Invader Relative Impact Potential: a new metric to understand and predict the ecological impacts of existing, emerging and future invasive alien species

Jaimie T A Dick ,Melanie J Hatcher,Anthony Ricciardi,Ryan J Wasserman,J Robert Britton,Peter B Banks,Calum Macneil,Paula J Rosewarne,Bruce R Ellender,Ciaran Laverty,Steven Crookes,Paul J Mensink,Nigel G Taylor,Meng Xu,Marcin R Penk,Pieter Boets,Alison M Dunn,Jack J Lennon,Mhairi E Alexander,Vincent Médoc,Hugh J Macisaac,David C Aldridge,Frances E Lucy,Jennifer A Dodd,Daniel Barrios-O’neill ,Olaf L F Weyl ,J M Caffrey

doi:10.1111/1365-2664.12849

Abstract

Summary Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardized metrics that reliably predict the likelihood and degree of impact of such invaders (i.e. measurable changes in populations of affected species). This need is especially pressing for emerging and potential future invaders that have no invasion history. Such a metric would also ideally apply across diverse taxonomic and trophic groups. We derive a new metric of invader ecological impact that blends: (i) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR × NR), with; (ii) the ‘Parker–Lonsdale equation’ for invader impact, where Impact = Range × Abundance × Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR × Abundance. The RIP metric is an invader/native ratio, where values >1 predict that invader ecological impact will occur, and increasing values above 1 indicate increasing impact. In addition, the invader/invader RIP ratio allows comparisons of the ecological impacts of different invaders. Across a diverse range of trophic and taxonomic groups, including predators, herbivores, animals and plants (22 invader/native systems with 47 individual comparisons), high‐impact invaders were significantly associated with higher FRs compared to native trophic analogues. However, the RIP metric substantially improves this association, with 100% predictive power of high‐impact invaders. Further, RIP scores were significantly and positively correlated with two independent ecological impact scores for invaders, allowing prediction of the degree of impact of invasive alien species with the RIP metric. Finally, invader/invader RIP scores were also successful in identifying and associating with higher impacting invasive alien species. Synthesis and applications. The Relative Impact Potential metric combines the per capita effects of invaders with their abundances, relative to trophically analogous natives, and is successful in predicting the likelihood and degree of ecological impact caused by invasive alien species. As the metric constitutes readily measurable features of individuals, populations and species across abiotic and biotic context‐dependencies, even emerging and potential future invasive alien species can be assessed. The Relative Impact Potential metric can be rapidly utilized by scientists and practitioners and could inform policy and management of invasive alien species across diverse taxonomic and trophic groups.

Highlights

In recent decades, invasion ecology has advanced substantially in providing understanding of the ecological impacts of invasive alien species, here defined as measurable changes in populations of affected species
Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardised metrics that reliably predict the likelihood and degree of impact of such invaders
We derive a new metric of invader ecological impact that blends: (1) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR × NR), with; (2) the “Parker equation” for invader impact, where Impact = Range ×

Summary

Introduction

Invasion ecology has advanced substantially in providing understanding of the ecological impacts of invasive alien species, here defined as measurable changes in populations of affected species (see Ricciardi & Cohen 2007; Simberloff et al 2013; Caffrey et al 2014; Jeschke et al 2014; Kumschick et al 2015). Beyond broad generalisations such as these, the search for species traits (e.g. body size, fecundity, behaviour) that reliably predict invasion success and ecological impact has generally failed (Parker et al 2013; Dick et al 2014) This has hindered those who require better risk assessments for invaders since, invasion history can inform likely future impacts of an invader (Kulhanek et al 2011; Ricciardi et al 2013; Blackburn et al 2014), there is currently no way of predicting the ecological impacts of emerging and future potential invaders that have no invasion history. Key criteria for listing such species are ostensibly based on “available scientific evidence” and that the species is “likely to have a significant adverse impact on biodiversity or the related ecosystem services” These lists are dynamic at the Member State and EU levels and there is an urgent need to identify and prioritise IAS of regional and global concern. Whilst horizon scanning has a good record in predicting new and damaging arrivals (Roy et al 2014), and such exercises are often based on “expert opinion” coupled with best available evidence (see Blackburn et al 2014), we still need a quantitative methodology to rapidly assess potential impacts of invaders that can be applied by stakeholders and practitioners

Results

Discussion

Conclusion