PhD Oral Exam - Alexandra Engler, Biology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Functional ecology offers a powerful lens to describe and understand ecological communities and the processes that structure them. Central to this framework is the concept of functional traits, defined as measurable characteristics of individuals or species that approximate their ecological niches. By examining patterns in species traits, functional ecology provides insights into the processes that shape ecological communities and how these processes influence biodiversity and ecosystem functioning.

However, common practices in functional ecology often overlook key dimensions of functional structure. In this thesis, I identify several of these blind spots and propose ways forward, using a dataset of more than 700 lake-fish communities from Ontario, Canada, as a case study.

First, I revisit the widely used metric of functional dispersion, a measure of trait dissimilarity among co-occurring species, and explore how trait selection influences its patterns. I developed two trait-pooling strategies: one based on prior knowledge of trait function, and another using a novel algorithm that separate traits that maximizes and minimizes variation in functional dispersion. Both approaches strengthen the development of a priori hypotheses about the processes shaping the structure of ecological communities and improve the predictive performance of environmental models for functional dispersion.

Second, I introduce the concept of community functional integration, defined as the pattern and strengths of trait correlations within communities, to examine how these relationships vary across communities and influence community structure. Through two empirical analyses, I demonstrate that functional integration captures important, overlooked variation in functional structure and provides novel ecological insights.

Finally, I assess temporal and spatial variation across three dimensions of functional structure - functional composition, dispersion, and integration – alongside taxonomic composition. Each dimension of community functional structure had their unique temporal shifts. We also conducted a spatial analysis to understand at which scale these shifts were structured: temporal shifts in functional composition and community functional integration could be explained by broad and fine scale spatial patterns, underscoring the importance of both broadscale and local processes in the temporal changes in the communities’ functional structure. Together, these findings call for an expanded view of functional ecology that integrates trait relationships and temporalspatial dynamics to more fully understand community structure and its drivers.

This work broadens the functional ecological framework by highlighting underexplored dimensions of trait structure. In doing so, it contributes new tools and perspectives for uncovering the mechanisms that shape biodiversity across space and time.