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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

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. Source

Resco de Dios V.,Hawkesbury Institute for the Environment
Plant signaling & behavior

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. Source

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

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. Source

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

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. Source

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

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. Source

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