Assessing the potential effects of climate change on bird functional diversity at global scale

Background/Question/Methods

Human-induced global climate change is of major scientific and political concerns, especially when considering potential impacts on biodiversity, ecosystem processes and human well-being. One of the major aims of global change research is the development of reliable predictions on future geographic distributions of species. To date, projections tend to be focused on changes in species richness level. However, biodiversity has many facets, and one critical of them in the context of ecosystem services and function is  functional diversity (FD). Assessing the predicted changes of ecosystem services is of special concern for decision makers. Here, we aimed at assessing the predicted changes of global bird FD in response to climate change. Using 1° resolution data and species distribution modeling, we modeled current and future (2100) ranges of all bird species (excluding marine and pelagic species) within an ensemble forecast framework. Then, using traits data (foraging type, foraging height, nocturnality and body mass) for all species, we calculated both current and future FD. Because FD is highly correlated with species richness, we further developed a null model allowing us to find out where the future FD was predicted to be lower or higher than expected given the predicted future species richness.

Results/Conclusions

Current FD was found to be the highest in central America, in the African Great Rift valley, southeastern Asia and northern South America and the highest decreases were predicted in the western Mediterranean basin, in the Yucatan peninsula, in central South America, in southern Africa and in northern Australia. Conversely, highest increases are predicted to occur at high northern latitudes, in southwestern China and in the Sahara. Predicted changes greatly differed between biomes and realms. Results from the null models underlined that the predicted future FD was either lower or higher than what could be expected given the predicted future richness in some areas. As an example, the predicted future FD is significantly lower than expected in southwestern Asian islands, revealing that the suitability of functionally unique species tended to decrease more than the suitability of redundant species. Functionally unique species being more likely to be keystone species, FD changes in these areas could potentially have more negative consequences on other groups of species and ecosystem services. These results therefore add important complementary insights to predictions of change in number of species alone and could be very useful for decision makers aiming at preserving ecosystem services.