Indices of Food Type Preference by a Predator

The forage ratio and Ivlev's electivity index as measures of preference by predators of different prey or food types were shown by Jacobs to depend on their abundance. Modifications proposed by Jacobs are shown here to be similarly affected by the abundance. However, an index of the preference that is indeed independent of the prey abundance can be based on standardized forage ratios, standardized so that the forage ratios for the different prey species sum to one. Key words: index of preference, prey selection, food selection, predator–prey relationship