University of Alberta Plant-Herbivore Interactions Across an Alpine
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University of Alberta Plant-herbivore interactions across an alpine meadow gradient by Kurt Illerbrun A thesis to be submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ecology Department of Biological Sciences © Kurt Illerbrun Spring 2013 Edmonton, Alberta Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author’s prior written permission. Abstract The Rocky Mountain apollo butterfly, Parnassius smintheus, and its host- plant Sedum lanceolatum, are endemic to open alpine meadows threatened by the encroachment of trees. I explore variability in interactions between P. smintheus and S. lanceolatum relative to the treeline-delimited meadow edge, and consider the consequences of continued tree encroachment for these and other species facing similar threats. First, I demonstrate that S. lanceolatum distribution and quality vary relative to the meadow edge, with plants near the treeline being both more abundant and more nutritious than those elsewhere in the meadow. Next, I show that this variation influences both oviposition and larval feeding by P. smintheus in unexpected ways: females actively oviposit in response to both the abundance and quality of hosts yet show no strong attraction to the meadow edge, while the spatial patterns of host-plants and herbivory upon those host-plants is decoupled (i.e., not ideal) only near the treeline, despite the abundance and apparent suitability of hosts there. I also show that, because larval P. smintheus can actively respond to the distribution of their hosts, the spatial pattern of herbivory is likely the product of choice, not chance. Finally, I explore how previous stress, including P. smintheus herbivory and flowering history, affect the growth of S. lanceolatum relative to the treeline, showing that while flowering is more stressful to S. lanceolatum overall than herbivory, herbivory may lead to compensatory growth away from the treeline. I conclude that P. smintheus-S. lanceolatum interactions vary spatially, that abundant host-plant resources near the meadow edge may in fact not be available to larvae, and that the extent of actually usable larval habitat may therefore differ from that of apparently suitable habitat. Overall, I propose that a synthetic assessment of habitat for both adults and larvae will give a clearer sense of likely butterfly responses to environmental change and, consequently, aid conservation of Lepidoptera. Acknowledgements Soon after I arrived in Edmonton, fresh from a Master’s degree in Japanese politics and media studies, I found myself trudging through the winter streetscape of snow and sand to an introductory course in general ecology that was mandatory for all incoming students. Were there any general laws in ecology? Single large or several small? And what was this business about hypervolumes? I had no clue. Studying ecology was an abstract idea, an impulse born of a rural childhood on Vancouver Island and the enjoyment of one or two undergrad courses, but soon it began to take shape. This thesis charts that evolution, from those early days to now, and the appreciation of a discipline made real both intellectually, in experience and study, and corporeally, in the ecologists I’ve learned from, lived with, and admired. It has been a long, sometimes unscientific process, with many digressions but also many rewards, and for that I owe thanks to many people: To Jens, who has been firm when needed and generous always. Thank you for your guidance as I felt my way, your support and patience as I explored and sometimes stumbled, and most of all for your example of how to balance life, success, and integrity. It’s been a privilege working with you. To my committee, J.C. Cahill and Pete Kershaw, who have provided helpful feedback right from the start, and especially to Steve Matter, who gave generously of his time, ideas, and conversation. To everyone who helped with my field work, lived under the same roof and, despite all the hikes and the long days on hands and knees, remained friends: Amanda Doyle, Julia Dyck, Tracy Flach, Matt Fong, Sarah McPike, Doug Meldrum, Suzey Ogle, David Roth, Crisia Tabacaru, Elyse Williams, Denise Wong, plus many others who volunteered for an hour or a day. To my lab-mates, Amanda Doyle, who wore the pants, Amy Nixon, who wore the stats pants, and Jen Waller, who was there almost from the beginning. Thanks for your support, your help, your conversation, and for a lot of good times. To Crisia, for statistical help, certainly, but more importantly for friend- ship, companionship, encouragement, and patience. Thanks, my dear; I owe you. To my family, for always being there to listen, laugh, encourage, chastise, cheerlead, and dispute as the occasion required. It has been, and continues to be, good. And finally, to numerous funding agencies. My research was supported by two grants from the Alberta Conservation Association, three from the Alberta Sport, Recreation, Parks and Wildlife Foundation, and one each from the Canadian Circumpolar Institute and Xerces Society for Invertebrate Conservation, plus the Natural Sciences and Engineering Research Council of Canada and the University of Alberta. Field support was provided by the Canadian Rockies & Foothills Biogeoscience Institute of the University of Calgary, and additional support for travel to conferences was provided by the University of Alberta. Contents Contents List of Tables List of Figures 1 Review and synthesis: toward the inclusion of larval resources in butterfly population ecology 1 1.1 Introduction . 1 1.2 Butterflies and butterfly larvae . 5 1.2.1 Larvae and adult butterflies interact differently with their environment . 5 1.2.2 Patch attributes and their importance for butterflies and larvae . 6 1.2.3 Two perspectives on habitat edge . 9 1.3 How edges affect butterfly larvae . 11 1.3.1 Edges as ecotones . 11 1.3.2 Abiotic processes acting at the habitat edge . 12 1.3.3 Biotic processes acting at the habitat edge . 12 1.4 Implications . 15 1.5 The Parnassius smintheus-Sedum lanceolatum system . 17 1.6 Study species . 19 1.6.1 Parnassius smintheus . 19 1.6.2 Sedum lanceolatum ................... 22 1.7 The pages ahead . 24 1.8 Literature cited . 27 2 Distribution of Parnassius smintheus host plant resources in an alpine meadow 44 2.1 Introduction and objectives . 44 2.1.1 Background and general ecology of Sedum lanceolatum 44 2.1.2 Distribution and abundance of S. lanceolatum . 45 2.1.3 Quality of S. lanceolatum as food . 46 2.1.4 Summary of objectives . 49 2.2 Methods . 50 2.2.1 Study site . 50 2.2.2 Spatial patterns of S. lanceolatum in relation to the treeline . 51 2.2.3 Sedum lanceolatum abundance and flowering rates in relation to the treeline . 54 2.2.4 The effect of nutrient enrichment on S. lanceolatum flowering and survival . 55 2.2.5 Effects of slope and cover on inflorescence height . 57 2.2.6 Nitrogen content analysis . 58 2.2.6.1 Nitrogen content of unfertilized S. lanceola- tum relative to the treeline . 59 2.2.6.2 Effects of nutrient enrichment relative to the treeline . 60 2.3 Results . 60 2.3.1 Sedum lanceolatum abundance and flowering rates in relation to the treeline . 61 2.3.2 Spatial patterns of S. lanceolatum in relation to the treeline . 62 2.3.3 The effects of nutrient enrichment on S. lanceolatum flowering and survival . 65 2.3.4 The effects of slope and vegetation cover on inflores- cence height . 65 2.3.5 Nitrogen content of S. lanceolatum relative to the treeline . 67 2.3.6 Effects of nutrient enrichment on S. lanceolatum ni- trogen content relative to the treeline . 75 2.4 Discussion . 75 2.5 Literature cited . 85 3 Oviposition preferences of the haphazard egg laying butterfly, Parnassius smintheus, in relation to host plant abundance and quality 97 3.1 Introduction . 97 3.2 Methods . 101 3.2.1 Study site and species . 101 3.2.2 Oviposition site preference and previous herbivory . 104 3.2.2.1 Oviposition circles . 104 3.2.2.2 Control circles . 106 3.2.2.3 Species censused . 106 3.2.3 Analysis . 108 3.2.3.1 Oviposition circles . 108 3.2.3.2 Oviposition substrate preference . 108 3.3 Results . 111 3.3.1 Oviposition circles . 111 3.3.2 Oviposition substrate preferences . 112 3.4 Discussion . 114 3.5 Literature cited . 123 4 Treeline proximity alters an alpine plant-herbivore interaction 131 4.1 Introduction . 131 4.2 Methods . 135 4.2.1 Study site and study species . 135 4.2.2 Spatial patterns in S. lanceolatum and herbivory . 138 4.2.3 Host abundance and larval feeding intensity . 139 4.2.4 Differential patterns of resource use . 141 4.3 Results . 142 4.3.1 Host abundance and larval feeding intensity . 142 4.3.2 Differential patterns of resource use . 145 4.4 Discussion . 149 4.5 Literature cited . 157 5 Age-dependent host recognition by larvae of the Rocky Moun- tain apollo butterfly, Parnassius smintheus 164 5.1 Introduction . 164 5.2 Methods .