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Title page for ETD etd-04102008-134103

Type of Document Dissertation
Author Hoekman, David
Author's Email Address
URN etd-04102008-134103
Title Top-Down and Bottom-Up Effects in a Detrital Food Web: The Pitcher Plant Inquiline Community as a Model Food Web
Degree Doctor of Philosophy
Department Biological Sciences
Advisory Committee
Advisor Name Title
Gary Belovsky Committee Chair
David Lodge Committee Member
Gary Lamberti Committee Member
Jessica Hellmann Committee Member
Tom Miller Committee Member
  • latitude
  • detritus processing
  • pitcher plants
  • temperature
  • detritus
  • top-down vs. buttom-up effects
  • food webs
  • community ecology
  • Sarracenia
  • top-down
  • predation
  • bottom-up
  • productivity
Date of Defense 2008-02-04
Availability unrestricted
Ecologists have long been interested in understanding factors that regulate food web dynamics. Both top-down and bottom-up forces affect populations within a food web, and their relative importance is influenced by many factors. Using the aquatic inquiline community found in pitcher plants as a model system, I conducted a series of field and laboratory experiments to explore various factors that influence the relative importance of top-down and bottom-up effects. Specifically, I examined the influence of 1) latitude 2) detritus processing and 3) temperature. I manipulated predator and resource density in factorial experiments and crossed these treatments with the three factors listed above. I measured the response of bacteria, protozoa and rotifers, the intermediate consumers in the food web.

I first demonstrated that strong top-down and bottom-up effects are present in the pitcher plant food web and comparison with another study suggested that these effects varied with latitude (chapter 2). To pursue the latitudinal effect (chapter 3), I conducted two field experiments at disparate sites (Michigan and Florida). Differences in top-down and bottom-up effects were detected both within and among

trophic levels and temperature was hypothesized as an important difference between the sites. I isolated the effect of temperature by manipulating top-down and bottom-up effects at 6 different temperatures in a laboratory experiment (chapter 5). Temperature was hypothesized to increase both top-down and bottom-up effects and to potentially alter their relative importance. Higher temperature resulted in faster predator metabolism and consequently an increase in the magnitude of top-down effects. This suggests that temperature may be an important regulator of top-down effects and that climate change can have major effects on biological communities.

I also examined the effect of detritus processing on the relative importance of top-down and bottom-up effects (chapter 4). Detritus processing did bolster bottom-up effects and surprisingly also resulted in some top-down effects, depending on the habitat preference of protozoa and rotifers. This demonstrated that detritus processors can also be important consumers in detritus-based food webs.

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