Stoichiometric Constraints Do Not Limit Successful Invaders: Zebra Mussels in Swedish Lakes

Kurt Pettersson,Rahmat Naddafi,Peter Eklöv,Andy Hector

doi:10.1371/journal.pone.0005345

Abstract

BackgroundElemental imbalances of carbon (C): nitrogen (N): phosphorus (P) ratios in food resources can constrain the growth of grazers owning to tight coupling between growth rate, RNA allocation and biomass P content in animals. Testing for stoichiometric constraints among invasive species is a novel challenge in invasion ecology to unravel how a successful invader tackles ecological barriers in novel ecosystems.Methodology/Principal FindingsWe examined the C∶P and N∶P ratios and the condition factor of a successful invader in lakes, the zebra mussel (Dreissena polymorpha), collected from two Swedish lakes. Concurrently, we analyzed the elemental composition of the food (seston) and tissue of the mussels in which nutrient composition of food and mussels varied over time. Zebra mussel condition factor was weakly related to the their own tissue N∶P and C∶P ratios, although the relation with the later ratio was not significant. Smaller mussels had relatively lower tissue N∶P ratio and higher condition factor. There was no difference in C∶P and N∶P ratios between seston and mussels' tissues. Our results indicated that the variation in nutrient stoichiometry of zebra mussels can be explained by food quality and quantity.Conclusions/SignificanceOur study suggests that fitness of invasive zebra mussels is not constrained by nutrient stoichiometry which is likely to be important for their proliferation in novel ecosystems. The lack of imbalance in C∶P and N∶P ratios between seston and mussels along with high tissue C∶P ratio of the mussel allow them to tolerate potential P limitation and maintain high growth rate. Moreover, zebra mussels are able to change their tissue C∶P and N∶P ratios in response to the variation in elemental composition of their food. This can also help them to bypass potential nutrient stoichiometric constraints. Our finding is an important step towards understanding the mechanisms contributing to the success of exotic species from stoichiometric principles.

Highlights

Biological invasion is an ubiquitous form of global change of biota, capable of causing native extinctions and affecting geographical speciation [1,2] as well as the ecology and economy of the recipient ecosystems [3,4,5,6,7]
Conclusions/Significance: Our study suggests that fitness of invasive zebra mussels is not constrained by nutrient stoichiometry which is likely to be important for their proliferation in novel ecosystems
We examined the relation between C:P and N:P ratios and the condition factor [(tissue condition index: TCI)] of zebra mussels collected from six sampling sites at each of two Swedish lakes: Lake Erken and Lake Ekoln

Summary

Introduction

Biological invasion is an ubiquitous form of global change of biota, capable of causing native extinctions and affecting geographical speciation [1,2] as well as the ecology and economy of the recipient ecosystems [3,4,5,6,7]. The proximate causes of invasion success are not well understood [8,9] and a major challenge in invasion ecology is to understand how a successful invader deals with ecological barriers in the novel ecosystems. Integrating the stoichiometric conceptual framework into the discipline of invasion biology can help us to address questions about how the structure of the invaded ecosystem interacts with the physiology of the invader to allow for the proliferation of the invader. This is critical to better understand the exotic species’ population dynamics and extend the implication of biological invasion to the ecosystem level [12,13]. Testing for stoichiometric constraints among invasive species is a novel challenge in invasion ecology to unravel how a successful invader tackles ecological barriers in novel ecosystems

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Results

Conclusion