The Flooding Gradient Affects Seed Dispersal by Fruit‐Eating Fishes in Amazonian Whitewater Floodplain Forests

ABSTRACT Seed dispersal by fish (ichthyochory) plays a key role in the structure of Amazonian floodplain forests. The hydrological regime creates broad variability in flooding depth and duration, and as a result, the tree species richness increases as the flooding depth and duration decrease. This flooding gradient leads to habitats, such as low várzea (LV) and high várzea (HV) forests, corresponding to flood durations of 50–230 and ≤ 50 days year −1 , respectively. Our study evaluated the fruit consumption by fish and the seed dispersal potential along the flood gradient. We tested the hypothesis that the role of fish as seed dispersers varies between LV and HV and that the seed dispersal network is modular and nested. We expect to find a greater contribution of fish to seed dispersal in LV forests. Based on fish collections from Paciência Island and a literature review, we identified 40 fish species that consumed fruits and seeds of 188 tree species in Amazon floodplains. Of these, 114 tree species were recorded on Paciência Island or in other floristic inventories along the flood gradient in várzea forests. When we considered only the tree species with distribution restricted to each forest type (LV or HV), the species richness of fruits and seeds consumed by fish was greater in LV forest. The ichthyochory network showed a significant nested structure. Although most forest inventories have found greater tree species richness in the HV, our study highlights the importance of fish consumption of fruit and seeds in LV forests.