Novel weapons testing: are invasive plants more chemically defended than native plants?

Eric M Lind,John D Parker,Juergen Kroymann

doi:10.1371/journal.pone.0010429

Abstract

BackgroundExotic species have been hypothesized to successfully invade new habitats by virtue of possessing novel biochemistry that repels native enemies. Despite the pivotal long-term consequences of invasion for native food-webs, to date there are no experimental studies examining directly whether exotic plants are any more or less biochemically deterrent than native plants to native herbivores.Methodology/Principal FindingsIn a direct test of this hypothesis using herbivore feeding assays with chemical extracts from 19 invasive plants and 21 co-occurring native plants, we show that invasive plant biochemistry is no more deterrent (on average) to a native generalist herbivore than extracts from native plants. There was no relationship between extract deterrence and length of time since introduction, suggesting that time has not mitigated putative biochemical novelty. Moreover, the least deterrent plant extracts were from the most abundant species in the field, a pattern that held for both native and exotic plants. Analysis of chemical deterrence in context with morphological defenses and growth-related traits showed that native and exotic plants had similar trade-offs among traits.Conclusions/SignificanceOverall, our results suggest that particular invasive species may possess deterrent secondary chemistry, but it does not appear to be a general pattern resulting from evolutionary mismatches between exotic plants and native herbivores. Thus, fundamentally similar processes may promote the ecological success of both native and exotic species.

Highlights

The tremendous ecological and economic costs of biological invasions have prompted intense interest in the mechanisms that control invasion success [1,2]
Conclusions/Significance: Overall, our results suggest that particular invasive species may possess deterrent secondary chemistry, but it does not appear to be a general pattern resulting from evolutionary mismatches between exotic plants and native herbivores
In support of this hypothesis, Cappuccino and Arnason [10] showed that invasive plants possess anti-herbivore chemistry that is generally unique from compounds in the native flora, implying that exotic plants are more chemically defended than native plants

Summary

Introduction

The tremendous ecological and economic costs of biological invasions have prompted intense interest in the mechanisms that control invasion success [1,2]. Anti-herbivore defenses may be evolutionarily novel but ineffective given that they evolved to repel enemies and competitors in the old but not the new range, whereas native plants may be better defended than exotics because they have long experienced natural selection from their co-occurring native enemies [5,11]. In support of this hypothesis, native herbivores can preferentially attack exotic over native plants [12], and suppress the abundance of exotics in field experiments [13]. Despite the pivotal long-term consequences of invasion for native food-webs, to date there are no experimental studies examining directly whether exotic plants are any more or less biochemically deterrent than native plants to native herbivores

Methods

Results

Conclusion