What determines where a species lives? And what determines its abundance? This book takes a fresh approach to some of the classic questions in ecology. Despite great progress in the twentieth century much more remains to be done before we can provide full answers to these questions. The methods described and deployed in this book point the way forward. The core message of the book is that the key insights come from understanding what determines population growth rate, and that application of this approach will make ecology a more predictive science. Topics covered include population regulation, density-dependence, the ecological niche, resource and interference competition, habitat fragmentation and the ecological effects of environmental stress, together with applications to conservation biology, wildlife management, human demography and ecotoxicology. After a substantial introduction by the editors the book brings together contributions from leading scientists from Australia, New Zealand, North America, Europe and the U.K.

Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward reviews the science that underpins the Bureau of Land Management's oversight of free-ranging horses and burros on federal public lands in the western United States, concluding that constructive changes could be implemented. The Wild Horse and Burro Program has not used scientifically rigorous methods to estimate the population sizes of horses and burros, to model the effects of management actions on the animals, or to assess the availability and use of forage on rangelands. Evidence suggests that horse populations are growing by 15 to 20 percent each year, a level that is unsustainable for maintaining healthy horse populations as well as healthy ecosystems. Promising fertility-control methods are available to help limit this population growth, however. In addition, science-based methods exist for improving population estimates, predicting the effects of management practices in order to maintain genetically diverse, healthy populations, and estimating the productivity of rangelands. Greater transparency in how science-based methods are used to inform management decisions may help increase public confidence in the Wild Horse and Burro Program.

Animal population densities are thought to be "regulated" by density-dependent processes (Haldane, 1953; Royama, 1977: Berryman, 1991). The perceived importance of these processes to biologists is evident from the vast amount of research dedicated to this idea (Inchausti, 1994). Most of this research addresses the problem(s) of detecting the effect of density-dependent regulatory processes using time series data. However, the question of the relative importance of density-dependent factors upon rates of change of population abundances is rarely addressed. In this thesis, I quantify the importance of density-dependent factors in 303 natural animal populations. I found that, on average, only $\approx$19% of the temporal variability in per capita growth rate could be statistically related to population density. Yet research effort concentrates overwhelmingly on density-dependent processes. I conclude that the effects of density-dependent processes within natural animal populations are generally weak and disproportionately studied.