Resource Partitioning between Two Piranhas ( and ) in an Amazonian Reservoir.

The exploitation of resources by closely related species with similar niches may be mediated by differences in activity patterns, which may vary in nycthemeral scale and seasonal scale. Piranhas and are Neotropical predators that occur sympatrically in many environments of the Amazon basin. To evaluate the strategies adopted by these two species in a restricted environment (a reservoir), nycthemeral and seasonal samples were made, identifying the composition of the diet and their activity patterns. A total of 402 specimens were collected: 341 and 61 . Both species fed themselves primarily on fish, with some seasonal variation being found in during the flood season, when plant material was consumed. There was considerable temporal overlap in the foraging behavior of the two species, although presented a bimodal pattern of abundance over the 24-hour cycle. was more active during the nighttime, between dusk and early morning, whereas was active throughout the nycthemeral cycle. These findings indicate low levels of competition between the two species, which allowed for a considerable overlap in nighttime foraging, following distinct nycthemeral patterns of foraging activity and allowing their coexistence.