Size matters: predation of fish eggs and larvae by native and invasive amphipods

N. G. Taylor,A. M. Dunn

doi:10.1007/s10530-016-1265-4

Abstract

Invasive predators can have dramatic impacts on invaded communities. Extreme declines in macroinvertebrate populations often follow killer shrimp (Dikerogammarus villosus) invasions. There are concerns over similar impacts on fish through predation of eggs and larvae, but these remain poorly quantified. We compare the predatory impact of invasive and native amphipods (D. villosus and Gammarus pulex) on fish eggs and larvae (ghost carp Cyprinus carpio and brown trout Salmo trutta) in the laboratory. We use size-matched amphipods, as well as larger D. villosus reflecting natural sizes. We quantify functional responses, and electivity amongst eggs or larvae and alternative food items (invertebrate, plant and decaying leaf). D. villosus, especially large individuals, were more likely than G. pulex to kill trout larvae. However, the magnitude of predation was low (seldom more than one larva killed over 48 h). Trout eggs were very rarely killed. In contrast, carp eggs and larvae were readily killed and consumed by all amphipod groups. Large D. villosus had maximum feeding rates 1.6–2.0 times higher than the smaller amphipods, whose functional responses did not differ. In electivity experiments with carp eggs, large D. villosus consumed the most eggs and the most food in total. However, in experiments with larvae, consumption did not differ between amphipod groups. Overall, our data suggest D. villosus will have a greater predatory impact on fish populations than G. pulex, primarily due to its larger size. Higher invader abundance could amplify this difference. The additional predatory pressure could reduce recruitment into fish populations.

Highlights

Alien invasive species continue to have negative impacts on populations, communities and ecosystems across the globe (Strayer 2010; Simberloff et al 2013; Gallardo et al 2016)
Analyses were carried out using number of prey consumed or number of prey killed as response variables, but for carp prey we present only the former in the main text (a) to be consistent with analyses of electivity experiments and (b) because partial consumption was rare, so consumption was closely associated with number of prey killed and a reasonable basis for predicting population impacts
To identify significant explanatory variables, generalised linear model (GLM) were simplified to minimum adequate models (MAMs) following Crawley (2007), discarding terms whose exclusion from the model did not significantly increase deviance. v2 tests of significance were employed for binomial models, and F tests of significance for models involving quasilikelihood

Summary

Introduction

Alien invasive species continue to have negative impacts on populations, communities and ecosystems across the globe (Strayer 2010; Simberloff et al 2013; Gallardo et al 2016). Predation is a fundamental ecological interaction with the capacity to shape and structure natural communities (Thorp 1986; Case and Bolger 1991; Wellborn et al 1996; Jackson et al 2001) Owing to factors such naivety in prey populations (Case and Bolger 1991; Cox and Lima 2006), release from natural enemies (Roy et al 2011) or intrinsic behavioural characteristics (Weis 2010), invasive predators frequently consume prey more rapidly than analogous native species and have stronger effects on resident prey populations (Dick et al 2014). All life stages are vulnerable, from adults (e.g. Lawrie 1970; Ogutu-Ohwayo 1990; Ruzycki et al 2003) to young fish (e.g. Garman and Nielsen 1982; Lemly 1985) to eggs and larvae (e.g. Meffe 1985; Ruzycki et al 2003)

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Results

Conclusion