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 Historical documents offer large amounts of records of a wide variety of species, which may be used to generate reference baselines on the historical distribution range of species.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.

On the misuse of historical data to set conservation baselines: Wolves in Spain as an example

“…None of these approaches take into account the information biases shown in Figure 1, and thus their range estimates are miniature representations of the actual historical wolf range. Acknowledging that our own range descriptions (Clavero et al, 2022) were minimum estimates (due to the nature of historical mentions to wolves, described above), our figures were up to three-fold larger than those provided by Nores & López-Bao (2022) (Figure 2). 2022) collected wolf records and mentions to other wildlife species to identify wolf presences and pseudoabsences, translating this information to 100 km 2 cells.…”

“…However, the results of these two exercises are strikingly different. While Nores & López-Bao (2022) estimated that the current wolf range in Spain represents more than 70% of the 19 th century range, we estimate this figure being only around 30% (Clavero et al 2022). This discrepancy is far from trivial, not only for its magnitude, but also because it has major conservation and legal implications for wolf management.…”

“…This means that in the areas where wolf was present but not perceived as a serious threat (either by its rarity or by low interactions with human interests) the species would have rarely been recorded. As a result, the collection of citations to wolf (or any other species) in the Madoz is only a subsample of the places where the species was present at that time, as explicitly acknowledged in Clavero et al (2022). As we argue below, the resulting information gaps should be compensated for using predictive modelling frameworks (Kissling et al 2018).…”

“…The existence of biases in species distribution records requires the implementation of spatial modelling approaches to counteract the effects of spatial gaps and biases in the primary data (Kissling et al, 2018;Jetz et al, 2019). In Clavero et al (2022), we followed such an approach to estimate wolf range in Spain in the 19 th century, using citations to other terrestrial species to generate wolf pseudo-absences, which have similar spatial biases in sampling effort to those of wolf citations (see Clavero & Hermoso, 2015 for a similar approach).…”

“…Two recent works have analysed the historical distribution range of the wolf in Spain with the aim of estimating conservation baselines for the species management (Nores & López-Bao, 2022;Clavero et al, 2022). Both of them used the same historical source, the 19 th century geographical dictionary edited by Pascual Madoz (1846-1850.…”