Watch the video for the answer to that question. Otherwise if you are not able too then read this text. Essentially biodiversity is a very essential aspect to the success of life on this planet. Every organism has specific ecosystem services or "jobs", if you will, to carry out in their respective niches. If one species dies then some others can potentially pick up the slack in a very biodiverse ecosystem, but if a great majority of species die out then the ecosystem collapses. This is also the case with so called "keystone species" where an ecosystem completely depends on that species survival. An example of a keystone species is Sea Otters in the Pacific northwest. Sea otters control the population of sea urchins and if they died out then the urchins would eat up all of the kelp and the entire ecosystem would collapse because kelp is the primary source of food and shelter in the ecosystem.