21.   Without periodic clearing by fire, a few invasive foreign species often take over an ecosystem and choke out the original and more numerous array of native plant species.

22.   Damage by the thumbnail-sized mollusk represents only a fraction of the costs being rung up by invasive species.

23.   In these areas, Barnes noted, natural debris has long served as rafts for such creatures, and the rubbish adds to the potential for spreading invasive species.

24.   Invasive species pose another problem, competing with native species for food and habitat.

25.   The U.S. Environmental Protection Agency has approved using caffeine to kill the tiny Caribbean tree frog, an invasive species known for its piercing mating calls.