A simple spatially explicit neutral model explains the range size distribution of reef fishes

Aim The great variation in range sizes among species has fascinated ecologists for decades. Reef-associated fish species live in highly spatially structured habitats and adopt a wide range of dispersal strategies. We consequently expect species with greater dispersal ability to occupy larger ranges. However, empirical evidence for such a positive relationship between dispersal and range size remains scarce. Here, we unveil the role of dispersal on the range size distribution of reef-associated fishes using empirical data and a novel spatially explicit model. Location Tropical Eastern Pacific. Major taxa studied Reef-associated fishes. Time period Underlying records are from the 20th and 21st centuries. Methods We estimated range size distributions for all reef-associated fishes separated into six guilds, each with different dispersal abilities. We used a one-dimensional spatially explicit neutral model, which simulates the distribution of species along a linear and contiguous coastline, to explore the effect of dispersal, speciation and sampling on the distribution of range sizes. Our model incorporates biologically important long-distance dispersal events with a fat-tailed dispersal kernel and also adopts a more realistic gradual protracted speciation process than originally used in neutral theory. We fitted the model to the empirical data using an approximate Bayesian computation approach, with a sequential Monte Carlo algorithm. Results Stochastic birth, death, speciation and dispersal events alone can accurately explain empirical range size distributions for six different guilds of tropical, reef-associated fishes. Variation in range size distributions among guilds are explained purely by differences in dispersal ability with the best dispersers being distributed over larger ranges. Main conclusions Neutral processes and guild-specific dispersal ability provide a general explanation for both within- and across-guild range size variation. Our results support the theoretically expected, but empirically much debated, hypothesis that high dispersal capacity promotes the establishment of large range size.