Allometric scaling of the extinction vortex

  • Nathan Williams

Student thesis: Master's ThesisMaster of Science by Research (MScR)


Previous work has demonstrated that a multitude of stressors acting synergistically on small populations can lead to a self-reinforcing downward spiral to extinction known as the extinction vortex. However, owing to a lack of studies, we currently have a poor understanding of what factors might affect how a population responds to the extinction vortex and therefore, the relative immediacy or intensity of conservation intervention required to save extinction-bound populations. In this thesis, I compile a dataset of 55 populations monitored to extirpation, test three pre-existing hypotheses of the extinction vortex, and investigate whether a key fitness-related phenotypic trait - body size - influences the population dynamics in the region of extinction. In support of extinction vortex theory, I find that time to extinction scales to the logarithm of population size, geometric growth rate becomes increasingly negative at closer proximity to extinction, and there is greater variability in geometric growth rate as populations approach extinction. I also find that the relationship between population size and population longevity is weaker for smaller-bodied taxa. This indicates a predisposition for more abrupt extinctions in smaller-bodied species and a stronger decline to extinction in larger-bodied species, which might be more difficult to reverse with conservation effort. Overall, the ability to predict how population size scales to population longevity based on the intrinsic biological traits of taxa could have implications for conservation management.
Date of Award21 Jan 2021
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMartin J Genner (Supervisor) & Chris F Clements (Supervisor)


  • Extinction vortex
  • Body size

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