Population dynamics and population genetics of the Critically Endangered Raso lark: implications for conservation

• Main Author: Dierickx, Elisa Gwenda Godelieve
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Trinity College 2018
• Subjects: Raso lark; Alauda; Cape Verde; larks; Raso; RADseq; population genetics; phylogenetics; Critically Endangered; island endemic; survival; capture-recapture; MARK; population dynamics; conservation; reintroduction; translocation; skylark; Oriental lark; Alauda razae; Alauda arvensis; Alauda gulgula; genetic diversity; bottleneck; resighting; Alaudidae; crested lark; Galerida cristata; skylark genome
• Online Access: https://doi.org/10.17863/CAM.21809; https://www.repository.cam.ac.uk/handle/1810/274676

The Raso lark is a Critically Endangered bird endemic to the islet of Raso, Cape Verde. This thesis investigates two phenomena that particularly put the species at risk: its extreme fluctuations in population size, and its potentially very low genetic diversity arising from small population size and severe past population contraction. More specifically, two chapters estimate year-to-year survival and explore the factors - environmental and individual - that influence it, while two other chapters examine the lark’s genetic characteristics compared to its two continental closest relatives, including phylogenetic relationships and levels of genetic diversity. The conclusion of the thesis then uses these results to make recommendations for the conservation of the Raso lark. Each of the data chapters is summarized below: Chapter 3 estimates adult survival in the Raso lark and tests whether it could be linked to two population phenomena observed in the field: a highly variable population size and a male-biased sex ratio in certain years. Using a dataset spanning 10 years, I estimated survival for both sexes to fluctuate between 0.76 and 0.94 over this period. This is much higher than the survival rate of its closest relative, the skylark. I also found strong evidence for survival fluctuating over time and differing between males and females (with males having higher survival until 2011, at which point the trend inverted), which could play a role in the aforementioned population size fluctuations and male-biased sex ratio, respectively. Chapter 4 aims at understanding which factors shape survival in the Raso lark. Two types of variables were considered: year-dependent (rainfall, population size, population mean clutch size) and individual-dependent (age, body size characters, size ratio with mate, Ase18 genotype). Amongst the year-dependent variables, only sameyear rainfall impacted survival, with a 13% decrease in survival in the wettest year compared to the driest year, making it the most likely explanation for the ...