On the RIP: using Relative Impact Potential to assess the ecological impacts of invasive alien species

James W E Dickey,Erfan Fadaei,Monica Mccard,Josie South,Frances E Lucy,Olaf L F Weyl,Ryan J Wasserman,Joe Caffrey,Ciara L O Mcglade,Hugh J Macisaac,Ciaran Laverty,J Robert Britton,Neil Reid,Kate Crane,Ross N Cuthbert,Anthony Ricciardi,Keith D Farnsworth,Jaimie T A Dick,Neil E Coughlan,Chunju Xu ,Stefanie M H Ismar‐Rebitz ,Patrick Joyce ,Matthew L Julius

doi:10.3897/neobiota.55.49547

Abstract

Invasive alien species continue to arrive in new locations with no abatement in rate, and thus greater predictive powers surrounding their ecological impacts are required. In particular, we need improved means of quantifying the ecological impacts of new invasive species under different contexts. Here, we develop a suite of metrics based upon the novel Relative Impact Potential (RIP) metric, combining the functional response (consumer per capita effect), with proxies for the numerical response (consumer population response), providing quantification of invasive species ecological impact. These metrics are comparative in relation to the eco-evolutionary baseline of trophically analogous natives, as well as other invasive species and across multiple populations. Crucially, the metrics also reveal how impacts of invasive species change under abiotic and biotic contexts. While studies focused solely on functional responses have been successful in predictive invasion ecology, RIP retains these advantages while adding vital other predictive elements, principally consumer abundance. RIP can also be combined with propagule pressure to quantify overall invasion risk. By highlighting functional response and numerical response proxies, we outline a user-friendly method for assessing the impacts of invaders of all trophic levels and taxonomic groups. We apply the metric to impact assessment in the face of climate change by taking account of both changing predator consumption rates and prey reproduction rates. We proceed to outline the application of RIP to assess biotic resistance against incoming invasive species, the effect of evolution on invasive species impacts, application to interspecific competition, changing spatio-temporal patterns of invasion, and how RIP can inform biological control. We propose that RIP provides scientists and practitioners with a user-friendly, customisable and, crucially, powerful technique to inform invasive species policy and management.

Highlights

In recent decades, the tourism, agriculture, aquaculture, horticulture and pet trades, among others, have been boosted by new globalised transport networks (Hulme 2009, Seebens et al 2018), facilitating novel pathways for invasive alien species (IAS; invasive species) to spread and establish (Zieritz et al 2016, Seebens et al 2019)
We demonstrate the versatility of the metrics across abiotic and biotic contexts, including the prediction of climate change effects on invasive species impacts, how native species and established invaders can offer biotic resistance, how evolution can affect impact, aspects of interspecific competition, spatio-temporal patterns of invasion and impact, and the assessment of biological control agent efficacy
An IP value by itself offers limited insight, but we relate the IP of an invasive species to the IP of a trophically analogous native, giving the “Relative Impact Potential” of the invader (RIP) as: RIP