The role of deterministic factors and stochasticity on the trophic interactions between birds and fish in temporary floodplain ponds

Trophic interaction between contiguous habitats is an understudied area despite their ecological importance. We tested four hypotheses related to the visit of foraging birds in temporary ponds inhabited by fish: the local characteristics of ponds influence the (1) abundance and (2) composition of foraging birds; (3) the number of foraging bird visits increases in higher fish abundance; and (4) pond characteristics lead to a non-random spatial structure of fish assemblage. We studied 18 temporary ponds in the floodplain area of Pantanal (center-west Brazil), where we measured environmental variables (pond size, depth, macrophyte coverage, and forest canopy coverage), recorded the number of foraging birds and sampled fish. Foraging birds' abundance and composition were mainly influenced by forest canopy coverage and pond size, corroborating our first and second hypotheses. The hypotheses 3 and 4 were rejected. Fish abundance was not correlated with higher number of visits of foraging birds and fish distribution was random. Local environmental variables did not affect significantly fish richness and composition. Our results suggest that the abundance of foraging birds and fish presence are determined by different assembly processes (deterministic vs. random), which may limit ponds selection by birds due to the uncertainty in fish distribution and ephemeral nature of temporary ponds.