Disentangling the latitudinal and altitudinal shifts in community composition induced by climate change: The case of riparian birds

11 pagesInternational audienceAim: This study investigates whether, and how, the composition of riparian bird communities has been affected by climate warming and habitat change. Although these two forces act separately, their respective contributions are rarely examined. Moreover, while the response of a given community may be a function of latitude and altitude, most studies have focused on these gradients separately. Riparian ecosystems are an opportunity to investigate community change along latitudinal and elevational gradients.Location: France, three major rivers (the Doubs, the Allier and the Loire)Taxon: Birds.Methods: Drawing upon bird community monitoring data over a period of 31 years (1982–2013, n = 1,286 point counts), we assessed community adjustment to temperature increase with the Community Temperature Index (CTI), and the homogenization pattern following habitat conversion with the Community Specialization Index (CSI). We evaluated the spatial climatic debt accumulated by communities, and the interaction between CTI and CSI trends. Furthermore, we tested differences in trends for lowland and highland elevations.Results: Over the study period, the temperature increased by 1.17°C, and the CTI by 0.12°C, which corresponds to a spatial climatic debt of 4.9 km/year. Lowland communities adjusted to warming but not highland communities, which have experienced a decline in species abundance. CSI trends revealed biotic homogenization in both lowland and highland communities. This finding was uncorrelated with the CTI increase, and is thought to be due to the pressure from land use change on community composition.Main conclusions: Riparian breeding bird communities have been affected by a temperature increase and, potentially, habitat change. Highland communities are most vulnerable to climate warming. Both climate warming and habitat change appear to have rapidly affected the composition of local communities, with expectable concerns on their diversity and specificity in the long term