Michael Kearney

Victoria University Melbourne, Melbourne, Victoria, Australia

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Publications (83)384.68 Total impact

  • James L Maino, Michael R Kearney
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    ABSTRACT: Abstract Design constraints imposed by increasing size cause metabolic rate in animals to increase more slowly than mass. This ubiquitous biological phenomenon is referred to as metabolic scaling. However, mechanistic explanations for interspecific metabolic scaling do not apply to ontogenetic size changes within a species, implying different mechanisms for scaling phenomena. Here, we show that the dynamic energy budget theory approach of compartmentalizing biomass into reserve and structural components provides a unified framework for understanding ontogenetic and interspecific metabolic scaling. We formulate the theory for insects and show that it can account for ontogenetic metabolic scaling during the embryonic and larval phases, as well as the U-shaped respiration curve during pupation. After correcting for the predicted ontogenetic scaling effects, which we show to follow universal curves, the scaling of respiration between species is approximated by a three-quarters power law, supporting past empirical studies on insect metabolic scaling and our theoretical predictions. The ability to explain ontogenetic and interspecific metabolic scaling effects under one consistent framework suggests that the partitioning of biomass into reserve and structure is a necessary foundation to a general metabolic theory.
    The American naturalist. 12/2014; 184(6):695-701.
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    ABSTRACT: 1.Ectotherms are taxa considered highly sensitive to rapid climate warming. This is because body temperature profoundly governs their performance, fitness and life history. Yet, whilst several modelling approaches currently predict thermal effects on some aspects of life-history and demography, they do not consider how temperature simultaneously affects developmental success and offspring phenotypic performance, two additional key attributes that are needed to comprehensively understand species responses to climate warming.2.Here, we developed a stepwise, individual-level modelling approach linking biophysical and developmental models with empirically derived performance functions to predict the effects of temperature-induced changes to offspring viability, phenotype and performance, using green sea turtle hatchlings as an ectotherm model. Climate warming is expected to particularly threaten sea turtles, as their life history traits may preclude them from rapid adaptation.3.Under conservative and extreme warming, our model predicted large effects on performance attributes key to dispersal, as well as a reduction in offspring viability. Forecast sand temperatures produced smaller, weaker hatchlings, which were up to 40% slower than at present, albeit with increased energy stores. Conversely, increases in sea surface temperatures aided swimming performance.4.Our exploratory study points to the need for further development of integrative individual based modelling frameworks to better understand the complex outcomes of climate change for ectotherm species. Such advances could better serve ecologists to highlight the most vulnerable species and populations, encouraging prioritization of conservation effort to the most threatened systems.This article is protected by copyright. All rights reserved.
    Functional Ecology 12/2014; · 4.86 Impact Factor
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    ABSTRACT: AimBody size often varies clinally, with dominant explanations centred on how body size influences heat exchange (e.g. Bergmann's rule). However, for endotherms, pelage properties can also dramatically alter heat exchange – a point emphasized by Scholander in the 1950s but which has received little attention in biogeographical analyses. Here, we investigate how geographical variation in both body size and fur properties of the koala (Phascolarctos cinereus) is related to climate.LocationEastern Australia.Methods We measured head length and fur depths of koala museum specimens from across its geographical range, and quantified the relationship between fur depth and insulation. We used linear regression and regression tree analyses to test for associations between morphological traits and climate variables relating to four hypotheses: heat conservation (Bergmann's rule), heat dissipation, fasting endurance/survival of extremes, and productivity.ResultsBoth body size and fur depth of koalas decrease substantially towards the tropics. Consistent with Scholander's view, fur properties showed stronger associations with climate than body size. Males, the larger sex, had shorter fur than females in hot environments but not in more temperate regions, suggesting that shorter fur compensates for sexual size dimorphism. While fur depth and male body size were more strongly associated with variables relating to heat dissipation, female body size was most strongly associated with minimum temperatures.Main conclusionsBody size interacts strongly with other traits, such as fur properties, to influence how animals experience climate. Our results emphasize how the consideration of geographical variation in suites of functionally related traits can provide important insight into how species persist across broad environmental gradients.
    Journal of Biogeography 12/2014; · 4.86 Impact Factor
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    Climate Change Responses. 10/2014; 1(1):3.
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    ABSTRACT: Accurate forecasts of biological invasions are crucial for managing invasion risk but are hampered by niche shifts resulting from evolved environmental tolerances (fundamental niche shifts) or the presence of novel biotic and abiotic conditions in the invaded range (realized niche shifts). Distinguishing between these kinds of niche shifts is impossible with traditional, correlative approaches to invasion forecasts, which exclusively consider the realized niche. Here we overcome this challenge by combining a physiologically mechanistic model of the fundamental niche with correlative models based on the realized niche to study the global invasion of the cane toad Rhinella marina. We find strong evidence that the success of R. marina in Australia reflects a shift in the species' realized niche, as opposed to evolutionary shifts in range-limiting traits. Our results demonstrate that R. marina does not fill its fundamental niche in its native South American range and that areas of niche unfilling coincide with the presence of a closely related species with which R. marina hybridizes. Conversely, in Australia, where coevolved taxa are absent, R. marina largely fills its fundamental niche in areas behind the invasion front. The general approach taken here of contrasting fundamental and realized niche models provides key insights into the role of biotic interactions in shaping range limits and can inform effective management strategies not only for invasive species but also for assisted colonization under climate change.
    Proceedings of the National Academy of Sciences of the United States of America. 06/2014;
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    ABSTRACT: How climate impacts organisms depends not only on their physiology, but also whether they can buffer themselves against climate variability via their behaviour. One of the way species can withstand hot temperatures is by seeking out cool microclimates, but only if their habitat provides such refugia. Here, we describe a novel thermoregulatory strategy in an arboreal mammal, the koala Phascolarctos cinereus. During hot weather, koalas enhanced conductive heat loss by seeking out and resting against tree trunks that were substantially cooler than ambient air temperature. Using a biophysical model of heat exchange, we show that this behaviour greatly reduces the amount of heat that must be lost via evaporative cooling, potentially increasing koala survival during extreme heat events. While it has long been known that internal temperatures of trees differ from ambient air temperatures, the relevance of this for arboreal and semi-arboreal mammals has not previously been explored. Our results highlight the important role of tree trunks as aboveground ‘heat sinks’, providing cool local microenvironments not only for koalas, but also for all tree-dwelling species.
    Biology letters 06/2014; 10(6):20140235. · 3.35 Impact Factor
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    ABSTRACT: Physiological thermal-tolerance limits of terrestrial ectotherms often exceed local air temperatures, implying a high degree of thermal safety (an excess of warm or cold thermal tolerance). However, air temperatures can be very different from the equilibrium body temperature of an individual ectotherm. Here, we compile thermal-tolerance limits of ectotherms across a wide range of latitudes and elevations and compare these thermal limits both to air and to operative body temperatures (theoretically equilibrated body temperatures) of small ectothermic animals during the warmest and coldest times of the year. We show that extreme operative body temperatures in exposed habitats match or exceed the physiological thermal limits of most ectotherms. Therefore, contrary to previous findings using air temperatures, most ectotherms do not have a physiological thermal-safety margin. They must therefore rely on behavior to avoid overheating during the warmest times, especially in the lowland tropics. Likewise, species living at temperate latitudes and in alpine habitats must retreat to avoid lethal cold exposure. Behavioral plasticity of habitat use and the energetic consequences of thermal retreats are therefore critical aspects of species' vulnerability to climate warming and extreme events.
    Proceedings of the National Academy of Sciences 03/2014; · 9.81 Impact Factor
  • Johannes Overgaard, Michael R Kearney, Ary A Hoffmann
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    ABSTRACT: Climatic factors influence the distribution of ectotherms, raising the possibility that distributions of many species will shift rapidly under climate change and/or that species will become locally extinct. Recent studies have compared performance curves of species from different climate zones and suggested that tropical species may be more susceptible to climate change than those from temperate environments. However, in other comparisons involving responses to thermal extremes it has been suggested that mid-latitude populations are more susceptible. Using a group of 10 closely related Drosophila species with known tropical or widespread distribution, we undertake a detailed investigation of their growth performance curves and their tolerance to thermal extremes. Thermal sensitivity of life history traits (fecundity, developmental success, and developmental time) and adult heat resistance were similar in tropical and widespread species groups, while widespread species had higher adult cold tolerance under all acclimation regimes. Laboratory measurements of either population growth capacity or acute tolerance to heat and cold extremes were compared to daily air temperature under current (2002-2007) and future (2100) conditions to investigate if these traits could explain current distributions and, therefore, also forecast future effects of climate change. Life history traits examining the thermal sensitivity of population growth proved to be a poor predictor of current species distributions. In contrast, we validate that adult tolerance to thermal extremes provides a good correlate of current distributions. Thus, in their current distribution range, most of the examined species experience heat exposure close to, but rarely above, the functional heat resistance limit. Similarly, adult functional cold resistance proved a good predictor of species distribution in cooler climates. When using the species' functional tolerance limits under a global warming scenario, we find that both tropical and widespread Drosophila species will face a similar proportional reduction in distribution range under future warming.
    Global Change Biology 02/2014; · 8.22 Impact Factor
  • Craig R White, Michael R Kearney
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    ABSTRACT: Life on earth spans a size range of around 21 orders of magnitude across species and can span a range of more than 6 orders of magnitude within species of animal. The effect of size on physiology is, therefore, enormous and is typically expressed by how physiological phenomena scale with mass(b). When b ≠ 1 a trait does not vary in direct proportion to mass and is said to scale allometrically. The study of allometric scaling goes back to at least the time of Galileo Galilei, and published scaling relationships are now available for hundreds of traits. Here, the methods of scaling analysis are reviewed, using examples for a range of traits with an emphasis on those related to metabolism in animals. Where necessary, new relationships have been generated from published data using modern phylogenetically informed techniques. During recent decades one of the most controversial scaling relationships has been that between metabolic rate and body mass and a number of explanations have been proposed for the scaling of this trait. Examples of these mechanistic explanations for metabolic scaling are reviewed, and suggestions made for comparing between them. Finally, the conceptual links between metabolic scaling and ecological patterns are examined, emphasizing the distinction between (1) the hypothesis that size- and temperature-dependent variation among species and individuals in metabolic rate influences ecological processes at levels of organization from individuals to the biosphere and (2) mechanistic explanations for metabolic rate that may explain the size- and temperature-dependence of this trait. © 2014 American Physiological Society. Compr Physiol 4:231-256, 2014.
    Comprehensive Physiology. 01/2014; 4(1).
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    ABSTRACT: Widespread species often show geographic variation in thermally-sensitive traits, providing insight into how species respond to shifts in temperature through time. Such patterns may arise from phenotypic plasticity, genetic adaptation, or their interaction. In some cases, the effects of genotype and temperature may act together to reduce, or to exacerbate, phenotypic variation in fitness-related traits across varying thermal environments. We find evidence for such interactions in life-history traits of Heteronympha merope, a butterfly distributed across a broad latitudinal gradient in south-eastern Australia. We show that body size in this butterfly is negatively related to developmental temperature in the laboratory, in accordance with the temperature-size rule, but not in the field, despite very strong temperature gradients. A common garden experiment on larval thermal responses, spanning the environmental extremes of H. merope's distribution, revealed that butterflies from low latitude (warmer climate) populations have relatively fast intrinsic growth and development rates compared to those from cooler climates. These synergistic effects of genotype and temperature across the landscape (co-gradient variation) are likely to accentuate phenotypic variation in these traits, and this interaction must be accounted for when predicting how H. merope will respond to temperature change through time. These results highlight the importance of understanding how variation in life-history traits may arise in response to environmental change. Without this knowledge, we may fail to detect whether organisms are tracking environmental change, and if they are, whether it is by plasticity, adaptation or both.
    PLoS ONE 01/2014; 9(4):e95258. · 3.53 Impact Factor
  • Madeleine Barton, Warren Porter, Michael Kearney
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    ABSTRACT: Poikilothermic animals are often reliant on behavioural thermoregulation to elevate core-body temperature above the temperature of their surroundings. Butterflies are able to do this by altering body posture and location while basking, however the specific mechanisms that achieve such regulation vary among species. The role of the wings has been particularly difficult to describe, with uncertainty surrounding whether they are positioned to reduce convective heat loss or to maximize heat gained through radiation. Characterisation of the extent to which these processes affect core-body temperature will provide insights into the way in which a species’ thermal sensitivity and morphological traits have evolved. We conducted field and laboratory measurements to assess how basking posture affects the core-body temperature of an Australian butterfly, the common brown (Heteronympha merope). We show that, with wings held open, heat lost through convection is reduced while heat gained through radiation is simultaneously maximized. These responses have been incorporated into a biophysical model that accurately predicts the core-body temperature of basking specimens in the field, providing a powerful tool to explore how climate constrains the distribution and abundance of basking butterflies.
    Journal of Thermal Biology 01/2014; · 1.54 Impact Factor
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    ABSTRACT: Research on the Dynamic Energy Budget (DEB) theory started 35 years ago. Initialy much emphasis was put on the development of a consistent theory. During recent years attention was paid on parameterizing DEB models for a huge collection of species. This enables the search for patterns in parameter values in an ecological and evolutionary context. This special issue presents some of the results of this quest, among other things focusing on the development of metabolic acceleration, combinedwith various applications of DEB theory in fisheries, aquaculture, climate science and ecotoxicology.
    Journal of Sea Research. 01/2014;
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    ABSTRACT: Spatio-temporal studies of hybrid zones provide an opportunity to test evolutionary hypotheses of hybrid zone maintenance and movement. We conducted a landscape genetics study on a classic hybrid zone of the south-eastern Australian frogs, Litoria ewingii and Litoria paraewingi. This hybrid zone has been comprehensively studied since the 1960s, providing the unique opportunity to directly assess changes in hybrid zone structure across time. We compared both mtDNA and male advertisement call data from two time periods (present and 1960s). Clinal analysis of the coincidence (same center) and concordance (same width) of these traits indicated that the center of the hybrid zone has shifted 1 km south over the last 40 years, although the width of the zone and the rate of introgression remained unchanged. The low frequency of hybrids, the strong concordance of clines within a time period, and the small but significant movement across the study period despite significant anthropogenic changes through the region, suggest the hybrid zone is a tension zone located within a low-density trough. Hybrid zone movement has not been considered common in the past but our findings highlight that it should be considered a crucial component to our understanding of evolution.
    Evolution 12/2013; 67(12):3442-54. · 4.86 Impact Factor
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    ABSTRACT: The microclimate experienced by organisms is determined by local weather conditions. Yet the environmental data available for predicting the effect of climate on the distribution and abundance of organisms is typically in the form of long-term average monthly climate measured at standardized heights above the ground. Here we demonstrate how hourly microclimates can be modelled mechanistically over decades at the continental scale with biologically suitable accuracy. We extend the microclimate model of the software package Niche Mapper to capture spatial and temporal variation in soil thermal properties, and integrate it with gridded soil and weather data for Australia at 0.05° resolution. When tested against historical observations of soil temperature, the microclimate model predicted 85% of the variation in hourly soil temperature across 10 years from the surface to 1 m deep with an accuracy of 2-3.3°C (~10% of the temperature range at a given depth) across an extremely climatically diverse range of sites. This capacity to accurately and mechanistically predict hourly local microclimates across continental scales creates new opportunities for understanding how organisms respond to changes in climate. This article is protected by copyright. All rights reserved.
    Methods in Ecology and Evolution 12/2013; · 5.92 Impact Factor
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    ABSTRACT: Species distribution models (SDMs) are increasingly proposed to support conservation decision making. However, evidence of SDMs supporting solutions for on-ground conservation problems is still scarce in the scientific literature. Here, we show that successful examples exist but are still largely hidden in the grey literature, and thus less accessible for analysis and learning. Furthermore, the decision framework within which SDMs are used is rarely made explicit. Using case studies from biological invasions, identification of critical habitats, reserve selection and translocation of endangered species, we propose that SDMs may be tailored to suit a range of decision-making contexts when used within a structured and transparent decision-making process. To construct appropriate SDMs to more effectively guide conservation actions, modellers need to better understand the decision process, and decision makers need to provide feedback to modellers regarding the actual use of SDMs to support conservation decisions. This could be facilitated by individuals or institutions playing the role of 'translators' between modellers and decision makers. We encourage species distribution modellers to get involved in real decision-making processes that will benefit from their technical input; this strategy has the potential to better bridge theory and practice, and contribute to improve both scientific knowledge and conservation outcomes.
    Ecology Letters 10/2013; 16:1424-1435. · 17.95 Impact Factor
  • Michael R Kearney
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    ABSTRACT: Correlative analyses predict that anthropogenic climate warming will cause widespread extinction but the nature and generality of the underlying mechanisms is unclear. Warming-induced activity restriction has been proposed as a general explanatory mechanism for recent population extinctions in lizards, and has been used to forecast future extinction. Here, I test this hypothesis using globally applied biophysical calculations of the effects of warming and shade reduction on potential activity time and whole-life-cycle energy budgets. These 'thermodynamic niche' analyses show that activity restriction from climate warming is unlikely to provide a general explanation of recent extinctions, and that loss of shade is viable alternative explanation. Climate warming could cause population declines, even under increased activity potential, through joint impacts on fecundity and mortality rates. However, such responses depend strongly on behaviour, habitat (shade, food) and life history, all of which should be explicitly incorporated in mechanistic forecasts of extinction risk under climate change.
    Ecology Letters 10/2013; · 17.95 Impact Factor
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    ABSTRACT: 1. Models of the regulatory behaviour of organisms are fundamental to a strong physiologically-based understanding of species' responses to global environmental change. Biophysical models of heat and water exchange in organisms (biophysical ecology) and nutritionally-explicit models for understanding feeding behaviour and its fitness consequences (the Geometric Framework of nutrition, GF) are providing such an underpinning. However, temperature, water and nutrition interact in fundamental ways in influencing the responses of the organism to their environment, and a priority is to develop an integrated approach for conceptualising and measuring these interactions. 2. Ideally, such an approach would be based on a thermodynamically-formalized energy and mass budgeting approach that is sparsely parameterised and sufficiently general to apply across a range of situations and organisms. Here we illustrate how mass-balance aspects of Dynamic Energy Budget theory can be applied to obtain first-principles estimates of fluxes of O 2 , CO 2 , H 2 O and nitrogenous waste. 3. Then, using an herbivorous lizard (Egernia cunninghami) as a case study, we demonstrate how these estimates can be integrated with heat/water exchange models and environmental data to provide a holistic understanding of how foraging strategy, food availability, habitat and weather interact with heat, water and nutrient/energy budgets across the life-cycle. 4. The analysis shows the potential importance of the water balance in affecting the energy budgets of 'dry skinned' ectotherms, especially early in ontogeny, and highlights a significant gap in our knowledge of the physiological and behavioural traits that affect water balance when compared with our knowledge of thermal traits. 5. In general, the modelling approach we describe can provide the thermodynamically-constrained stage on which other evolutionary and ecological interactions play out; the 'thermodynamic niche'. This in turn provides a solid foundation from which to tackle key questions about organismal responses to environmental change.
    Functional Ecology 08/2013; 27(4):950-965. · 4.86 Impact Factor
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    ABSTRACT: Metabolic theory specifies constraints on the metabolic organisation of individual organisms. These constraints have important implications for biological processes ranging from the scale of molecules all the way to the level of populations, communities and ecosystems, with their application to the latter emerging as the field of metabolic ecology. While ecologists continue to use individual metabolism to identify constraints in ecological processes, the topic of metabolic scaling remains controversial. Much of the current interest and controversy in metabolic theory relates to recent ideas about the role of supply networks in constraining energy supply to cells. We show that an alternative explanation for physicochemical constraints on individual metabolism, as formalised by dynamic energy budget (DEB) theory, can contribute to the theoretical underpinning of metabolic ecology, while increasing coherence between intra- and interspecific scaling relationships. In particular, we emphasise how the DEB theory considers constraints on the storage and use of assimilated nutrients and derive an equation for the scaling of metabolic rate for adult heterotrophs without relying on optimisation arguments or implying cellular nutrient supply limitation. Using realistic data on growth and reproduction from the literature, we parameterise the curve for respiration and compare the a priori prediction against a mammalian data set for respiration. Because the DEB theory mechanism for metabolic scaling is based on the universal process of acquiring and using pools of stored metabolites (a basal feature of life), it applies to all organisms irrespective of the nature of metabolic transport to cells. Although the DEB mechanism does not necessarily contradict insight from transport-based models, the mechanism offers an explanation for differences between the intra- and interspecific scaling of biological rates with mass, suggesting novel tests of the respective hypotheses.
    Journal of Animal Ecology 05/2013; · 4.84 Impact Factor
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Publication Stats

2k Citations
384.68 Total Impact Points

Institutions

  • 2009–2014
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
    • James Cook University
      • Anton Breinl Centre for Public Health & Tropical Medicine
      Townsville, Queensland, Australia
  • 2005–2014
    • University of Melbourne
      • • School of Botany
      • • Department of Zoology
      • • School of Earth Sciences
      • • Centre for Environmental Stress and Adaptation
      Melbourne, Victoria, Australia
    • Washington University in St. Louis
      • Department of Biology
      Saint Louis, MO, United States
  • 2012
    • University of Queensland
      • School of Biological Sciences
      Brisbane, Queensland, Australia
  • 2011
    • Australian National University
      • Fenner School of Environment & Society
      Canberra, Australian Capital Territory, Australia
  • 2004–2009
    • University of Wisconsin, Madison
      • Department of Zoology
      Madison, MS, United States
  • 2008
    • Victoria University of Wellington
      • School of Biological Sciences
      Wellington, Wellington, New Zealand
  • 2001–2005
    • University of Sydney
      • School of Biological Sciences
      Sydney, New South Wales, Australia