Unveiling spatial patterns of multi-trophic biodiversity using the metaweb approach
EMBARGOED UNTIL 2026-12-11
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Date
2024
Publication Type
Doctoral Thesis
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EMBARGOED UNTIL 2026-12-11
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Abstract
Species in nature interact with each other and the environment as they move through the landscape in search of better living conditions, reproduction, and food. Human activities have resulted in widespread habitat degradation, fragmentation, and loss, as well as significant changes to the climate—a trend that has only accelerated in recent times. As species respond to these changes in their environment, they trigger cascading effects on species they interact with to destabilise entire food webs. This has serious implications, as links shared by species in the food web represent the flows of energy and material—within and across multiple habitats—which underpin vital ecosystem functions, such as nutrient cycling, pollination, and pest control. Though traditionally studied at local scales, we now know that food webs are influenced by global change drivers that operate across broader spatial scales and environmental gradients. Understanding the consequences of these drivers on complex ecological systems requires spatially explicit, large-scale knowledge of how empirical food webs vary along these gradients—a task that has historically proven difficult for ecologists. The collection of necessary information on species occurrences and interactions across multiple taxonomic groups and environmental conditions, at fine spatial resolutions and along vast spatial scales, is logistically challenging and often practically infeasible. In this thesis, I compile and standardise historical and contemporary ecological data to construct a national-scale metaweb, which I use to investigate the impact of global change drivers on food web structure, species interactions, and habitat connectivity across multiple spatial scales in Switzerland.
In Chapter 1, I provide a historical overview of the current knowledge and gaps therein. In Chapter 2, I describe the compilation of the trophiCH dataset, an empirically-based metaweb consisting of 1,112,073 interactions between 23,151 species, spanning 160 years of ecological knowledge within the national boundaries of Switzerland. This metaweb provides an unprecedented resource for ecological research and biodiversity conservation in Switzerland. In Chapter 3, I use the trophiCH metaweb in combination with occurrence data to build twelve regional multi-habitat food webs to explore how habitat loss-driven species extinctions impact food web robustness at biogeographic scales. The results emphasise the importance of protecting multiple habitats, as the loss of species in one habitat can cascade to impact the stability of the whole multi-habitat food web. I also demonstrate the value of common species, as they contribute more than rare species to food web stability under sequential extinctions. While differences between montane and lowland regions are observed, the food webs across the six biogeographic regions respond similarly to species extinctions. This highlights the need to consider smaller, ecologically meaningful spatial units to provide a more nuanced understanding of food web dynamics and species interactions. In Chapter 4, I use an environmental DNA-based sampling approach to demonstrate that river catchments encapsulate distinct taxon assemblages, whose differences can be explained by the environmental properties of the catchments. These results support the idea that catchments are biologically meaningful local units for studying regional-scale biodiversity patterns. In Chapter 5, I combine the trophiCH metaweb with catchment-level species distribution maps to infer 18,099 catchment-level food webs. I demonstrate that catchment-level food web properties and structural connectivity are shaped by human footprint and elevation. I also develop an index to quantify trophic connectivity, providing new insights into how species movement driven by resource availability is influenced by environmental gradients, structural connectivity, and food web topology. In Chapter 6, I summarise the contributions and limitations of this dissertation, and consider potential new directions in scientific exploration branching from my work.
This thesis combines biogeography, food web ecology and network theory to advance macroecological explorations of food webs by providing one of the first large-scale empirical investigations into how multi-trophic food webs and trophic connectivity vary along topographical, climatic and human footprint gradients in anthropogenically modified landscapes. The ongoing climate change and biodiversity crises are contemporary “wicked problems”: complex, interconnected issues that are resistant to definitive solutions. Understanding the underlying patterns—such as how food webs and ecological connectivity vary along environmental axes—can guide continuous, adaptive actions. By providing new insights into the patterns driving food web structure in fragmented landscapes, this thesis helps to inform interventions that address biodiversity loss as an ongoing, evolving challenge.
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Examiner : Pellissier, Loïc
Examiner : Bersier, Louis-Félix
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ETH Zurich
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Subject
food webs; metaweb; biodiversity; Multi-trophic interactions; Swiss Alps; macroecology; Plant-animal interactions; network ecology
Organisational unit
09553 - Pellissier, Loïc / Pellissier, Loïc
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Related publications and datasets
Is part of: https://doi.org/10.3929/ethz-b-000628135
Is part of: https://doi.org/10.3929/ethz-b-000745253
Is part of: https://doi.org/10.3929/ethz-b-000745878