Seasonal changes at population and individual levels in the diet of juvenile catfish in a Neotropical floodplain

Intra-population variation in niches is a widespread phenomenon in animal populations, but, in fish, this knowledge is still scarce. Here, we investigated the population and between-individuals variations in the diet of juvenile Pimelodus maculatus, in dry and wet seasons, in a floodplain from Pantanal, Brazil. A significant difference was verified, being that during the dry season, the diet was mainly composed of fish remains and detritus, while in the wet season, the main food item was fruit/seed. Values of trophic niche breadth were low and seasonally similar. High values of diet variation between individuals and low values of clustering degree, as well as the nestedness metric based on overlap and decreasing fill (NODF), were found. This combination showed that there are generalist and specialist individuals within the population, in which the diet of the last is composed of a subset of food items consumed by generalists. In addition, the median individual specialization index was statistically lower in the wet season, suggesting that individuals could be more diet specialists during this period. Thus, the seasonality in the food resources supply seems to be the main mechanism driving diet variations of juvenile P. maculatus at both population and individual level.