Harrison, P.J., Buckland, S.T., Yuan, Y., Elston, D.A., Brewer, M.J., Johnston, A. and Pearce-Higgins, J.W.
Journal of Applied Ecology 51, 1650-1660.
change points in trends, generalized additive models, geometric mean index, goodness-of-fit measures, long-term trends, rare species, spatio-temporal modelling
1. Partitioning biodiversity change both spatially and temporally is required for effective management at regional and local scales. As biodiversity is a multifaceted concept, comparative analyses of different indices, focussing on different components of biodiversity change (evenness versus abundance), give better information than a single headline index.
2. We model changes in the spatial and temporal distribution of British breeding birds using generalized additive models applied to count data collected between 1994 and 2011. Abundance estimates, taking account of differences in detectability, are then used in community-specific (farmland, near human habitation and woodland) biodiversity indices. Temporal trends in biodiversity, and change points in those trends, are assessed at different spatial scales. The geometric mean of relative abundance, a headline indicator of biodiversity change, is assessed together with a goodness-of-fit evenness measure focussing separately on the rare and common species in the communities.
3. Temporal trends in biodiversity at the national level in certain instances will miss opposing trends occurring at different locations within the nation. How the trends vary for the rare and common species at different locations can also generate testable hypotheses regarding the possible processes responsible for those patterns.
4. Synthesis and Applications. Bird populations are seen as good indicators of ecosystem health and trends for different communities can be indicative of wider biodiversity changes within their respective habitats. Our analysis reveals predominantly declining trends in biodiversity for all three bird communities in the south-east corner of England around the London area, signalling environmental deterioration in this part of the country that needs further exploration. Our results also show generally more positive trends in the north and negative in the south of Britain consistent with north-south gradient expectations from the effects of climate change. We also reveal predominantly positive changes in evenness for the common species and negative changes for the rarer species in the communities, again consistent with expectations of climate-induced homogenisation in bird communities.