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Foraging ecology of two piscivores in woody habitat and effects of their introduction on lake ecosystems

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Title: Foraging ecology of two piscivores in woody habitat and effects of their introduction on lake ecosystems
Author(s): Deboom, Corey
Advisor(s): Wahl, David H.
Department / Program: Natural Res & Env Sci
Discipline: Natural Res & Env Sciences
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Predation Trophic Cascade Habitat
Abstract: Predation is a major ecological force affecting the abundance and species composition of natural communities. Predation from piscivorous fish is a strong driver of these patterns in freshwater aquatic communities. My research is directed at testing whether the introduction and augmentation of piscivore populations, as well as the alteration of littoral habitats, in Illinois lakes affects the consequences of predation for other ecologically and recreationally important species in these ecosystems. Some studies in lentic ecosystems have found large effects of introducing piscivores to systems that previously lacked them, as well as, to the artificial enhancement of piscivore populations. While the evidence for such “trophic cascades” is plentiful, a large body of subsequent research has suggested that certain properties of lakes found in lower latitude systems in the central and southern United States may buffer these systems from cascading effects of piscivore manipulations. Therefore, there is a need to test the generality of cascading trophic interactions in these lower latitude lentic ecosystems. Thus, in chapter 1 I tested for the effects of supplemental piscivore enhancements on the food webs of several Illinois lakes in a series of whole-lake experiments incorporating unmanipulated control systems. I found that piscivore enhancements in Illinois lakes did not cause the predicted pelagic food web changes predicted by the traditional trophic cascade theory; however, there was a significant effect upon littoral macroinvertebrates. This effect was driven by a reduction in the abundance of small bodied littoral fishes (primarily juvenile bluegills) after the initiation of supplemental largemouth bass stocking. My results highlight the importance of system-specific characteristics in determining the effects of piscivore enhancement measures. In addition to piscivore enhancement, there is a need to better understand the effects of introducing new piscivore species. Previous studies suggest that the introduction of new species can drive a nearly limitless array of food web consequences, with the most common including direct and indirect interactions between top predators and changes in prey mortality rates. In a controlled experimental design, I tested for changes in population characteristics including size structure, condition, and relative abundance of several ecologically and recreational important resident fish species in response to muskellunge introduction across several Illinois lakes. I found that contrary to popular concerns, the dominant resident piscivore largemouth bass generally increased in relative abundance in response to muskellunge introduction. I also found few effects of introduced muskellunge on common prey species, with the exception of Pomoxis spp., which exhibited increases in size structure and/or decreases in relative abundance. My results indicate that the current trend of muskellunge introduction in lower Midwestern lakes does not appear to be significantly harming resident populations; however, much future work remains in this area. Physical habitat can be an important determinant of the strength of piscivory on freshwater fish populations. Thus, I conducted a manipulative laboratory experiment to test for the effects of coarse woody habitat complexity on the piscivore-prey interaction between four species with contrasting predatory and anti-predatory behavioral traits. I found that woody habitat in the form of deadfall conifer branches did not reduce total prey fish mortality rates inflicted by piscivores in experimental arenas. I did find an increase in mortality rate with increasing coarse woody habitat complexity for an obligate shoaling prey fish. Furthermore, there were significant effects of coarse woody habitat complexity on foraging efficiency of piscivores, which may influence metabolic costs and therefore piscivore energy balance (as net energy for reproduction and growth is equal to energy consumption minus losses due to excretion, egestion and metabolism). Collectively, my results suggest that coarse woody habitat may influence piscivore-prey interactions principally through behavioral mechanisms and subsequent effects of behavior on piscivore energy balance as defined above.
Issue Date: 2012-09-18
URI: http://hdl.handle.net/2142/34331
Rights Information: Copyright 2012 Corey Deboom
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08
 

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