Millions of years in the making, underground caves sustain delicate ecosystems that are rich in biodiversity. In this short film by Drew Perlmutter , explorers of the vast cave networks in the southern United States explain the importance of preserving these subterranean worlds.Instagram: @drewperlmutter The Short Film Showcase spotlights exceptional short videos created by filmmakers from around the web and selected by National Geographic editors. We look for work that affirms National Geographic's belief in the power of science, exploration, and storytelling to change the world. The filmmakers created the content presented, and the opinions expressed are their own, not those of National Geographic Partners.See more from National Geographic's Short Film Showcase at documentary.com #shortfilmshowcase @natgeo