A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

All animals face the possibility of limitations in food resources that could ultimately lead to starvation-induced mortality. The primary goal of this review is to characterize the various physiological strategies that allow different animals to survive starvation. The ancillary goals of this work are to identify areas in which investigations of starvation can be improved and to discuss recent advances and emerging directions in starvation research. The ubiquity of food limitation among animals, inconsistent terminology associated with starvation and fasting, and rationale for scientific investigations into starvation are discussed. Similarities and differences with regard to carbohydrate, lipid, and protein metabolism during starvation are also examined in a comparative context. Examples from the literature are used to underscore areas in which reporting and statistical practices, particularly those involved with starvation-induced changes in body composition and starvation-induced hypometabolism can be improved. The review concludes by highlighting several recent advances and promising research directions in starvation physiology. Because the hundreds of studies reviewed here vary so widely in their experimental designs and treatments, formal comparisons of starvation responses among studies and taxa are generally precluded; nevertheless, it is my aim to provide a starting point from which we may develop novel approaches, tools, and hypotheses to facilitate meaningful investigations into the physiology of starvation in animals.

Starvation physiology: reviewing the different strategies animals use to survive a common challenge.

Lizard life-history characteristics vary widely among species and populations. Most authors seek adaptive or phylogenetic explanations for life-history patterns, which are usually presumed to reflect genetic differences. However, lizard life histories are often phenotypically plastic, varying in response to temperature, food availability, and other environmental factors. Despite the importance of temperature to lizard ecology and physiology, its effects on life histories have received relatively little attention. We present a theoretical model predicting the proximate consequences of the thermal environment for lizard life histories. Temperature, by affecting activity times, can cause variation in annual survival rate and fecundity, leading to a negative correlation between survival rate and fecundity among populations in different thermal environments. Thus, physiological and evolutionary models predict the same qualitative pattern of life-history variation in lizards. We tested our model with published ...

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Temperature, activity, and lizard life histories

Stevens, C. Edward, and Ian D. Hume. Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients. Physiol. Rev. 78: 393–427, 1998. — The vertebrate ga...

Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients

Synopsis. Operative and standard operative temperatures (Te and Tes, respectively) are thermal indices that allow single-number representations of the complex thermal environ? ment. They can be measured directly using various physical models ofthe animal of interest. These models explore the thermal environment at the same spatial scale that the animal experiences, and can be replicated relatively easily to measure conditions at multiple sites. Thus, they offer a complementary approach to elaborate computer models, and have proven valuable in integrating biophysical and population ecology. This workshop paper is primarily a summary and critical review of the uses and mea? surement of Te and Tes. I first review the principles behind Te and Tes. I then describe the various methods used to construct Te and Tes "thermometers," and discuss their relative merits for various classes of animals and types of studies. Finally, I review typical applications. The most important is in mapping the nanoclimate experienced by small animals and in defining indices of thermal quality of home ranges based on such maps. Others include use as null models in physiological studies, and use as single-number descriptors of complex thermal environments in behavioral, physiological, and energetics studies.

Measurement and Application of Operative and Standard Operative Temperatures in Ecology

Herbivorous reptiles are a comparatively rare group of animals, likely in part because of constraints resulting from interactions between ectothermy and herbivory. Herbivorous lizards, as a group, are characterized by a unique set of morphological, anatomical, and physiological properties. Additionally, most herbivorous lizards are found in (and perhaps partially confined to) the tropics. The most northerly distributed herbivorous lizards, the chuckwalla (Sauromalus obsesus) and the desert iguana (Dipsosaurus dorsalis), occur only in very hot regions of the desert southwestern United States. Herbivorous lizards digest their food much less efficiently than nonherbivorous lizards, and digestive efficiency is affected little by body temperature. However, the rate at which food passes through the gut is affected by body temperature in chuckwallas; specifically, food passes through the gut more slowly at lower body temperatures. Throughout the activity season, free-ranging chuckwallas exploit microhabitats all...

Interactions between the Environment and Ectothermy and Herbivory in Reptiles

Many of the threats to the persistence of populations of sensitive species have physiological or pathological mechanisms, and those mechanisms are best understood through the inherently integrative discipline of physiological ecology. The desert tortoise was listed under the Endangered Species Act largely due to a newly recognized upper respiratory disease thought to cause mortality in individuals and severe declines in populations. Numerous hypotheses about the threats to the persistence of desert tortoise populations involve acquisition of nutrients, and its connection to stress and disease. The nutritional wisdom hypothesis posits that animals should forage not for particular food items, but instead, for particular nutrients such as calcium and phosphorus used in building bones. The optimal foraging hypothesis suggests that, in circumstances of resource abundance, tortoises should forage as dietary specialists as a means of maximizing intake of resources. The optimal digestion hypothesis suggests that tortoises should process ingesta in ways that regulate assimilation rate. Finally, the cost-of-switching hypothesis suggests that herbivores, like the desert tortoise, should avoid switching food types to avoid negatively affecting the microbe community responsible for fermenting plants into energy and nutrients. Combining hypotheses into a resource acquisition theory leads to novel predictions that are generally supported by data presented here. Testing hypotheses, and synthesizing test results into a theory, provides a robust scientific alternative to the popular use of untested hypotheses and unanalyzed data to assert the needs of species. The scientific approach should focus on hypotheses concerning anthropogenic modifications of the environment that impact physiological processes ultimately important to population phenomena. We show how measurements of such impacts as nutrient starvation, can cause physiological stress, and that the endocrine mechanisms involved with stress can result in disease. Finally, our new syntheses evince a new hypothesis. Free molecules of the stress hormone corticosterone can inhibit immunity, and the abundance of "free corticosterone" in the blood (thought to be the active form of the hormone) is regulated when the corticosterone molecules combine with binding globulins. The sex hormone, testosterone, combines with the same binding globulin. High levels of testosterone, naturally occurring in the breeding season, may be further enhanced in populations at high densities, and the resulting excess testosterone may compete with binding globulins, thereby releasing corticosterone and reducing immunity to disease. This sequence could result in physiological and pathological phenomena leading to population cycles with a period that would be essentially impossible to observe in desert tortoise. Such cycles could obscure population fluctuations of anthropogenic origin.

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The importance of physiological ecology in conservation biology

Animals that are unable to meet their metabolic needs should adopt compensatory behaviors to mitigate their energetic deficits. Voluntary hypothermia is one such energy-saving strategy. Physiological constraints associated with the digestion of plant tissues, however, may limit the thermoregulatory options of herbivorous ectotherms. In this laboratory study, selected body temperatures of Desert Iguanas (Dipsosaurus dorsalis), subjected to two different rations of a carnivorous and a herbivorous diet, were measured in a laboratory thermal gradient. Lizards fed a carnivorous diet and rationed to 50% of their daily energetic requirement selected significantly lower body temperatures than did lizards in the other diet/ration treatments. Lizards fed a herbivorous diet selected higher body temperatures than did the same lizards fed a carnivorous diet regardless of ration. Our study indicates that selected temperatures are influenced by both diet quality and quantity. These results support the hypothesis that herbivorous reptiles require elevated body temperatures to digest plant tissues. Our findings do not fully support the behavioral hypothermia hypothesis, which posits that diurnal lizards will seek cool temperatures at night to reduce their energy expenditure. Thermoregulatory strategies of Desert Iguanas and other herbivorous lizards may be influenced by the need to balance high body temperatures to digest plant material with the high metabolic costs of maintaining high temperatures.

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Herbivory Imposes Constraints on Voluntary Hypothermia in Lizards

Diet quality and body size affected passage time of 2 diets (higher and lower in fiber) in hatchling and juvenile desert tortoises (Gopherus agassizii). Mean retention time of the liquid fraction of each diet was significantly shorter than that of the solid fraction, and hatchlings had shorter passage times than juveniles. Habitat disturbances that limit access of hatchlings to diets lower in fiber may negatively impact the physiological and behavioral ecology of young desert tortoises.

Linda C. Zimmerman

Papers

Interactions between the Environment and Ectothermy and Herbivory in Reptiles

The importance of physiological ecology in conservation biology

Herbivory Imposes Constraints on Voluntary Hypothermia in Lizards

Rates of Food Passage in the Digestive Tract of Young Desert Tortoises: Effects of Body Size and Diet Quality

Thermal responses to feeding in a secretive and specialized predator (Gila monster, Heloderma suspectum)