Habitat type shapes long-term plant biodiversity budgets in two densely populated regions in north-western Europe
Résumé
Aim: At a global scale, biodiversity changes are mainly driven by extinction, resulting in an overall decrease in species richness. At regional and local scales, although immigration often (over)compensates for local extinction, biodiversity changes have no clear trends. We tested the hypotheses that (1) at both regional and local scales, biodiversity changes result from the differential dynamics of local extinction and immigration, ultimately leading to increases in biodiversity following periods of transient surplus or deficit and (2) habitats are differentially affected by human activities, resulting in contrasting trends and dynamics that together shape the regional biodiversity budget.
Location: Northern France and Belgian Flanders, north-western Europe.
Methods: We analysed changes in plant species richness over one century in two adjacent and densely populated regions. Because local to regional changes are expected to be driven by species–environment interactions, and because species ecology and environmental change are largely embodied by the habitat, we assessed biodiversity budgets according to the type of habitat.
Results: We observed major changes in species composition at the regional scale with about one of every five to six species becoming regionally extinct or newly naturalized. Immigration offset or exceeded losses, with local extinctions generally preceding gains. Overall, regional dynamics were driven by contrasting changes in a few habitat types, with either local extinction or immigration predominating. Transient biodiversity surpluses or deficits were observed at the regional scale and in certain habitat types.
Main conclusions: Including habitat types bridges the gap between regional and local studies and provides a more accurate assessment of the biodiversity budget: integrating habitat type into regional analyses or meta-analyses can lead future research towards the understanding of the determinisms of biodiversity change across spatial scales.