As I explained earlier, biodiversity simultaneously means diversity of species and populations as well as genetic and ecosystem diversity. To answer your question more specifically, some species may definitely be harmful, particularly invasive exotic species. To maintain the natural heritage, the goal is not to conserve the biodiversity of those species but, on the contrary, the biodiversity that is already in place, the indigenous diversity of our country.
On April 26th, 2012. See this statement in context.