This article reviews and summarizes data sets that attempt to compare performance, population dynamics, and herbivory of invasive plant species. Specifically, we review results from studies comparing (1) individual and population parameters of plant invaders in their native and exotic range, (2) herbivore pressure and natural enemy guilds associated with plant invaders in their native and exotic range, and (3) performance and defense levels of native and exotic populations of the invasive under standardized conditions and the performance of selected herbivores. We found a total of 39 published and 2 unpublished studies, investigating 40 plant species. The majority of studies within the first category showed that invaders form larger populations, grow denser, have higher reproductive output, larger seed banks, and higher regeneration rates in the exotic compared with the native range. In contrast, plant vigor was not always greater, presumably because of increased intraspecific competition. Nearly all studies within the second category showed that herbivory (percentage of attack, species number and load) was reduced and, if investigated, that the herbivore community shifted from specialists to generalists and from endophagous to exophagous species in the exotic compared with the native range. Under standardized conditions (category 3), an equal number of studies found increased vigor or no significant differences between plants from the exotic and native range. In a few cases, plants from the exotic range grew less vigorous. Specialist herbivores generally preferred or developed better on plants from exotic compared with native populations, which were also better defended. Studies comparing plant invaders at field sites in their native and exotic range or under standardized conditions can help identify factors facilitating successful invasions, which in turn can improve the selection and efficiency of biological control agents and the development of integrated management strategies. We therefore suggest to include comparative studies more frequently in biological control programs and to extend them to include manipulative experiments and comparisons of control agents.

Additional index words: Biological weed control, comparative studies, enemy release hypothesis, evolution of increased competitive ability hypothesis.

Abbreviations: EICA, evolution of increased competitive ability; ERH, enemy release hypothesis.