Disentangling factors mediating diversity by modeling dynamics from populations to communities.

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Biological Sciences
Degree name
Doctor of Philosophy
Publisher
University of Canterbury
Journal Title
Journal ISSN
Volume Title
Language
English
Date
2021
Authors
Marraffini, Michelle
Abstract

Ecologists have worked for over a century to disentangle biotic and abiotic factors that regulate populations; I am no exception. Species interactions influence population dynamics by affecting abundance and distribution of species. Interactions form the backbone of foundation paradigms in ecology such as keystone species, trophic cascades, ecological niche, and com- munity stability. Yet the bulk of understanding about interactions comes from pairwise inter- actions in simplified communities, likely missing processes and mechanisms that only emerge in diverse systems. These processes emerging in diverse systems may ultimately be responsible for maintenance of diversity seen in nature. Beyond interactions, several other factors may reg- ulate populations and coexistence including heterogeneous environments, life-history traits, and the interaction of multiple ecological processes among members of the community. With the goal of improving our understanding of factors shaping the distribution, abundance, and diversity of natural communities, in this thesis I combined theoretical models and real-world data across three ecosystems. Specifically, for my first chapter I explored the relative roles of biotic and abiotic drivers of alpine plant communities at multiple scales. Here I found that individual populations responded to experimental treatments, while the whole community remained relatively constant suggesting weak treatment effects. Additionally, neither populations nor communities responded to the same drivers or in the same manner. I concluded that variable responses to these drivers allow some populations to persist and communities to re- main stable as different species vary in response to the treatments. My second chapter focused on the role of facilitation and indirect interactions in an annual plant community. I found that both direct and indirect facilitation had measurable effects on annual plant fitness outcomes. I measured, for the first time in a natural system, the presence of ‘native turncoats’: native species indirectly facilitating introduced species. Indirect facilitative interactions may increase the fitness of some introduced species allowing them to succeed in spite of biotic resistance. In my third chapter, I focused on population dynamics of a space-limited community finding that it is structured by a competitive hierarchy but inferior competitors persist. I used inferred pairwise interaction coefficients to rank functional groups by competitive ability and used inferred recruitment to examine life-history trade-offs. I conclude that coexistence in this space-limited community is maintained by multiple, non-mutually exclusive mechanisms: trait differences acting as an equalizing mechanism, life-history trade-offs, and facilitation across a gradient of neighbor density. Together these projects provide insights into the various ways populations and communities are shaped by ecological processes. Cumulatively my work emphasizes the importance of quantifying variability and the diverse mechanisms that influence populations and ultimately the diversity of ecological communities.

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All Rights Reserved