Physiological Ecology of Water Balance in Terrestrial Animals

by

Sue Nicolson

• LAST REVIEWED: 29 May 2014
• LAST MODIFIED: 29 May 2014
• DOI: 10.1093/obo/9780199830060-0084

Introduction

Physiological ecology is concerned with the interactions between physiological systems and the environment. Water and temperature are the two most important abiotic factors affecting animals, and water plays a major role in their distribution and abundance patterns. The water relations of terrestrial animals have received much attention from physiological ecologists, with a bias, not surprisingly, toward assessing the performance of desert animals in extreme environments. There has been a general move from mainly comparative studies carried out under laboratory conditions to an increasing number of field studies of water balance physiology, with more emphasis on the ecological and evolutionary context, and behavior becoming more evident as the first level of response. The evaporating power of air depends on its water vapor density and temperature, and avoidance of desiccation when it cannot be tolerated physiologically depends on minimizing the vapor pressure gradient between the body and the environment. Small animals have a relatively large ratio of surface area to volume, yet despite this constraint, insects are highly successful in terrestrial environments. The focus in this article is on arthropods, reptiles, birds, and mammals as the main terrestrial groups. Water turnover may differ by orders of magnitude, with endothermic vertebrates having far-higher rates of metabolism and water use. Aquatic animals have a different set of environmental problems and will be dealt with in a separate article, except for occasional mention of some of the more terrestrial amphibians. There is huge variety in the ways that animals use water, and the avenues of water exchange with the environment vary greatly in both absolute and relative terms in different animals.

General Overviews

Textbooks on physiological ecology all have substantial sections dealing with the water relations of both terrestrial and aquatic animals. Schmidt-Nielsen 1997 (the last of several editions) is clear and approachable, while Withers 1992 is more comprehensive and strong on technical details. Willmer, et al. 2005 has a strong environmental slant. McNab 2002 is biased toward the author’s favorite topic of energetics. The most recent is Karasov and Martínez del Rio 2007, which focuses on nutritional ecology and treats water as a nutrient (not commonly done). Two smaller volumes, both characterized by a personal touch, are Louw 1993 and Bradshaw 2003.

• Bradshaw, Don. 2003. Vertebrate ecophysiology: An introduction to its principles and applications. Cambridge, UK: Cambridge Univ. Press.

  DOI: 10.1017/CBO9780511840906

  Short, readable text with an emphasis on field studies related to stress and homeostasis (or the lack of it). Valuable for the Australian case studies, many from the author’s own research. Includes useful summaries of many techniques used in ecophysiological studies.

• Hill, Richard W., Gordon A. Wyse, and Margaret Anderson. 2012. Animal physiology. 3d ed. Sunderland, MA: Sinauer.

  The final section consists of three chapters on water and salt physiology and excretion, with an “at work” chapter dealing with mammals of deserts and dry savannas. The companion website is also useful.

• Karasov, William H., and Carlos Martínez del Rio. 2007. Physiological ecology: How animals process energy, nutrients, and toxins. Princeton, NJ: Princeton Univ. Press.

  This refreshingly different textbook is basically a broad account of how animals process and use food resources. Contains useful boxes on technical topics such as the doubly labeled water technique. Chapter 12 (pp. 608–644) deals with the water requirements and water fluxes of animals (mainly vertebrates).

• Louw, Gideon N. 1993. Physiological animal ecology. Harlow, UK: Longman Scientific & Technical.

  Short and readable volume aimed at bridging the gap between physiology and ecology.

• McNab, Brian K. 2002. The physiological ecology of vertebrates: A view from energetics. Ithaca, NY: Cornell Univ. Press.

  Uses energetics as the unifying theme in a synthesis of the literature on physiological ecology of vertebrates. Chapter 7 (pp. 174–218) deals with water and salt exchange in terrestrial vertebrates.

• Schmidt-Nielsen, Knut. 1997. Animal physiology: Adaptation and environment. 5th ed. Cambridge, UK: Cambridge Univ. Press.

  The first edition of this hugely successful textbook appeared in 1975, and it has remained a favorite because of the clarity of its writing. Chapter 8 (pp. 301–354) deals with water and osmotic regulation; chapter 9 (pp. 355–391), with excretion.

• Willmer, Pat, Graham Stone, and Ian Johnston. 2005. Environmental physiology of animals. 2d ed. Oxford: Blackwell.

  Comprehensive overview of the comparative physiology of animals, placed in a strong environmental context. Emphasizes behavioral as well as physiological responses and includes broad coverage of animal phyla.

• Withers, Philip C. 1992. Comparative animal physiology. Philadelphia: Saunders College.

  Chapter 16 (“Water and Solute Balance”; pp. 777–830) and chapter 17 (“Excretion”; pp. 831–891) are the most relevant. The author uses a quantitative approach emphasizing the physicochemical basis of physiology.