By Mackenzie Myers @kenzwrites Large organisms such as whales, elephants, and redwoods are often featured in awe-inspiring nature documentaries, but they’re more than just oohs and ahs. Their existence or extinction could make or break the planet as we know it.  Megabiota—the largest plants and animals—are more likely than smaller organisms to go extinct as a result of climate change. And the rest of us could be in big trouble if they do, according to a recent study.  The charisma conundrum Think of successful conservation campaigns. Which animals are deemed…