Time-lags in the responses of agro-steppe species to landscape changes
Farming intensification, land abandonment and urbanization are considered to be the main drivers behind species loss in farmlands. They can cause immediate loss of species but also time-delayed extinctions, known as the extinction debt. Accumulating evidence suggests that such extinctions debts pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Differently to other ecosystems, multifunctional agrarian social-ecological systems have been shaped by the interaction between human populations and nature. Indeed, the traditional management of these systems is largely responsible for its high biodiversity especially in the Mediterranean basin. The species linked to agro-steppe landscapes are especially worthy of consideration because they have suffered severe declines during the last century. The Iberian Peninsula holds both well-preserved agro-steppes as highly affected agro-steppes by intensification, abandonment and urbanization. We investigated to what extent the current species richness and functional homogenization of different animal taxa is related to the current and past levels of agricultural intensification, land abandonment, landscape fragmentation and urban sprawl. Besides, we identified the most vulnerable groups of species and estimated the magnitude of their possible extinction debt, for which we developed a new methodology. More than a hundred landscapes of 100 km2 were studied across the agro-steppes of the Iberian Peninsula covering low and high values for each driver. The landscape structure and dynamics analyses were based on aerial photographs taken from 1956 to 2009. According to our results, the landscape structure dynamic over the past half century influenced the present-day value of richness and homogenization patterns of species in agro-steppe landscapes and we found differences in the extinction debt of species from different taxa. Thus, conservation decisions based on the analysis of how species respond to present-day landscapes may be insufficient to prevent the species loss in the future.