School of BioSciences - Research Publications
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ItemEfficient effort allocation in line-transect distance sampling of high-density species: When to walk further, measure less-often and gain precision(WILEY, 2021-06)Abstract Line‐transect distance sampling is widely used to estimate population densities using distances of observed targets from transect lines to model detectability. When the target taxa are high density, the frequent measuring of distances may make the method seem impractical. We present a method that improves the efficiency of distance sampling when the target species occurs at high density. Only a proportion of targets are measured to model the detection function, and the time saved on the survey is then used to cover a longer total length of transect and accrue a larger ‘count only’ sample. This approach can improve the precision of the population density estimate when the cost of measuring the distance to a detected target is more than half the cost of walking to the next target. We find the optimal proportion of distances to measure that minimises the variance of the density estimate for a fixed survey budget. We quantify how much this optimised strategy increases the precision of the density estimate compared with conventional line‐transect distance sampling. We then use simulated distance sampling data to test our expressions, and illustrate circumstances under which the optimised approach would be beneficial using distance sampling data on high‐density plants. The simulations indicate that the optimised method delivers benefits in precision, but the magnitude of the benefit is lower than predicted from our expressions, which are based on an asymptotic approximation of the variance. We apply an adjustment to the predicted benefit equation to account for this difference, and show that, in all three plant case studies, the optimised approach could improve the precision gained from a distance sampling survey between 20% and 50%. This new approach could broaden the ecological contexts in which distance sampling is applied, to include estimation of densities of abundant taxa where plots are conventionally used. The method may have interesting applications for other survey types, including multispecies surveys or those using cues or signs that occur at high density.
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ItemSurvival and growth of a high-mountain daisy transplanted outside its local range, and implications for climate-induced distribution shifts.(Oxford University Press (OUP), 2022-04)Field transplant experiments can improve our understanding of the effects of climate on distributions of plants versus a milieu of biotic factors which may be mediated by climate. We use a transplant experiment to test how survival and growth of a mountain-top daisy (Podolepis robusta), when planted within and outside its current local range, varies as a function of individual plant size, elevation, aspect and the presence of other vegetation. We expected a home-site advantage for the species, with highest survival and growth within the species' current elevational limits, and a decline in vital rates above (due to physiological limitations) and below (due to competition with near-neighbours) these limits. Transplant survival during the beginning of the census was high (89 %), though by the third growing season, 36 % of initial transplants were remaining. Elevation had a significant negative effect on individual mortality rates; plants growing at higher elevations had a lower estimated hazard rate and thus, higher survival relative to those planted at elevations below the current lower limit of the distribution. By contrast, we detected no significant effect of elevation on growth rates. Small vegetation gaps had no effect on growth rates, though we found a negative, but non-significant, effect on mortality rates. Aspect had a very strong impact on growth. Plants transplanted to cool aspects had a significantly lower growth rate relative to transplants growing on a warm aspect. Conversely, aspect was not a significant predictor of individual mortality rates. Restrictions on the local distribution of P. robusta appear to be governed by mortality drivers at lower elevation and by growth drivers associated with aspect. We highlight that our ability to understand the drivers of distributions in current and future climates will be limited if contextual- and individual-level plant responses remain understudied.
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ItemAusTraits, a curated plant trait database for the Australian flora(NATURE PORTFOLIO, 2021-09-30)We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.
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ItemSpecies origin affects the rate of response to inter-annual growing season precipitation and nutrient addition in four Australian native grasslands(WILEY, 2016-11)QUESTIONS: Predicted increases in temperature and changes to precipitation are expected to alter the amount of plant available nutrients, in turn, altering rates of primary production and exotic plant invasions. However, it remains unclear whether increased responses occur in wetter than average years, even in low fertility and low rainfall regions. LOCATION: Four Australian grasslands, including sites in arid Western Australia, semi‐arid Victoria, alpine Victoria and sub‐tropical Queensland. METHODS: Using identical nutrient addition experiments, we use 6‐years of biomass, cover and species richness data to examine how rates of biomass production and native and exotic cover and richness are affected by growing season precipitation [proportion of yearly growing season precipitation (GSP) to long‐term mean GSP] and nutrient (N, P, K and micronutrients) addition. RESULTS: Rates of grassland productivity strongly increased with increasing GSP. GSP increased rates of native cover but not native or exotic richness, nor rates of exotic cover change. We detected no significant NPK effect on rates of grassland productivity, exotic cover or exotic richness change. In contrast, NPK addition decreased rates of native cover change and fertilized plots had significantly fewer native species. We did not detect a significant interaction between NPK and GSP. CONCLUSIONS: Grassland productivity was more strongly predicted by variation in growing season precipitation than by nutrient addition, suggesting it will vary with future changes in rainfall. Response to nutrients, however, depend on species origin, suggesting that increasing soil nutrient availability due to anthropogenic activities is likely to lead to negative effects on native species richness and cover.
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ItemForecasting species range dynamics with process-explicit models: matching methods to applications(WILEY, 2019-11)Knowing where species occur is fundamental to many ecological and environmental applications. Species distribution models (SDMs) are typically based on correlations between species occurrence data and environmental predictors, with ecological processes captured only implicitly. However, there is a growing interest in approaches that explicitly model processes such as physiology, dispersal, demography and biotic interactions. These models are believed to offer more robust predictions, particularly when extrapolating to novel conditions. Many process-explicit approaches are now available, but it is not clear how we can best draw on this expanded modelling toolbox to address ecological problems and inform management decisions. Here, we review a range of process-explicit models to determine their strengths and limitations, as well as their current use. Focusing on four common applications of SDMs - regulatory planning, extinction risk, climate refugia and invasive species - we then explore which models best meet management needs. We identify barriers to more widespread and effective use of process-explicit models and outline how these might be overcome. As well as technical and data challenges, there is a pressing need for more thorough evaluation of model predictions to guide investment in method development and ensure the promise of these new approaches is fully realised.
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ItemClimate change: Alpine shrubs as ecosystem engineers(WILEY, 2019-08)
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ItemImpacts of recent climate change on terrestrial flora and fauna: Some emerging Australian examples(WILEY, 2019-02)The effects of anthropogenic climate change on biodiversity are well known for some high‐profile Australian marine systems, including coral bleaching and kelp forest devastation. Less well‐published are the impacts of climate change being observed in terrestrial ecosystems, although ecological models have predicted substantial changes are likely. Detecting and attributing terrestrial changes to anthropogenic factors is difficult due to the ecological importance of extreme conditions, the noisy nature of short‐term data collected with limited resources, and complexities introduced by biotic interactions. Here, we provide a suite of case studies that have considered possible impacts of anthropogenic climate change on Australian terrestrial systems. Our intention is to provide a diverse collection of stories illustrating how Australian flora and fauna are likely responding to direct and indirect effects of anthropogenic climate change. We aim to raise awareness rather than be comprehensive. We include case studies covering canopy dieback in forests, compositional shifts in vegetation, positive feedbacks between climate, vegetation and disturbance regimes, local extinctions in plants, size changes in birds, phenological shifts in reproduction and shifting biotic interactions that threaten communities and endangered species. Some of these changes are direct and clear cut, others are indirect and less clearly connected to climate change; however, all are important in providing insights into the future state of terrestrial ecosystems. We also highlight some of the management issues relevant to conserving terrestrial communities and ecosystems in the face of anthropogenic climate change.
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ItemEffects of drought and fire on resprouting capacity of 52 temperate Australian perennial native grasses(WILEY, 2019-02)It remains uncertain how perennial grasses with different photosynthetic pathways respond to fire, and how this response varies with stress at the time of burning. Resprouting after fire was examined in relation to experimentally manipulated pre-fire watering frequencies. We asked the following questions: are there response differences to fire between C3 and C4 grasses? And, how does post-fire resprouting vary with pre-fire drought stress? Fifty-two perennial Australian grasses (37 genera, 13 tribes) were studied. Three watering frequencies were applied to simulate increasing drought. Pre-fire tiller number, tiller density, specific leaf area and leaf dry matter content were measured as explanatory variables to assess response. Most species (90%) and individuals (79%) resprouted following experimental burning. C4 grasses had higher probabilities of surviving fire relative to C3 grasses. Responses were not related to phylogeny or tribe. High leaf dry matter content reduced the probability of dying, but also reduced the re-emergence of tillers. Post-fire tiller number increased with increasing drought, regardless of photosynthetic type, suggesting that drought plays a role in the ability of grasses to recover after fire. This has implications for understanding the persistence of species in landscapes where fire management is practiced.
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ItemCorrelation of drought traits and the predictability of osmotic potential at full leaf turgor in vegetation from New Zealand(WILEY, 2018-06)Abstract Scientists do not know precisely how severe will be the impact of climate change on species. Evidence suggests that for some species, their future distributions might be jeopardized by local extinctions and drought‐induced tree mortality. Thus, we require models capable of estimating drought tolerance across many species. We can approach this goal by assessing functional traits. The trait osmotic potential at full turgor, πO, is potentially a good drought indicator; however, few studies address its importance as a drought‐tolerance predictor and it is difficult to measure in the field with accuracy. In this work, we aim to answer the questions: which drought traits correlate with πO?; do morpho‐anatomical traits correlate with πO?; and which trees and shrubs are more (or less) vulnerable to drought? To achieve this aim, we assessed physiological and morpho‐anatomical traits for 14 native species from New Zealand forests. We included leaf‐ and wood‐related traits, πO, water potential and stomatal conductance. We examined how these traits correlate with πO and sought to generate models to predict πO as a function of other traits. We tested 33 different models and evaluated them using Akaike's information criterion. Unfortunately, none of the morpho‐anatomical traits correlated well with πO. Instead, water potential correlated most strongly with πO. None of the models using only morpho‐anatomical traits produced plausible results. The model with the best predictive performance incorporated the effects of both morpho‐anatomical and physiological traits: water potential and wood saturated water content. Of the species analysed, and based on their πO response, Lophozonia menziesii was considered the most vulnerable to drought stress, whereas Plagianthus regius was the least vulnerable. Our findings imply that it is potentially valuable to keep exploring the use of πO as a drought indicator and that the effort required to measure some physiological traits, such as water potential, may be essential to consider plant drought responses and to predict πO.
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ItemPredicting species and community responses to global change using structured expert judgement: An Australian mountain ecosystems case study(WILEY, 2021-09)Conservation managers are under increasing pressure to make decisions about the allocation of finite resources to protect biodiversity under a changing climate. However, the impacts of climate and global change drivers on species are outpacing our capacity to collect the empirical data necessary to inform these decisions. This is particularly the case in the Australian Alps which have already undergone recent changes in climate and experienced more frequent large-scale bushfires. In lieu of empirical data, we use a structured expert elicitation method (the IDEA protocol) to estimate the change in abundance and distribution of nine vegetation groups and 89 Australian alpine and subalpine species by the year 2050. Experts predicted that most alpine vegetation communities would decline in extent by 2050; only woodlands and heathlands are predicted to increase in extent. Predicted species-level responses for alpine plants and animals were highly variable and uncertain. In general, alpine plants spanned the range of possible responses, with some expected to increase, decrease or not change in cover. By contrast, almost all animal species are predicted to decline or not change in abundance or elevation range; more species with water-centric life-cycles are expected to decline in abundance than other species. While long-term ecological data will always be the gold standard for informing the future of biodiversity, the method and outcomes outlined here provide a pragmatic and coherent basis upon which to start informing conservation policy and management in the face of rapid change and a paucity of data.