Time filter

Source Type

Macinnis-Ng C.,University of Auckland | Webb T.,University of Auckland | Lin Y.-S.,French National Institute for Agricultural Research | Schwendenmann L.,University of Auckland | Medlyn B.,Hawkesbury Institute for the Environment
New Zealand Journal of Botany | Year: 2016

New Zealand kauri (Agathis australis) (D.Don) Lindl. is a large and long-lived tree species endemic to the species-rich forests of the north of the North Island. Agathis australis are culturally and ecologically significant, but little is known about their ecophysiology. In particular, environmental drivers of fluxes of carbon and water for A. australis trees have not been quantified. We measured leaf gas exchange to explore the effect of leaf age, tree size, foliar nitrogen concentration, photosynthetically active radiation (PAR) and vapour pressure deficit (D) on assimilation rates (A) and stomatal conductance (gs). We also measured carbon isotope discrimination of leaves and applied an optimal stomatal behaviour model. Both gs and A were highest for year one leaves (130 mmol m−2 s−1 and 5 μmol m−2 s−1, respectively) then declined with leaf age to < 80 mmol m−2 s−1 and < 3 μmol m−2 s−1, respectively, in 4–5-year-old leaves. Instantaneous water use efficiency (A/gs) was highly variable, but there was no leaf age-related pattern. Our diurnal results indicate that A. australis gs peaks early in the day (before 0900 h at 250 mmol m−2 s−1) and A is comparatively low, remaining below 9 μmol m−2 s−1 throughout the day. Overall, water use efficiency is low based on intrinsic water use efficiency and the stomatal model. Isotopic analysis indicated moderate water use efficiency over the life of leaves compared to other temperate conifers. This information is valuable for modelling carbon and water fluxes of A. australis and for improving our understanding of the threat of summer droughts to these forest giants. © 2016 The Royal Society of New Zealand


Dalziell A.H.,Australian National University | Dalziell A.H.,Cornell University | Welbergen J.A.,Hawkesbury Institute for the Environment | Welbergen J.A.,James Cook University | And 3 more authors.
Biological Reviews | Year: 2015

Mimicry is a classical example of adaptive signal design. Here, we review the current state of research into vocal mimicry in birds. Avian vocal mimicry is a conspicuous and often spectacular form of animal communication, occurring in many distantly related species. However, the proximate and ultimate causes of vocal mimicry are poorly understood. In the first part of this review, we argue that progress has been impeded by conceptual confusion over what constitutes vocal mimicry. We propose a modified version of Vane-Wright's (1980) widely used definition of mimicry. According to our definition, a vocalisation is mimetic if the behaviour of the receiver changes after perceiving the acoustic resemblance between the mimic and the model, and the behavioural change confers a selective advantage on the mimic. Mimicry is therefore specifically a functional concept where the resemblance between heterospecific sounds is a target of selection. It is distinct from other forms of vocal resemblance including those that are the result of chance or common ancestry, and those that have emerged as a by-product of other processes such as ecological convergence and selection for large song-type repertoires. Thus, our definition provides a general and functionally coherent framework for determining what constitutes vocal mimicry, and takes account of the diversity of vocalisations that incorporate heterospecific sounds. In the second part we assess and revise hypotheses for the evolution of avian vocal mimicry in the light of our new definition. Most of the current evidence is anecdotal, but the diverse contexts and acoustic structures of putative vocal mimicry suggest that mimicry has multiple functions across and within species. There is strong experimental evidence that vocal mimicry can be deceptive, and can facilitate parasitic interactions. There is also increasing support for the use of vocal mimicry in predator defence, although the mechanisms are unclear. Less progress has been made in explaining why many birds incorporate heterospecific sounds into their sexual displays, and in determining whether these vocalisations are functionally mimetic or by-products of sexual selection for other traits such as repertoire size. Overall, this discussion reveals a more central role for vocal mimicry in the behavioural ecology of birds than has previously been appreciated. The final part of this review identifies important areas for future research. Detailed empirical data are needed on individual species, including on the structure of mimetic signals, the contexts in which mimicry is produced, how mimicry is acquired, and the ecological relationships between mimic, model and receiver. At present, there is little information and no consensus about the various costs of vocal mimicry for the protagonists in the mimicry complex. The diversity and complexity of vocal mimicry in birds raises important questions for the study of animal communication and challenges our view of the nature of mimicry itself. Therefore, a better understanding of avian vocal mimicry is essential if we are to account fully for the diversity of animal signals. © 2014 Cambridge Philosophical Society.


Montgomery R.A.,University of Minnesota | Palik B.J.,U.S. Department of Agriculture | Boyden S.B.,University of Minnesota | Boyden S.B.,Clarion University of Pennsylvania | And 2 more authors.
Forest Ecology and Management | Year: 2013

There is significant interest in silvicultural systems such as variable retention harvesting (VRH) that emulate natural disturbance and increase structural complexity, spatial heterogeneity, and biological diversity in managed forests. However, the consequences of variable retention harvesting for new cohort growth and survival are not well characterized in many forest ecosystems. Moreover, the relative importance of resource preemption by existing ground layer vegetation after variable retention harvests is unclear. We addressed both in a VRH experiment implemented as a randomized block design replicated four times in red pine forest in Minnesota, USA. Treatments included a thinning with residual trees dispersed evenly throughout the stand (dispersed) and two patch cuts that left 0.1. ha gaps (small gap) or 0.3. ha gaps (large gap) in a forest matrix. Residual basal area was held near constant in the three harvest treatments. We planted seedlings of three common pines (Pinus banksiana, P. strobus and P. resinosa) and measured light, soil nutrients and growth over seven growing seasons. We hypothesized that forests with equivalent average structures (e.g., basal area) would have higher stand-level seedling growth and survival in aggregated retention versus dispersed retention stands. However, variable retention harvest resulted in relatively small differences in growth and survival across the three retention treatments (although all differed as expected from uncut controls). Species specific responses to overstory treatments were partially related to shade tolerance. Tolerant white pine had high survival across all overstory treatments whereas intolerant red and jack pine had lower survival in uncut controls. In general, jack pine had the strongest growth response to reduction of overstory density. However, both white and jack pine achieved highest growth in the dispersed treatment despite differences in shade tolerance. Regardless of species, shrubs had a strong impact on seedling growth. Indeed, differences in growth were often larger across shrub treatments than among retention treatments. Our results support the hypothesis that shrubs preempt resources and dampen the impacts of different overstory retention patterns on new cohort growth and survival. Our results imply that managers have considerable flexibility to employ various types of retention patterns coupled with planting in red pine ecosystems at least at the levels of retention studied here. © 2013 Elsevier B.V.


Reside A.E.,James Cook University | Welbergen J.A.,James Cook University | Welbergen J.A.,Hawkesbury Institute for the Environment | Phillips B.L.,James Cook University | And 6 more authors.
Austral Ecology | Year: 2014

Identifying refugia is a critical component of effective conservation of biodiversity under anthropogenic climate change. However, despite a surge in conceptual and practical interest, identifying refugia remains a significant challenge across diverse continental landscapes. We provide an overview of the key properties of refugia that promote species' persistence under climate change, including their capacity to (i) buffer species from climate change; (ii) sustain long-term population viability and evolutionary processes; (iii) minimize the potential for deleterious species interactions, provided that the refugia are (iv) available and accessible to species under threat. Further, we classify refugia in terms of the environmental and biotic stressors that they provide protection from (i.e. thermal, hydric, cyclonic, pyric and biotic refugia), but ideally refugia should provide protection from a multitude of stressors. Our systematic characterization of refugia facilitates the identification of refugia in the Australian landscape. Challenges remain, however, specifically with respect to how to assess the quality of refugia at the level of individual species and whole species assemblages. It is essential that these challenges are overcome before refugia can live up to their acclaim as useful targets for conservation and management in the context of climate change. © 2014 Ecological Society of Australia.


News Article | November 29, 2016
Site: phys.org

The findings, published in Nature Plants, show the potential to improve crop yields for staple foods such as wheat and rice by transplanting enzymes from Panic grasses. The research was conducted by members of the ARC Centre of Excellence for Translational Photosynthesis, the ANU Research School of Biology and Western Sydney University's Hawkesbury Institute for the Environment. "Panic grasses contain an enzyme that captures carbon dioxide from the atmosphere more efficiently than other plants in the extreme climate conditions predicted in coming decades," said lead researcher Dr Robert Sharwood from The Australian National University (ANU). "We are aiming to enhance the growth and yield of crops such as wheat and rice by transplanting this more efficient enzyme into them," he said. The discovery is a significant development in the quest to use the natural genetic diversity of grasses to increase crop yields in response to concerns that improvements in global crop productivity have stalled. The researchers have focused on the Rubisco enzyme, which captures carbon dioxide from the air to begin the production of sugars that plants need to grow. "We were very excited to discover considerable variability in the efficiency of Rubisco from different Panic grasses to convert carbon dioxide into carbohydrates under a wide range of temperatures," said Associate Professor Oula Ghannoum from Western Sydney University. "Using mathematical simulations of the data, we identified Rubisco enzymes that are best-suited to crops growing under both hotter and cooler temperature conditions," she said. Associate Professor Spencer Whitney from ANU highlighted that as viable agricultural land runs out, the world needs to do more with the available farming lands. "On top of this are the changes in climate coming our way in the next few decades and the growing demand for food," he said. Dr Sharwood indicated that the ARC Centre of Excellence in Translational Photosynthesis aims to discover how to use the world's plant diversity to secure important food crops in a changing world. Explore further: Research to help develop next-generation food crops More information: Robert E. Sharwood et al. Temperature responses of Rubisco from Paniceae grasses provide opportunities for improving C3 photosynthesis, Nature Plants (2016). DOI: 10.1038/nplants.2016.186 For more information please visit www.photosynthesis.org.au


Aslam T.J.,University of St. Andrews | Johnson S.N.,Hawkesbury Institute for the Environment | Karley A.J.,James Hutton Institute
Journal of Applied Entomology | Year: 2013

The effects of predicted climate change on aphid-natural enemy interactions have principally considered the effects of elevated carbon dioxide concentration and air temperature. However, increased incidence of summer droughts are also predicted in Northern Europe, which could affect aphid-plant interactions and aphid antagonists. We investigated how simulated summer drought affected the bird cherry-oat aphid, Rhopalosiphum padi L., and its natural enemy the parasitoid wasp Aphidius ervi. Drought and, to a greater extent, aphids reduced barley ( Hordeum vulgare) dry mass by 33% and 39%, respectively. Drought reduced leaf and root nitrogen concentrations by 13% and 28%, respectively, but foliar amino acid concentrations and composition remained similar. Aphid numbers were unaffected by drought, but population demography changed significantly; adults constituted 41% of the population on drought-treated plants, but only 26% on those receiving ambient irrigation. Nymphs constituted 56% and 69% of the population on these plants, respectively, suggesting altered aphid development rates on drought-stressed plants. Parasitism rates were significantly lower on drought-stressed plants (9 attacks h-1 compared with 35 attacks h-1 on ambient-irrigated plants), most likely because of lower incidence of nymphs and more adults, the latter being more difficult to parasitize. Any physiological changes in individual aphids did not affect parasitoid preferences, suggesting that attacks were postponed because of drought-induced changes in aphid demography. This study demonstrates the potential for sporadic climate change events, such as summer drought, to be disruptive to herbivore-antagonist interactions. © 2012 Blackwell Verlag, GmbH.


Johnson S.N.,Hawkesbury Institute for the Environment | Ryalls J.M.W.,Hawkesbury Institute for the Environment | Karley A.J.,James Hutton Institute
Annals of Applied Biology | Year: 2014

Predicted increases in atmospheric carbon dioxide (CO2) concentrations could modify crop resistance to insect herbivores by altering plant quality. The short generation times of aphids may allow them to exploit such changes and colonise previously resistant plant genotypes. Lucerne (Medicago sativa) has undergone global selective breeding against aphids, including the pea aphid, Acyrthosiphon pisum. The purpose of this study was to characterise how ambient CO2 (aCO2) and elevated (eCO 2) (400 and 600 μmol mol-1, respectively) affected plant physiological traits potentially linked to aphid resistance, focussing on foliar amino acid concentrations, across five M. sativa genotypes with varying resistance to A. pisum. These included susceptible (Hunter River), low (Trifecta), moderate (Aurora and Genesis) and high resistance (Sequel). Under eCO2, root nodulation doubled and essential amino acid concentrations increased by 86% in resistant Sequel, whereas essential amino acid concentrations decreased by 53% in Genesis. Moreover, concentrations of lysine, an amino acid whose deficiency has been linked previously to A. pisum resistance in M. sativa, increased by 127% in Sequel at eCO2. Compared with aCO2, aphid colonisation of Sequel plants rose from 22% to 78% and reproduction rates increased from 1.1 to 4.3 nymphs week-1 under eCO2 conditions. In contrast, Genesis became more resistant at eCO2 compared with plants at aCO2; aphid colonisation rates fell from 78% to 44% of plants and reproductive rates decreased from 4.9 to 1.7 nymphs week-1. In conclusion, predicted changes in atmospheric CO2 concentrations could either reduce (Sequel) or enhance (Genesis) resistance to aphids, which might be linked to quantitative and qualitative changes in foliar amino acids. © 2014 Association of Applied Biologists.


Resco de Dios V.,Hawkesbury Institute for the Environment
Plant signaling & behavior | Year: 2013

The circadian clock is considered a central "orchestrator" of gene expression and metabolism. Concomitantly, the circadian clock is considered of negligible influence in the field and beyond leaf levels, where direct physiological responses to environmental cues are considered the main drivers of diel fluctuations. I propose to bridge the gap across scales by examining current evidence on whether circadian rhythmicity in gas exchange is relevant for field settings and at the ecosystem scale. Nocturnal stomatal conductance and water fluxes appear to be influenced by a "hard" clock that may override the direct physiological responses to the environment. Tests on potential clock controls over photosynthetic carbon assimilation and daytime transpiration are scant yet, if present, could have a large impact on our current understanding and modeling of the exchanges of carbon dioxide and water between terrestrial ecosystems and the atmosphere.


Johnson S.N.,Hawkesbury Institute for the Environment | Johnson S.N.,James Hutton Institute | Young M.W.,Hawkesbury Institute for the Environment | Young M.W.,James Hutton Institute | And 2 more authors.
Agricultural and Forest Entomology | Year: 2012

Aphid population dynamics in crops are often driven by interactions with their host plants, which can be extensively influenced by environmental change. Protective environments (i.e. plastic tunnels) are now frequently used for soft fruit production, which may affect the localized climate and alter such interactions. This two year study on red raspberry (Rubus idaeus) addressed how protected environments affected two aphid species; the large raspberry aphid Amphorophora idaei (LRA) and the small raspberry aphid Aphis idaei (SRA). Temperatures were higher (up to 7-10 °C) in tunnels compared with the field. Plants in tunnels grew approximately 1.4 cm/week faster and had lower (approximately 35%) foliar amino acid concentrations than plants in the field. Aphids affected plant growth differently depending on growing environment; they promoted plant growth by 18-37% in tunnels, although they had no such effect in the field. Aphids reduced total and essential amino acid concentrations, with SRA causing greatest reductions (approximately 40% and 33%, respectively). Aphid population sizes were similar in both environments, although individual LRA were smaller in tunnels (30% smaller in 2007) compared with those in the field. We suggest that faster aphid development rates inside warmer tunnels were not realized as a result of the variable effects of the growing environment on amino acid composition. We conclude that the increasing use of protected environments in crop production will not necessarily cause predictable increases in aphid populations, although it may alter aphid-plant interactions in terms of aphid-induced changes to plant growth. © 2011 The Authors. Agricultural and Forest Entomology © 2011 The Royal Entomological Society.

Loading Hawkesbury Institute for the Environment collaborators
Loading Hawkesbury Institute for the Environment collaborators