Exploring trophic role similarity and phylogenetic relatedness between species in food webs

Understanding the mechanism shaping species assemblages is a fundamental goal in ecology. In the past, two hypotheses have been suggested. One is the filtering hypothesis, where environmental factors select for species of similar traits such that they co-occur in similar niches. The other is the competitive exclusion hypothesis, where related species are driven far apart by competition such that they overdisperse across various niches. Here, we investigate the relationship between species assemblages and their phylogenetic relatedness from a network perspective by using five separate ecosystems ranging from oceans to an inland lake. We quantified the similarity in species network positions in a food web and clustered them into different trophic role groups; using an online database, we quantified their phylogenetic distances. We then investigated whether related species tend to underdisperse or overdisperse across different trophic role groups. In general, our results suggest that the environmental filtering process is the dominant force shaping the species assemblage of those ecosystems. However, there are some possible cases where related species are driven by competition such that they evolve to adopt different trophic roles in relatively closed ecosystems.