TABLE OF CONTENTS
Preface
Classifying Rodent Population Changes - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0001
[rodent populations, population change, population density, lemmings, voles, myodes]
This chapter discusses the rise and fall of rodent populations, and classifies these population changes. First, it defines four background issues that must be reviewed before classifying patterns of rodent population changes: population, population density, time step of sampling population attributes, and data needed to test hypotheses about population limitation. Next, the chapter examines data sets to illustrate empirical patterns of population change: (1) lemmings in Siberia and Norway; (2) gray-sided voles on Hokkaido, Japan, and at Kilpisjärvi, Finland; and (3) meadow voles in Central Illinois, USA. Finally, it discusses the time series analysis of population changes and illustrates calculations for several populations of myodes (Clethrionomys) in North America. (pages 1 - 22)
This chapter is available at:
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Biogeography of Rodent Population Fluctuations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0002
[population change, population variability, population density, coefficient of variation]
This chapter discusses the amplitude of population change in a variety of small rodent species, focusing on the latitudinal variations in population variability and population density. The coefficient of variation is used to measure population variability. The chapter begins by identifying the data needed to calculate the coefficient of variation. It then addresses whether population fluctuations are stronger at high latitudes and whether small rodent maximum densities are higher in more productive habitats or lower in predator-rich habitats. (pages 23 - 42)
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Reproductive Rates in Fluctuating Populations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0003
[reproduction, voles, lemmings, reproductive rates, sexual maturity, breeding season, litter size, pregnancy rate]
Rodents are well known for their high rates of reproduction. A vole population with an adult weight of 30 grams would increase fivefold over a year while an 80-gram lemming would increase about three times. This chapter discusses the role that changes in reproductive rates plays in causing changes in rodent population growth rates, and four key parameters which affect population growth rates: sexual maturity, length of breeding season, litter size, and pregnancy rate. (pages 43 - 63)
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Mortality Rates in Fluctuating Populations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0004
[mortality rates, population growth rates, prenatal mortality, nestling mortality, juvenile mortality, adult mortality, mortality]
This chapter focuses on the role that changes in mortality rates play in determining population growth rates in a variety of small rodent species, and discusses the four components of mortality in small mammals: prenatal mortality, nestling mortality, juvenile mortality, and adult mortality. (pages 64 - 80)
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Immigration and Emigration - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0005
[immigration, emigration, population dynamics, source-sink dynamics, dispersal, dispersers, natal dispersal, breeding dispersal]
This chapter, which investigates studies of rodent immigration and emigration, and their contribution to the understanding of rodent population dynamics, begins by illustrating source-sink dynamics—sources, in which births exceed deaths, and sinks, in which deaths exceed births. This is followed by a discussion on the classification of dispersal movements in relation to population changes in field populations, as well as methoids that define dispersers in the field. The chapter also examines natal dispersal and breeding dispersal and the ways in which social interactions influence population fluctuations, before finally discussing the mechanisms that underlie dispersal in small rodents. (pages 81 - 97)
This chapter is available at:
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Spatial Dynamics of Populations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0006
[rodent populations, synchrony, dispersal, predation, weather]
Fluctuations in small rodent populations tend to occur at the same time over large geographical areas. This chapter discusses the patterns of synchrony among rodent populations, and identifies three mechanisms as sources of synchrony among populations: dispersal, predation, and weather effects. It also discusses the methods used for analyzing synchrony in more detail. (pages 98 - 112)
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How Can We Determine What Drives Population Changes? - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0007
[population change, food supply, predation, population fluctuations, Chitty approach, Lidicker approach]
This chapter, which investigates the variables that determine the rate of population change in any species, suggests that food supply and predation are the two critical factors affecting population growth rate. It also discusses two general approaches to studying the causes of population fluctuations in rodents: the Chitty approach and the Lidicker approach. (pages 113 - 126)
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The Food Hypothesis - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0008
[food hypothesis, starvation, food quantity, food quality, food resource, habitat]
One of the first hypotheses suggested for the explanation of population fluctuations in rodents was the food hypothesis, which suggests that rodents simply run out of food when they reach peak numbers and then decline from starvation. This chapter discusses four variants of the food hypothesis and the observations needed to test teach. These variants are the food quantity hypothesis, the food quality hypothesis, the specific food resource hypothesis, and the food–habitat quality hypothesis. The chapter also illustrates the quantitative attempts carried out by small rodent ecologists to test the food hypotheses. (pages 127 - 142)
This chapter is available at:
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Predation as the Explanation for Fluctuations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0009
[predation, population growth rates, rodents, lemming, Alaska, predator reduction, weasel removal]
This chapter reviews the basic principles of predation, addresses whether predation is both necessary and sufficient to determine population growth rates in small rodents, and analyzes some empirical studies of predation in small rodents. These include a study on predator impact on the high brown lemming population in Barrow, Alaska; experimental predator reduction experiments in western Finland; and a weasel removal experiment in Scotland. (pages 143 - 161)
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Disease as a Potential Factor in Population Changes - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0010
[diseases, rodent population, vole, tuberculosis, population fluctuations, survival rates, population declines]
This chapter discusses diseases as the most likely cause for rodent population fluctuations. It first describes a study carried out on vole tuberculosis and population fluctuations, and then discusses the impact of parasitism and disease on the survival rates of small rodents. The chapter also presents two models that illustrate how the interaction of disease with other factors causes population declines. (pages 162 - 174)
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Self-Regulation Hypotheses for Fluctuations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0011
[self-regulation hypotheses, population, population fluctuations, rodents, stress, polymorphic behavior]
Self-regulation hypotheses suggest that interactions between individuals in a population cause demographic changes which produce population fluctuations. Two types of self-regulation mechanisms cause population fluctuations in rodents: the stress hypothesis and the polymorphic behavior hypothesis. This chapter discusses the formulation of these hypotheses and the experiments used to test both hypotheses on small rodents. (pages 175 - 189)
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Multifactor Explanations of Fluctuations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0012
[multiple factor explanations, population fluctuations, multiple-factor hypotheses, food quality, predation, social behavior, exploitation ecosystems hypothesis]
This chapter discusses multiple factor explanations for population fluctuations in rodents. The following multiple-factor hypotheses are considered: (1) many factors affect population changes; (2) food quality and predation are key parameters causing density changes in small rodents; and (3) food quality, predation, and social behavior interact to cause density changes in small rodents. The chapter also elaborates the exploitation ecosystems hypothesis, which is a useful template with which ecologists can fit small rodent dynamics into ecosystems of differing primary productivity. (pages 190 - 208)
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Models for Fluctuating Rodent Populations - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0013
[mathematical models, population cycles, population dynamics, vegetation–herbivore population, predator–prey dynamics, reproductive timing, maternal effects]
This chapter describes the mathematical models of rodent population cycles or fluctuations. It first provides a brief historical background of mathematical models that have been put forward to explain rodent population dynamics, and then discusses six models for vegetation–herbivore population interactions and the parameters contained in these models. The chapter also discusses models of predator–prey dynamics, reproductive timing, and maternal effects. (pages 209 - 226)
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Key Studies Yet to Be Done - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0014
[population fluctuations, demographics, food, predators, maternal effects, stress, climate change]
This chapter presents a list of desirable studies that need to be done to resolve outstanding issues about rodent population fluctuations, and suggests further studies on demographics, food, predators, and intrinsic mechanisms such as maternal effects and stress. It also discusses the current research on the impact of climate change on fluctuating rodent populations, including the constraints encountered by ecologists attempting to project the effect of climatic variables. (pages 227 - 240)
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Synthesis of Rodent Population Dynamics - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0015
[population, population dynamics, density, growth rate, rodents]
This chapter outlines a synthesis for rodent population dynamics, focusing on two fundamental problems of population dynamics. These problems involve what determines the population's average density, and what determines the population's growth rate. The chapter concludes with six points of debate that have arisen in the study of small rodent populations. (pages 241 - 252)
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Comparative Dynamics of Rodents and Other Mammals - Charles J. Krebs
DOI: 10.7208/chicago/9780226010496.003.0016
[comparative population dynamics, rodents, mammals, population growth rates, population control, herbivorous mammals, population change]
This chapter provides a comparative population dynamics of rodents and other mammals. Its main objective is to identify the factors that affect population growth rates, and it begins by discussing the evolution of intrinsic processes which regulate population. The chapter then examines the population control of large herbivorous mammals, in which human hunting or poaching is the main cause of population change. A multiple-factor explanation for population changes in small herbivorous mammals is also discussed. (pages 253 - 268)
This chapter is available at:
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Bibliography
Index