Enhanced fitness due to higher fecundity, increased defence against a specialist and tolerance towards a generalist herbivore in an invasive annual plant

Abstract

Aims: The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to dis- placement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction. To as- sess the importance of the different mechanisms governing the suc- cess of Conyza canadensis, a globally successful invader, we simultaneously tested several recent hypotheses potentially explain- ing the factors leading to biological invasion. Methods: We tested (i) whether plants from the non-native range showed a higher fitness than plants from the native North American range, (ii) whether they differed in resistance against an invasive generalist herbivore, the slug Arion lusitanicus and against a recently estab- lished specialist aphid herbivore, Uroleucon erigeronense and (iii) experimentally assessed whether C. canadensis releases allelopathic chemicals that have harmful effects on competing species in the non- native range. We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.