Endotherm Energetics - From a Scalable Individual-Based Model to Ecological Applications

A key challenge in ecology is to define species' niches on the basis of functional traits. Size and shape are important determinants of a species' niche but their causal role is often difficult to interpret. For endotherms, size and shape define the thermal niche through their interaction with core temperature, insulation, and environmental conditions, determining the thermoneutral zone (TNZ) where energy and water costs are minimized. Laboratory measures of metabolic rate used to describe TNZs cannot be generalized to infer the capacity for terrestrial animals to find their TNZ in complex natural environments. Here, we derive an analytical model of the thermal niche of an ellipsoid furred endotherm that accurately predicts field and laboratory data. We use the model to illustrate the relative importance of size and shape on the location of the TNZ under different environmental conditions. The interaction between body shape and posture strongly influences the location of the TNZ and the expected scaling of metabolic rate with size at constant temperature. We demonstrate that the latter relationship has a slope of approximately 1 ⁄2 rather than the commonly expected surface area/volume scaling of 2 ⁄3. We show how such functional traits models can be integrated with spatial environmental datasets to calculate null expectations for body size clines from a thermal perspective, aiding mechanistic interpretation of empirical clines such as Bergmann's Rule. The combination of spatially explicit data with biophysical models of heat exchange provides a powerful means for studying the thermal niches of endotherms across climatic gradients.biophysical ecology ͉ functional traits ͉ lower critical temperature ͉ metabolic scaling ͉ thermoneutral zone T he ecological niche reflects the interaction between an organism and its environment and how that interaction affects its fitness (1, 2). An understanding of a species' niche requires knowledge of its traits (morphology, physiology, and behavior) and how that species interacts with its habitat to construct environments (2). This two-way interaction between organism and environment is also key to understanding how a species' traits, and hence its niche, evolves (3, 4). A species' energy and water balance are key determinants of its niche, reflecting both its requirements for life (Grinnellian niche) and its impact on the other species with which it interacts (Eltonian niche). Here, we illustrate how biophysical principles can be used to link variation in the size, shape, and other functional traits of organisms with environmental data to predict the thermal niches of endotherms. Such a model can be conceived as a mechanistic depiction of the Hutchinsonian niche, a hypervolume describing conditions suitable for survival, growth, and reproduction along trait and environmental axes. Biophysical models provide a way to calculate spatially explicit null models of selective pressures on functional traits from the perspectives of energy and water conservation (5).Basal metabolic rate ...

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“…S2). More detailed, computationally intensive approaches can be applied in more complex environmental settings (15,38,39).…”

Section: Resultsmentioning

confidence: 99%

Size, shape, and the thermal niche of endotherms

Porter

Kearney

2009

Proc. Natl. Acad. Sci. U.S.A.

226

250

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“…Biophysical models achieve this aim by incorporating realistic levels of complexity in thermal environments as well as in behavioral, morphological, and physiological attributes that can modify the link between ''ambient'' temperature and ectotherm body temperature. Although we have considered terrestrial ectothermic animals only, biophysical analyses can readily be extended to endotherms, plants, and marine organisms (18,(35)(36)(37).…”

Section: Discussionmentioning

confidence: 99%

The potential for behavioral thermoregulation to buffer “cold-blooded” animals against climate warming

Kearney

Shine

Porter³

2009

Proc. Natl. Acad. Sci. U.S.A.

936

1,000

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Increasing concern about the impacts of global warming on biodiversity has stimulated extensive discussion, but methods to translate broad-scale shifts in climate into direct impacts on living animals remain simplistic. A key missing element from models of climatic change impacts on animals is the buffering influence of behavioral thermoregulation. Here, we show how behavioral and mass/energy balance models can be combined with spatial data on climate, topography, and vegetation to predict impacts of increased air temperature on thermoregulating ectotherms such as reptiles and insects (a large portion of global biodiversity). We show that for most ''cold-blooded'' terrestrial animals, the primary thermal challenge is not to attain high body temperatures (although this is important in temperate environments) but to stay cool (particularly in tropical and desert areas, where ectotherm biodiversity is greatest). The impact of climate warming on thermoregulating ectotherms will depend critically on how changes in vegetation cover alter the availability of shade as well as the animals' capacities to alter their seasonal timing of activity and reproduction. Warmer environments also may increase maintenance energy costs while simultaneously constraining activity time, putting pressure on mass and energy budgets. Energy-and mass-balance models provide a general method to integrate the complexity of these direct interactions between organisms and climate into spatial predictions of the impact of climate change on biodiversity. This methodology allows quantitative organism-and habitat-specific assessments of climate change impacts.T he response of organisms to climate warming will have implications for conservation, pest management, and the spread of disease. To respond effectively to these changes, we must be able to predict how changes in climate, especially air temperature, will affect biodiversity (1, 2). Current approaches to predicting these impacts are largely based on statistical correlations between a species' observed distribution and coarse-scale macroclimatic data (3-5). Correlative approaches provide little insight into the mechanisms by which species respond to climate (6-8), particularly the potential for behavioral, plastic, or genetic adaptation. For example, most organisms are ectotherms, and many of them can exploit complex microclimatic mosaics to regulate their body temperatures behaviorally (9, 10). For a complete understanding of their response to climate change, we need to consider not only the physiological sensitivity of ectotherms to temperature but their capacity to buffer the impact of climate change through behavior, morphology, and physiology (11)(12)(13)(14).Recent research suggests that the physiological sensitivity of tropical ectotherms may render them more vulnerable to a given magnitude of climate warming than are temperate species (15), under the assumption that body temperature is equal to ambient air temperature. As the authors of that study point out, the actual impact will depend ...

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“…A more marked distinction is the seasonal differentiation in foraging activity whereby varanids in the southern latitudes are mostly inactive and undertake limited or no foraging at all in the cooler months [35,53,54] and in the tropics are less active towards the end of the dry season [53,55]. Conversely, mammalian predators must continue to forage and balance greater energetic demands at these times to overcome elevated heat and water loss [56].…”

Section: Niche Overlap Between Varanid Lizards and Eutherian Carnivoresmentioning

confidence: 99%

Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

Sutherland¹,

Glen²,

Tores³

2010

Proc. R. Soc. B.

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Emerging evidence increasingly illustrates the importance of a holistic, rather than taxon-specific, approach to the study of ecological communities. Considerable resources are expended to manage both introduced and native mammalian carnivores to improve conservation outcomes; however, management can result in unforeseen and sometimes catastrophic outcomes. Varanid lizards are likely to be apex-or mesopredators, but being reptiles are rarely considered by managers and researchers when investigating the impacts of mammalian carnivore management. Instances of mesopredator release have been described for Varanus gouldii as a result of fox and cat management in Australia, with cascading effects on faunal community structure. A meta-analysis showing extensive dietary niche overlap between varanids, foxes and cats plus a review of experimental and circumstantial evidence suggests mesopredator release of V. gouldii and about five other medium to large species of varanid lizard is likely in other regions. This highlights the need for managers to adopt a whole-of-community approach when attempting to manage predators for sustained fauna conservation, and that additional research is required to elucidate whether mesopredator release of varanids is a widespread consequence of carnivore management, altering the intended faunal responses.

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Endotherm Energetics - From a Scalable Individual-Based Model to Ecological Applications

Cited by 86 publications

References 37 publications

Size, shape, and the thermal niche of endotherms

Size, shape, and the thermal niche of endotherms

The potential for behavioral thermoregulation to buffer “cold-blooded” animals against climate warming

Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

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