Chapter 37
Recruitment and Trophic Dynamics
of Gizzard Shad
The exquisite manipulation of the master gives to each atom of
the multitude its own character and expression.
(Ruskin, 1843)
37.1 Gizzard Shad Model
The previous chapter provides one example of ways in which ecosystems can be
managed via the deliberate manipulation of food webs. In this chapter, we develop a
model of the addition of piscivorous (fish-eating) predators to a system that may
enhance water quality by reducing algal biomass. These effects are obtained when
predators diminish for example planktivore biomass, which in turn release zooplankton production. Increased numbers of zooplankton then result in lower numbers of algae, which increases water quality for human uses.
Unfortunately, numerous exceptions have been found within this simple “cascading” mechanism. For instance, due to rapid turnover of primary production,
highly eutrophic systems are not easily limited by top-down regulation. Systems
with many littoral plants also resist biomanipulation, since these plants serve as a
reservoir of production and nutrients apart from the limnetic community.
The model developed in this chapter examines the recruitment and trophic
dynamics of a freshwater clupeid, gizzard shad, in a flood control reservoir. Due
to rapid growth, omnivorous food habits, and a high fecundity, populations of this
fish species may escape both regulation by predators, and competition for food
resources. As a result they may often impact predator and zooplankton populations
more than they are impacted themselves. Such “middle-out” effects in the trophic
A save-disabled version of STELLA and the computer models of this book are available at
www.iseesystems.com/modelingdynamicbiologicalsystems.
B. Hannon and M. Ruth, Modeling Dynamic Biological Systems,
Modeling Dynamic Systems, DOI 10.1007/978-3-319-05615-9_37,
© Springer International Publishing Switzerland 2014
327
Recruitment and Trophic Dynamics
of Gizzard Shad
The exquisite manipulation of the master gives to each atom of
the multitude its own character and expression.
(Ruskin, 1843)
37.1 Gizzard Shad Model
The previous chapter provides one example of ways in which ecosystems can be
managed via the deliberate manipulation of food webs. In this chapter, we develop a
model of the addition of piscivorous (fish-eating) predators to a system that may
enhance water quality by reducing algal biomass. These effects are obtained when
predators diminish for example planktivore biomass, which in turn release zooplankton production. Increased numbers of zooplankton then result in lower numbers of algae, which increases water quality for human uses.
Unfortunately, numerous exceptions have been found within this simple “cascading” mechanism. For instance, due to rapid turnover of primary production,
highly eutrophic systems are not easily limited by top-down regulation. Systems
with many littoral plants also resist biomanipulation, since these plants serve as a
reservoir of production and nutrients apart from the limnetic community.
The model developed in this chapter examines the recruitment and trophic
dynamics of a freshwater clupeid, gizzard shad, in a flood control reservoir. Due
to rapid growth, omnivorous food habits, and a high fecundity, populations of this
fish species may escape both regulation by predators, and competition for food
resources. As a result they may often impact predator and zooplankton populations
more than they are impacted themselves. Such “middle-out” effects in the trophic
A save-disabled version of STELLA and the computer models of this book are available at
www.iseesystems.com/modelingdynamicbiologicalsystems.
B. Hannon and M. Ruth, Modeling Dynamic Biological Systems,
Modeling Dynamic Systems, DOI 10.1007/978-3-319-05615-9_37,
© Springer International Publishing Switzerland 2014
327