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

• DOI: 10.1111/1365-2664.12849
• Publication Date: 2016-12-10T12:47:08Z
• Authors: Jaimie T.A. Dick; Ciaran Laverty; Jack J. Lennon; Daniel Barrios‐O'...; Paul J. Mensink; J. Robert Britton; Vincent Médoc; Pieter Boets; Mhairi E. Alexander; Nigel G. Taylor; Alison M. Dunn; Melanie J. Hatcher; Paula J. Rosewarne; Steven Crookes; Hugh J. MacIsaac; Meng Xu; Anthony Ricciardi; Ryan J. Wasserman; Bruce R. Ellender; Olaf L.F. Weyl; Frances E. Lucy; Peter B. Banks; Jennifer A. Dodd; Calum MacNeil; Marcin R. Penk; David C. Aldridge; Joseph M. Caffrey
• Keywords: Composite material; 0106 biological sciences; 570; Metric (unit); relative impact potential metric; Impact of Pesticides on Honey Bee Health; Economics; Invasive Species; Abundance (ecology); maximum feeding rate; Plant Science; species abundance; 01 natural sciences; Trophic level; Agricultural and Biological Sciences; Range (aeronautics); functional response; Introduced species; Biology; invasive alien species; Ecological Impact of Invasive Species on Islands; Ecology; Invasive species; taxonomic and trophic groups; numerical response; 500; risk assessment; Life Sciences; prediction; 15. Life on land; Materials science; Operations management; FOS: Biological sciences; Insect Science; ecological impacts; Environmental Science; Physical Sciences; Herbivore; Botanical Insecticides in Agriculture and Pest Management

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.