An Assessment of Diet-Overlap Indexes

Abstract

Dietary components of Mississippi silversides (Menidia audens) and juvenile largemouth bass (Micropterus salmoides) were tabulated by the percentage of occurrence, the percentage of total number, the percentage of total volume, the average of the volume percentages, and the relative importance index. Each of these diet measures was then applied to three published overlap indexes and a correlation method (Spearman rank correlation coefficient). Each measure of diet resulted in different values for a particular overlap index (0.04 to 1.06) and for the Spearman rank correlation coefficient (0.06 to −0.30). Likewise, each index gave different values for different diet measures. Of these indexes and diet measures, the Schoener index based on the average of volume percentages is recommended with reservations.