Population Fluctuations and Cycles

by

John M. Fryxell

• LAST REVIEWED: 16 August 2022
• LAST MODIFIED: 24 July 2013
• DOI: 10.1093/obo/9780199830060-0061

Introduction

Population fluctuations are undoubtedly one of the most fascinating phenomena in ecology. Some of the earliest writings known to man describe outbreaks of pests, such as the fabled locust plagues in Egypt. Some species, such as the snowshoe hare or larch budmoth, cycle through changes in abundance as regular as clockwork. Many other species exhibit more irregular patterns of oscillation, and some have even been shown to fluctuate in truly chaotic fashion. Making sense of this bewildering array of dynamical patterns has been a central theme in population ecology, involving some of the leading scientists in both the experimental and theoretical realms. Key elements in this search for ecological understanding relate to measuring and characterizing different patterns of population fluctuation, theoretical modeling of hypothetical processes and mechanisms that can cause cycles or other patterns of population fluctuation, and developing ways to test these hypotheses and/or models using observational and experimental data.

General Overviews

By definition, population dynamics requires a quantitative point of view. Hastings 1997 presents an excellent introduction to the theoretical basis for population dynamics, developing many of the key concepts employed by contemporary ecologists. Lande, et al. 2003 and Ranta, et al. 2006 provide more sophisticated reviews of contemporary issues in population modeling, including effects of age and stage structure, environmental and demographic stochasticity, and the interplay between evolution and ecology. From the outset there was simmering debate among ecologists about the importance of density-dependent processes in regulating animal populations. Early lab experiments had clearly demonstrated how increases in population density were associated with diminished per capita rates of population growth. Nonetheless, many field ecologists were skeptical, arguing that climatic forcing made density-dependent processes essentially irrelevant. Andrewartha and Birch 1954 nicely summarizes many of these arguments but also introduces novel topics such as spatial heterogeneity and movement processes that have emerged in their own right as important research topics for contemporary ecologists. Sinclair 1989 provides an excellent review of the historical debate about the importance of population regulation. While most ecologists agree that the issue has now been largely resolved, Bjǿrnstad and Grenfell 2002 and Coulson, et al. 2004 point out some of the considerable remaining challenges in clarifying the relative importance of population processes versus climatic forcing in causing population fluctuations. The highly relevant monograph Turchin 2003 provides the most comprehensive review of both the theoretical basis and empirical evidence for complex population dynamics with heavy emphasis on population cycles.

• Andrewartha, H. G., and L. C. Birch. 1954. The distribution and abundance of animals. Chicago: Univ. of Chicago Press.

  Provides an extreme counterpoint to the population regulation school of thought initially promoted in Nicholson 1933 (cited under Historical Background), arguing that climatic variation over time precludes a shortage of resources or other density-dependent processes needed to stabilize populations at an equilibrium.

• Bjǿrnstad, O. N., and B. T. Grenfell. 2002. Noisy clockwork: Time series analysis of population fluctuations in animals. Science 293:638–643.

  DOI: 10.1126/science.1062226

  A compact, yet comprehensive summary of contemporary views of population dynamics as influenced by density-dependent versus density-independent processes, time lags, and non-linear dynamics.

• Coulson, T., P. Rohani, and M. Pascual. 2004. Skeletons, noise and population growth: The end of an old debate. Trends in Ecology and Evolution 19:359–364.

  DOI: 10.1016/j.tree.2004.05.008

  Reviews the debate between proponents of density-dependent population regulation versus climate as a limiting factor, arriving at a synthesis incorporating both points of view.

• Hastings, Alan. 1997. Population biology: Concepts and models. New York: Springer.

  DOI: 10.1007/978-1-4757-2731-9

  An excellent primer on population dynamics, evolution, and ecological interactions among species.

• Lande, Russell, Steinar Engen, and Bernt-Erik Sǽther. 2003. Stochastic population dynamics in ecology and conservation. Oxford: Oxford Univ. Press.

  DOI: 10.1093/acprof:oso/9780198525257.001.0001

  A fairly advanced textbook covering theoretical topics of contemporary interest in population and conservation biology in sophisticated fashion, including stochastic population growth, population viability analysis, structured population dynamics, and harvesting.

• Ranta, Esa, Per Lundberg, and Veijo Kaitala. 2006. Ecology of populations. Cambridge, UK: Cambridge Univ. Press.

  A sophisticated textbook covering various aspects of population dynamics, with particularly strong emphasis on integration of spatial with temporal population dynamics.

• Sinclair, A. R. E. 1989. Population regulation. In Ecological concepts: Contributions of ecology to an understanding of the world: 29th Symposium of the British Ecological Society, University College, London, 12–13 April 1988. Edited by J. M. Cherrett and A. E. Bradshaw, 197–241. Boston: Blackwell.

  A historical review of the concept of population regulation, methods of testing, and extensions to multiple equilibrium systems.

• Turchin, Peter. 2003. Complex population dynamics: A theoretical/empirical synthesis. Princeton, NJ: Princeton Univ. Press.

  Undoubtedly the most useful general reference available on theory, evidence, and methods of analysis of population fluctuations. Covers a wide range of case studies, ranging from insects to large mammals with extensive original analysis. Essential reading for anyone seriously interested in the topic.