INTRODUCTION

Conservationists seek to prevent the global extinction of species and local extinctions that lead to loss of geographical range. Although populations of some species listed as threatened with global extinction are not declining (IUCN 1994), preventing the extinction of any species requires the ability to identify action that will arrest or reverse future population declines. Practical conservationists often rely on experience and common sense to identify remedial actions, but this approach runs a serious risk of misapplying conservation effort and delaying the implementation of effective measures (Green & Hirons 1991; Caughley & Gunn 1995; Sutherland 2000). Scientific study of the causes of population declines and the responsiveness of populations to conservation actions has been advocated as a means of improving the effectiveness of conservation action (Caughley 1994: Caughley & Gunn 1995), but ecology is a complicated science and it is usually diffi cult to achieve a detailed understanding of the factors driving population processes without expensive and long-term studies. The challenge of conserving global biodiversity is urgent and resources for conservation are limited, making such research seem an expensive luxury to many. This chapter examines the kinds of scientific investigations that conservation biologists can conduct that are rigorous enough to reduce the risk of serious error, but also cheap and rapid enough to aid recovery before the population has declined to the point where only heroic efforts can hope to sustain it.