Population abundances, geographic ranges and conservation: 1994 Witherby Lecture

Birds make up a trivial proportion of species on earth. Yet they are extremely important, simply because there are so few species of birds and we know so much about so many of them. This rich source of information can be used to develop and test general theories about the distribution and abundance of organisms, important both for ecologists and conservationists. This paper examines the relationship between local population abundance and the size of species' geographic ranges, textures of population abundance within ranges, and what happens at the edges of species' geographic distributions. Implications for conservation are emphasized. Within the highly modified landscape of Britain, birds are apparently not good indicators of species-rich sites of high conservation importance for other taxa, but in many other ways are perfect 'model organisms' for monitoring and understanding human impacts on ecological systems. The biggest threat to all species over the next century is human-induced global environmental change; bird populations are, and will increasingly be, of crucial importance both for monitoring and for designing policies to deal with global change.