Where wolves were: setting historical baselines for wolf recovery in Spain

Abstract

Reference conditions are necessary to assess the conservation status of species, understand their declines, and manage their recovery. Historical documents offer large amounts of records of a wide variety of species, which may be used to generate reference baselines on the historical distribution range of species. We collected information on the Iberian wolf Canis lupus signatus presence or assumed absence for 6734 localities in Spain from the geographical dictionary edited by Pascual Madoz in the mid-19th century. We used probabilistic distribution models to estimate the wolf historical range with unprecedented detail, allowing the quantification of the historical reduction in occupancy area. Wolf records were widely distributed in mid-19th century Spain, being present in all its mainland provinces. The probability of occurrence was positively associated with landscape roughness and negatively with human population density and the landscape suitability for agriculture. The area estimated to be occupied by wolves ranged between 212 200 and 317 600 km2, depending on the approach used to set cut-off values from the predictions. Our estimations represented an average range reduction of 68% between the mid-19th century and present time, resulting in the current restriction of the species to the country's north-western quadrant. The putative recent recovery of the wolf in Spain consists mainly of the accumulation of wolf records in areas where the species had persisted and the recolonization of some peripheral areas, but there is no indication of widespread recovery of the historical distribution range. We show that the compilation of historical species records allows producing baseline range scenarios with much higher resolution than usually available to inform species status and set recovery targets, an approach that can be implemented in other areas and taxa.