Directionality of recent bird distribution shifts and climate change in Great Britain

Abstract

There is good evidence that species' distributions are shifting poleward in response to climate change and wide interest in the magnitude of such responses for scientific and conservation purposes. It has been suggested from the directions of climatic changes that species' distribution shifts may not be simply poleward, but this has been rarely tested with observed data. Here, we apply a novel approach to measuring range shifts on axes ranging through 360°, to recent data on the distributions of 122 species of British breeding birds during 1988-1991 and 2008-2011. Although previously documented poleward range shifts have continued, with an average 13.5 km shift northward, our analysis indicates this is an underestimate because it ignores common and larger shifts that occurred along axes oriented to the north-west and north-east. Trailing edges contracted from a broad range of southerly directions. Importantly, these results are derived from systematically collected data so confounding observer-effort biases can be discounted. Analyses of climate for the same period show that whilst temperature trends should drive species along a north-north-westerly trajectory, directional responses to precipitation will depend on both the time of year that is important for determining a species' distribution, and the location of the range margin. Directions of species' range centroid shift were not correlated with spatial trends in any single climate variable. We conclude that range shifts of British birds are multidirectional, individualistic and probably determined by species-specific interactions of multiple climate factors. Climate change is predicted to lead to changes in community composition through variation in the rates that species' ranges shift; our results suggest communities could change further owing to constituent species shifting along different trajectories. We recommend more studies consider directionality in climate and range dynamics to produce more appropriate measures of observed and expected responses to climate change.

Does functional homogenization accompany taxonomic homogenization of British birds and how do biotic factors and climate affect these processes?

“…The variation in results with spatial scale may represent the scale at which dispersal becomes a limiting factor to a species’ distribution. Additionally, using a more recent bird atlas (i.e., Gillings, Balmer & Fuller, 2015) to study changes over a longer and more recent time period, such as that studied by Wilson et al. (2004), may yet reveal greater changes in turnover driven by measures of the spatial structure of distributions.…”

Geographical variation in species' population responses to changes in temperature and precipitation

“…If these ecological parameters are indeed determined by the same underlying process, we would expect climatic changes that lead to population increases to cause species' range expansions which, when replicated across multiple species, will then alter species-richness patterns. Matching this expectation, recent warming in the UK has led to increases in the abundance of common and widespread resident breeding birds [35], which have expanded their distributions [38], leading to an increase in species' richness [9], while UK butterflies that have shown positive population increases have also tended to expand their distributions [39].…”

How Should Beta-Diversity Inform Biodiversity Conservation?

“…These shifts tend to follow poleward and upward temperature shifts in terrestrial biomes, and downward shifts in aquatic biomes, although all species within a community will not necessarily shift in the same direction [89,90]. Species differ markedly in rates of climate-driven movement, reflecting variation in dispersal capacity and phenotypic plasticity [81].…”

“…Therefore, we must understand biodiversity loss at spatial scales relevant to conservation goals. Carefully interpreted metrics of beta-diversity can help to meet this challenge 90 by revealing the scaling relationship between alpha-and gamma-diversity. Diversity partitioning beta-diversity metrics (Box 1) directly provide the scaling factors that relate alpha-and gamma-diversity, but their calculation requires prior knowledge of gamma-diversity.…”