Use of Geometric Forms to Estimate Volume of Invertebrates in Ecological Studies of Dietary Overlap

Abstract

Abstract Studies of diet overlap of insectivores, especially lizards, have been important for the development of much ecological theory. However, measures of overlap, usually based on dietary volumes, vary widely among studies. Most researchers estimated the volumes of prey in stomach contents subjectively or attempted to reconstruct the volume of individual prey items from linear measurements of length (L), width (W) and/or height (H), or from mass. We studied the relationship between indices of volume based on indirect measures and direct measures of volume by fluid displacement for a collection of arthropods that simulated the diet of a generalist lizard. For each individual arthropod, we calculated the proportional error [(measured volume—estimated volume)/measured volume)] for each estimation method. For individual large insects, there were significant differences between orders in the proportional error for all methods. The methods based on linear measurements had only weak relationships (r2 ≤ 0.4 i...