Drivers of cooperative breeding and population dynamics in Seychelles warblers

This thesis investigates the interplay of social evolution and population dynamics in Seychelles warblers, passerine birds with facultative cooperative breeding where some breeders receive help from other individuals when raising offspring. The thesis aims to elucidate how individual fitness is determined by the combination of individual traits and life-history events with its social and non-social environment and how fitness variation may result in complex eco-evolutionary dynamics. To this end, by combining advanced statistical methods with data-driven simulations, I analyzed field data collected between 1995 and 2019 on the life-history and demography of Seychelles warblers inhabiting Cousin Island in the Republic of Seychelles. By employing a data-driven matrix model, in Chapter 2, I show that the presence of helpers could have a stabilizing effect on the population dynamics under density dependence and environmental stochasticity. Chapter 3 evaluates the performance of structural equation modelling in inferring causal mechanisms that drive variations in individual fitness by applying an individual-based model. I show that structural equation models are useful but data-hungry. In Chapter 4, I examine the causal relationships between individual-, group- and population-level drivers of fitness in breeding females. Fitness drivers might have played an essential role in the evolution of individual differences between dominant females. Chapter 5 investigates how experience, social environment, and territory quality influenced the overall reproductive success of highly promiscuous dominant females and males.