History of co-occurrence shapes predation effects on functional diversity and structure at low latitudes

Abstract

The intensity of biotic interactions is hypothesized to increase towards the equator. Predation can have a stronger effect on prey composition, biomass and taxonomic diversity in tropical regions compared to higher latitudes. Whether predation also shapes patterns of functional diversity and structure of prey communities, however, has rarely been explored across a latitudinal gradient. History of co-occurrence between predators and prey may also shape the outcome of the interaction, and increased novelty of introduced prey may lead to stronger trait responses. We investigated the influence of predation on trait responses of prey communities across 12 sites in four regions, from the sub-arctic to the tropics, using a field experiment in invaded coastal habitats. Prey communities experienced ambient or reduced predation pressure during assembly, and the effect of predation on functional diversity and structure of whole communities as well as their native and introduced components was assessed. Overall, predation increased functional diversity in the tropics, but effects were evident for introduced species only. Predation also shaped functional structure of low-latitude communities, but effects were strongest for native species in subtropical Mexico and introduced species in tropical Panama. Key traits driving shifts in functional structure were related to palatability and reproduction. In the tropics, the strong predation present under ambient conditions reduced the abundance of palatable traits in introduced prey relative to low-predation treatments, while in the subtropics, ambient predation increased the abundance of palatable traits in native prey. Reproductive traits that require high parental or energetic investment were favoured in low-predation treatments at both low-latitude regions. In summary, predation had a stronger influence on trait responses of prey communities at lower latitudes where biotic interactions are expected to be more intense, but changes in functional diversity and structure hinged on co-occurrence histories of local predators with native or introduced prey. This study provides one of the first examinations of the effects of predation on functional trait responses of prey communities across a latitudinal gradient.