A proposal for occupancy-rank curves to read the dietary composition of animals: a device to avoid masking the information by averaging

Abstract

Although dietary compositions of animals are often expressed as average values for sample groups, there is variation even if the average values are similar. We propose an occupancy-rank curve, obtained by arranging the occupancies of a food component from the highest to the lowest values. We used data of the fecal compositions of sika deer Cervus nippon, Japanese serow Capricornis crispus, wild boar Sus scrofa, raccoon dog Nyctereutes procyonoides, red fox Vulpes vulpes, and Japanese marten Martes melampus. There were various types of curves. A pattern of high-value and high frequency was common in sika deer, Japanese serow, and wild boar. Various patterns were recorded in carnivoran species. Food categories of abundant but low quality often showed a pattern of low value and high frequency, while foods of lower abundance but high quality like mammals and birds often showed a pattern of high value and low frequency (L-shaped occupancy-rank curve). Fruits showed a pattern of high value and high frequency in martens’ feces. These patterns of curves reflected the food availability and needs of the animal side. We discuss the characteristics of these curves and recommend their use.