Superior predatory ability and abundance predicts potential ecological impact towards early-stage anurans by invasive \u2018Killer Shrimp\u2019 (Dikerogammarus villosus)

Daniel A Warren,Stephanie J Bradbeer,Alison M Dunn

doi:10.1038/s41598-021-82630-5

Abstract

Invasive alien species negatively impact upon biodiversity and generate significant economic costs worldwide. Globally, amphibians have suffered considerable losses, with a key driver being predation by large invasive invertebrate and vertebrate predators. However, there is no research regarding the potential ecological impact of small invertebrate invaders. The invasive freshwater amphipod Dikerogammarus villosus can act as a top predator capable of displacing native amphipods and preying heavily upon a range of native species. Listed as one of Europe’s top 100 worst invaders, D. villosus has significantly restructured freshwater communities across western Europe and is expected to invade North America in the near future. Here we explore the ecological impact of invasive D. villosus upon UK native and invasive amphibians (Rana temporaria and Xenopus laevis respectively) using the “Relative Impact Potential” (RIP) metric. By combining estimations of per capita effects (i.e. functional response; FR) and relative field abundances, we apply the RIP metric to quantify the potential ecological impact of invasive D. villosus upon embryonic and larval amphibian prey, compared to the native amphipod Gammarus pulex. Both native and invasive amphipods consumed early-stage amphibians and exhibited potentially destabilising Type II FRs. However, larger body size in invasive D. villosus translated into a superior FR through significantly lower handling times and subsequently higher maximum feeding rates—up to seven times greater than native G. pulex. Higher invader abundance also drove elevated RIP scores for invasive D. villosus, with potential impact scores predicted up to 15.4 times greater than native G. pulex. Overall, D. villosus is predicted to have a greater predatory impact upon amphibian populations than G. pulex, due primarily to its larger body size and superior field abundance, potentially reducing amphibian recruitment within invaded regions.

Highlights

Biological invasions are of increasing global concern, with invasive alien species (IAS) generating a substantial cost to the global economy, estimated to be more than $974 billion U SD1
Of the ~7000 amphibian species listed on the International Union for Conservation of Nature (IUCN) Red List, 17% of species are directly threatened by invasive alien species, of which 11% of species are categorised as vulnerable, endangered or critically endangered[30,31,32]
Our findings suggest that D. villosus may present a predatory threat to other native amphibian species with relatively small embryos, such as the great crested newt (Triturus cristatus; embryo diameter = ~ 4.5 mm), the smooth newt and the palmate newt (Lissotriton vulgaris and L. helveticus; embryo diameter = ~ 3 mm53); of which several species have been recorded in regions invaded by D. villosus (e.g. Grafham Water and Pitsford Reservoir; Anglian Water, pers. comm; The Wildlife Trust for Bedfordshire, Cambridgeshire & Northamptonshire, pers. comm)

Summary

Introduction

Biological invasions are of increasing global concern, with invasive alien species (IAS) generating a substantial cost to the global economy, estimated to be more than $974 billion U SD1. Compared to trophically analogous native species, invasive predators often consume prey at a higher rate (reviewed by Dick et al.[7, 8]; Cuthbert et al.[9]). Given that stable isotope analysis suggests that D. villosus can occupy the same trophic level as some predatory fish s pecies[41], this invasive amphipod may pose a potential risk to larval amphibians. We present the first empirical study comparing the ecological impacts of invasive and native freshwater amphipod predators upon the early, aquatic life-stages of two amphibian species. We apply the Relative Impact Potential metric (see Dick et al.8), which incorporates relative consumer abundance as a means of scaling relative per capita effects to compare the relative impact potential of these freshwater amphipod species towards amphibians present in Great Britain

Methods

Results

Discussion

Conclusion