Assessing the relative potential ecological impacts and invasion risks of emerging and future invasive alien species

Abstract

Invasive alien species (IAS) cause myriad negative impacts, such as ecosystem disruption, human, animal and plant health issues, economic damage and species extinctions. There are many sources of emerging and future IAS, such as the poorly regulated international pet trade. However, we lack methodologies to predict the likely ecological impacts and invasion risks of such IAS which have little or no informative invasion history. This study develops the Relative Impact Potential (RIP) metric, a new measure of ecological impact that incorporates per capita functional responses (FRs) and proxies for numerical responses (NRs) associated with emerging invaders. Further, as propagule pressure is a determinant of invasion risk, we combine the new measure of Pet Propagule Pressure (PPP) with RIP to arrive at a second novel metric, Relative Invasion Risk (RIR). We present methods to calculate these metrics and to display the outputs on intuitive bi- and triplots. We apply RIP/RIR to assess the potential ecological impacts and invasion risks of four commonly traded pet turtles that represent emerging IAS: Trachemysscriptascripta, the yellow-bellied slider; T.s.troostii, the Cumberland slider; Sternotherusodoratus, the common musk turtle; and Kinosternonsubrubrum, the Eastern mud turtle. The high maximum feeding rate and high attack rate of T.s.scripta, combined with its numerical response proxies of lifespan and fecundity, gave it the highest impact potential. It was also the second most readily available according to our UK surveys, indicating a high invasion risk. Despite having the lowest maximum feeding rate and attack rate, S.odoratus has a high invasion risk due to high availability and we highlight this species as requiring monitoring. The RIP/RIR metrics offer two universally applicable methods to assess potential impacts and risks associated with emerging and future invaders in the pet trade and other sources of future IAS. These metrics highlight T.s.scripta as having high impact and invasion risk, corroborating its position on the EU list of 49 IAS of Union Concern. This suggests our methodology and metrics have great potential to direct future IAS policy decisions and management. This, however, relies on collation and generation of new data on alien species functional responses, numerical responses and their proxies, and imaginative measures of propagule pressure.

In a Pinch: Mechanisms Behind Potential Biotic Resistance Toward Two Invasive Crayfish by Native African Freshwater Crabs

“…The results presented here indicate that chelae closing force can be predicted by body mass and sex of the individual for all three decapod species but in order to correctly predict biotic resistance these must be validated further by assessing actual resource holding potential. Consequently, when trait based analysis should be complemented with other predictive assessments such as the comparative functional response and relative impact potential metrics (Dick et al, 2017;Dickey et al, 2018;South et al, 2019; but see Vonesh et al, 2017), but also with contest based experiments (Lopez et al, 2019;Zeng et al, 2019). Unfortunately, there is a severe paucity of data on the ecological impact of C. quadricarinatus but also on the basic ecology of Potamonautid crabs in southern Africa.…”

The Functional Response Ratio (FRR): advancing comparative metrics for predicting the ecological impacts of invasive alien species

“…Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Chlorine Gardens, Belfast BT9 5DL, Northern Ireland, UK e-mail: rcuthbert03@qub.ac.uk Cuthbert et al 2018a, b;Dickey et al 2018;Joyce et al 2019).…”

Impacts of non-native fishes under a seasonal temperature gradient are forecasted using functional responses and abundances

“…The identification of temporal shifts in impact across seasons and habitats in our study presents novel insights into invader impact. In many ecosystems, data on species abundances are still lacking, but since the relative impact potential metric enables impact predictions for species without invasion histories, we recommend more surveys to estimate abundance of potential invaders and/or for practitioners to incorporate other proxies (such as fecundity) into the metric (see Dickey et al 2018). Crucially, the ability of both Mozambique Tilapia and Western Mosquitofish to thrive in novel habitats highlights their ecological plasticity, and with an increase in environmental temperatures, their impacts may be intensified through changes to functional responses and fish abundances.…”

“…Methodological developments, which incorporate native/non-native species resource utilization across context-dependencies, have recently provided robust predictive tools for invasion science (Laverty et al 2015;Dick et al 2017;Dickey et al 2018;Cuthbert et al 2019). In particular, the functional response quantifies resource consumption as a function of resource density, and, in a predator-prey context, can quantify per capita ecological impacts of predators towards lower trophic groups (Holling 1959;Adams 1980;Dick et al 2013Dick et al , 2014Dick et al , 2017Alexander et al 2014;Cuthbert et al 2018).…”

“…The numerical response describes the consumer population-level response to changes in resource densities, while 'total response' can be defined as the multiplication of species' numerical response with functional response (Solomon 1949;Holling 1959). Given that the numerical response, in comparison to the functional response, is difficult to ascertain, consumer abundance has recently been proposed as a proxy for numerical response in the development of the 'impact potential' and 'relative impact potential' metrics (Dick et al 2017;Dickey et al 2018). The 'impact potential' is the product of functional responses and abundance of consumers, while the relative impact potential compares the impact of the invader to that of a native (Dick et al 2017).…”