Invasive species harm ecosystems around the world and cost the global economy $423 billion a year, according to a new report backed by the UN. A number of researchers believe that estimate may be just the tip of the iceberg. William Brangham speaks with one of the study's authors, Laura Meyerson of the University of Rhode Island, about the ways invasive species affect us. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders