Level Invasive species Native habitat of invaders New habitat of introduced species How have invasive species spread Original species Level Invasive species Native habitat of invaders New habitat of introduced species How have invasive species spread Original species 1 the introduced species maintains itself in a limited range of habitats without spreading and without upsetting the equilibrium of the ecosystem. The species thus occupies an "empty" ecological niche a) alteration of the ecosystem by an alien element b) this introduction as beneficial because it has enhanced local biodiversity 2 spreads to the detriment of one or a few native species, threatens native biodiversity Populations of the native species have continued to decline gray squirrel eastern North America Great Britain 19st cent deciduous woodlands and manmade habitats red squirrel 3 becomes dominant and alters or upsets the entire ecosystem. the entire pelagic ecosystem was profoundly modified comb jellyfish to estuaries along the western Atlantic coast from the northern United States to the Valdés peninsula in Argentina the Black Sea 1982 the adjacent Azov Sea and Sea of Marmara the Mediterranean through the Turkish strait of Bosporus by a ship that loaded Mnemiopsis-laden ballast water in the western Atlantic and then emptied its tanks in the Black Sea pelagic fishes (primarily anchovy, sprat, and horse mackerel) A simple little comb jellyfish caused more damage to the fishery than the various pollutants so often decried! 4 affects several ecosystems, thus threatening an even larger swath of biodiversity they disturb all the ecosystems surrounding the one they inhabit Water hyacinth the Amazon basin the southeastern United States aquatic ecosystems, both planktonic and on the bottom Florida waters reached Africa in 1892, then Asia in 1894 (after being brought to a botanical garden in Indonesia). Today water hyacinth is present around the globe on thousands of miles of streams and rivers. It first appeared in great quantity in Lake Victoria in 1989; today it covers well over 12,000 acres and is spreading. was imported to a horticultural exposition in New Orleans in 1884. Visitors were impressed by its beauty and planted it in several water bodies. Caulerpa taxifolia, the killer alga