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

Abstract

Summary1. 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. 2. 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 9 NR), with; (ii) the 'Parker-Lonsdale equation' for invader impact, where Impact = Range 9 Abundance 9 Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR 9 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. 2017, 54, 1259-1267 doi: 10.1111/1365-2664.12849 3. 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. 4. 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. 5. 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. Journal of Applied Ecology

Effects of acute and chronic temperature changes on the functional responses of the dogfish Scyliorhinus canicula (Linnaeus, 1758) towards amphipod prey Echinogammarus marinus (Leach, 1815)

“…Prediction of consumer impact has been assessed through the use of comparative functional response analyses (Smout et al 2010;Alexander et al 2012;Alexander et al 2013;Dick et al 2013;Dick et al 2014;Laverty et al 2014;Wasserman et al 2016a, b;Dick et al 2017). This method has been pioneered for the prediction of invasive species impacts in comparison to trophically analogous native species Paterson et al 2015;Dick et al 2017).…”

“…This method has been pioneered for the prediction of invasive species impacts in comparison to trophically analogous native species Paterson et al 2015;Dick et al 2017). It is particularly useful in assessing ecological impact under a number of abiotic contexts (e.g.…”

“…Within these response types, it is also possible to quantify the associated parameters of attack rate, handling time and maximum feeding rates (Juliano 2001;Dick et al 2013). Functional response analysis therefore presents itself as a robust assessment method whereupon ecological impact can be explained and predicted across numerous biotic and abiotic contexts Dick et al 2017).…”

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“…This species might be a specific non-native fish for which there is minimal extant information on their impacts in wild situations and thus the experiment aims to predict their potential impacts for invasive species that can be used as the basis of invasion impact assessments (Copp et al, 2009(Copp et al, , 2016. Alternatively, the focal non-native fish can be used as a model that is representative of a wider range of nonnative taxa that enables conclusions to be drawn on impact predictions that are relevant beyond the study system (Dick et al, 2017a). Irrespective of the focal non-native fish being used in the study, the ethos of the three 'R's of animal experimentation ('replace, reduce and refine') need to be embedded within experimental designs.…”

“…the comparisons between invasive and trophically analogous native species of the relationship between the resource use of a consumer and its availability, can predict invasion impacts on prey populations . By their description of the resource use of the species over a range of resource availabilities, these experiments provide foraging metrics capable of testing differences between the species, such as attack rates (a), food handling times (h) and maximum consumption rates (Dick et al, , 2017a. There is then potential for testing of the likely population-level outcomes of invasions for affected species .…”