Structural complexity and turbidity do not interact to influence predation rate and prey selectivity by a small visually feeding fish

Structural complexity and turbidity decrease predation by respectively providing a physical and visual refuge for prey. It is still unclear how the covariance between these variables could drive predation and prey selectivity. We experimentally simulated scenarios that are temporally observed in floodplain rivers. In the experiments, we crossed different prey types, structural complexity and turbidity. We hypothesised that the negative relationship between structural complexity and predation would become stronger with a linear increase in the turbidity level and that an increase in structural complexity and in turbidity would change prey selectivity from a selective to a random pattern. Our results showed that the effects of structural complexity and turbidity on predation may not covary; a linear increase in turbidity did not significantly change the patterns of predation or prey selectivity. In contrast, structural complexity significantly reduced prey consumption according to prey size. We argue that areas with low macrophyte cover may provide an efficient refuge for smaller prey, whereas an efficient refuge for larger prey can be attained only in areas with high macrophyte cover. In highly complex habitats, specificity in prey consumption is precluded because both prey species can hide amid the interstices of the macrophytes, leading to random prey selectivity.