Interindividual Diet Variation Research Articles

Sex and Season Affect Individual‐Level Diet Variation in the Neotropical Marsupial Gracilinanus microtarsus (Didelphidae)

ABSTRACTIndividual‐level diet variation was investigated in Gracilinanus microtarsus, an insectivorous marsupial whose diet is affected by sex and season in the highly seasonal Brazilian Cerrado. To measure individual‐level diet variation, the diets of individual males and females were compared to that of their population in the warm‐wet and cool‐dry seasons using the proportional similarity index (PSi). This index varies from 1 (complete overlap between the individual i 's and population's diets) toward 0 (decreasing overlap). Mean PSi values were computed as a measure of the degree of interindividual diet variation (the larger the mean PSi value, the smaller the variation among individuals’ diets). Interindividual diet variation among females was similar between seasons, whereas among males it decreased from the warm‐wet to the cool‐dry season. Diet variation among males is probably reduced in the cool‐dry season because of constraints on food consumption generated by interactions between endogenous (physiological needs associated with high rates of body mass growth) and exogenous (food limitation) factors.

Diet variability and foraging strategies in brown trout (Salmo trutta): an analysis from subpopulations to individuals

Field studies were conducted to examine intra- and inter-individual diet variation in subpopulations of brown trout (Salmo trutta) at different spatial scales (between sites, between habitats (riffle and pool) within a site, and between individuals within a habitat) and different temporal scales (within subpopulations and within individuals over time) at four sites in the Glenfinish River, County Cork, Ireland. Electrofishing and stomach flushing techniques were used whereby fish larger than 85 mm were uniquely coded, allowing for repeated capture and diet analysis of individuals. A considerable degree of variation within and between subpopulations and individual diets was apparent. On the basis of novel and recent graphical models of feeding strategies, the trend was for a generalized strategy amongst trout subpopulations occupying riffles throughout most seasons, whilst specialization tended to be more frequent amongst trout occupying pools during summer and autumn. Using similarity indices and dendrograms, we illustrate that individual fish showed both feeding strategies within one habitat over time.