Climate change puts pressure on species to shift ranges in order to track their preferred habitat. Connected landscapes, such as those with climate corridors that lead to climate refugia, can help ensure that they get there. However, there are many factors that can prevent effective range shifts from happening.
One of the most prominent physical factors is the location of a community in relation to ecological barriers, such as bodies of water or mountain ranges. While past studies have looked at how barriers affect range shifts at local or regional scales, few have looked at how barriers influence entire communities and their composition over large, continent-wide scales.
Marjakangas, E.L., Bosco, L., Versluijs, M., Xu, Y., Santangeli, A., Holopainen, S., Mäkeläinen, S., Herrando, S., Keller, V., Voříšek, P. and Brotons, L. 2023. Ecological barriers mediate spatiotemporal shifts of bird communities at a continental scale. Proceedings of the National Academy of Sciences 120: e2213330120.
A recent study takes a look at how bird community composition has shifted across Europe from the 1980’s to the 2010’s. Using the extensive European Breeding Bird Atlas, it quantifies how ecological barriers – specifically biome boundaries, coastlines, and elevational changes – have impacted the distance and direction of community composition shifts. Over 2,000 breeding bird communities were included in the analysis, which spanned the entire continent.
Results showed that 2/3 of bird communities have shifted over time, and that these shifts averaged almost 150km. The most important barrier impacting the shift distance was the proximity of the coastline, with biome boundary and elevation significantly less important. Communities shifted much farther when they were located farther away from the coastline.
In terms of shift direction, communities mostly shifted along most similar elevations and away from biome boundaries and coastlines. They also generally shifted every cardinal direction except south.
These directions were not strongly correlated with shifts in observed temperatures. Over 90% of the communities had a shift that lagged behind temperature shifts, by an average of over 200km. This suggests that even when communities aim to track temperature shifts, they are prevented from doing so by barriers both large and small. Communities that did not shift at all had an even greater distance from temperature shifts, meaning that tracking climate changes is likely a necessary strategy for communities to maintain their composition.
A small percentage of bird communities (6%) went extinct in the time period. These were mostly located along coastlines and were composed of unique species. The combination of rare community composition plus being located next to a strong ecological barrier makes these communities particularly vulnerable to changing climate conditions.
Community response to barriers can be combined with other information, such as abundance data or species’ traits, to better predict biodiversity shifts in both space and time. Much work has been done looking at how species might shift upward in elevation or pole-ward in latitude, but ecological barriers are another piece of the puzzle in predicting movement patterns. Incorporating barriers can lead to more realistic projections of range shifts, allowing for better conservation planning and policies.
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