The abundance of European breeding birds: present and future

Abstract

Global environmental changes are predicted to have severe consequences for biodiversity and the provisioning of ecosystem services and functions. Historic biodiversity losses have been principally attributed to habitat loss and degradation, and human overexploitation. Today, however, biodiversity is increasingly threatened by anthropogenic climate change. Establishing the relative importance of climate and land use in determining species abundance is important if we are to fully understand the potential impacts of future environmental change. Designating species of conservation concern relies principally on measures of population change, and is inevitably backward- rather than forward-looking. Yet, with projections of substantial future climate change, knowing species that will become imperilled in future is also important for conservation planning. To date, studies of the impacts of future climate change have focussed on projecting range shifts of species, but rarely on projecting species’ abundances, which limits their utility for conservation. In this thesis, I investigate the relative importance of climate and land use in determining the recent abundance of breeding birds across Europe, and I assess the potential impacts of future climate change. I use species abundance models, applying novel approaches, to improve the understanding of species-environment relationships. From these, I demonstrate that climate is generally more important than land use in determining recent species abundances at a European scale. Importantly, however, the importance of abiotic factors for determining species abundance varies across Europe, with climate being most important in the north, and land-use in the south. This suggests that northerly distributed species will be particularly susceptible to climate change; unfortunate, given that this is exactly where climate change is projected to be most pronounced. I further demonstrate, for the first time, that the population trends of migratory birds are more closely related to climate on their breeding grounds than climate on their non-breeding grounds. My species’ abundance models, using climate and habitat data, estimate national abundances of species well, even when projected into novel parameter space. I then use these models to project the abundance of species under climate change, and demonstrate that substantial changes in both the abundance and distribution of species are highly likely. Furthermore, species responses will be individualistic, leading to significant changes in the distribution of avian communities. In this thesis I have, in part, been able to address some fundamental questions in ecology, including: ‘What limits the abundance of migratory species?’ and ‘Is climate or habitat the primary determinant of population size in species?’. The work presented here advances our understanding of the potential future shape of biodiversity, and should inform forward-thinking conservation.