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

Abstract

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.