Trust: The Social Virtues and the Creation of Prosperity

The impact of anthropogenic climate change on terrestrial organisms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are relatively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal tolerance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest.

https://www.pnas.org/content/pnas/105/18/6668.full.pdf

Impacts of climate warming on terrestrial ectotherms across latitude.

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Temperature and Organism Size—A Biological Law for Ectotherms?

A citizen scientist is a volunteer who collects and/or processes data as part of a scientific enquiry. Projects that involve citizen scientists are burgeoning, particularly in ecology and the environmental sciences, although the roots of citizen science go back to the very beginnings of modern science itself.

A new dawn for citizen science.

Species distribution models (SDMs) use spatial environmental data to make inferences on species' range limits and habitat suitability. Conceptually, these models aim to determine and map components of a species' ecological niche through space and time, and they have become important tools in pure and applied ecology and evolutionary biology. Most approaches are correlative in that they statistically link spatial data to species distribution records. An alternative strategy is to explicitly incorporate the mechanistic links between the functional traits of organisms and their environments into SDMs. Here, we review how the principles of biophysical ecology can be used to link spatial data to the physiological responses and constraints of organisms. This provides a mechanistic view of the fundamental niche which can then be mapped to the landscape to infer range constraints. We show how physiologically based SDMs can be developed for different organisms in different environmental contexts. Mechanistic SDMs have different strengths and weaknesses to correlative approaches, and there are many exciting and unexplored prospects for integrating the two approaches. As physiological knowledge becomes better integrated into SDMs, we will make more robust predictions of range shifts in novel or non-equilibrium contexts such as invasions, translocations, climate change and evolutionary shifts.

http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Kearney2009.pdf

Mechanistic niche modelling: combining physiological and spatial data to predict species' ranges.

synopsis. An understanding of interactions between the thermal physiology and ecology of ectotherms remains elusive, partly because information on the relative performance of whole-animal physiological systems at ecologically relevant body temperatures is limited. After discussing physiological systems that have direct links to ecology (e.g., growth, locomotor ability), we review analytical methods of describing and comparing certain as? pects of performance (including optimal temperature range, thermal performance breadth), apply these techniques in an example on the thermal sensitivity of locomotion in frogs, and evaluate potential applications.

https://faculty.washington.edu/hueyrb/new/HueyStevenson%201989%20Am%20Zool.pdf

Integrating Thermal Physiology and Ecology of Ectotherms: A Discussion of Approaches

We describe a research protocol for evaluating temperature regulation from data on small field-active ectothermic animals, especially lizards. The protocol requires data on body temperatures (Tb) of field-active ectotherms, on available operative temperatures (Te, "null temperatures" for nonregulating animals), and on the thermoregulatory set-point range (preferred body temperatures, Tset). These data are used to estimate several quantitative indexes that collectively summarize temperature regulation: the "precision" of body temperature (variance in Tb, or an equivalent metric), the "accuracy" of body temperature relative to the set-point range (the average difference between Tb and Tset), and the "effectiveness" of thermoregulation (the extent to which body temperatures are closer on the average to the set-point range than are operative temperatures). If additional data on the thermal dependence of performance are available, the impact of thermoregulation on performance (the extent to which performance is enhanced relative to that of nonregulating animals) can also be estimated. A sample analysis of the thermal biology of three Anolis lizards in Puerto Rico demonstrates the utility of the new protocol and its superiority to previous methods of evaluating temperature regulation. We also discuss several ways in which the research protocol can be extended and applied to other organisms.

Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question.

A series of simple heat-transfer models (termed the basic, conduction, physiological, and wet-skin models) is derived to examine a large number of behavioral and physiological mechanisms that are used by terrestrial ectotherms to control body temperature (Tb; table 1). The models reaffirm two generalizations: (1) in environments where solar radiation is available, behavioral mechanisms may provide a range of Tb's that is many times greater than the range in Tb's that results from physiological adjustments; and (2) among behavioral mechanisms, the times of seasonal and daily activity appear to be the most critical in determining Tb. Furthermore, microhabitat selection is more important than postural adjustments for controlling Tb. The models calculate Tb as the sum of air temperature (Ta) and the body-air temperature difference (Td). The direct effects of body size are expressed as functions of Td. Many behavioral mechanisms can then be expressed as some fraction of Td. The models (eqs. 3, 6, 8, 11), in co...

The relative importance of behavioral and physiological adjustments controlling body temperature in terrestrial ectotherms

Biologists have developed a wide range of morphological, biochemical and physiological metrics to assess the health and, in particular, the energetic status of individual animals. These metrics originated to quantify aspects of human health, but have also proven useful to address questions in life history, ecology and resource management of game and commercial animals. We review the application of condition indices (CI) for conservation studies and focus on measures that quantify fat reserves, known to be critical for energetically challenging activities such as migration, reproduction and survival during periods of scarcity. Standard methods score fat content, or rely on a ratio of body mass rationalized by some measure of size, usually a linear dimension such as wing length or total body length. Higher numerical values of these indices are interpreted to mean an animal has greater energy reserves. Such CIs can provide predictive information about habitat quality and reproductive output, which in turn can help managers with conservation assessments and policies. We review the issues about the methods and metrics of measurement and describe the linkage of CIs to measures of body shape. Debates in the literature about the best statistical methods to use in computing and comparing CIs remain unresolved. Next, we comment on the diversity of methods used to measure body composition and the diversity of physiological models that compute body composition and CIs. The underlying physiological regulatory systems that govern the allocation of energy and nutrients among compartments and processes within the body are poorly understood, especially for field situations, and await basic data from additional laboratory studies and advanced measurement systems including telemetry. For now, standard physiological CIs can provide supporting evidence and mechanistic linkages for population studies that have traditionally been the focus of conservation biology. Physiologists can provide guidance for the field application of conditions indices with validation studies and development of new instruments.

Condition indices for conservation: new uses for evolving tools

A nonequilibrium heat-transfer model is used to calculate the extreme range of body temperatures available to ectotherms of different masses. At about 1 kg a transition occurs in the amplitudes imposed on a terrestrial ectotherm's potential range in body temperature by the daily cycling of the thermal environment. Animals smaller than 1 kg can choose a wide range of temperatures, whereas animals larger than 1 kg experience smaller ranges in Tb. The range in Tb that small insects experience is limited by the range in Ta, which, however, can be large in the boundary layer of perching surfaces. Data from the literature indicate that ectotherms in the range of sizes from 0.01 to 1 kg have limited ranges of Tb (about 30⚬ C). The model predicts that it could be as large as 55⚬ C, 15⚬ C greater than the range of lethal temperatures of reptiles. That the observed range is only about half of that predicted reaffirms our understanding of the importance of behavioral thermoregulation for these animals. Body size app...

Robert D. Stevenson

Papers

Integrating Thermal Physiology and Ecology of Ectotherms: A Discussion of Approaches

Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question.

The relative importance of behavioral and physiological adjustments controlling body temperature in terrestrial ectotherms

Condition indices for conservation: new uses for evolving tools

Body Size and Limits to the Daily Range of Body Temperature in Terrestrial Ectotherms