2 - Population growth rate and its determinants: an overview

Summary

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 (= N_t+1/N_t), or as r = log_e 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’.