APPENDIX 3: Methodology of Chivers' and Hladik's index |

To compare the dimensions of gastrointestinal tracts across species, the raw data obtained must be adjusted for body size (referred to as an allometric scaling; see Martin [1992] for an introduction to the topic of scaling). To determine the nature of such an adjustment, volume and surface area (of the components of the specimen GI tracts) were regressed (ordinary least squares) in logarithmic equations, fitting separate equations per dietary grouping against a measure of body size--

A logarithmic equation was used because of Kleiber's Law. Recall that Kleiber's Law relates metabolic energy (dependent variable) to body weight (a measure of size; independent variable), via an exponential/

To analyze the differences in gut morphology of faunivores vs. folivores, Chivers and Hladik next regressed the log of volume of (stomach + caecum + colon) versus the log of body size (body weight, estimated using a formula based on body length, cubed), separately, by dietary categories. The structure of the analysis--

The index of gut specialization is computed by taking the value, for a given body weight, of the frugivore regression line as 0, the folivore line as 1, and the faunivore line as -1. These values are then rescaled, via a non-

Thus the index of gut specialization is an effort to produce an index, that is, one single number, that measures the degree of "gut specialization" for an animal. That is, it is an index whose value varies according to the morphological adaptations displayed by each animal, i.e., whether the animal has the adaptations typically associated with folivores, faunivores, or frugivores.

*Return to beginning of article*

*Back to Research-Based Appraisals of Alternative Diet Lore*