NO EVIDENCE FOR TRADE-OFFS:CENTAUREAPLANTS FROM AMERICA ARE BETTER COMPETITORS AND DEFENDERS

Abstract

The natural enemies hypothesis has led to a number of ideas by which invaders might evolve superior competitive ability. In this context, we compared growth, reproduction, competitive effect, competitive response, and defense capabilities between invasive North American populations of Centaurea maculosa and populations in Europe, where the species is native. We found that Centaurea from North America were larger than plants from European populations. North American Centaurea also demonstrated stronger competitive effects and responses than European Centaurea. However, competitive superiority did not come at a cost to herbivore defense. North American plants were much better defended against generalist insect herbivores and slightly better defended against specialists. North Americans showed a stronger inhibitory effect on the consumers (resistance) and a better ability to regrow after attack by herbivores (tolerance). Better defense by North Americans corresponded with higher constitutive levels of a biochemical defense compound precursor, tougher leaves, and more leaf trichomes than Europeans. North American F1 progeny of field collected lines retained the traits of larger size and greater leaf toughness suggesting that genetic differences, rather than maternal effects, may be the cause of intercontinental differences, but these sample sizes were small. Our results suggest that the evolution of increased competitive ability may not always be driven by physiological trade‐offs between the allocation of energy or resources to growth or to defense. Instead, we hypothesize that Centaurea maculosa experiences strong directional selection on novel competitive and defense traits in its new range.

Plant-borne flavonoids released into the rhizosphere: impact on soil bio-activities related to plant nutrition. A review

“…However, experimental conditions can markedly affect the concentration of the bio-available fraction of flavonoids. This has been found to range from 0 to 2.4 (Blair et al 2005), 5 to 35 (Weir et al 2003), 0 to 113 (Ridenour et al 2008), and 83 to 185 μg ml −1 (Bais et al 2002). These variable data are likely due to the efficiency of the extraction method and soil type.…”

Exotic Plant Invasion in the Context of Plant Defense against Herbivores

“…Some generalist herbivores prefer native plants over exotic plants (Cappuccino and Carpenter, 2005;Han et al, 2008;Ridenour et al, 2008;Tallamy et al, 2010). Herbivores from Portuguese coast, including gastropods (Gibbula umbilicalis, Gibbula pennanti), sea hare (Aplysia punctata), and sea urchin (Paracentrotus lividus) prefer native seaweeds, Laminaria ochroleuca, Bifurcaria bifurcata, Mastocarpus stellatus, Chondrus crispus, and Osmundea osmunda, and avoid the invasive Sargassum muticum (Monteiro et al, 2009).…”

“…Exotic plants are also less likely to be attacked by generalist herbivores in introduced ranges (Mü ller-Schärer et al, 2004;Schaffner et al, 2011). In the absence of specialist herbivores in introduced ranges, resources previously allocated to plant defense in the native range might get reallocated to: (1) growth or reproduction of the exotic plant, so leading to enhanced competitiveness, as suggested by the evolution of increased competitive ability hypothesis (EICA; Blossey and Nö tzold, 1995;Bossdorf et al, 2005;Ridenour et al, 2008), (2) the production of less-costly chemical compounds such as terpenes and glucosinolates, as predicted by the shift in defense hypothesis (SDH; Doorduin and Vrieling, 2011), and/or (3) the higher production of allelochemicals novel for invaded communities, as assumed by the novel weapons hypothesis (NWH; Callaway and Ridenour, 2004;Supplemental Box S1).…”

No improved resistance against generalist herbivores found for invasive genotypes: a case study of Senecio vulgaris (Asteraceae) and a generalist snail (Achatina fulica)

“…For examples, Oduor et al (2011) found that the invasive populations of Brassica nigra s resisted against herbivore better than native ones. Introduced populations of Defense against both specialists and generalists of introduced populations of Centaurea maculosa (Asteraceae) were better than their native counterparts (Ridenour et al, 2008). In addition, the invasive Verbascum thapsus populations grew better than the native ones but the defense between the two range were remarkably similar (Alba et al, 2011).…”