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Thesis defences

PhD Oral Exam - Elizabeth R. Lawrence, Biology

Synthesizing vertebrate population richness and genetic diversity across the American continents

Date & time

Friday, September 11, 2020 (all day)


This event is free


School of Graduate Studies


Daniela Ferrer



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.


Intraspecific diversity is an important facet of biodiversity, both for the understanding of broad-scale biodiversity distribution and for the prioritization of conservation hotspots below the species level. It is the level of biodiversity that responds firstto environmental change, yet few studies have assessed its broad-scale distribution. By constructing and analyzing an extensive population-genetics database, my thesis aims to demonstrate both the links and differences between species richness, populationrichness, and population-specific genetic diversity(PGD). Chapter 1 details the database and provides an exploration of population genetic data across five vertebrate taxonomic groups. The database collated geo-referenced information from 895 vertebrate species, 1308 studies, and 9090 genetically distinct populations. I found that anadromous species tended to be both the most population rich and genetically diverse, while mammals had lower levels of genetic diversity. In Chapter 2, I synthesized the conceptual foundation for broad-scale expectations of genetic and population diversity patterns by drawing from theories in the species diversity literature. I also tested the relationship between range size and population richness or PGD, finding a positiveand a non-significant relationship for population richness and PGD, respectively. For Chapter 3, I assessed the latitudinal gradient in vertebrate PGD and assessed how environmental variables and variation among genera may mediate patterns in PGD. I foundminimal evidence for a latitudinal gradient in PGD, a weak influence of environmental variables,and strong evidence for genera-specific patterns.In Chapter 4, I evaluated the influence of anthropogenic impacts (namely human population density andheterogeneityinland use intensity) on metrics of PGD across broad-scales. I found inconsistent support for the expected negative impacts, instead finding that human impact varies both between and within taxonomic groups. Collectively, my thesis demonstrates the difficulties in applying species theories to intraspecific diversity and that species-centric views overlook important variation below the species level. Taxonomic-dependent responses are common, and there is no “broad brush” for biodiversity –considering differences among taxa, even down to the genus-level, can be vital for biodiversity conservation. Intraspecific diversity does not have the same distribution as species diversity, and more extensive sampling would be needed to investigate these patternsmore clearly.

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