Siobhan C. de Little

Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals

BackgroundDetermining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long periods, spanning an array of population densities or levels of food availability. Using age-structured mark-recapture models and datasets spanning five decades (1950–1999), and two periods of differing relative population density, we estimated age-specific probabilities of survival and examined the combined effects of population density and environmental conditions on juvenile survival of southern elephant seals at Macquarie Island.ResultsFirst-year survival decreased with density during the period of highest population size, and survival increased during years when the Southern Oscillation Index (SOI) anomaly (deviation from a 50-year mean) during the mothers previous foraging trip to sea was positive (i.e., El Niño). However, when environmental stochasticity and density were considered together, the effect of density on first-year survival effectively disappeared. Ignoring density effects also leads to models placing too much emphasis on the environmental conditions prevailing during the naïve pups first year at sea.ConclusionOur analyses revealed that both the state of the environment and population density combine to modify juvenile survival, but that the degree to which these processes contributed to the variation observed was interactive and complex. This underlines the importance of evaluating the relative contribution of both the intrinsic and extrinsic factors that regulate animal populations because false conclusions regarding the importance of population regulation may be reached if they are examined in isolation.

Environmental flows can reduce the encroachment of terrestrial vegetation into river channels: a systematic literature review.

Encroachment of riparian vegetation into regulated river channels exerts control over fluvial processes, channel morphology, and aquatic ecology. Reducing encroachment of terrestrial vegetation is an oft-cited objective of environmental flow recommendations, but there has been no systematic assessment of the evidence for and against the widely-accepted cause-and-effect mechanisms involved. We systematically reviewed the literature to test whether environmental flows can reduce the encroachment of terrestrial vegetation into river channels. We quantified the level of support for five explicit cause-effect hypotheses drawn from a conceptual model of the effects of flow on vegetation. We found that greater inundation, variously expressed as changes in the area, depth, duration, frequency, seasonality, and volume of surface water, generally reduces riparian vegetation abundance in channels, but most studies did not investigate the specific mechanisms causing these changes. Those that did show that increased inundation results in increased mortality, but also increased germination. The evidence was insufficient to determine whether increased inundation decreases reproduction. Our results contribute to hydro-ecological understanding byxa0using the published literature to test for general cause-effect relationships between flow regime and terrestrial vegetation encroachment. Reviews of this nature provide robust support for flow management, and are more defensible than expert judgement-based approaches. Overall, we predict that restoration of more natural flow regimes will reduce encroachment of terrestrial vegetation into regulated river channels, partly through increased mortality. Conversely, infrequent deliveries of environmental flows may actually increase germination and subsequent encroachment.

Quantifying the drivers of larval density patterns in two tropical mosquito species to maximize control efficiency

ABSTRACT Understanding the contributions of environmental variation and density feedbacks to changes in vector populations is essential for designing effective vector control. We analyzed monitoring datasets describing larval densities over 7 yr of the two dominant mosquito species, Aedes vigilax (Skuse) and Culex annulirostris (Skuse), of the greater Darwin area (Northern Territory, Australia). Using generalized linear and linear mixed-effects models, we tested hypotheses regarding the environmental determinants of spatio-temporal patterns in relative larval abundance in both species. The most important spatial drivers of Ae. vigilax and Cx. annulirostris larval densities were elevation and water presence. Ae. vigilax density correlates negatively with elevation, whereas there was a positive relationship between Cx. annulirostris density and elevation. These results show how larval habitats used by the saltwater-influenced breeder Ae. vigilax and the obligate freshwater breeder Cx. annulirostris are separated in a tidally influenced swamp. The models examining temporal drivers of larval density also identified this discrimination between freshwater and saltwater habitats. Ae. vigilax larval densities were positively related to maximum tide height and high tide frequency, whereas Cx. annulirostris larval densities were positively related to elevation and rainfall. Adult abundance in the previous month was the most important temporal driver of larval densities in both species, providing a clear dynamical link between the two main life phases in mosquito development. This study shows the importance of considering both spatial and temporal drivers, and intrinsic population dynamics, when planning vector control strategies to reduce larval density, adult population density, and disease transmission effectively.

An online database and desktop assessment software to simplify systematic reviews in environmental science

We describe software to facilitate systematic reviews in environmental science. Eco Evidence allows reviewers to draw strong conclusions from a collection of individually-weak studies. It consists of two components. An online database stores and shares the atomized findings of previously-published research. A desktop analysis tool synthesizes this evidence to test cause-effect hypotheses. The software produces a standardized report, maximizing transparency and repeatability. We illustrate evidence extraction and synthesis. Environmental research is hampered by the complexity of natural environments, and difficulty with performing experiments in such systems. Under these constraints, systematic syntheses of the rapidly-expanding literature can advance ecological understanding, inform environmental management, and identify knowledge gaps and priorities for future research. Eco Evidence, and in particular its online re-usable bank of evidence, reduces the workload involved in systematic reviews. This is the first systematic review software for environmental science, and opens the way for increased uptake of this powerful approach. Systematic review is a powerful, but underused, technique in environmental science.We developed software and a database designed to simplify such reviews.The online database stores and shares evidence, reducing the workload for users.The analysis software guides users through a previously-published review method.The software produces a standard report to maximize transparency and repeatability.

Overcoming the challenges of monitoring and evaluating environmental flows through science–management partnerships

ABSTRACT Environmental flows programmes can be controversial, given that they transfer water from consumptive to environmental uses. It is, therefore, imperative that their performance is assessed against their anticipated ecological benefits. However, environmental flows present both technical and institutional challenges that cannot be addressed by traditional approaches to monitoring and evaluation. We present a framework that is currently being employed to evaluate the effectiveness of environmental flows in Victoria, Australia. The framework encourages a shift from expert-based models of ecological response to flow variation to those developed using the so-called ‘evidence-based’ methods that have become commonplace in medicine. The framework relies on close collaboration between scientists and managers for the design of monitoring programmes, collection and collation of data, and analysis and interpretation of results. Results will inform adaptive management of environmental flows in Victoria and improve basic understanding of the ecological impacts of changes in flow regime. Our experience suggests that the technical and institutional challenges for monitoring and evaluating environmental flows can be mostly overcome by close and continuing collaboration between managers and researchers. We are unaware of any equivalent programmes anywhere in the world and believe that our framework is transferable to any other large-scale environmental flows monitoring programme.

Discovery of metabolic resistance to neonicotinoids in green peach aphids (Myzus persicae) in Australia.

BACKGROUNDnMyzus persicae is a serious pest that attacks a broad range of agricultural crops. This species has developed chemical resistance to many insecticides globally, and within Australia resistance to multiple chemical groups has been identified. Resistance to neonicotinoid insecticides has been discovered in several countries, but has not previously been confirmed in Australia. We use biomolecular assays and bioassays on field-collected populations to investigate neonicotinoid resistance in M. persicae within Australia.nnnRESULTSnSeveral geographically and genetically distinct populations showed evidence for resistance in bioassays. Genetic markers identified that the mechanism of neonicotinoid resistance in Australia is metabolic resistance through the enhanced expression of a cytochrome P450 gene, CYP6CY3.nnnCONCLUSIONnM. persicae populations in parts of Australia are now resistant to four different insecticide chemical groups, raising concerns about the long-term management of this pest. While higher copy numbers of CYP6CY3 were seen in all resistant populations, the number of gene copies was not strongly correlated with the level of resistance as determined by LD50 values generated through bioassays. This finding sheds further light on the complexity of the P450 genes in regulating neonicotinoid resistance.

Minimising biases in expert elicitations to inform environmental management: Case studies from environmental flows in Australia

Abstract Environmental managers often do not have sufficient empirical data to inform decisions, and instead must rely on expert predictions. However, the informal methods often used to gather expert opinions are prone to cognitive and motivational biases. We developed a structured elicitation protocol, where opinions are directly incorporated into Bayesian Network (BBN) models. The 4-stage protocol includes approaches to minimise biases during pre-elicitation, workshop facilitation and output analysis; and results in a fully functional BBN model. We illustrate our protocol using examples from environmental flow management in Australia, presenting models of vegetation responses to changes in riverine flow regimes. The reliance on expert opinion and the contested nature of many environmental management decisions mean that our structured elicitation protocol is potentially of great value for developing robust environmental recommendations. This method also lends itself to effective adaptive management, because the expert-populated ecological response models can be readily updated with field data.

Rainfall and temperature variation does not explain arid species diversity in outback Australia

Steps toward conserving biodiversity should start at understanding the components across spatial scales and a determination of the drivers of these. Here we determine additive species diversity for arid South Australia, based on over 50 years of survey data. Elevation and soil data were sourced through the Australian Government, and climate data from the WorldClim database. Alternative hypotheses relating the effect of climatic and environmental parameters to diversity were tested using generalized linear models and ranked according to information-theoretic statistics. Total species richness for the region was 1824, similar to all arid regions. α-diversity values were low, relative to the contributions made by β-diversity toward total γ-diversity, similar to additive diversity indices for nonarid biomes. There was a lack of statistical support for our hypothesis that regional spatial variation in arid region diversity can be explained by climate topography. Arid South Australian species diversity appears to be largely driven by environmental parameters at the localized scale – beyond the resolution of available survey data. Heterogeneity in habitat, provided by mountainous regions, likely contributes toward the high β-diversity values. Our research is the first application of the additive (not multiplicative) approach toward understanding diversity within arid Australia.

Experimental comparison of aerial larvicides and habitat modification for controlling disease carrying Aedes vigilax mosquitoes

BACKGROUNDnMicrobial and insect-growth-regulator larvicides dominate current vector control programmes because they reduce larval abundance and are relatively environmentally benign. However, their short persistence makes them expensive, and environmental manipulation of larval habitat might be an alternative control measure. Aedes vigilax is a major vector species in northern Australia. A field experiment was implemented in Darwin, Australia, to test the hypotheses that (1) aerial microbial larvicide application effectively decreases Ae. vigilax larval presence, and therefore adult emergence, and (2) environmental manipulation is an effective alternative control measure. Generalised linear and mixed-effects modelling and information-theoretic comparisons were used to test these hypotheses.nnnRESULTSnIt is shown that the current aerial larvicide application campaign is effective at suppressing the emergence of Ae. vigilax, whereas vegetation removal is not as effective in this context. In addition, the results indicate that current larval sampling procedures are inadequate for quantifying larval abundance or adult emergence.nnnCONCLUSIONSnThis field-based comparison has shown that the existing larviciding campaign is more effective than a simple environmental management strategy for mosquito control. It has also identified an important knowledge gap in the use of larval sampling to evaluate the effectiveness of vector control strategies.

Will environmental flows increase the abundance of native riparian vegetation on lowland rivers? A systematic review protocol

BackgroundThe extraction of water and alteration of flow regimes by humans have profound negative effects on river ecosystems. Returning water as “environmental flows” is a primary method for restoration, but evidence linking flow restoration to ecological benefits is weak. In order to draw more informative conclusions about the effects of environmental flows on ecosystems, reviews of ecological responses to altered flow regime need to focus on relationships between causes (flow components) and effects (ecological responses). We will review the literature on the responses of native riparian vegetation to flow alterations on regulated rivers. This review should improve river restoration efforts by identifying which flow components can be targeted by environmental flows to improve vegetation condition and increase abundance at the individual, population, and community levels.MethodsWe will conduct our review using the Eco Evidence framework, a novel, freely-available systematic review method and software that employs a standardised methodology to assess cause-effect hypotheses in the face of weak evidence. We will search published and grey literature for studies that present primary data on the responses of native riparian vegetation on lowland river banks to changes in flow regime. The review will assess evidence for seven distinct hypotheses that include different flow components (flood area, depth, duration, frequency, seasonality, and volume) and vegetation responses (condition, germination rates, reproduction, and survival). We will extract information from relevant studies on the trajectories of causes and effects, the type of study design, and the number of control and impact sampling units. This information will be used to weight studies, where studies with more sampling units or stronger study designs are given a higher weighting, as spurious results are less likely. The amount of weighted evidence supporting and refuting each hypothesis will determine which of four possible outcomes we will reach: “Support for hypothesis”, “Support for alternative hypothesis”, “Inconsistent evidence”, or “Insufficient evidence”. We will then collectively consider the conclusions for each hypothesis in order to answer our primary question, summarise the evidence, identify any gaps in knowledge, and provide recommendations for whether and how environmental flows could be used in the management of native riparian vegetation.