Invasive congeners differ in successional impacts across space and time.

Aaron S David,Peter Ruggiero,Sally D Hacker,Reuben G Biel,Eric W Seabloom,Phoebe L Zarnetske,Stefan Lötters

doi:10.1371/journal.pone.0117283

Abstract

Invasive species can alter the succession of ecological communities because they are often adapted to the disturbed conditions that initiate succession. The extent to which this occurs may depend on how widely they are distributed across environmental gradients and how long they persist over the course of succession. We focus on plant communities of the USA Pacific Northwest coastal dunes, where disturbance is characterized by changes in sediment supply, and the plant community is dominated by two introduced grasses – the long-established Ammophila arenaria and the currently invading A. breviligulata. Previous studies showed that A. breviligulata has replaced A. arenaria and reduced community diversity. We hypothesize that this is largely due to A. breviligulata occupying a wider distribution across spatial environmental gradients and persisting in later-successional habitat than A. arenaria. We used multi-decadal chronosequences and a resurvey study spanning 2 decades to characterize distributions of both species across space and time, and investigated how these distributions were associated with changes in the plant community. The invading A. breviligulata persisted longer and occupied a wider spatial distribution across the dune, and this corresponded with a reduction in plant species richness and native cover. Furthermore, backdunes previously dominated by A. arenaria switched to being dominated by A. breviligulata, forest, or developed land over a 23-yr period. Ammophila breviligulata likely invades by displacing A. arenaria, and reduces plant diversity by maintaining its dominance into later successional backdunes. Our results suggest distinct roles in succession, with A. arenaria playing a more classically facilitative role and A. breviligulata a more inhibitory role. Differential abilities of closely-related invasive species to persist through time and occupy heterogeneous environments allows for distinct impacts on communities during succession.

Highlights

Ecologists have sought to understand the processes and mechanisms of succession for well over a century (e.g. [1,2,3,4,5,6]) with a focus on the way in which individual species can shape community composition through time
Using plant community transect surveys from southwestern Washington, USA, we investigated how Ammophila cover and plant species richness changed over a 21-year period (1988–2009), during which time A. breviligulata became the dominant species at all transects (S1 Appendix)
Ammophila breviligulata occupied a wider span of chronosequence age and dune gradient compared to A. arenaria (Fig. 2; Bayesian model Gelman-Rubin diagnostic statistic < 1.01 for all parameters)

Summary

Introduction

Ecologists have sought to understand the processes and mechanisms of succession for well over a century (e.g. [1,2,3,4,5,6]) with a focus on the way in which individual species can shape community composition through time. Invasive plant species in particular are often uniquely positioned to influence succession because many are well-adapted to the disturbed conditions which initiate succession [10,11,12,13] In some cases, their high abundance or life-history strategies can make them ecosystem engineers, capable of transforming habitats and having long lasting effects after they are gone [14], especially if they are capable of changing the disturbance regime themselves [10,13]. Invasive species may give way to later successional species or persist in the community but cease to limit establishment of colonizing species (see facilitation and tolerance models in [4,16]). Different invasive species that play inhibitory or facilitative roles will have distinct effects on the ecological succession of the community

Methods

Results

Conclusion