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Ecological Processes Responsible for Species Co-Occurrence Patterns in Two Species of Plethodon Salamanders" (2008)

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Ecological Processes Responsible for Species Co-Occurrence Patterns in Two Species of Plethodon Salamanders Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2008 Ecological processes responsible for species co- occurrence patterns in two species of Plethodon salamanders Jennifer Deitloff Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Ecology and Evolutionary Biology Commons Recommended Citation Deitloff, Jennifer, "Ecological processes responsible for species co-occurrence patterns in two species of Plethodon salamanders" (2008). Retrospective Theses and Dissertations. 15681. https://lib.dr.iastate.edu/rtd/15681 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Ecological processes responsible for species co-occurrence patterns in two species of Plethodon salamanders by Jennifer Deitloff A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Ecology and Evolutionary Biology Program of Study Committee: Dean Adams, Co-major Professor Nicole Valenzuela, Co-major Professor Brent Danielson John Nason Bonnie Bowen Iowa State University Ames, Iowa 2008 Copyright © Jennifer Deitloff, 2008. All rights reserved. 3316198 3316198 2008 ii TABLE OF CONTENTS LIST OF FIGURES iv LIST OF TABLES v ABSTRACT vi CHAPTER 1. INTRODUCTION: COMPETITION AND SPECIES INTERACTIONS 1 The Importance of Competition in Communities 1 Competition and Territoriality 3 Study System: Plethodon salamanders 5 Study System: Plethodon cinereus and Plethodon electromorphus 9 Dissertation Organization 10 Literature Cited 11 CHAPTER 2. INTERSPECIFIC AGGRESSION IN OHIO PLETHODON: 24 IMPLICATIONS FOR COMPETITION Abstract 24 Introduction 25 Methods 29 Results 33 Discussion 34 Acknowledgements 38 Literature Cited 38 CHAPTER 3. INTERSPECIFIC AGONISTIC BEHAVIOURS IN A 46 SALAMANDER COMMUNITY: IMPLICATIONS FOR ALPHA-SELECTION Abstract 46 Introduction 47 Methods 50 Results 55 Discussion 57 Acknowledgements 61 Literature Cited 61 CHAPTER 4. A NATURAL DISTURBANCE ACCELERATES THE PROCESS OF 72 COMPETITIVE EXCLUSION IN OHIO PLETHODON SALAMANDERS Abstract 72 Introduction 73 Methods 76 Results 77 iii Discussion 78 Acknowledgements 80 Literature Cited 81 CHAPTER 5. COEXISTENCE OR CO-OCCURRENCE? DETERMINING THE 88 ECOLOGICAL PROCESSES RESPONSIBLE FOR GEOGRAPHIC DISTRIBUTIONS OF OHIO PLETHODON Abstract 88 Introduction 89 Methods 92 Results 100 Discussion 104 Acknowledgements 107 Literature Cited 108 CHAPTER 6. CONCLUDING REMARKS 128 General Discussion 128 Future Research 135 Literature Cited 138 ACKNOWLEDGEMENTS 142 iv LIST OF FIGURES Figure 1.1. Geographic distribution of Plethodon cinereus. 20 Figure 1.2. Geographic distribution of P. electromorphus. 21 Figure 1.3. Geographic distribution of P. cinereus and P. electromorphus in Ohio 22 showing presence and absence for each county. Figure 1.4. Geographic distribution of P. cinereus and P. electromorphus in Ohio 23 showing presence and absence for each township. Figure 3.1. Comparison of time spent in all-trunk-raised (ATR) behavior. 67 Figure 3.2. Comparison of time spent in edging (EDGE) behavior. 68 Figure 4.1 Photograph of one collection site after a flood. 85 Figure 5.1. Map of geographic locations used in this study in Ohio. 118 Figure 5.2. Positions of 10 landmarks used in geometric morphometric methods. 119 Figure 5.3. Results of landscape surveys of P. cinereus and P. electromorphus in Ohio 120 showing townships in which I surveyed. Figure 5.4. Profile of stomach contents of sympatric P. cinereus and P. 121 electromorphus. Figure 5.5. Correspondence plot describing differences in food-use overlap among 122 allopatry and sympatric populations. Figure 5.6. Principle components plot describing differences in head shape variation 123 among allopatric and sympatric populations. Figure 5.7. Multivariate association of head shape and food utilization. 124 v LIST OF TABLES Table 2.1. Average time spent in aggressive and submissive behaviors and frequency 44 of biting during intraspecific trials. Table 2.2. Average time spent in aggressive and submissive behaviors and frequency 45 of biting during interspecific trials. Table 3.1. Average snout-vent length (SVL) of salamanders used in chapter 3. 69 Table 3.2. Summary of residents’ response to allopatric and sympatric interspecific 70 intruders. Table 3.3. Results for randomizations using the linear mixed model on behavior data. 71 Table 4.1. Summary of collection seasons, dates collection occurred, and which sites 86 were visited during each collection season for the study presented in chapter 4. Table 4.2. Number of P. cinereus and P. electromorphus collected during various 87 collecting seasons during the study presented in chapter 4. Table 5.1. Location information for geographical localities (sites) used in the study 125 presented in chapter 5. Table 5.2. Average SVL of salamanders collected for the study presented in chapter 5. 126 Table 5.3. Pairwise overlap between species in food types for sympatric sites and all 127 possible allopatric comparisons. vi ABSTRACT The competitive interactions of closely-related and ecologically similar species have long been considered an important topic in evolutionary ecology. These species interactions can have considerable effects on community composition and species distributions. Furthermore, ecological, behavioral, and morphological traits of species can be influenced by interactions with competitors. Throughout Ohio, two closely related and ecologically similar salamander species, Plethodon cinereus and P. electromorphus, occur in similar habitats and can be found in sympatry. Interestingly, the contact zone of these two species is much broader than has been observed in other pairs of Plethodon species that competitively interact. However, when these distributions are viewed at a finer scale, the two species do not always co-occur. I examined the interactions of P. cinereus and P. electromorphus through a variety of methods to better understand how the interactions between these two species lead to their distributions in Ohio. I found that in sympatry, both species were more aggressive towards individuals of the other species than when each was found in allopatry, indicating that the process of alpha-selection may have led to the evolution of enhanced aggressive behavior in sympatry. Within some sympatric areas, P. cinereus may be excluding P. electromorphus through these interference mechanisms. In addition, disturbance processes, such as flooding, may have sped up this process of competitive exclusion in areas where flooding occurred. These two species were using the same resources, both refuge sites and prey resources, which suggests that if these resources are limiting, they would compete for them. At different sympatric sites, morphology is evolving in different ways, such that these two species vii become more divergent at some sites, more similar at some sites, and do not seem to be changing at other sites. Furthermore, morphological differences are associated with differences in food use across all the sites that were examined. The distribution and persistence patterns of sympatric localities between P. cinereus and P. electromorphus suggest that these species respond to community processes in complex ways. It appears that competitive interactions between these two species in sympatry can lead to the evolution of character displacement or competitive exclusion of one species (likely P. electromorphus). Additionally, at least one sympatric site appears to be stable where intense aggression may have resulted in interspecific territoriality. In this system, complex interactions of competition and disturbance are shaping the observed distribution patterns of these two species. While the results of my research have shed light on these species interactions, further studies could reveal the potential impacts that additional competitors or predators may have on these distributions. 1 CHAPTER 1. INTRODUCTION: COMPETITION AND SPECIES INTERACTIONS The Importance of Competition in Communities The competitive interactions of closely-related species have long been considered important determinants of community composition. Competition is thought to be an important influence in niche separation, specialization, and diversification of many species (Gause 1934, Connell 1980) and in a diverse array of ecological communities (reviewed in Schluter, 2000). However, competition is not the only factor that can influence community structure. Predation is also an important factor that can determine which species occupy the same area (Bouskila 1995). In addition, disturbance, human-induced or natural, can influence species composition in communities (McNaughton 1977, Sousa 1979). The relative importance of each of these factors may vary in different communities (Menge and Sutherland 1976). These factors can also influence each other (Wiens 1977). Natural disturbance may interact with competition and predation (Picket and White 1985). For instance, when environments are harsh or disturbance is common, competition between species can be stronger than the effects of predation. Alternatively, competing species may coexist because disturbance reduces the
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