Native and invaded-range surveys provide mixed support for enemy-release of Nymphoides peltata in the invaded range

Natural or anthropogenic movement of plant species outside their historical ranges may result in exposure to new environmental conditions and a lack of natural enemies, thus promoting their establishment and spread into new areas. A biogeographical comparison of native and invasive populations can provide insight into the mechanisms of successful invasions and guide effective management strategies, such as biological control, by targeting plant traits that promote invasiveness. We studied the Eurasian aquatic plant, Nymphoides peltata, in situ in the native (China, Korea) and invaded (USA) ranges to determine whether there were differences in natural enemy attack rates (percent leaf damage, frequency of leaf herbivory or disease), productivity (plant cover, reproduction), and leaf traits (leaf elemental content, leaf toughness, dry matter content, specific leaf area) between areas. We also investigated whether there was evidence of a tradeoff between natural enemy attack and growth or reproduction, as would be predicted by invasion theory. Plant cover (23–29 % higher) and reproductive output (eight times more seeds / m²) were consistently higher in the invaded range. Leaf traits consistently differed between ranges, which we would expect if plants in the invaded range had fewer herbivores or other pests. The amount of leaf damage present was similar between ranges, but the frequency of herbivory was 50 % greater, on average, in the native than invaded range. Although we did not quantify suppression of N. peltata by natural enemies, we found evidence of more frequent herbivory in Asia and reduced reproduction and plant cover compared to the USA, which supports further investigation into viability of biological controls.