Distinguishing between dispersal and vicariance: A novel approach using anti‐tropical taxa across the fish Tree of Life

Abstract

Abstract AimAnti‐tropical taxa are species split by the tropics into disjunct northern and southern populations. These distributions occur throughout the Tree of Life, but the mechanisms proposed to drive this pattern are debated and generally fit into two categories: dispersal and vicariance. Here, we quantitatively test the prevalence of dispersal and vicariance as plausible drivers of anti‐tropical marine distributions using intraspecific anti‐tropical marine fishes as a model system.LocationPrimarily Indo‐Pacific.TaxonMarine fishes.MethodsTo test between dispersal and vicariance in latitudinally disjunct marine fishes, we used an ecological niche modelling framework to predict the spatio‐temporal suitability of tropical habitats during contemporary and glacial time periods. Three different model configurations were used per species to test: (a) presence of contemporary tropical suitable habitat for northern populations, (b) the same for southern populations and (c) presence of tropical suitable habitat during the last glacial maximum for the entire species. These models were examined in an evolutionary context to determine if there was any phylogenetic signal in biogeographic predictions. Additionally, we tested if life history traits could account for biogeographic predictions.ResultsOur analyses resulted in 87 strongly supported models for 29 anti‐tropical fishes across the fish Tree of Life (northern population model, southern population model, and full species model for each taxon). Model projections consistently matched predictions of vicariance in 13 fishes and 10 fishes matched predictions of dispersal regardless of thresholding approach. We failed to find any phylogenetic signal for anti‐tropicality in general, or for dispersal and vicariant species specifically. Furthermore, dispersal and vicariant tendencies were not found to be correlated with life history traits.Main conclusionsThese data quantitatively support both dispersal and vicariance as active mechanisms driving disjunct distributions in marine systems and suggest that they occur stochastically across the fish Tree of Life. This novel approach for examining dispersal and vicariance hypotheses supports the species‐specific nature of biogeographic mechanisms structuring distributions, and that a “one‐size‐fits‐all” prediction for current and future species’ responses to environmental change is unlikely to be informative.