Bayesian analysis of multi-species demography : synchrony and integrated population models for a breeding community of seabirds

In the study of wildlife populations, demographic data have traditionally been analysed independently for different species, even within communities. With environmental conditions changing rapidly, there is a need to move beyond single-species models and consider how communities respond to environmental drivers. This thesis proposes a modelling framework to study multi-species synchrony in demographic parameters, using random effects to partition year-to-year variation into synchronous and asynchronous components. The approach also allows us to quantify the contribution of environmental covariates as synchronising/desynchronising agents.

We apply the framework to long-term data from a breeding community of seabirds at the Isle of May, Scotland, studying synchrony in adult survival and parameters related to breeding success. We then combine demographic data with population counts and propose the first multi-species integrated population model (IPM), which estimates simultaneously the abundance of puffins, guillemots and razorbills and the demographic parameters that drive their fluctuations, while estimating synchrony in adult survival and productivity.

Most analyses are carried out within the Bayesian framework. Results indicate that for these three auk species the same climatic covariates act simultaneously as synchronising and desynchronising agents of a mostly synchronous adult survival, based on resighting data of ringed birds. They also reveal varying degrees of productivity synchrony in a set of five species, with the synchronous terms, a potential community based indicator of local marine ecosystem health, indicating a decline in productivity during the study period.

The thesis also investigates options to optimise the monitoring of guillemot juveniles at the Isle of May. Using the historic data set, we show that ringing effort is adequate but that resighting effort could be substantially reduced while still being able to detect the dramatic variations in first-year survival and ecological relationships with individual-level covariates investigated. We finally explore the limitations of an IPM to compensate for the lack of direct juvenile data in the case of stopping the ringing of guillemot chicks.

Both synchrony models and the multi-species IPM are readily applicable to any species assemblage in any ecosystem, provided long-term data are available. They represent new steps towards more integrative approaches to modelling demographical parameters. The study of synchrony may facilitate the generation of further hypotheses about similarities and differences in species’ ecology.