Bio-climate models highlight winners and losers among British seabirds
Prof. Keith Hamer is a Professor of animal ecology in the Faculty of Biological Sciences, where he focuses on trophic ecology – the relationship between animals’ food sources and environmental change and wider ecosystem processes.
If climate change makes life difficult for species, they can respond in three ways; by moving, by adapting or by going extinct. One way that researchers can gauge how difficult life might become for different species as a result of climate change is to construct bio-climate models that describe the range of climatic conditions under which species currently occur. These models can then be used to predict how species would need to alter their geographical distributions in future to keep pace with climate change, and to identify parts of a species’ current range that may not be habitable in future. One limitation with this approach, though, is that it examines only occupancy (the presence of a species in some places and its absence from others) whereas it’s changes in abundance that are often most important from a conservation perspective. For instance, if a formerly large thriving population were reduced to just a few individuals eking out an existence, that wouldn’t be any change in occupancy.
With this in mind, we’ve been developing the use of bio-climate models to examine impacts of climate change on species abundance as well as occupancy. The group we’ve been studying most to date is seabirds breeding in the British Isles (the UK and Ireland), for which there are excellent supporting data. The British Isles are also of international importance for seabirds, supporting >50% of the world population of several species.
Our models have given us important insights into why different species of seabird in Britain have shown contrasting population trends over the past 30 years, when climatic suitability seems to have decreased for all species. Those species whose geographical distributions and local population sizes were not greatly constrained by climate in the mid-1980s have typically increased in abundance since then, continuing the long-term trend observed for most seabirds in the UK over much of the 20th century following legal protection from exploitation. In contrast, those species whose distributions and abundance conformed closely to climate have reversed this trend and gone into decline, by as much as 80% in one case.
These findings highlight the potential for bio-climate models to elucidate impacts of climate change on species abundance as well as occupancy. They also reveal a pervasive influence of climate on the population sizes of seabirds across the British Isles. We’ve not directly examined the mechanisms driving these changes. However we did find that the ability of our occupancy models to predict local population sizes of different species was related to species’ foraging ecology. This finding suggests a tighter relationship between climate and population size among those species most affected by changes in food availability at sea, supporting a link between seabird populations and bottom-up processes affecting prey quality and availability.