be expended on trialing such an action. We constructed a two‐time‐step scenario where a manager is choosing between two possible management actions. The manager has a total budget that can be split between a learning phase and an implementation phase. We use this scenario to investigate when and how much a manager should invest in learning about the management actions available. The optimal investment in learning can be understood intuitively by accounting for the expected value of sample information, the benefits that accrue during learning, the direct costs of learning, and the opportunity costs of learning. We find that the optimal proportion of the budget to spend on learning is characterized by several critical thresholds that mark a jump from spending a large proportion of the budget on learning to spending nothing. For example, as sampling variance increases, it is optimal to spend a larger proportion of the budget on learning, up to a point: if the sampling variance passes a critical threshold, it is no longer beneficial to invest in learning. Similar thresholds are observed as a function of the total budget and the difference in the expected performance of the two actions. We illustrate how this model can be applied using a case study of choosing between alternative rearing diets for hihi, an endangered New Zealand passerine. Although the model presented is a simplified scenario, we believe it is relevant to many management situations. Managers often have relatively short time horizons for management, and might be reluctant to consider further investment in learning and monitoring beyond collecting data from a single time period.
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ItemDisentangling the four demographic dimensions of species invasiveness(WILEY, 2016-11)A definitive list of invasive species traits remains elusive, perhaps due to inconsistent ways of identifying invasive species. Invasive species are typically identified using one or more of four demographic criteria (local abundance, geographic range, environmental range, spread rate), referred to here as the demographic dimensions of invasiveness. In 112 studies comparing invasive and non‐invasive plant traits, all 15 combinations of the four demographic dimensions were used to identify invasive species; 22% of studies identified invasive species solely by high abundance, while 25% ignored abundance. We used demographic data of 340 alien herbs classified as invasive or non‐invasive in Victoria, Australia, to test whether the demographic dimensions are independent and which dimensions influence invasive species listing in practice. Species' abundances, spread rates and range sizes were independent. Relative abundance best explained the invasiveness classification. However, invasive and non‐invasive species each spanned the full range of each demographic dimension, indicating that no dimension clearly separates invasive from non‐invasive species. Graminoids with longer minimum residence times were more frequently classified as invasive, as were forbs occurring near edges of native vegetation fragments. Synthesis. Conflating multiple forms of invasiveness, by not distinguishing invasive species that are identified using different demographic criteria, may obscure traits possessed by particular subsets of invasive species. Traits promoting high abundance likely differ from those enabling fast spread and broad ranges. Examining traits linked with the four demographic dimensions of invasiveness will highlight species at risk of becoming dominant, spreading quickly or occupying large ranges.
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ItemEffects of fire on pollinators and pollination(Wiley, 2017-02-01)Summary 1. Increased incidence of landscape fire and pollinator declines with co‐extinctions of dependent plant species are both globally significant. Fire can alter species distributions, but its effects on plant–pollinator interactions are poorly understood so its present and future role in coupled plant–pollinator declines cannot be assessed. 2. We develop a conceptual model of fire effects on plant–pollinator interactions. We review the empirical literature in the context of this model to identify important knowledge gaps regarding the processes underlying these effects and the phenotypic traits of flowering plants and pollinators mediating these effects. Fire generates, and plant–pollinator interactions respond to, heterogeneity at multiple spatial scales. There is evidence of local‐scale fire effects on these interactions, but landscape‐scale effects are poorly understood. Nest location and floral resource utilization primarily mediate pollinator survival during and after fire. Voltinism and mobility traits are potentially important, but poorly studied. Plant traits mediating flowering responses to fire include growth form, phenology and potentially bud location, seasonal changes in bud exposure and response to bud damage. 3. Synthesis and applications. We suggest management actions and an agenda for future research to fill knowledge gaps currently inhibiting predictions of fire effects on plant–pollinator interactions. Fire regimes promoting floral diversity at local scales provide a surrogate means of managing pollinators and pollination while empirical research continues. Above‐ground nesting, univoltine pollinators may be particularly vulnerable under expected fire regime changes. Improved knowledge of traits mediating the exploitation of landscape heterogeneity could be used to enhance the persistence of these species. Ultimately, our conceptual framework could be used as a basis for understanding fire effects on aggregate network properties to inform fire management strategies buffering plant–pollinator networks against secondary species extinctions.
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ItemNo Preview AvailableImproving the transparency of statistical reporting in Conservation Letters(WILEY, 2018-03-01)
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ItemPlan S and publishing: reply to Lehtomaki et al. 2019(WILEY, 2019-10)
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ItemSimultaneous-count models to estimate abundance from counts of unmarked individuals with imperfect detection(WILEY, 2019-06)We developed a method to estimate population abundance from simultaneous counts of unmarked individuals over multiple sites. We considered that at each sampling occasion, individuals in a population could be detected at 1 of the survey sites or remain undetected and used either multinomial or binomial simultaneous-count models to estimate abundance, the latter being equivalent to an N-mixture model with one site. We tested model performance with simulations over a range of detection probabilities, population sizes, growth rates, number of years, sampling occasions, and sites. We then applied our method to 3 critically endangered vulture species in Cambodia to demonstrate the real-world applicability of the model and to provide the first abundance estimates for these species in Cambodia. Our new approach works best when existing methods are expected to perform poorly (i.e., few sites and large variation in abundance among sites) and if individuals may move among sites between sampling occasions. The approach performed better when there were >8 sampling occasions and net probability of detection was high (>0.5). We believe our approach will be useful in particular for simultaneous surveys at aggregation sites, such as roosts. The method complements existing approaches for estimating abundance of unmarked individuals and is the first method designed specifically for simultaneous counts.
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ItemOpen access and academic imperialism(WILEY, 2019-02)
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ItemAn experimental test of whether pyrodiversity promotes mammal diversity in a northern Australian savanna(WILEY, 2018-09)The increasing awareness that a fire regime that promotes biodiversity in one system can threaten biodiversity in another has resulted in a shift away from fire management based on vague notions of maximising pyrodiversity, towards determining the optimal fire regime based on the demonstrated requirements of target species. We utilised a long‐running, replicated fire experiment on Melville Island, the largest island off the northern Australian coast, to test the importance of pyrodiversity for native mammals in a northern Australian savanna landscape. We first developed statistical models to determine how native mammal abundance has responded to nine years of experimentally‐manipulated fire frequency. Next, given each species' modelled response to fire frequency, we identified the level of pyrodiversity and optimal mix of fire frequencies that would be expected to maximise mammal diversity and abundance, and minimise extinction risk. This was done for both the entire mammal assemblage and for the mammal species currently declining on Melville Island. Fire frequency was a significant predictor of abundance of the northern brown bandicoot Isoodon macrourus, black‐footed tree‐rat Mesembriomys gouldii, brush‐tailed rabbit‐rat Conilurus penicillatus, grassland melomys Melomys burtoni, pale field‐rat Rattus tunneyi, and mice/dunnarts but not for the common brushtail possum Trichosurus vulpecula. The geometric mean abundance (GMA) of the entire mammal assemblage was positively associated with pyrodiversity, but peaked at an intermediate value. Hence, maximising pyrodiversity would reduce native mammal assemblage GMA below its potential maximum. The fire history for an area that maximised the entire native mammal assemblage GMA consisted of 57% long‐unburnt, 43% triennially burnt and <1% annually burnt. Pyrodiversity did not reduce the extinction risk, nor increase the GMA of declining mammals above that predicted in areas entirely annually or triennially burnt. Synthesis and applications. We demonstrate a useful approach with which to develop fire management strategies based on the demonstrated requirements of target species. By comparing the optimal fire regime identified for the conservation of threatened species and that identified for the entire mammal assemblage, we demonstrate the flexibility of this approach to tailor fire management to address specific management priorities in other fire‐prone environments.
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ItemDeclining populations in one of the last refuges for threatened mammal species in northern Australia(WILEY, 2018-08)Australia has contributed a disproportionate number of the world's mammal extinctions over the past 200 years, with the greatest loss of species occurring through the continent's southern and central arid regions. Many taxonomically and ecologically similar species are now undergoing widespread decline across the northern Australian mainland, possibly driven by predation by feral cats and changed fire regimes. Here, we report marked recent declines of native mammal species in one of Australia's few remaining areas that support an intact mammal assemblage, Melville Island, the largest island off the northern Australian coast. We have previously reported a marked decline on Melville Island of the threatened brush‐tailed rabbit‐rat (Conilurus penicillatus) over the period 2000–2015, linked to predation by feral cats. We now report a 62% reduction in small mammal trap‐success and a 36% reduction in site‐level species richness over this period. There was a decrease in trap‐success of 90% for the northern brown bandicoot (Isoodon macrourus), 64% for the brush‐tailed rabbit‐rat and 63% for the black‐footed tree‐rat (Mesembriomys gouldii), but no decline for the common brushtail possum (Trichosurus vulpecula). These results suggest that populations of native mammals on Melville Island are exhibiting similar patterns of decline to those recorded in Kakadu National Park two decades earlier, and across the northern Australian mainland more generally. Without the implementation of effective management actions, these species are likely to be lost from one of their last remaining strongholds, threatening to increase Australia's already disproportionate contribution to global mammal extinctions.
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ItemNo Preview AvailableThe neglected tool in the Bayesian ecologist's shed: a case study testing informative priors' effect on model accuracy(WILEY-BLACKWELL, 2015-01)Despite benefits for precision, ecologists rarely use informative priors. One reason that ecologists may prefer vague priors is the perception that informative priors reduce accuracy. To date, no ecological study has empirically evaluated data-derived informative priors' effects on precision and accuracy. To determine the impacts of priors, we evaluated mortality models for tree species using data from a forest dynamics plot in Thailand. Half the models used vague priors, and the remaining half had informative priors. We found precision was greater when using informative priors, but effects on accuracy were more variable. In some cases, prior information improved accuracy, while in others, it was reduced. On average, models with informative priors were no more or less accurate than models without. Our analyses provide a detailed case study on the simultaneous effect of prior information on precision and accuracy and demonstrate that when priors are specified appropriately, they lead to greater precision without systematically reducing model accuracy.