Food Web Architecture and Population Dynamics: Theory and Empirical EvidencePeter J. Morin; Sharon P. LawlerAnnual Review of Ecology and Systematics, Vol. 26. (1995), pp. 505-529.Stable URL:http://links.jstor.org/sici?sici=0066-4162%281995%2926%3C505%3AFWAAPD%3E2.0.CO%3B2-DAnnual Review of Ecology and Systematics is currently published by Annual Reviews.Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtainedprior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content inthe JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. 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Morin Department of Biological Sciences, Rutgers University, New Brunswick, New Jersey 08855-1059 Sharon P. L.awlerl Center for Ecology, Evolution and Behavior, Biological Sciences, University of Kentucky, Lexington, Kentucky 40506-0225 KEY WORDS: complexity, food web, food chain length, omnivory, population dynamics, productivity, stability Food web theory makes quantitative and qualitative predictions about the patterns of population dynamics to be expected in food webs with particular structures. Some of these predictions can be tested by comparing population dynamics in simple food chains of different architecture. Few studies have been designed specifically to manipulate food chain properties as a test of food web theory, but relevant information can be gleaned from studies of predator- prey dynamics in which food chain structure is known to vary in important ways. For example, comparisons of prey population dynamics in the presence or absence of a predator can be used to infer the consequences of a small change in food chain length. Common consequences of increased food chain length include greater temporal variation in abundance and a greater frequency of local extinctions. Studies that compare the impact of omnivore and nonom- nivore predators are so infrequent that few conclusions can be reached. Ex- 'present Address: Department of Entomology, University of California, Davis, California 95616 505506 MORIN & LAWLER perimental studies of links between productivity and food chain length or population dynamics are also scarce. However, an emerging theme is that both increased and decreased productivity sometimes result in shorter food chains, probably for different mechanistic reasons. Studies of trophic cascades indicate that differences in the length of linear food chains have important consequences for the standing stock of species in different trophic levels, regardless of any effects on dynamics. Finally, a few studies of relations between food web complexity and the dynamics suggest that more complex systems can be less stable than simple systems, although these effects probably depend on how complexity is distributed among trophic levels. INTRODUCTION Food Web Theory Food web theory remains controversial, largely because it is difficult to test its chief predictions about population dynamics in natural systems (65). Al- though Elton (29) sensitized ecologists to the importance of basic food web concepts during the formative years of modem ecology, the quantitative study of food webs has only recently come into its own. The recent growth of interest in food webs has been stimulated largely by theoretical work on factors that might constrain patterns of trophic connections within webs (16,83,117,172). Many generalizations about the structure and function of food webs are based on the dynamic properties of relatively simple models of food webs or food chains (65,117, 123, 172). Other generalizations about the architecture of food webs arise from the comparative study of patterns in natural food webs (16, 80, 81, 161). Indeed, Lawton & Warren (67) noted that food web theory can be divided into studies providing a population dynamic explanation for the static patterns of food webs (8,23,36,47,49,82,83,102,113-115, 117,120, 121, 124, 131, 137) and other approaches that provide descriptive statistical or graphical generalizations about web structure, without explicit reference to the effects of web structure on dynamics (16-19, 64, 80, 81, 101, 116, 122, 147, 165-172). We are primarily interested in examining the effects of food web architecture on population dynamics, because theory suggests some clearly testable hypotheses about the population dynamics of species embedded in webs of different structure. We focus here on a restricted set of issues selected from within the broad realm of food web theory. Those issues include: 1. factors that limit the length of food chains, including constraints imposed by population dynamics and energetics, 2. relations between the length and complexity of food chains and the existence of trophic cascades, and 3. relations between food web complex-FOOD WEB DYNAMICS 507 ity and population dynamics. All of these issues have a rich if not entirely realistic theoretical underpinning. Often, more than one theoretical framework has been proposed to account for a particular pattern. In contrast to the wealth of theoretical work addressing food web patterns, the amount of experimental work that can be mustered to test food web theory is surprisingly limited. This limitation reflects two factors. Fist, the data needed to address the predictions made