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4 - The fish populations
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 43-68
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Summary
Introduction
Fundamental to the cascade hypothesis are the effects that fish populations can exert on species composition, biomass and productivity at other trophic levels. These may be direct or indirect (nonlethal) effects. Direct effects such as prey consumption, and indirect effects such as those influencing behavior (avoidance of predators) have been widely documented at the population level (e.g. Stroud & Clepper, 1979; Werner et al., 1983) and the indirect effects expressed at the community and ecosystem levels such as those reviewed in Kerfoot & Sih (1987) & Northcote (1988). Indirect effects pertinent in the case of our studies would include behavioral responses, such as migration from or selection of specific refugia from predation (e.g. diel vertical migration of zooplankton and onshore–offshore migration of small fishes), that result in changes in foraging patterns of prey species (Carpenter et al., 1987; He & Kitchell, 1990; He & Wright, 1992; Chapter 5). Another category of effects includes changes in nutrient flux due to shifts in the behavioral or structural properties of the fish populations (Carpenter et al., 1992b).
Fish in our study lakes (Fig. 4.1) are common to the Great Lakes region, but some are near the limits of their geographic distributions. Largemouth bass and golden shiner are at the northern limits, while finescale and northern redbelly dace are near the southern limits (Scott & Crossman, 1973; Becker, 1983). Adult largemouth bass and rainbow trout can be keystone piscivores (Keast, 1985; Carpenter et al., 1985, 1987) with an ability to limit the abundance of forage fish.
16 - Simulation models of the trophic cascade: predictions and evaluations
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 310-331
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Summary
Introduction
Previous chapters have detailed the responses of Peter and Tuesday Lakes to fish manipulations. Some of the changes were anticipated, while others were surprises. Our research was guided by models of the trophic cascade in lakes. To what extent did these models forecast the experimental results? The purpose of this chapter is to assess how our predictions fared, and how our view of the trophic cascade has been modified by the experimental outcome. First, we must explain why we developed simulation models of the trophic cascade, how the models were structured, and the predictions that derived from the models.
The trophic cascade is, in essence, a simple idea. In the complexity of real lakes, however, it involves the collective outcome of life history, predator–prey, and physical–chemical processes that cannot be adequately represented by simple verbal, graphical or mathematical models. Computer simulations are one way of integrating these complex interactions. They elaborate the conceptual framework and develop specific, testable predictions. We began simulation studies of the trophic cascade in 1981, three years before initiating the ecosystem experiments. Many of the predictions of those models can now be evaluated.
This chapter has four parts. First, we review three simulation models that produced the hypotheses we tested in the field. Second, we address predictions specific to the outcome of our ecosystem experiments. Third, we turn to more general expectations that should apply to trophic cascades in many lakes.
15 - Annual fossil records of food-web manipulation
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 278-309
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Introduction
Limnologists are interested in why lakes vary from year to year. Studies of temporal variability under baseline conditions are needed to quantify the relative importance of mechanisms regulating production, to interpret ecosystem experiments and to help solve lake management problems (McQueen et al., 1986; Benndorf, 1987; Carpenter, 1988a).
Long-term studies, ecosystem experiments and paleolimnology provide information on interannual variation in lakes. Long-term studies potentially span many short and intermediate-length processes (10−4−101 y) (Edmondson & Litt, 1982; Goldman, Jassby & Powell, 1989; Schindler et al., 1990) but are rare and sometimes purely descriptive or site-specific. Results of ecosystem experiments may apply more broadly (Carpenter, 1991), but are also costly and rare. Further, many are too brief (<10−1 y) to detect the long-term responses of lakes to perturbation. Paleolimnology is relatively inexpensive and can yield records that are otherwise unobtainable.
Paleolimnology is the study of lake ecosystem structure and function using the historical record in sediments. Lake sediments accumulate through time and integrate material from the lake, its basin and catchment, and atmospheric sources (Frey, 1969; Binford, Deevey & Crisman, 1983; Battarbee et al., 1990). Development of high resolution sampling techniques (Glew, 1988; Davidson, 1988; Leavitt et al., 1989), well-defined taxonomy and autecology (e.g. Walker, 1987; Kingston & Birks, 1990) and automated analysis of some fossils (Mantoura & Llewellyn, 1983) allows paleoecological analysis on time scales relevant to population interactions in lakes and watersheds (10−1−104 y).
1 - Cascading trophic interactions
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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Introduction
The extent to which physical–chemical or biotic factors influence community structure and ecosystem function continues as one of the fundamental issues of ecology. The action and interaction of abiotic and biotic factors was recognized in early concepts of plant succession (McIntosh, 1985) and continues in the most contemporary reviews of plant-animal interaction (Strong, 1992). In animal community ecology, there have been several recent syntheses of the effects of multiple controlling factors (Menge & Sutherland, 1976, 1987; Fretwell, 1977; Oksanene et al., 1981; Power, 1992; Strong, 1983, 1992). Vigorous debate has surrounded the relative roles of predation and competition (Hairston, Smith & Slobodkin, 1960; Murdoch, 1966). Predation has been viewed from the standpoints of predator control of prey communities (Oksanen, 1983, 1990) and of prey constraints on predator communities (Price et al., 1980; Kareiva & Sahakian, 1990; Hunter & Price, 1992).
Like the other branches of ecology, limnology has evolved through debates about the roles of abiotic and biotic factors (Edmondson, 1991). In some respects, lakes are ideal systems for the study of multifactor interactions at the ecosystem scale (Carpenter, 1988a, pp. 4–5). Boundaries are clear and the difficulties of system definition that plague some areas of ecology (McIntosh, 1985) are lessened. Lakes are amenable to experimentation on a variety of scales, including whole-lake manipulations (Frost et al., 1988). At a global scale, insolation and climate have dominant effects on lake ecosystems (Brylinsky & Mann, 1973).
17 - Synthesis and new directions
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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Introduction
Preceding chapters provide the theoretical, analytical and empirical background for food-web interactions in an ecosystem context. In this chapter, we summarize what we consider to be the major accomplishments of our work and our interpretation of certain important, unexpected results. We also provide our view of the next generation of research issues involving the interactions of food-web structure and nutrient status in lakes, and speculate about the generality of trophic cascades in terrestrial and aquatic ecosystems.
Our primary goal in designing these experiments was to evaluate the role of food-web interactions in regulating primary production rates of planktonic algae. Regressions based on data from many lakes revealed that nutrient loading rates could account for only about half of the observed variance in primary production; roughly an order of magnitude of variability among lakes remained unexplained (Carpenter & Kitchell, 1984; Carpenter et al., 1985). We reasoned that a substantial share of that was due to differences in trophic interactions and developed a set of experiments designed to test that idea. Manipulations of fish populations in Peter and Tuesday Lakes were intended to yield maximum contrast in food web structure while the reference system, Paul Lake, remained as a monitor of interannual variance due to other sources.
We found that piscivores had rapid, massive effects on planktivores (Chapters 4–6). Predator avoidance behavior exhibited by small fishes caused planktivory in the pelagic zone to decrease much more rapidly than it would have done through piscivory alone (Chapter 5).
6 - Roles of fish predation: piscivory and planktivory
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- 19 August 1993, pp 85-102
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Introduction
Understanding the impacts of fish predation on lower trophic levels is a generally important goal (Wootton, 1990). In the special case of our studies, fishes are the reagents of whole-lake experiments. Because many fishes are opportunistic predators capable of complex behavior (Chapters 4 and 5; Hodgson & Kitchell, 1987), manipulation of fish populations may change predation pressure on lower trophic levels in unexpected ways. Therefore, it was essential to measure rates of predation on key food web components during the course of our experiments.
In piscivore-dominated systems, some species of planktivorous fishes may not persist or may be maintained at very low population densities (Tonn & Magnuson, 1982). Juvenile fishes are typically planktivorous and may be very abundant after hatching. Although a cohort of juveniles may be dramatically reduced owing to intense, continuous predation by adult piscivores, their effect as predators of zooplankton may be intense for very short periods. The prospect for a pulse of zooplanktivory followed by a pulse of piscivory heightened our interest in providing quantitative measures of intensity and duration of such short-term dynamics in predator–prey interactions revolving around fishes.
Habitat heterogeneity and habitat selection also influence predator–prey interactions (Werner & Gilliam, 1984). The relatively simple habitats in our study lakes provide only a modest amount of refuge where prey fishes may escape piscivores. Lack of refugia in Peter Lake explains the quick disappearance of the minnows introduced in 1985 and the rapid decline of rainbow trout in 1989 (Chapter 4).
5 - Fish behavioral and community responses to manipulation
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- By X. He, R. Wright, J. F. Kitchell
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 69-84
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Introduction
As detailed in Chapters 2 and 4, we manipulated individual fish populations to change food web structure. In addition, we were able to follow dramatic responses in the fish community structure. Shifting a system from dominance by planktivores to one dominated by piscivores was accomplished relatively simply by introducing large numbers of piscivores. Establishing a planktivore-dominated system by eliminating piscivores first and then introducing planktivores has also worked well. These techniques were used in the manipulations in Tuesday Lake (Chapters 2 and 4). The resulting dominance by planktivores or piscivores provided dramatic contrasts in food web structure; however, most natural lake systems (such as those regularly subjected to fisheries exploitation) have mixed assemblages of piscivores and planktivores. The greater diversity and complexity of many fish communities encourages a search for general ecological principles (Werner & Gilliam, 1984). Fish communities are often further influenced by stocking and/or species- and size-selective harvest regulations. Thus, the interests of managers in facilitating or diminishing the relative abundance of selected species suggests that we must better understand the interactions among piscivorous and planktivorous fishes, and the resulting effects on other trophic levels.
In Peter Lake, attempts to establish dominance by planktivorous fishes in 1985 and 1989 failed (Chapters 2 and 4). The minnow population introduced in 1985 declined much more rapidly than could be accounted for by direct predation by known numbers of largemouth bass in the lake.
2 - Experimental lakes, manipulations and measurements
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 15-25
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The experimental lakes
Our studies were conducted in Paul, Peter, and Tuesday Lakes (Fig. 2.1). These lakes lie on the grounds of the University of Notre Dame Environmental Research Center (UNDERC) near Land o' Lakes, Wisconsin, U.S.A. (89°32′ W, 46°13′N). UNDERC occupies more than 2800 ha of land donated to the University of Notre Dame in the 1940s ‘for the scientific purposes of Forestry, Botany, Biology and allied sciences’ (Gillen, 1939). The limnological potential of the property had been recognized in the 1920s, when E. A. Birge, C. Juday and associates sampled most of its lakes (Beckel, 1987).
Because the UNDERC facility is privately owned and protected, it offers remarkable opportunities for field experimentation. Fish populations in the experimental lakes are unexploited, and can be manipulated without the complications of sport or commercial fishing. The drainage basins are undeveloped and lie entirely within the UNDERC property, so disturbances or chemical inputs to the lakes that might confound ecosystem experiments are minimized. UNDERC is about 40 km from the University of Wisconsin's Trout Lake Station, a national center of limnological activity for more than 50 years (Magnuson & Bowser, 1990). The array of intensively studied lakes in the region provides additional reference (or ‘control’) systems for manipulative experiments (Carpenter et al., 1989) as well as opportunities for comparative studies (Carpenters et al., 1991).