Trophic Levels

by

Lee A. Dyer

• LAST REVIEWED: 23 May 2012
• LAST MODIFIED: 23 May 2012
• DOI: 10.1093/obo/9780199830060-0075

Introduction

Trophic levels are determined by feeding relationships, with basal levels consisting of primary producers or detritus and upper levels based on consumption of these basal levels. Organisms on the second trophic level are referred to as primary consumers, which are in turn consumed by secondary consumers, and so on up a theoretical trophic chain. Primary consumers consist of herbivores and detritivores, while the third trophic level and those above include predators and parasites. Energy and matter move up trophic chains, and some compounds, including various toxins, may bioaccumulate at upper trophic levels. The concept of trophic level has generated a sizeable literature yielding useful ecological models, such as trophic cascades, and debates about top-down versus bottom-up regulation of herbivores. This article focuses on the contributions of the trophic-level concept to ecological theory, evolutionary biology, and the applied fields of agricultural and global change biology.

Textbooks

All basic ecology textbooks include a definition and discussion of trophic levels and present the basic ideas of bioaccumulation, food webs, stable isotope analysis, trophic cascades, and applied issues (Cain, et al. 2008; Ricklefs and Miller 1999). On the other hand, general ecology textbooks do not usually include good coverage of trophic diversity (e.g., interaction diversity or diversity cascades, but see Kricher 2011) or network modeling. Other textbooks, including general textbooks on aquatic or marine ecology (Kaiser, et al. 2011; Wetzel 2001) and agricultural ecology (Pedigo and Rice 2008), also include thorough coverage of the trophic-level concept. Specialized textbooks that include complete coverage and analysis of trophic-level theory include books on plant-animal interactions (Herrera and Pellmyr 2002) and insect ecology (Price, et al. 2011).

• Cain, Michael L., William D. Bowman, and Sally D. Hacker. 2008. Ecology. Sunderland, MA: Sinauer.

  This textbook includes clear and concise summaries of most of the issues in ecology relating to trophic levels. The examples, data, and figures are current and well documented, and the book is supplemented by multiple online resources.

• Herrera, Carlos M., and Olle Pellmyr. 2002. Plant-animal interactions: An evolutionary approach. Oxford: Blackwell.

  There are no thorough modern texts on plant-animal interactions, despite the fact that the field is large and growing and this is a popular upper-division course at most large universities. It is also the discipline for which trophic-level theory is most relevant. This textbook attempts to fill that void but does not include rigorous treatments of all the issues in trophic-level interactions.

• Kaiser, Michel J., M. J. Attrill, S. Jennings, et al. 2011. Marine ecology: Processes, systems, and impacts. 2d ed. New York: Oxford Univ. Press.

  An introductory textbook that covers important issues in marine ecology. Several chapters include sections and discussions of trophic levels, trophic cascades, food webs, and bioaccumulation. Also includes relevant examples from terrestrial ecosystems.

• Kricher, John C. 2011. Tropical ecology. NJ: Princeton Univ. Press.

  This textbook offers complete coverage of issues in tropical ecology, with a focus on community ecology, biogeography, and evolution. It provides introductory coverage of the trophic-level concept and complex tropical food webs, systems for which trophic levels are the most difficult to study.

• Pedigo, Larry P., and Martin E. Rice. 2008. Entomology and pest management. 6th ed. Upper Saddle River, NJ: Prentice Hall.

  An easy-to-read textbook with good documentation, this book covers agricultural applications of trophic-level theory, particularly biological control and trophic cascades. A good source of information on the effects of modern insecticides on trophic chains.

• Price, Peter W., Robert F. Denno, Micki D. Eubanks, Deborah L. Finke, and Ian Kaplan. 2011. Insect ecology: Behavior, populations and communities. Cambridge, UK: Cambridge Univ. Press.

  This is the most thorough and best-designed book on insect ecology, and it includes excellent coverage of trophic-level interactions, including applied issues such as biological control.

• Ricklefs, Robert E., and Gary L. Miller. 1999. Ecology. 4th ed. New York: W. H. Freeman.

  Although this textbook is becoming outdated, it is the most thorough college-level textbook on ecology and has multiple sections on trophic levels, including discussions of problems with the trophic-level concept.

• Wetzel, Robert G. 2001. Limnology. 3d ed. Lake and River Ecosystems. San Diego, CA: Academic Press.

  All aspects of trophic-level research have been better studied in aquatic systems, partly because it is easier to manipulate entire trophic levels. Thus, the aquatic ecology and limnological textbooks usually have the most thorough coverage of issues pertaining to trophic levels. This textbook has it all.