Research Collection Doctoral Thesis Functional Characterization of Plant-Herbivore Interactions and the Response of Alpine Plants to Climate Change Author(s): Descombes, Patrice Publication Date: 2018 Permanent Link: https://doi.org/10.3929/ethz-b-000304133 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Functional Characterization of Plant-Herbivore Interactions and the Response of Alpine Plants to Climate Change Patrice Descombes DISS. ETH NO. 25269 DISS. ETH NO. 25269 FUNCTIONAL CHARACTERIZATION OF PLANT- HERBIVORE INTERACTIONS AND THE RESPONSE OF ALPINE PLANTS TO CLIMATE CHANGE A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by PATRICE DESCOMBES MSc in Behaviour, Evolution and Conservation, University of Lausanne born on 29.05.1987 citizen of Lignières NE accepted on the recommendation of Prof. Dr. Loïc Pellissier Prof. Dr. Sergio Rasmann Prof. Dr. Konrad Fiedler 2018 - 2 - TABLE OF CONTENTS SUMMARY …………………………………………………………………………………… 5 RESUME ……………………………………………………………………………………… 7 INTRODUTION ……………………………………………………………………………… 11 CHAPTER 1 …………………………………………………………………………………... 35 Uneven rate of plant turnover along elevation in grasslands CHAPTER 2 …………………………………………………………………………………... 65 Community‐level plant palatability increases with elevation as insect herbivore abundance declines CHATPER 3 …………………………………………………………………………………... 115 Alpine plant palatability is associated with physical and chemical traits in situ and under a warming treatment CHATPER 4 …………………………………………………………………………………... 155 Trophic conservatism predicts alpine plants responses to herbivore ecosystem incursion CHATPER 5 …………………………………………………………………………………... 213 Simulated shifts in trophic niche breadth modulate range loss of alpine butterflies under climate change CONCLUSION ……………………………………………………………………………….. 245 ACKNOWLEDGEMENTS ………………………………………………………………….. 261 CURRICULUM VITAE ……………………………………………………………………… 263 - 3 - - 4 - SUMMARY Climate change drives rapid altitudinal and latitudinal range shifts of species worldwide. Insects, which have a higher sensitivity to thermal changes and greater ability to disperse, exhibit a faster response to climate change than less mobile organisms such as plants. Consequently, asynchronous migration rates between insects and plants might lead to reshuffled communities and new ecological interactions between species that never co-occurred. Herbivores, which occupy primary consumer positions in trophic chains, can have a major influence on ecosystem processes by altering the nutrient cycling and plant species assemblages. Therefore, modifications of plant- herbivore interactions and herbivory rates under climate change might have important consequences on plant communities, especially on high-elevation grasslands, which are generally less defended against herbivores. Changes in top-down herbivore pressure on high-elevation grasslands might favor plant community turnover and profoundly impact extant alpine grasslands. However, shifts in trophic interactions, such as those between insect herbivores and plants, have been poorly investigated and may play a primary role in how plant and insect herbivore communities will respond to climate change. Forecasting future changes in ecosystems under climate change requires a deeper understanding of the biological mechanisms shaping trophic interactions. This thesis aimed at providing a better understanding on how plant and insect herbivore communities will respond to changes in trophic interactions under climate change. To tackle this question, this thesis focused on the plant-orthopteran and plant-butterfly bi-trophic networks, and combined several field experiments and statistical modelling techniques together with phylogenetic and functional trait information of the species. The first three chapters of this thesis investigated how plant communities are structured and defended against insect herbivores along an elevational gradient and tested the effect of temperature warming on plant functional traits. The fourth chapter experimentally simulated climate-driven insect herbivore incursion on alpine grasslands by translocating a lowland community of orthopteran herbivores on high elevation grasslands. This experiment was contrasted to a temperature warming treatment by using open-top chamber greenhouses, and the effect of both treatments on plant community composition was analyzed. The fifth chapter combined contemporary modelling techniques with phylogenetic and functional trait information to simulate trophic shifts and assess herbivore population persistence under future climate change. Chapters 1 and 2 revealed a strong structuration of plant communities along the elevation gradient. In particular, the first chapter identified a transitional zone near the treeline with important rates of grassland compositional changes that delimits lowland and alpine ecosystems. Chapter 2 - 5 - found a lower resistance of alpine plant communities to herbivores. Chapter 3 determined that plant-herbivore interactions are mostly driven by chemical profiles and physical leaf traits specific to plant families. Chapter 4 revealed a strong shift in the top-down selective pressure of translocated lowland herbivores on high-elevation plant communities due to different feeding behaviors between lowland and native insects on the recipient site. In particular, we found a phylogenetic and functional conservatism in the feeding behavior of insect herbivores when moved to higher elevation, resulting in predictable responses of plants to herbivore incursion. In addition, herbivore incursion induced a stronger effect than temperature warming on the plant community composition by increasing plant species richness and strengthening community dissimilarity. Finally, Chapter 5 revealed that dietary shifts may favor herbivore population persistence under future climate change. Taken together, the results suggest that insect herbivore incursion on high elevation grasslands might be a stronger driver of plant community turnover than temperature warming. This effect might be particularly strong near and above the treeline, where extant plant communities show higher rates of compositional turnover and an overall lower defence against herbivores. This thesis contributed to a better understanding of the chemical and physical factors influencing plant-herbivore interactions. In particular, this thesis provides the experimental evidence for a diet conservatism during climate-driven range shifts of insect herbivores on high- elevation plant communities, resulting in predictable responses of plants to new herbivore incursions. Together, the predictability of reshuffled plant-herbivore interactions using functional and phylogenetic approaches has important implications for future research in ecological community modelling, as it allows to forecast future community trends under climate change. Possible shifts in trophic interactions should be carefully considered in future research aimed at understanding and predicting the dynamics of plants. - 6 - RESUME Sous l’influence des changements climatiques actuels, les espèces migrent à de plus hautes altitudes et latitudes. Les insectes tendent à répondre plus rapidement aux changements climatiques que les espèces moins mobiles tel que les plantes, car ils disposent d’une plus forte sensibilité aux variations thermiques et une plus grande capacité de dispersion. Par conséquent, des migrations asynchrones entre insectes et plantes risquent de réorganiser les communautés et engendrer de nouvelles interactions entre espèces qui n’ont jamais été en contact auparavant. Les herbivores sont des consommateurs primaires dans les chaines trophiques. Ils peuvent avoir un impact très important sur les processus écosystémiques tel que les cycles nutritifs et les assemblages d’espèces de plantes. Ainsi, des modifications dans la nature et l’intensité des interactions trophiques sous l’impulsion des changements climatiques pourraient avoir de sérieuses conséquences sur les communautés de plantes, et plus particulièrement sur les prairies alpines qui sont généralement moins défendues contre les herbivores. Un changement dans la pression de sélection des plantes par les herbivores pourrait favoriser le remplacement de certaines espèces de plantes dans les communautés et profondément modifier les prairies alpines telles que nous les connaissons de nos jours. Cependant, les changements dans les interactions plantes-insectes n’ont été que rarement étudiés et pourraient jouer un rôle fondamental dans la réponse des communautés de plantes et d’incsectes herbivores aux changements climatiques. Afin de prédire les effets des changements climatiques sur les écosystèmes, une meilleure connaissance des processus biologiques influençant les interactions trophiques est nécessaire. La présente thèse a pour but de fournir une meilleure compréhension de la réponse des communautés de plantes et d’insectes herbivores à des modifications dans les interactions trophiques sous l’effet des changements climatiques. Afin de répondre à cette question, cette thèse utilise les réseaux trophiques plantes-lépidoptères et plantes-orthoptères, ainsi que différentes expérimentations sur le terrain et des analyses statistiques combinant des informations sur les traits fonctionnels et les relations phylogénétiques entre