This book takes a fresh approach to some of the classic questions in ecology. In particular, what determines where a species lives and what determines its abundance? Despite great progress in the twentieth century much more remains to be done before we can provide full answers to these questions so that reliable predictions can be made as to what will be found in unstudied areas or times. We believe that the methods described and deployed in this book point the way forward. The core message of the book is that key insights come from understanding what determines population growth rate (pgr). We believe that application of this approach will make ecology a more predictive science.

In this chapter we begin with an introduction to the major themes of the book, and then after briefly indicating how population growth rate is defined, we describe the contents of the book in more detail. Those who require more background material will find a brief guide to available texts at the end.

Major themes

In briefest outline, the approach taken in this book is as follows. Questions as to what determines where species live are questions about what values of environmental factors allow populations to persist. Populations persist where pgr ≥ o, so the environmental conditions that produce pgr ≥ o are the conditions in which the species can live. This line of reasoning suggests that to understand what determines where species live, we should study the relationships between environmental factors and pgr.

Introduction

With the persistent increase of the human population – now exceeding six billion – all species face increased pressure on resources. Understanding the factors responsible for limiting populations or causing species' extinctions therefore has increased urgency. Recent developments in population analysis, described below, have refined our understanding of the determinants of population growth rate and linked the theory to field data, and there is increasing interest in applying methods of this kind in conservation, wildlife management and ecotoxicology. This paper emphasizes the central role of population growth rate and reviews the use of data to test relevant theory and models primarily for wildlife populations. In this section we consider the definition and importance of population growth rate and briefly examine its historical background.

Definitions and estimation of population growth rate

Population growth rate is the summary parameter of trends in population density or abundance. It tells us whether density and abundance are increasing, stable or decreasing, and how fast they are changing. Population growth rate describes the per capita rate of growth of a population, either as the factor by which population size increases per year, conventionally given the symbol λ (= Nt+1/Nt), or as r = loge λ. Generally here, population growth rate will refer to r. λ is referred to variously as ‘finite growth rate’, ‘finite rate of increase’, ‘net reproductive rate’ or ‘population multiplication rate’, r is known as ‘rate of natural increase’, ‘instantaneous growth rate’, ‘exponential rate of increase’ or ‘fitness’.