Physics of chewing in terrestrial mammals

Emmanuel Virot,Christophe Clanet,Sunghwan Jung,Grace Ma

doi:10.1038/srep43967

Abstract

Previous studies on chewing frequency across animal species have focused on finding a single universal scaling law. Controversy between the different models has been aroused without elucidating the variations in chewing frequency. In the present study we show that vigorous chewing is limited by the maximum force of muscle, so that the upper chewing frequency scales as the −1/3 power of body mass for large animals and as a constant frequency for small animals. On the other hand, gentle chewing to mix food uniformly without excess of saliva describes the lower limit of chewing frequency, scaling approximately as the −1/6 power of body mass. These physical constraints frame the −1/4 power law classically inferred from allometry of animal metabolic rates. All of our experimental data stay within these physical boundaries over six orders of magnitude of body mass regardless of food types.

Highlights

Previous studies on chewing frequency across animal species have focused on finding a single universal scaling law
Fortelius proposed that the volume of food per chew is proportional to the animal mass and that the food per unit time is proportional to the metabolic rate[4], which scales as the 3/4 power of body mass according to Kleiber’s law[5,6,7]
Black circles denote data that we measured from Virginia Tech farms, boxed rectangles are data that we estimated from online sources and triangles are measurements reported by[8,9,13,14,15]

Summary

Introduction

Previous studies on chewing frequency across animal species have focused on finding a single universal scaling law. Gentle chewing to mix food uniformly without excess of saliva describes the lower limit of chewing frequency, scaling approximately as the −1/6 power of body mass. These physical constraints frame the −1/4 power law classically inferred from allometry of animal metabolic rates. The chewing frequency should be proportional to the −1/4 power of body mass (Mfchew ~ M3/4) This model was supported by experimental observations of fchew ~ M−0.20 4. Druzinsky observed a different scaling fchew ~ M−0.13 by including small animals over three orders of magnitude in body mass, and concluded that the chewing frequency might not directly be related to the metabolic rate[8]. In analogy to the chewing motion, by assuming that the speed of muscle contraction is proportional to the motion speed and by assuming an amplitude of motion proportional to the jaw length (with Ljaw ~ M1/3 as precised in the present article), the chewing frequency fchew ~ V/Ljaw is expected to lie between the −0.16 and −0.11 power of body mass

Methods

Results

Conclusion