Geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata

Abstract

We investigated geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata, to test the hypothesis that escape from herbivory in invasive species permits enhanced growth and lower production of defensive chemicals. We quantified herbivore damage, concentrations of sinigrin, and growth and reproduction inside and outside herbivore exclusion treatments, in field populations in the native and invasive ranges. As predicted, unmanipulated plants in the native range (Hungary, Europe) experienced greater herbivore damage than plants in the introduced range (Massachusetts and Connecticut, USA), providing evidence for enemy release, particularly in the first year of growth. Nevertheless, European populations had consistently larger individuals than US populations (rosettes were, for example, eightfold larger) and also had greater reproductive output, but US plants produced larger seeds at a given plant height. Moreover, flowering plants showed significant differences in concentrations of sinigrin in the invasive versus native range, although the direction of the difference was variable, suggesting the influence of environmental effects. Overall, we observed less herbivory, but not increased growth or decreased defense in the invasive range. Geographical differences in performance and leaf chemistry appear to be due to variation in the environment, which could have masked evolved differences in allocation.

Lower P contents and more widespread terpene presence in old Bornean than in young Hawaiian tropical plant species guilds

“…The results thus indicate that higher or lower concentrations of different chemical compounds may not only depend on a defence strategy or soil nutrient content. Other environmental factors such as UV radiation, temperature or drought could explain changes of secondary metabolites concentrations such as phenolics since they are also involved in protection mechanisms in the face of abiotic stressors (Filella and Peñuelas 1999, Lewis et al 2006, Georgieva et al 2010. In Hawaii, we had both the dry sites that receive more UV, and the wet sites where it is very cloudy.…”

Higher Allocation to Low Cost Chemical Defenses in Invasive Species of Hawaii

“…The higher or lower content of different chemical compounds does not depend only on a defense strategy. Other environmental factors such as temperature or drought could explain changes of secondary metabolites contents such as terpenes since they are also involved in protection mechanisms in the face of abiotic Llusià, 2003, 2004;Peñuelas and Munné-Bosch, 2005;Lewis et al, 2006) and biotic (Viiri et al, 2001;Gershenzon and Dudareva 2007) stressors. Volatile terpenes also are involved in plant defense by multitrophic signalling (Dicke and Baldwin, 2010).…”

Conceptual Frameworks and Methods for Advancing Invasion Ecology

“…For example, some studies compare populations of invasive species in the new range to populations of the same species in the indigenous range and quantify infestation, i.e., abundance or diversity of predators or parasites that can be found on the species (Mitchell and Power 2003;Vignon et al 2009). Other studies use the same comparison but quantify damage typically caused by predators, e.g., leaf damage (Lewis et al 2006;Ebeling et al 2008). Another approach is to compare invasive to similar or related native species, and again, in some cases infestation is quantified (Frenzel and Brandl 2003;Blakeslee and Byers 2008), in others damage (Carpenter and Cappuccino 2005;Sugiura 2010).…”