Living at the Physiological Limits: Field and Maximum Metabolic Rates of the Common Shrew (Sorex araneus)

Shrews (genusSorex, small insectivorous mammals) are well known for their extremely high basal metabolic rates (BMRs) even when corrected for their small body size. We measured energy expenditure of the common shrew (Sorex araneus) under natural conditions (field metabolic rate [FMR]) by doubly labeled water method to test whether FMR is proportional to high BMR in this species. The study was performed in summer in northeastern Poland. In addition to the FMR, we also measured maximum metabolic rates induced by cold exposure and by intense activity (MMRCOLDand MMRRUN, respectively) to evaluate the aerobic reserve ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\mathrm{MMR}\,-\mathrm{FMR}\,$ \end{document} ) inS. araneus. This aerobic reserve was used as an indicator of the potential for metabolic constraints. The FMR averaged \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $2.31\pm 0.32$ \end{document} L CO2d−1(±SD) or \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $58.1\pm 8.0$ \end{document} kJ d−1in 8.2‐g animals. This figu