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8 - Zooplankton community dynamics
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- Book:
- The Trophic Cascade in Lakes
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- 06 August 2010
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- 19 August 1993, pp 116-152
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Summary
Introduction
Whole-lake manipulations of the fish assemblages in Peter and Tuesday Lakes provided an excellent opportunity to ask how vertebrate and invertebrate predators affect zooplankton communities. A central element of the cascade hypothesis is the regulation of large herbivores by visually feeding planktivores. In the light of the prominent position that large herbivores can occupy in zooplankton communities, repercussions in populations of less conspicuous taxa are expected (Lewis, 1979; Zaret, 1980; Kerfoot & Sih, 1987). These include compensatory shifts in the dominant species and increases in previously rare species.
Planktivory by fishes and invertebrates (such as Chaoborus) has both direct and indirect effects on zooplankton populations (Zaret, 1980; Neill, 1981; Vanni, 1986). Fish predation can constrain the maximum adult body size of prey, while invertebrate predation can restrict the minimum size. Either can interact with effects of food limitation to alter zooplankton populations (Hall et al., 1976). At the community level, however, the significance of predation is less clear. Changes in density alone may not be sufficient to alter competitive exclusion, diversity, or their consequences for the community (Thorp, 1986). Interpretations of zooplankton community structure must consider competitive interactions among species, especially among the dominant herbivores (Lynch, 1979).
In this chapter, we focus on the changes in the zooplankton communities of Peter and Tuesday Lakes as a result of fish manipulations and contrast them to the natural variation exhibited by Paul Lake.
10 - Zooplankton biomass and body size
- 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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- 06 August 2010
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- 19 August 1993, pp 172-188
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Summary
Introduction
Zooplankton affect lake ecosystem processes by grazing on phytoplankton, recycling nutrients through excretion, and serving as prey for both vertebrate and invertebrate planktivores (Brooks & Dodson, 1965; Peters, 1975; Neill, 1981). Consequently, the zooplankton can be analyzed from two points of view: as a dependent variable with respect to planktivores, and as an independent variable with respect to algal community dynamics and nutrient recycling. In this chapter, we focus primarily on the responses of zooplankton biomass and body size to manipulations of fish populations. Responses of the phytoplankton to changes in the zooplankton community are addressed in Chapters 11 and 13.
Planktivorous fish feed selectively on larger and more conspicuous zooplankton (Zaret, 1980; Neill, 1984; Vanni, 1986). Zooplankton community changes associated with fish manipulations were discussed in Chapter 8. Here, we examine the implications for the total biomass and the size structure of the zooplankton, which are associated with rates of key ecosystem processes. Rates of grazing or nutrient excretion per unit biomass are proportional to the body mass of individual zooplankters (Peters, 1983). The range of particle sizes consumed by filter-feeding cladocerans is also proportional to body size (Burns, 1968).
Total rates of grazing or nutrient excretion scale directly with zooplankton biomass. Therefore, zooplankton body size and biomass indicate the potential rates of ecosystem processes, such as grazing and nutrient excretion, that are performed by the herbivorous zooplankton.
13 - Primary production and its interactions with nutrients and light transmission
- 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 225-251
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Summary
Introduction
The trophic cascade from fish to ecosystem processes is the central theme of this book. Previous chapters have documented the changes in piscivore, planktivore and herbivore trophic levels in our experimental lakes. Effects of changes in herbivory on phytoplankton communities have been discussed (Chapter 11) and we have compared the distinctive habitats for algae provided by the epilimnion and metalimnion (Chapter 12). This chapter turns to the central ecosystem variates of our study: biomass and metabolism of primary producers.
In lakes, dynamics of herbivores, primary producers nutrients, and light have strong feedbacks. Excretion by herbivores is a major source of nutrients for phytoplankton. Limnetic grazers affect their prey negatively, through grazing, and positively, through nutrient recycling. The phytoplankton also respond to inputs of nutrients from outside the lake, and to mixing of nutrients upward from the hypolimnion. Light drives photosynthesis, and phytoplankton attenuate light as it passes down-ward through the water column. In lakes where substantial aggregations of algae exist in deep, low-light habitats, feedbacks between algal biomass and light extinction may strongly influence primary production (Chapter 12).
These strong feedbacks imply that primary production cannot be addressed without considering physical–chemical factors such as mixing depth, irradiance, and nutrient limitation. This chapter focuses on dynamics of algal biomass (measured as chlorophyll) and production, in the context of selected physical and chemical characteristics of the water column. These include indicators of nutrient deficiency, light penetration, and mixing depth.
9 - Effects of predators and food supply on diel vertical migration of Daphnia
- 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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- 06 August 2010
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- 19 August 1993, pp 153-171
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Summary
Introduction
The Cascade Project provided a perfect opportunity to study one of the great puzzles of limnology, a puzzle which has occupied numerous aquatic biologists over the past century-and-three-quarters. Hardy (1956) called it ‘the planktonic problem No. 1’ and more recent research has still not succeeded in providing an ultimate explanation that satisfies all cases. The adaptive significance of nocturnal diel vertical migration (DVM), a phenomenon whereby organisms throughout 15 aquatic phyla (Kerfoot, 1985) ascend through the water column around dusk and descend before dawn on a daily basis, is one of limnology's longest-standing enigmas.
Initial research on DVM was not published until almost sixty years after Baron Cuvier (1817) first documented its existence among fresh-water crustaceans. The phenomenon received attention from many of the crowned heads of nineteenth century European biology. August Weismann (1874, 1877), one of Darwin's strongest supporters on the Continent, and Forel (1876) both speculated on the causes of the behavior, as did Thienemann in the next century (1919). Most explanations from the nineteenth century, as well as from the first half of the twentieth, focused on the proximal causes of the behavior. Many abiotic factors were proposed as cues for the initiation of migratory behavior, including diel changes in temperature, pH, light intensity and density (Kikuchi, 1930). It eventually became apparent that no single factor could explain the many behavioral variations exhibited by migrators, including differences in the same species' migratory behavior in lakes near each other, and even substantial differences in migration by the same species in the same body of water (Juday, 1904; Kikuchi, 1930).
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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- The Trophic Cascade in Lakes
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- 19 August 1993, pp 85-102
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Summary
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).
7 - Dynamics of the phantom midge: implications for zooplankton
- Edited by Stephen R. Carpenter, University of Wisconsin, Madison, James F. Kitchell, University of Wisconsin, Madison
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- Book:
- The Trophic Cascade in Lakes
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- 06 August 2010
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- 19 August 1993, pp 103-115
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Summary
Introduction
Invertebrate planktivores occupy an intriguing position in the pelagic food web. Like other zooplankton, they are vulnerable to planktivory by fishes, yet they can prey heavily on certain zooplankton (Dodson, 1972; Neill, 1981; Black & Hairston, 1988; Hanazato & Yasuno, 1989). In Paul, Peter, and Tuesday Lakes, the most important invertebrate planktivores are larvae of three species of Chaoborus, the phantom midge. Owing, in part, to behavioral responses and ontogenetic diet shifts of both fishes and Chaoborus, the interaction between the two and consequences for zooplankton communities can be difficult to predict (Luecke, 1986; Elser et al., 1987b; Neill, 1988; Hanazato & Yasuno, 1989). The trophic cascade hypothesis states that planktivory by invertebrates is inversely related to planktivory by fishes (Carpenter et al., 1985). Nevertheless, we anticipated little change in Chaoborus during our experiments, because of their cryptic morphology and pronounced diel vertical migration behavior (Carpenter & Kitchell, 1987). Here we examine how Chaoborus populations responded to the fish manipulations, and consider the consequences for the trophic cascade.
Chaoborus develop through four instars as planktonic larvae before pupating. Their body is relatively transparent, except for well-developed hydrostatic organs, hence the common name phantom midge (Fig. 8.1, Chapter 8). Nevertheless, they are susceptible to predation by fishes. In lakes with fish, third- and fourth-instar Chaoborus will spend the days in either the hypolimnion, metalimnion, or bottom sediments and come to the surface at night to feed (Roth, 1968; von Ende, 1979; Luecke, 1986).