Dispersal evolution in currents: spatial sorting promotes philopatry in upstream patches

R L Allgayer,L Lancaster,G Bocedi,P J Wright,P G Fernandes,A Scarpa,J M J Travis

doi:10.1111/ecog.05315

Abstract

Substantial literature is devoted to understanding dispersal evolution, but we lack theory on how dispersal evolves when populations inhabit currents. Such theory is required for understanding connectivity in freshwater and marine environments; moreover, many animals, fungi and plants rely on wind‐based dispersal, but the effects of currents on dispersal evolution in these organisms is unknown. We develop an individual‐based model for evolution of dispersal probability along a linear environment with a unidirectional current. Even a slight current substantially reduces overall emigration probability compared to no current. Under stronger currents, emigration can be drastically reduced, especially in the upstream patches. When introducing rare long‐distance dispersal that is not subject to the current, higher emigration probabilities evolve and the spatial variability in emigration propensity along the stream is reduced. Our results provide an alternative solution to the long debated ‘drift paradox' concerning the loss of individuals from upstream populations due to advective forces. A combination of natural selection and spatial sorting generates and maintains downstream gradients in dispersal propensity, where individuals from upstream populations tend to be substantially more philopatric. This is likely to have major implications for ecological and genetic connectivity that will impact effective management strategies for populations inhabiting currents.

Highlights

Understanding the role of currents, whether in air or water, is important in many ecological applications such as habitat restoration, predicting the spread of invasive species or species expanding their ranges into newly suitable climate space, and estimating connectivity loss due to anthropogenic impacts (Levine 2008)
While the effects of currents on dispersal have been investigated for decades (Müller 1954, Waters 1972, Anholt 1995, Speirs and Gurney 2001, Levine 2008), the topic remains largely unexplored from an evolutionary perspective
Our results show a striking effect of currents on dispersal evolution that can be strong relative to several key drivers of dispersal

Summary

Introduction

Understanding the role of currents, whether in air or water, is important in many ecological applications such as habitat restoration, predicting the spread of invasive species or species expanding their ranges into newly suitable climate space, and estimating connectivity loss due to anthropogenic impacts (Levine 2008). The problems associated with dispersal in currents in terms of population persistence have been well-documented, focusing mainly on river and stream systems (Müller 1954, Waters 1972, Anholt 1995, Speirs and Gurney 2001, Pollux et al 2005) Dispersal in these systems is considered to be more restricted than in marine or terrestrial systems as there are more well-defined corridors imposed by the landscape (Fagan 2002, Bohonak and Jenkins 2003, Pollux et al 2005, PazVinas et al 2015), especially for fully aquatic species that do not have the option of aerial dispersal. One point of agreement is that without any mechanism to ensure even infrequent upstream movement of individuals, any slight advective forcing (i.e. involuntary downstream movement) would eventually move the population downstream like a moving wave and cause extinction of upstream patches. Speirs and Gurney (2001) speculated that a population could reduce individuals’ advection probability by reducing the amount of time spent in the active current to the point that small amounts of random movement alone could be sufficient to retain upstream populations, but did not model this possibility explicitly (Speirs and Gurney 2001)

Methods

Results

Conclusion