Spatial distribution and performance of native and invasive Ardisia (Myrsinaceae) species in Puerto Rico: the anatomy of an invasion

Comparisons between native and invasive congeners are potentially useful approaches for identifying characteristics that promote invasiveness. Those traits for which an invasive exhibits superior ecological performance are likely to contribute to its invasiveness. We tested the hypothesis that invasive tree species have better ecological performance in early life cycle stages than native species in forests where they coexist. We studied locally sympatric populations of the invasive Ardisia elliptica and the native A. obovata (Myrsinaceae) in Puerto Rico. We compared spatial distribution, herbivory and growth in seedlings, seed germination in the field and under controlled conditions, and fruit production. We found the distribution of each species was aggregated in the three categories of size (seedlings, juveniles and adults) and the populations partially overlapped. The invasive species was the most abundant species in every category of size. The two species did not differ in percentage of leaf area consumed and seedlings of both species had the same relative growth rate (RGR) in the forest. However, the invasive species had higher germination success in the field, faster mean germination time in the lab and higher fruit production. It appears that the success of A. elliptica is not through escape from pathogens or herbivores, but by a better performance in fruiting and seed germination in the forest.