TROPHIC INTERACTIONS in SOUTHEASTERN WETLANDS by RICHARD D. SCHULTHEIS (Under the Direction of Darold Batzer) ABSTRACT Wetlands
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TROPHIC INTERACTIONS IN SOUTHEASTERN WETLANDS by RICHARD D. SCHULTHEIS (Under the Direction of Darold Batzer) ABSTRACT Wetlands are naturally dynamic systems. In this study, I explored the effects of predation by a dynamic vertebrate complex on the aquatic invertebrate community of a southeastern wetland. A two-year predator exclusion experiment was used to test for effects of predation by marbled salamanders ( Ambystoma opacum ), spotted salamanders ( Ambystoma maculatum ), red- spotted newts ( Notophthalmus viridescens viridescens ), bluegill ( Lepomis macrochirus ), mosquitofish ( Gambusia sp.) and bullfrogs ( Rana catesbeiana ). Overall invertebrate responses to vertebrate reductions were minimal. Of sixty-five invertebrate taxa observed in the study, abundances of few differed with predator treatments, and these patterns were restricted to mainly April of both years. These findings suggest that vertebrate predation was only seasonally important in this habitat, and complex interactions within the vertebrate community likely limited our ability to detect a response to predation in the invertebrate community. INDEX WORDS: Invertebrate, trophic, predation, salamander, fish TROPHIC INTERACTIONS IN SOUTHEASTERN WETLANDS by RICHARD D. SCHULTHEIS B.S., Allegheny College, 2002 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2005 © 2005 Richard D. Schultheis All Rights Reserved TROPHIC INTERACTIONS IN SOUTHEASTERN WETLANDS by RICHARD D. SCHULTHEIS Major Professor: Darold P. Batzer Committee: Sara H. Schweitzer Barbara E. Taylor Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2005 iv ACKNOWLEDGEMENTS I would like to thank my committee members, Dr. Barbara Taylor, Dr. Sara Schweitzer, and my advisor Dr. Darold Batzer, with whom this project would have never happened. I would additionally like to thank the ladies of the Batzer lab, Elizabeth Reese, Missy Churchill, and Jennifer Henke, for all insight, assistance, and entertainment over the last three years. Valuable assistance with amphibians was provided by Scott Connelly, to whom I am grateful. I would like to thank my parents, family, and friends for the support, assistance, and distraction I needed the last few years. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS........................................................................................................... iv LIST OF TABLES......................................................................................................................... vi LIST OF FIGURES ...................................................................................................................... vii CHAPTER 1 INTRODUCTION .........................................................................................................1 2 METHODS ....................................................................................................................5 STUDY AREA..........................................................................................................5 EXPERIMENTAL DESIGN.....................................................................................7 STATISTICAL ANALYSIS.....................................................................................9 3 RESULTS ....................................................................................................................11 VERTEBRATE COMMUNITY.............................................................................11 INVERTEBRATE COMMUNITY.........................................................................12 EFFICACY OF VERTEBRATE EXCLUSION.....................................................12 CAGE EFFECTS ....................................................................................................13 INVERTEBRATE RESPONSE TO VERTEBRATE EXCLUSION.....................13 FIGURES AND TABLES.......................................................................................16 4 DISCUSSION..............................................................................................................21 CONCLUSIONS.....................................................................................................25 LITERATURE CITED ..................................................................................................................26 vi LIST OF TABLES Page Table 1: SPECIES RICHNESS OF VERTEBRATE AND INVERTEBRATE PREDATORS ...20 vii LIST OF FIGURES Page Figure 1: VERTEBRATE PREDATOR ABUNDANCE..............................................................16 Figure 2: INVERTEBRATE ABUNDANCE – CAGE EFFECTS ...............................................17 Figure 3: SIGNIFICANT TAXA, APRIL 2003 ............................................................................18 Figure 4: SIGNIFICANT TAXA, APRIL 2004 ............................................................................19 1 CHAPTER 1 INTRODUCTION The effect of fish predation on invertebrate communities has been well documented. Although recent studies suggest interaction strength varies with habitat complexity (see Dahl and Greenberg 1998), strong interactions have been demonstrated in lakes (Carpenter et al. 1987, Bronmark et al. 1992, Diehl 1995, Osenberg and Mittelbach 1996), ponds (Hall et al. 1970, Hambright et al. 1986, Warren 1989, Diehl 1992), and streams or rivers (Koetsier 1989, Power 1990, 1992, Bechara et al. 1992, 1993). The effect of fish predation on invertebrates in wetlands, however, has received less attention. Batzer (1998) found that small insectivorous fish in a New York marsh strongly influenced the benthic midge community in open water habitat. A similar study in weedy habitats, however, suggested that the influence of fish predation was more complex, with midge abundance actually increasing with fish presence in some areas (Batzer et al. 2000). In semi- permanent prairie pothole wetlands of North America, fathead minnows ( Pimephales promelas ) affected the composition, abundance, and biomass of benthic invertebrate communities (Hanson and Riggs 1995, Zimmer et al. 2001a, 2001b, 2002a, 2002b). These and other fish have been implicated as a possible cause for a decline in abundance of a number of waterfowl species that rely on invertebrate prey (Anteau and Afton 2004). Overall, it appears that patterns of fish predation in wetlands are similar to results in other aquatic habitats. In many wetlands, the presence of fish is restricted by periodic drying, winter-kill events, or limitations to colonization. In these habitats, the important vertebrate predators on 2 invertebrates are amphibians. Diet analyses (see review in Schultheis and Batzer 2005) indicate that a number of salamander species feed primarily on invertebrate fauna as maturing larvae and/or adults. The effects of this predation, however, are not well understood, and have been focused within the family Ambystomatidae. In subalpine wetlands of central Colorado, the tiger salamander ( Ambystoma tigrinum nebulosum ) plays a keystone role in determining macroinvertebrate community composition (Wissinger et al. 1999). In prairie pothole wetlands, tiger salamanders alter the macroinvertebrate community to the extent that they may deter use by migrating waterfowl (Benoy et al. 2002). In a South Carolina temporary wetland, increases in larval abundance of marbled ( Ambystoma opacum ) and mole salamanders ( Ambystoma talpoideum ) are proposed as a cause for annual variations in chironomid abundance (Leeper and Taylor 1998). When present in a more complex community with dwarf salamanders ( Eurycea quadridigitata ) and red-spotted newts ( Notophthalmus viridescens viridescens ) in a similar habitat, however, mole salamanders consumed chironomid larvae with no visible impact on the chironomid assemblage (Taylor et al. 1988). There has been much research done on density-dependent life history traits of salamander larvae. Although these studies do not directly address the effects of salamander predation on invertebrates, most of the studies monitored some aspects of invertebrate abundances with varying densities of salamander larvae. They therefore provide a reasonable estimate of the effects of varying salamander predation on invertebrate communities. In a study on marbled salamander density in southeastern wetlands, Scott (1990) monitored zooplankton abundance in an experimental setup of large enclosures that varied in salamander density. Zooplankton densities were lowest in treatments with the highest density of salamanders, but showed no significant pattern across all treatments. In a similar study with marbled salamanders, the 3 abundance of zooplankton in an experimental setup in natural ponds did not differ as salamander abundance changed (Petranka 1989). In a study on blue-spotted salamanders ( Ambystoma laterale ), Van Buskirk and Smith (1991) manipulated salamander abundance in natural splash pools on Lake Michigan. No associated differences in zooplankton abundance were detected between salamander density treatments. A weakness of these studies, however, was their failure to monitor benthic invertebrate populations. Both of the latter studies admit that their conclusions on the role of food limitation in the habitat were limited by their failure to monitor benthic prey items. Although these studies may suggest that salamander predation on zooplankton communities shows little density-related variation, their application