Invasive alien shredders clear up invasive alien leaf litter.

Joel Brittain,Thomas M Doherty‐Bone,Lee Eric Brown,Alison M Dunn

doi:10.1002/ece3.4430

Abstract

Biological invasions have the potential to alter ecosystem processes profoundly, but invaders are rarely found alone. Interactions between different invasive alien species, and their cumulative impact on ecosystem functioning, have led to hypotheses of invasion meltdown whereby effects become additive leading to further ecosystem stress. Invasive riparian plants (e.g., Rhododendron ponticum) deposit leaf litter in freshwaters, which may be unconsumed by indigenous species, potentially affecting habitat heterogeneity and flow of energy to the food web. However, invasive alien decapod crustaceans are effective consumers of leaf litter, and it was hypothesized that they would also consume inputs of invasive riparian leaf litter. This study shows that invasive alien signal crayfish (Pacifastacus leniusculus) and Chinese mitten crab (Eriocheir sinensis) effectively break down different types of leaf litter, including invasive alien R. ponticum, at higher rates than indigenous white‐clawed crayfish. Secondary products were more varied, with more fine particulate organic matter generated for the less palatable alien leaf litter species. Leaf species caused different changes in body mass of decapods but effects were heterogeneous by leaf and decapod: P. leniusculus showed lower mass loss when consuming R. ponticum while E. sinensis lost mass when consuming A. pseudoplatanus. Impacts of riparian invasions on detritus accumulation in freshwaters are thus potentially buffered by invasive alien decapods, illustrating a need for a more detailed consideration of both positive and negative interspecific feedbacks during biological invasions.

Highlights

Invasive alien species (IAS) threaten global biodiversity, ecosystems, and economies, occurring at many trophic levels simultaneously (Simberloff et al, 2013)
This study provides new insights into the impacts of invasive decapods on invasive alien leaf litter and vice versa
These findings are significant because all four of these IAS are expanding their range in the same regions, often co-occurring, yet little is known about the consequences of these multi-invasions

Summary

| INTRODUCTION

Invasive alien species (IAS) threaten global biodiversity, ecosystems, and economies, occurring at many trophic levels simultaneously (Simberloff et al, 2013). Invasive alien omnivorous animals (e.g., amphipods, decapods) affect freshwater ecosystems through the direct consumption (shredding) of detritus, as well as trophic cascades following consumption of detritivores and ecosystem engineering (Doherty-Bone, Dunn, Liddell, & Brown, 2018; Gallardo et al, 2015; Harvey et al, 2013) These two guilds of IAS (riparian plants, shredders) when considered in isolation have the potential to impact detrital processing in freshwater ecosystems. Milne-Edwards 1853 (the Chinese Mitten Crab) originating from Korea and eastern China Both these decapod species are widespread IAS in the British Isles (Figure 1b), mainland Europe and North America and are rapidly expanding their range (Herborg, Rudnick, Siliang, Lodge, & Macisaac, 2007), likely impacting ecosystems through strong top-down regulation of smaller animals, plants, and detritus (Rosewarne et al, 2016; Rudnick & Resh, 2005). As a consequence, (H3) the assimilation (measured by gain in mass) of invasive alien leaf litter will be higher for invasive alien decapods compared to the native crayfish

| MATERIALS AND METHODS

| DISCUSSION

CONFLICT OF INTEREST