268
CHARLES J. KREBS AND JUDITH H. MYERS
VII. Evolution of Microtine Cycles
.
. 384
VIII. Summary .
. 386
Acknowledgements
.
. 389
References .
. 389
I. INTRODUCTION
Vole and lemming populations undergo fluctuations which comprise
one of the classic unsolved problems of animal ecology. Two facets of
these fluctuations have interested ecologists: their cyclic periodicity
and their amplitude. Many small rodents reach high densities every
three to four years, and the word cycle has been used in a loose sense
to describe the alternating sequence of high and low populations. The
amplitude of fluctuation is great. Fields which were essentially empty
one year may be scarred with microtine runways the next year.
Lemmings which were hard to catch one fall may be swarming everywhere the next spring. Rodent populations thus seem to incorporate
fluctuations (common in many organisms) and a cyclic rhythm longer
than a year (uncommon).
Voles and lemmings have always been an enigma to population
ecologists because they have never seemed to fit into the current
orthodoxy. Population changes in voles and lemmings cannot be
explained or predicted. We cannot apply current theories on population
control to these rodents and this lack of understanding may have three
explanations: (1) these small rodents are poor subjects in which to
study population ecology; (2) ecologists working on these animals
have been particularly inept; or (3) our current views on population
control may be incomplete. Each of these explanations may be supported by a survey of the literature on this problem.
The purpose of this review is to summarize current information on
population cycles in small rodents. We will look first at some general
questions about cycles, then discuss the demographic machinery which
drives the changes in numbers, and finally analyze the current theories
which purport to explain population cycles in rodents.
11. HISTORICAL PERSPECTIVE
Outbreaks or plagues of voles and mice have been described in the
Old Testament, and Charles Elton has gathered much of this historical
material into his classic book “Voles, Mice and Lemmings” (1942).
Elton describes (p. 3) the response of people to plagues of mice:
The affair runs always along a similar course. Voles multiply. Destruction reigns. There is dismay, followed by outcry, and demands to
CHARLES J. KREBS AND JUDITH H. MYERS
VII. Evolution of Microtine Cycles
.
. 384
VIII. Summary .
. 386
Acknowledgements
.
. 389
References .
. 389
I. INTRODUCTION
Vole and lemming populations undergo fluctuations which comprise
one of the classic unsolved problems of animal ecology. Two facets of
these fluctuations have interested ecologists: their cyclic periodicity
and their amplitude. Many small rodents reach high densities every
three to four years, and the word cycle has been used in a loose sense
to describe the alternating sequence of high and low populations. The
amplitude of fluctuation is great. Fields which were essentially empty
one year may be scarred with microtine runways the next year.
Lemmings which were hard to catch one fall may be swarming everywhere the next spring. Rodent populations thus seem to incorporate
fluctuations (common in many organisms) and a cyclic rhythm longer
than a year (uncommon).
Voles and lemmings have always been an enigma to population
ecologists because they have never seemed to fit into the current
orthodoxy. Population changes in voles and lemmings cannot be
explained or predicted. We cannot apply current theories on population
control to these rodents and this lack of understanding may have three
explanations: (1) these small rodents are poor subjects in which to
study population ecology; (2) ecologists working on these animals
have been particularly inept; or (3) our current views on population
control may be incomplete. Each of these explanations may be supported by a survey of the literature on this problem.
The purpose of this review is to summarize current information on
population cycles in small rodents. We will look first at some general
questions about cycles, then discuss the demographic machinery which
drives the changes in numbers, and finally analyze the current theories
which purport to explain population cycles in rodents.
11. HISTORICAL PERSPECTIVE
Outbreaks or plagues of voles and mice have been described in the
Old Testament, and Charles Elton has gathered much of this historical
material into his classic book “Voles, Mice and Lemmings” (1942).
Elton describes (p. 3) the response of people to plagues of mice:
The affair runs always along a similar course. Voles multiply. Destruction reigns. There is dismay, followed by outcry, and demands to