Species invasions are considered one of the leading causes of global biodiversity loss (Wonham,2005)and are the second cause of species endangerment in the United States(Brooksand Pyke, 2002. The African grass, Megathyrsus maximus, has established extensive stand on Mona Island and there is no information about its effect on its natural communities. When grasses get to colonize a space they may influence species composition and ecosystem stability” (D'Antonio and Vitousek, 1992).National Science Foundation, HRD #0734826, NSF-UMEB DBI 0602642 and University of Puerto Rico, Central Administration and Río Piedras Campus