Background: Predator assemblages can differ substantially in their top down effects on community composition and ecosystem function, but few studies have sought to explain this variation in terms of the phylogenetic distance between predators. The effect of a local predator assemblage will depend on three things: which predators tend to co-occur, how similar their prey preferences are, and how they interact with each other and the whole community. Phylogenetic distance between predators may correlate with each of these processes, either because related predators are more likely to share the same traits, and therefore have similar habitat and prey preferences, or because predators are more likely to compete, and therefore diverge in habitat and prey preferences. Therefore, the phylogenetic structure of predator assemblages could provide a unifying framework for predicting how predators will impact their prey and therefore any ecosystem functions mediated by their prey. Methods: We examined the effects of predators on macroinvertebrate food webs found in bromeliads, combining field observations, laboratory feeding trials and a manipulative experiment. We determined whether the phylogenetic distance between predators could explain: the co-observed occurrence of predator species among bromeliads, overlap in prey preferences under no-choice conditions, and effects of predator composition on prey survival, prey composition and ecosystem processes. Results: We found that phylogenetic distance does not predict either the co-occurrence of predator species nor the overlap in their prey preferences. However, our manipulative experiment showed that prey mortality decreased as the phylogenetic distance between predator species increased, reflecting antagonistic interactions among more distant predators. These effects of phylogenetic distance on prey mortality did not translate into effects on ecosystem function, as measured by rates of detrital decomposition and nitrogen cycling. Discussion: We conclude that the effects of predator phylogenetic diversity on the bromeliad food web are primarily determined by antagonistic predator-predator interactions, rather than habitat distribution or diet overlap. This study illustrates the potential of a phylogenetic community approach to understanding food webs dynamics.