Human efforts to preserve as many species as possible are a (somewhat feeble) attempt at repairing the damage we have done to the environment as a “thinking”, greedy species interested in much more than simple survival of our own species.  In other words, Darwin’s and Huxley’s observations of how species survive and vary do not take into account the “seven deadly sins” of the human species.  The damage to rain forests, to water sources, to the atmosphere, etc., have caused an unnatural depletion of habitats throughout the world.  The “balance of nature” has been tipped—think, for example, of how unnatural it is to use fossil fuels.  While it is true that in Nature, species must vie for habitat, those beasts do not have “choice” as an ingredient in the same way that humans do. 

So, a little fish in southern rivers may not affect the balance all alone, but when human organizations seek to protect them, we are simply putting our standards into practice; it may appear that the panda or the orangutan are legitimate targets for our survival efforts, but that is just more false value on the part of our species.  It is “honorable” to try to save a specific species, no matter how far down on the list of phyla and families.  Incidentally, in a ruined world, it would not be humans, but cockroaches that would survive.  Credit the human species with long-range vision and ethical practices.  Many species have already disappeared directly due to human beings--Dodo birds, passenger pigeons, etc.--We may have dominion over the animals, but they shouldn't become victims of our greed.