Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach

Abstract

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical 'functional response' (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of 'snapshot' assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses, within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive 'bloody red shrimp' Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could -013-0550-8 have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the 'enemy release' and 'biotic resistance' hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts.Biol Invasions (2014) 16:735-753 DOI 10.1007/s10530

Assessing the ecological impacts of invasive species based on their functional responses and abundances

“…However, recent comparisons of invader and native functional responses (FRs) have often yielded excellent explanatory and predictive power of invader impact on native prey populations (Alexander et al 2014a, b;Dick et al 2013Dick et al , 2014Dick et al , 2017, and this has recently been extended to damaging herbivorous invaders (e.g. golden apple snail; Xu et al 2016).…”

“…In particular, scientists and practitioners have been frustrated by a lack of predictive methodologies to reliably identify potentially damaging invaders and their likely degree of ecological impact (i.e. measureable changes in populations of affected species; see Dick et al 2014). Presently, invaders may be prioritised for management based on their documented impacts elsewhere, that is, their invasion history (Kulhanek et al 2011;Ricciardi et al 2013); however, this precludes the assessment of novel or potential invaders, or those for which relevant data are missing or scarce.…”

“…This has, however, received little application in invasion ecology, in particular because measures of per capita effects have been lacking . However, as detailed by Dick et al (2013Dick et al ( , 2014, the per capita effect of an invasive species may be quantified by its 'Functional Response' (FR), a classic metric used in ecology to describe and quantify the per capita effect of a predator on its prey as the density of the prey increases (Solomon 1949;Holling 1959a,b), but which can be applied across all taxonomic and trophic groups in any consumer/resource interaction (Dick et al , 2017. Together with the 'Numerical Response' (NR), which describes the change in a predator population as the density of prey increases, this forms the 'Total Response' (TR), such that:…”

“…We supplement this with FR data from N. melanostomus and another native comparator, the mottled sculpin Cottus bairdi, towards Gammarus prey (see Dubs and Corkum 1996), again with available abundance data. Then, we repeat this exercise with the highly invasive and ecologically damaging topmouth gudgeon, Pseudorasbora parva, an Asian fish which has also invaded European waters (Britton et al 2010;Gozlan et al 2010), and its native analogue the European bitterling, Rhodeus amarus, towards two prey species, Daphnia magna and Chironomus spp.. We stress that this exercise is to compare and quantify the impacts of the invaders on the broader prey community and it is not intended to examine any interaction, such as competition, among the invader and native fishes (but see Dick et al 2014Dick et al , 2017. Amphipods and isopods were chosen as common prey items of these fish species (see Welton et al 1991;Dubs and Corkum 1996;Corkum et al 2004;Barton et al 2005).…”

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).…”