Nutrient availability and invasive fish jointly drive community dynamics in an experimental aquatic system

Daniel L Preston,Pieter T J Johnson,Hayden D Hedman

doi:10.1002/ecs2.2153

Daniel L Preston, Pieter T J Johnson + Show 1 more

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https://doi.org/10.1002/ecs2.2153

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Abstract

AbstractSpecies invasions increasingly occur alongside other forms of ecosystem change, highlighting the need to understand how invasion outcomes are influenced by environmental factors. Within freshwaters, two of the most widespread drivers of change are introduced fishes and nutrient loading, yet it remains difficult to predict how interactions between these drivers affect invasion success and consequences for native communities. To test competing theories about interactions between nutrients and invasions, we conducted a 2 × 3 factorial mesocosm experiment, varying western mosquitofish (Gambusia affinis) presence and nutrient availability within aquatic communities. Based on theory, increased nutrients could either (1) facilitate coexistence between predatory mosquitofish and native species by increasing prey availability (the invader attenuation hypothesis) or (2) strengthen predation effects by enhancing fish productivity more than native community members (the invader amplification hypothesis). In outdoor mesocosms designed to mimic observed nutrient conditions and local community structure, mosquitofish directly reduced the abundances of zooplankton and three native amphibian species, leading to indirect increases in phytoplankton, periphyton, and freshwater snail biomass through trophic cascades. Nutrient additions increased native amphibian growth but had especially pronounced effects on the productivity of invasive mosquitofish. The elevated nutrient condition supported ~5 times more juvenile mosquitofish and 30% higher biomass than the low nutrient condition. Increased nutrients levels did not weaken the top‐down effects of mosquitofish on invertebrates or amphibians. Collectively, our results support the invader amplification hypothesis, suggesting that increased nutrient loading may benefit invasive species without attenuating their undesirable effects on native community members.

Highlights

Ecosystems that support invasive species increasingly experience other concurrent drivers of ecosystem change, including habitat alteration, pollution, resource extraction, and climate change (Kolar and Lodge 2000, MacDougall and Turkington 2005, Rahel and Olden 2008)
Freshwaters are often simultaneously affected by nutrient pollution (Carpenter et al 2011, Ricciardi and MacIsaac 2011)
The Rift Valley Lakes in East Africa have been invaded by numerous nonnative species—including water hyacinth and Nile perch—while simultaneously experiencing nutrient pollution from agriculture and a growing human population (OgutuOhwayo et al 1997, Odada et al 2003)

Summary

Introduction

Ecosystems that support invasive species increasingly experience other concurrent drivers of ecosystem change, including habitat alteration, pollution, resource extraction, and climate change (Kolar and Lodge 2000, MacDougall and Turkington 2005, Rahel and Olden 2008). The Rift Valley Lakes in East Africa have been invaded by numerous nonnative species—including water hyacinth and Nile perch—while simultaneously experiencing nutrient pollution from agriculture and a growing human population (OgutuOhwayo et al 1997, Odada et al 2003). In both examples, the co-occurrence of invasive species and nutrient pollution was associated with wholesale shifts in community structure and ecosystem processes, leading to declines in native species and economic losses totaling billions of dollars (Pitcher and Hart 1995, Pimentel et al 2005)

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