In the remainder of this course we will focus more on conservation problems posed by systems, whether groups of interacting species or merely sets of species that happen to co-occur for reasons of history or ecological requirements. They conserve none of the interaction biodiversity that John Thompson argues is so important. The vast number of species threatened with extinction and our vast ignorance about most of them means that we can only hope to save many of them if we can save the systems on which they depend. Relatively natural, undisturbed systems provide a benchmark against which we can measure human impacts.
Biotic systems provide a variety of services necessary for human health and welfare.