The article by Jürgen Jacobs, titled "A Modification of the Forage Ratio and Ivlev's Electivity Index," addresses the limitations of the Forage Ratio (FR) and Ivlev's Electivity Index (E) in quantifying food selection. These indices are commonly used but are influenced by the relative abundances of food types in the environment, making them unreliable for comparing food types with different abundances or studying the relationship between selection and abundance. To overcome these limitations, Jacobs proposes modified versions of both indices that are based on the rates of decrement (mortality) of food due to feeding. The modified indices are independent of the relative abundance and provide a more accurate measure of selective feeding. Selective feeding is defined as the consumption of co-occurring food sources at different rates, with positive selection occurring when the rate of mortality of one food type is higher than that of another. The Forage Ratio (FR) is defined as the ratio of the fraction of a given food type in the feeder's ration to the fraction in the environment, while Ivlev's Electivity Index (E) is the relative difference between these fractions. Both indices can vary over a wide range, but they are affected by the relative abundance of the food types. Jacobs demonstrates that the modified indices are equivalent to the original indices in terms of their mathematical relationships, but they are more robust in situations where the relative abundances of food types are not constant. This modification ensures that the indices provide a more reliable measure of selective feeding, regardless of the relative abundances of the food types in the environment.The article by Jürgen Jacobs, titled "A Modification of the Forage Ratio and Ivlev's Electivity Index," addresses the limitations of the Forage Ratio (FR) and Ivlev's Electivity Index (E) in quantifying food selection. These indices are commonly used but are influenced by the relative abundances of food types in the environment, making them unreliable for comparing food types with different abundances or studying the relationship between selection and abundance. To overcome these limitations, Jacobs proposes modified versions of both indices that are based on the rates of decrement (mortality) of food due to feeding. The modified indices are independent of the relative abundance and provide a more accurate measure of selective feeding. Selective feeding is defined as the consumption of co-occurring food sources at different rates, with positive selection occurring when the rate of mortality of one food type is higher than that of another. The Forage Ratio (FR) is defined as the ratio of the fraction of a given food type in the feeder's ration to the fraction in the environment, while Ivlev's Electivity Index (E) is the relative difference between these fractions. Both indices can vary over a wide range, but they are affected by the relative abundance of the food types. Jacobs demonstrates that the modified indices are equivalent to the original indices in terms of their mathematical relationships, but they are more robust in situations where the relative abundances of food types are not constant. This modification ensures that the indices provide a more reliable measure of selective feeding, regardless of the relative abundances of the food types in the environment.