Top-Down and Bottom-Up Regulation of Communities

by

Jonathan B. Shurin

• LAST REVIEWED: 23 May 2012
• LAST MODIFIED: 23 May 2012
• DOI: 10.1093/obo/9780199830060-0029

Introduction

The dichotomy between top-down and bottom-up forces acting on populations and communities has informed and motivated research in ecology over its entire history. Early practitioners emphasized the importance of bottom-up control because of the apparent association between many species and the supply of resources from the environment. Consumers and predators, the sources of top-down control, were often assumed to exert little influence over the composition of communities or the dynamics of ecosystems. Thomas Huxley’s famous assertion in 1883 that “all the great sea fisheries, are inexhaustible; that is to say, that nothing we do seriously affects the number of the fish” reflects the general impression about the effects of many consumers, including humans, on populations of their prey (“The abundance of the seas,” New York Times, 17 November 1895). Predators were considered to be agents of natural selection, removing unfit individuals but having little impact on the numbers of their prey, which were often thought to be capable of mounting effective defensive strategies and prodigious reproduction. Top-down regulation became a strong contender as an alternative to bottom-up control in the 1960s, when theoretical and empirical evidence began to accumulate that consumers exert considerable influence over the ecosystems they inhabit. Since then a much-richer picture has emerged of how, where, and when top-down and bottom-up forces come into play and of the interaction between the two. This article deals with approaches to disentangling the effects of predators and resources on communities and ecosystems and what they have revealed about the structure and dynamics of nature.

General Overviews

The references listed here provide a broad overview of top-down and bottom-up regulation of communities of organisms and ecosystems. Elton 2001 (originally published in 1927) and Andrewartha and Birch 1954 describe the early explanations for community structure that date from the beginning of modern ecology. May 1973, Pimm 1982, and DeAngelis 1992 are theoretical works that detail mathematical formulations for hypotheses about population dynamics and community structure involving predation and resources. Estes and Terborgh 2010 and Strong and Frank 2010 synthesize the empirical and theoretical literature in showing a rich and surprising array of examples of indirect effects of different perturbations as they percolate through food webs.

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

  Describes the elements of niches, or aspects, of the biological and physical environment that determine where and when organisms live and in what numbers.

• DeAngelis, Donald L. 1992. Dynamics of nutrient cycling and food webs. New York: Chapman and Hall.

  DOI: 10.1007/978-94-011-2342-6

  A theoretical treatment of the flow of chemicals and biomass through food webs and between the living and nonliving components of the environment.

• Elton, Charles. 2001. Animal ecology. Chicago: Univ. of Chicago Press.

  Outlines the factors contributing to variation in the community structure of organisms, including environmental fluctuations, disturbances, predation, parasitism, and dispersal. Elton introduces the extremely influential concept of the “pyramid of numbers,” or the decline in abundance of organisms with trophic position (the number of feeding links that separates them from plants at the base of the food web). Originally published in 1927.

• Estes, John A., and J. Terborgh. 2010. Trophic cascades: Predators, prey, and the changing dynamics of nature. Washington, DC: Island.

  A collection of reviews emphasizing top-down forces and dramatic examples of predators and consumers shaping the structure and dynamics of the ecosystems where they live. Provides a detailed account of many of the most compelling examples of the complex effects of consumers on ecosystems.

• May, Robert M. 1973. Stability and complexity in model ecosystems. Princeton, NJ: Princeton Univ. Press.

  The earliest complete treatment of the factors that give rise to stability, or fail to do so, in population dynamics. Overturned an early paradigm that more-diverse communities are inherently more stable, showing how intrinsic and extrinsic forces affect the ways populations fluctuate through time.

• Pimm, Stuart L. 1982. Food webs. New York: Chapman and Hall.

  Develops mathematical theories of food web structure and the influence of aspects such as omnivory and food chain length on dynamic stability and persistence of populations.

• Strong, Donald R., and Kenneth T. Frank. 2010. Human involvement in food webs. Annual Review of Environment and Resources 35.1: 1–23.

  DOI: 10.1146/annurev-environ-031809-133103

  A detailed review of the many ways people altered the processes that regulate food webs both from the top down and the bottom up; an engaging read with many fascinating examples. Available online for purchase or by subscription.