What Threats do Invasive Species Pose to Ecosystems? Ecological Society of America 02.01.01 Invasive species may negatively impact native species in any number of ways including: eating them, competing with them, mating with them and decreasing genetic diversity, introducing pathogens and parasites that sicken or kill them, and disrupting available nutrients. An introduced species can change the look and makeup of an entire system-changing species composition, decreasing rare species, and even changing or degrading the normal functioning of the system. Maintaining intact natural systems is important to ensure the continuation of ecosystem goods and services upon which humans depend.     Invasive plants can smother native vegetation or change the timing and severity of fires, floods, and other disturbances. Introduced diseases and parasites can attack and eliminate dominant native plant species. For example, the chestnut blight fungus from Asia all but wiped out the American Chestnut, thus changing the makeup of eastern forests. Intentionally and accidentally introduced herbivorous mammals, such as goats, rabbits, pigs, and horses, can threaten native (and often rare) plants by eating and trampling them. Often introduced herbivores diminish the quality of the habitat for native species, for example by transforming shrublands and forests into grasslands.   Prepared by the Ecology Society of America   1707 H St., NW   Suite 400   Washington, DC 20006 ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.