Altitudinal Effects on Water Fluxes of Deer Mice: A Physiological Application of Structural Equation Modeling with Latent Variables

Abstract

An animal's physiological capacities, the environment it inhabits, and their interaction determine the animal's water flux (turnover rate). The proximate physiological determinants of water flux (e.g., urinary concentrating ability, evaporative water loss, dietary water content, and oxidative water yield) are well understood. Excluding effects of diet type (e.g, herbivory vs. granivory) and free water availability (e.g., xeric vs. mesic habitats), ecological and environmental effects on water fluxes are less well known. We used labeled water to study the effects of large altitudinal differences (~ 3,000 m) on water fluxes of free-living deer mice. In absolute terms, high-altitude mice had higher water fluxes and field metabolic rates, but were smaller, than low-altitude mice. A multiple regression with altitude coded as a dummy variable indicated that after adjusting for mass and field metabolic rate, altitude had no effect on water flux. However, using mass and field metabolic rate as independent variabl...