Patch history and spatial scale modulate local plant extinction and extinction debt in habitat patches

Abstract

Aim Many species exhibit a time-lag between habitat loss and its extinction, resulting in extinction debt. Although extinction debt is considered a widespread phenomenon, differences in methodological approaches can affect its detection. We aim to contribute to this methodological debate by exploring whether extinction debt is either a phenomenon common to all patches or idiosyncratic to the patch and landscape attributes of a given patch. We also aim to determine whether the scale dependency of species richness might help to explain extinction debt. Location Southern Catalonia (NE Iberian Peninsula). Methods We studied the effects of habitat loss on plant species richness (total, specialists and generalists) in stable (habitat loss < 40% since 1956) and regressive (habitat loss more than 40% since 1956) patches of Mediterranean grasslands at both quadrat and patch scales using general linear models. Results We detected extinction debt at patch scale but only in regressive patches. The magnitude of extinction debt was not constant but was related to the percentage of patch area reduction. Contrastingly, regressive patches presented fewer species than stable patches at quadrat scale. Main conclusion Quadrat scale extinctions in regressive patches lead to rarefaction, but not immediate extinction, of some species at patch scale and created an extinction debt. Species loss at quadrat scale constitutes an early warning indicator of the effects of habitat loss on biodiversity, while delayed extinctions offer an opportunity for conservation initiatives.