Perturbations in plant-pollinator networks: integrating theoretical and empirical approaches to understand responses to global change Restricted; Files Only

Morozumi, Connor (Summer 2022)

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Mutualisms—mutually beneficial ecological interactions— are critically important for sustaining life on this planet. Unfortunately, we know little about how these species interactions—including plant-pollinator relationships that are key for agricultural production as well as ongoing wild plant reproduction—will fare with rapid and ongoing anthropogenic change. When changes do perturb these enmeshed systems of multiple species and many interactions, we lack predictive understanding of how these perturbations will ripple through communities. Many studies of plant-pollinator interactions have depicted the relationships as networks, commonly with non-random structures which organize these interactions. Yet we do not understand how these structures influence how the networks will handle changes. Additionally, our understanding of these network structures needs to be better connected to the underlying ecological mechanisms such as resource competition and niche partitioning that are likely contributing to the overarching organization of plant-pollinator interactions across the network. This dissertation combines synthesis, theoretical, and empirical approaches to investigate how perturbation to plant-pollinator networks may alter these important partnerships. My thesis has three substantive chapters beyond the introduction (Chapter 1) and conclusion (Chapter 5). The first of these, Chapter 2, synthesizes and makes recommendations for how modeling and empirical approaches can be better integrated into network studies of plant-pollinator interactions. In Chapter 3, I use a modeling approach to examine how responses to perturbations, in this case robustness to sequential species extinctions, are driven by networks structure both in terms of who interacts with whom as well as their foraging intensities. I found that both topological and quantitative network structure were important in driving robustness, and amplified one another under certain extinction scenarios. In Chapter 4 I use an empirical approach to examine the effects of multiple drought events on restructuring networks within montane meadows in the Colorado Rocky Mountains. I found that under drought, networks simultaneously became more generalized in terms of the number of partnerships species were involved in, yet quantitatively more specialized in terms of their interaction intensities.

Table of Contents

Table of Contents

Chapter 1: Introduction

1.1. Overview

1.2. Plant-pollinator systems

1.3. Ecological Networks

1.4. Chapter 2: Integrating plant-pollinator theory and empiricism

1.5. Chapter 3: Modeling robustness and network structure

1.6. Chapter 4: Simultaneous niche expansion and contraction in plant-pollinator networks under drought

Chapter 2: Integrating plant-pollinator theory and empiricism

2.1. Introduction

2.2. Box 1: The Submodel Approach

2.3. Section 1: Applying functional and numerical responses to improve plant-pollinator models

2.4. Box 2: Functional Response Formulations

2.5. Section 2: Niche-based predictions

2.6. Section 3: Conclusions

2.7. References

Chapter 3: Modeling robustness and network structure

3.1. Introduction

3.2. Methods

3.3. Results

3.4. Discussion

3.5. Conclusion

3.6. References

Chapter 4: Simultaneous niche expansion and contraction in plant-pollinator networks under drought

4.1. Introduction

4.2. Methods

4.3. Results

4.4. Discussion

4.5. Conclusion

4.6. References

Chapter 5: Conclusions and Future Directions

5.1 Integrating theory and empiricism

5.2 Understanding how perturbation responds to topological and quantitative network structure

5.3 Drought perturbations in plant-pollinator networks

5.4 Future directions

Introduction and Conclusion References

About this Dissertation

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