Wednesday, April 20, 9-11 pm ET Find out what is causing the invasion of alien species of plants and animals, and what can be done to stop the rising tide.
When predators disappear, the consequences can be dramatic. If predators are so vital, should they be brought back - and can they be?
Scientists believe that disparate phenomena may be linked to global climate change.
Have Earth's vibrant waterways become massive delivery systems for invisible poisons?
