Abiotic factors, not herbivorous pressure, are primarily responsible for the performance of an invasive aquatic plant

Abstract

Morphological performance of invasive plants can be determined by abiotic factors (e.g. water temperature) and biotic factors (e.g. herbivory). This study investigates the performance of an exotic plant in its native and introduced environments. The questions of study are: Is the performance of Egeria densa in both its native and introduced areas associated with abiotic and/or biotic factors? Is the performance of this plant better in the native or in the introduced area? In order to answer these questions, E. densa individuals collected in France (introduced range) were compared with individuals collected in Brazil (native range). The results demonstrate that E. densa populations sampled in its native areas included a higher percentage of plants grazed than in the introduced range populations, but they also exhibited a superior performance in terms of length and dry mass. In both regions, the performance of the plants was associated mainly with abiotic factors. Whereas the higher temperature in its native area may have promoted greater growth in terms of length and dry mass, a lower temperature and high levels of ammonium in French waters might have reduced the development of this plant in its introduced range. The lower performance of E. densa in France should not be associated with abiotic factors alone, since other factors can also be involved, as limited resources or low clonal adaptation. Thus, future studies concerning E. densa performance in France should consider these factors in order to assist in understanding the nature of the plant’s invasiveness in this region.