Is the enhanced dispersal rate seen at invasion fronts a behaviourally plastic response to encountering novel ecological conditions?

Lachlan J Pettit,Richard Shine,Matthew J Greenlees

doi:10.1098/rsbl.2016.0539

Abstract

As a population expands into novel areas (as occurs in biological invasions), the range edge becomes dominated by rapidly dispersing individuals-thereby accelerating the rate of population spread. That acceleration has been attributed to evolutionary processes (natural selection and spatial sorting), to which we add a third complementary process: behavioural plasticity. Encountering environmental novelty may directly elicit an increased rate of dispersal. When we reciprocally translocated cane toads (Rhinella marina) among study sites in southern Australia, the transported animals massively increased dispersal rates relative to residents (to an extent similar to the evolved increase between range-core versus invasion-front toad populations in Australia). The responses of these translocated toads show that even range-core toads are capable of the long-distance dispersal rates of invasion-front conspecifics and suggest that rapid dispersal (rather than evolving de novo) has simply been expanded from facultative to constitutive expression.

Highlights

The speed at which invasive species spread into new areas often increases through time because traits that enhance dispersal rate accumulate in the invasion vanguard [1]
We used data from the study of Alford et al [10] based on 43 toads tracked for 6 – 56 days in the species’ Australian range-core in northeastern QLD in 1992 – 1993, and 30 range-edge toads tracked on a coastal floodplain in the Northern Territory (NT) in 2005
The movement parameters of translocated toads differed from resident toads, to a similar degree as range-edge toads differ from range-core toads

Summary

Introduction

The speed at which invasive species spread into new areas often increases through time because traits that enhance dispersal rate accumulate in the invasion vanguard [1]. The accumulation of dispersal-enhancing traits at expanding range edges has been attributed to evolutionary processes; natural selection (via fitness benefits to faster dispersal [6]) and spatial sorting (via the non-adaptive concentration of ‘fast-dispersal’ alleles through successive founder events at the leading edge in each generation [7,8]). Rates of dispersal may increase as a direct (behaviourally plastic) response to encountering novel environments at the expanding population edge. Lacking information on the distribution of critical resources (food, water, refuge from predators and abiotic extremes), an individual that finds itself in uncharted waters may benefit from increasing its dispersal rate [9]

Methods

Results

Conclusion