Introduction

In the last couple of lectures we've begun to explore some of the ways in which a single-species focus on conservation is incomplete. First, we pointed out that 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. ``Hotsposts'' may or may not be the best way to identify those larger systems, but clearly we're going to have to have some means of protecting many species at once if we are to prevent the extinction of the vast majority of species. Kareiva and Marvier [5] point out that there are several other reasons for conservationists to be concerned about systems, not just individual species:

• 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. Part of our concern about the loss of biological diversity stems from the potential impacts of losing those services.

• Wild places inspire the human spirit.

We're going to continue in this vein for several more weeks. Today we'll step back a bit from the ecosystem- or landscape-scale perspective associated with the diversity-stability debate and focus on the many ways in which species interactions are vital to conserving the structure and function of ecological systems.