It is quite easy to find threats to biodiversity e.g. the sacrifice of eve and avoiding genetic holocaust however, it is often difficult to find reasons why we should protect. There are many potential reasons, Ecological Ethics, Science replacing tradition, natural perspectives and biodiversity all provide viewpoints but are probably ones you could second guess. The following however,
                                    'to allow evolutionary processes to continue'
                                    'to safeguard the role of ecosystems in regulating the biosphere'
                                    'to safeguard watersheds - preventing flooding and soil erosion and maintaining water supplies'
                                    'to provide products like building materials and food'
                                    'to conserve gene pools for future use by humans'
                                    'to provide wild areas for recreation and education'
                                    'to provide income through tourism'
                                                                                          might also be potential reasons. Use the search engines or follow some of the following tiger herbs, nitrogen fixation, oxygen and life, new drugs, "un-mined" resources and economic rationales to investigate.