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Sibling Species and Secondary Contact: Habitat Use by Regionally Sympatric Alder

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Sibling Species and Secondary Contact: Habitat Use by Regionally Sympatric Alder UNIVERSITY OF CALGARY Sibling Species and Secondary Contact: Habitat Use by Regionally Sympatric Alder (Empidonax alnorum) and Willow Flycatchers (E. traillii) in Alberta by Sarah D. Hechtenthal A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF BIOLOGICAL SCIENCES CALGARY, ALBERTA APRIL, 2007 © Sarah Dawn Hechtenthal 2007 UNIVERSITY OF CALGARY FACULTY OF GRADUATE STUDIES The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies for acceptance, a thesis entitled “Sibling Species and Secondary Contact: Habitat Use by Regionally Sympatric Alder (Empidonax alnorum) and Willow Flycatchers (E. traillii) in Alberta” submitted by Sarah Dawn Hechtenthal in partial fulfilment for the degree of Master of Science. ____________________________________________________________ Supervisor, M. Ross Lein, Department of Biological Sciences ____________________________________________________________ Steven M. Vamosi, Department of Biological Sciences ___________________________________________________________ Darren Bender, Department of Geography ____________________________________________________________ Steig Johnson, Department of Anthropology ____________________ Date ii ABSTRACT Coexisting congeneric species often are segregated ecologically via resource partitioning. Sympatric sibling species provide the ideal situation for investigating resource partitioning and mechanisms of coexistence because of their recent common ancestry and great phenotypic similarity. Avian sibling species, such as Alder Flycatchers (Empidonax alnorum) and Willow Flycatchers (E. traillii), are often segregated into distinctive climate-vegetation zones, and are thus essentially allopatric during the breeding season. However, secondary contact occurs where preferred habitats abut, providing opportunities to study coexistence between recently-diverged species. I quantified habitat use by Alder and Willow flycatchers in areas of local allopatry and local sympatry in a region of secondary contact in southwestern Alberta. I measured numerous variables pertaining to horizontal and vertical components of vegetation structure and ground cover at three spatial scales on territories of each species. Using both univariate and multivariate analyses, I tested for differences in habitat use between the species within site types, and compared habitat use by each species between sites of local sympatry and local allopatry to test for possible effects of coexistence. I found numerous differences in habitat use between territories of each species in local allopatry across all three spatial scales. They differed in the amount of water cover and the structure and composition of vegetation on their territories. Alder Flycatcher territories were located in dry areas and contained very tall, partially-dead bushes. Willow Flycatcher territories were located in low-lying areas that always contained still or moving water, saturated soil and mossy ground cover and low, wide, dense bushes. Local iii coexistence of Alder and Willow flycatchers occurred only where environmental conditions produced a mosaic of habitats at the boundary of their respective ranges. When in local sympatry, the species vigorously defended interspecific territories. Although fewer significant differences in habitat use were detected than in allopatry, they remained microspatially segregated along the hydrological gradient at the sympatric sites. Therefore, differential habitat use is probably the key factor in the ecological segregation of the species in areas of secondary contact. Comparisons of habitat use between areas of local allopatry and areas of local sympatry revealed non-experimental evidence for an asymmetrical competitive relationship. Alder Flycatchers showed numerous differences in habitat use between the two site types at all scales of measurement, whereas Willow Flycatchers showed very little change in their habitat use whether in the presence of absence of their sibling species. The observed shift in habitat use by Alder Flycatchers in local sympatry may be the result of competitive displacement. In the contact zone in eastern North America, Willow Flycatchers use dry, upland thickets and meadows and Alder Flycatchers use boggy to wet alder. My study suggests that the pattern of habitat use by the two species in their western range may be opposite to that shown by eastern populations. This is an unusual ecological and evolutionary phenomenon and is the first documentation of regional reversal of habitat use by sympatric species. iv ACKNOWLEDGMENTS I would like to thank M. Ross Lein, my supervisor, for his patience, scientific guidance, encouragement, and amazing editing expertise. I am also grateful to Steve Vamosi and Darren Bender for serving on my thesis supervisory and examination committees and for adding many helpful comments and suggestions which improved my thesis. Steig Johnson also served on my thesis examination committee and offered useful comments. This research was funded by the Challenge Grants in Biodiversity Program (supported by the Alberta Conservation Association). Additional funding was provided by an operating grant from the Natural Sciences and Engineering Research Council of Canada to MRL. I received support from the University of Calgary in the form of Graduate Teaching Assistantships and Graduate Research Assistantships and was awarded a University of Calgary Graduate Entrance Scholarship, the Dennis Parkinson Graduate Scholarship, and the Sharon Wilkens Teaching Excellence Award. I also received support from the Alberta government in the form of an Alberta Heritage Graduate Scholarship and an Alberta Graduate Scholarship. During my Master’s program, I presented my research at 123rd Stated Meeting of the American Ornithologists’ Union in Santa Barbara, CA in 2005, and the 4th North American Ornithological Conference in Veracruz, Mexico in 2006. I received financial support to attend these meetings from the American Ornithologists’ Union, the North American Ornithological Conference, the University of Calgary Graduate Student Association , and University of Calgary Research Services. v My field assistants (Jessie Malcolm, Erin Brock and Cecilia Kung) were invaluable to this project, as were the numerous volunteers and friends who assisted me in the field. Additional logistical support for field work was provided by the Kananaskis Field Stations of the University of Calgary. The support staff at the research station, especially Dave Billingham and Judy Buchanan-Mappin, were incredibly knowledgeable and helpful. I would also like to thank Alvin Kumlin and Terry Raymonds for allowing me to work on their private land. I would very much like to acknowledge my academic peers for their comradery, support, encouragement, and words of wisdom throughout my Master’s program. I feel very fortunate to have worked with such intelligent, talented and fun-loving people. Also, my phenomenal lab colleague, Scott Lovell, was a never-ending source of knowledge and inspiration. My project was greatly improved by his comments and I will miss our stimulating conversations about ornithology and life in general. Finally, I am extremely grateful to all my friends and family who have spent hours patiently listening to my musings about “my little green birds” and multivariate statistics. I would especially like to thank my Mom. Her infinite courage and compassion has been a constant source of inspiration to me. I thank her for her strength, support and love, and for being a survivor. vi TABLE OF CONTENTS APPROVAL PAGE .................................................... ii ABSTRACT ..........................................................iii ACKNOWLEDGMENTS ................................................v TABLE OF CONTENTS ............................................... vii LIST OF TABLES ..................................................... ix LIST OF FIGURES .................................................... xii CHAPTER ONE: INTRODUCTION .......................................1 1. COEXISTENCE AMONG CONGENERIC SPECIES ..................1 2. BIOLOGY OF EMPIDONAX FLYCATCHERS ......................7 3. RESEARCH OBJECTIVES AND SCIENTIFIC SIGNIFICANCE .......10 CHAPTER TWO: METHODS ...........................................12 1. BIOLOGY OF THE STUDY SPECIES ............................12 A. Willow Flycatchers ......................................12 B. Alder Flycatchers ........................................20 2. STUDY AREAS ..............................................25 A. 2004 Study Sites .........................................25 B. 2005 Study Sites .........................................28 3. BIRD-FOCUSED FIELD WORK .................................30 A. Territory and Perch Assignment ............................30 B. Nest Searching and Monitoring.............................31 4. HABITAT SAMPLING .........................................32 A. Sampling Methodology ...................................32 B. Habitat Variables ........................................37 i. Microplot.........................................38 a. Song perch..................................38 b. Nest plant ..................................41 ii. Mesoplot.........................................41 iii. Macroplot........................................44 5. DATA ANALYSIS .............................................45 A. Microplot..............................................45
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