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

James Rosindell,Adriana Alzate,Thijs Janzen,Dries Bonte,Jonathan Belmaker,Rampal S. Etienne

doi:10.1111/geb.12899

Abstract

AbstractAimThe 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.LocationTropical Eastern Pacific.Major taxa studiedReef‐associated fishes.Time periodUnderlying records are from the 20th and 21st centuries.MethodsWe 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.ResultsStochastic 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 conclusionsNeutral 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.

Highlights

Comparing the richness gradients predicted by the model fitted to the range size distribution with habitat fragmentation to the em‐ pirical richness gradients along the Tropical Eastern Pacific (TEP) coast, we show that our model supports qualitatively the basic pattern of species richness gradients in the TEP, especially for species appearing outside the first 18% of the region (Figure 8)
Macroecologists have long sought to understand the large varia‐ tion in range sizes across species by correlating species ranges with other factors, such as traits, that are believed to influence range size
Our model shows that high dispersal rates generate distributions where many species have large ranges, whereas low dispersal leads to the emergence of a large proportion of small ranged species, consistent with a positive relationship between dispersal and range size

Summary

| INTRODUCTION

What is driving the large natural variation in the range size of spe‐ cies (Gaston, 2003)? only a few ecological processes should be important in determining a species’ range size: dispersal to a new habitat, successful colonization of that habitat and (avoid‐ ance of) local extinction (Brown & Kondric‐Brown, 1977; Gaston & He, 2002; Hanski, 1982; Holt & Gomulkiewicz, 1996; MacArthur & Wilson, 1967). We extend the neutral model of Hubbell (2001) to include spatially explicit dynamics and a more realistic speciation process (Rosindell, Cornell, Hubbell, & Etienne, 2010; Rosindell, Wong, & Etienne, 2008), both of which we expect to be important for a study of interspecific variation in range sizes. This mechanistic model provides a way to quantitatively assess how dispersal can influence species range size distributions, while at the. Our spatially explicit neutral model, which incorporates stochastic birth–death dynamics, speciation and dispersal, can generate testable predictions on range size distribution and species richness patterns

| METHODS

Findings

| DISCUSSION